GLUCONIC ACID

GLUCONIC ACID

GLUCONIC ACID

Gluconic acid is an organic compound with molecular formula C6H12O7 and condensed structural formula HOCH2(CHOH)4COOH. 
It is one of the 16 stereoisomers of 2,3,4,5,6-pentahydroxyhexanoic acid.

In aqueous solution at neutral pH, gluconic acid forms the gluconate ion. 
The salts of gluconic acid are known as “gluconates”. 

Gluconic acid, gluconate salts, and gluconate esters occur widely in nature because such species arise from the oxidation of glucose. 
Some drugs are injected in the form of gluconates.
The chemical structure of gluconic acid consists of a six-carbon chain, with five hydroxyl groups positioned in the same way as in the open-chained form of glucose, terminating in a carboxylic acid group. 
In aqueous solution, gluconic acid exists in equilibrium with the cyclic ester glucono delta-lactone.

EC / List no.: 208-401-4
CAS no.: 526-95-4

D-gluconic acid

D-gluconic acid

CAS names
D-Gluconic acid
IUPAC names
(2R,3S,4R,5R)-2,3,4,5,6-pentahydroxyhexanoic acid
2,3,4,5,6-pentahydroxyhexanoic acid

D(-)pentahydroxycaproic acid
D-GLUCONIC ACID
D-Gluconic acid
D-gluconic acid
D-gluconic acid/EC 208-401-4
gluconic acid

Gluconic acid
Gluconic Acid, 50% wt

Gluconic acid- 
Ácido 2,3,4,5,6-pentahidroxihexanóico

Gluconic acid has applications in the food industry, as in meat and dairy products, baked goods, flavoring agent, and reducing fat absorption in doughnuts

Gluconic acid (2,3,4,5,6-pentahydroxy caproic acid, C6H12O7) (Figure 6) is a noncorrosive, nontoxic, mild organic acid with a brown clear appearance. 
It is very soluble in water and has a mild and refreshing taste. It is a good chelator at high pH, with better activity than commonly used chelators.

Gluconic acid, a mild organic acid derived from sugar, mainly used as an acidity regulator and chelating agent in food with the European food additive number E574. 
This ingredient is also used to produce gluconates (E576, 577, 578, 579, 585) and glucono delta-lactone (E575) to be used in different food applications and other fields.

Gluconic acid is widely used in the food industry, cosmetics, medicine and daily chemical industry, metal cleaning, electroplating polishing, construction industry, plastics, and resin modification. It can be used for shampoos, rinses, lotions, cleansing foams…

Gluconic acid was discovered in 1870 by Hlasiwetz and Habermann, when glucose was oxidized with chlorine. 
In 1922 it was isolated from a strain of A. niger. 
Later, other filamentous fungi, such as Penicillium, Scopulariopsis, Gonatobotrys, and Gliocladium, and also oxidative bacteria, such as strains of Pseudomonas, Gluconobacter (Acetobacter), Moraxella, Micrococcus, Enterobacter, and Zymomonas were found to produce gluconic acid. 
Already in the 1940s it was possible to obtain good yields of gluconic acid using A. niger by fermentation, neutralizing the accumulating acid with calcium carbonate.

The physiological functions of gluconic acid accumulation for these organisms are not clear; one possibility is its contribution to the competitiveness of the organism, removing glucose from the close environment. 
In the case of P. expansum (a phytopathogenic fungus), it was demonstrated that secreted gluconic acid contributed to the colonization and disease development of apple tissues by this fungus.

Gluconic acid is used in the manufacture of metal, leather, and food. 
It has been accredited with the capability of inhibiting bitterness in foods. 
Sodium gluconate is permitted in food and it has GRAS (generally recognized as safe) status. 
This salt is also utilized as a sequestering agent in many detergents, and added to cement to improve the hardening process.

The formation of gluconic acid is different from most other organic acids, since it is formed outside the cytoplasmic membrane, by the enzyme glucose oxidase. 
This enzyme has been shown to be localized in the cell wall, at least for fungi known to accumulate gluconic acid. 
Glucose in the medium is oxidized in a two-step reaction to gluconic acid; first glucose oxidase oxidizes β-d-glucopyranose to d-glucono-1,5 lactone with the formation of hydrogen peroxide, acted upon by catalase to form water and oxygen (Figure 7). 
The hydrolysis of the lactone is spontaneous in aqueous solutions, but occurs six times faster with the enzyme gluconolactonase, resulting in gluconic acid

D-Gluconic acid is the oxidized form of D-glucose (or dextrose), one of the fundamental building blocks for sugars, polysaccharides, and cellulose. 
Like glucose, it cyclizes in solution, in this case to form an ester (glucono-δ-lactone) rather than a hemiacetal.

Gluconic acid widely exists in nature, especially in fruits and in sucrose-containing substances such as honey. 
Early methods of synthesizing gluconic acid from glucose included hypobromite oxidation and alkaline hydrolysis. 
Now it is commercially produced by using microbes such as Aspergillus niger to oxidize glucose enzymatically.

Gluconate, gluconic acid’s conjugate base, is useful as a metal-chelating agent in alkaline solutions. 
It is a component of many cleaning products; and it is used to prevent formation of solids in dairy processing and beer brewing.

Gluconic acid is used as an acidity regulator, buffering agent, pigment stabilizer as well as a preservative due to its antibacterial action.

Category: Food and Beverages Additives

Gluconic acid is widely used in the food industry, cosmetics, medicine and daily chemical industry, metal cleaning, electroplating polishing, construction industry, plastics, and resin modification. It can be used for shampoos, rinses, lotions, cleansing foams…

Gluconic acid is an oxide of glucose, and its anhydride is glucono-8-lactone. 
Gluconic acid forms gluconate salts with various cations such as sodium, calcium, potassium and zinc. 
These gluconic acid salts are widely utilised in various food products as acids, coagulant and mineral supplement. 
Gluconic acid exists naturally in rice, honey, wine (60450 p.p.m.), vinegar, beer (40-60 p.p.m.) and grape juice (60-380 p.p.m.). 
On an industrial scale, gluconic acid is produced from starch by fermentation. 
There are few reports on the effect of gluconic acid on the growth of bacteria or its absorption in animals. 

Gluconic acid is an organic compound with molecular formula C6H12O7 and condensed structural formula HOCH2(CHOH)4COOH. 
It is one of the 16 stereoisomers of 2,3,4,5,6-pentahydroxyhexanoic acid. 
In aqueous solution at neutral pH, gluconic acid forms the gluconate ion. 
The salts of gluconic acid are known as “gluconates”. 
Gluconic acid, gluconate salts, and gluconate esters occur widely in nature because such species arise from the oxidation of glucose. 
Some drugs are injected in the form of gluconates.

Gluconic acid, also known as D-gluconate or D-glukonsaeure, belongs to the class of organic compounds known as sugar acids and derivatives. 
Sugar acids and derivatives are compounds containing a saccharide unit which bears a carboxylic acid group. 
Gluconic acid is a drug which is used for use as part of electrolyte supplementation in total parenteral nutrition. 
It is also used in cleaning products where it helps cleaning up mineral deposits. 
The salts of gluconic acid are known as “gluconates”. 
Gluconic acid is an extremely weak basic (essentially neutral) compound (based on its pKa). 
Gluconic acid or Gluconic acid is used to maintain the cation-anion balance on electrolyte solutions. 
Gluconic acid exists in all living species, ranging from bacteria to humans. In humans, gluconic acid is involved in the metabolic disorder called the transaldolase deficiency pathway. 
Outside of the human body, Gluconic acid has been detected, but not quantified in, milk (cow). 
This could make gluconic acid a potential biomarker for the consumption of these foods. 
Gluconic acid has been found to be a metabolite in Aspergillus
It chelates the anions of calcium, iron, aluminium, copper, and other heavy metals. 
Gluconic acid occurs naturally in fruit, honey, kombucha tea, and wine.

Gluconic acid, the oxidation product of glucose, is a mild neither caustic nor corrosive, non toxic and readily biodegradable organic acid of great interest for many applications. 
As a multifunctional carbonic acid belonging to the bulk chemicals and due to its physiological and chemical characteristics, gluconic acid itself, its salts (e.g. alkali metal salts, in especially sodium gluconate) and the gluconolactone form have found extensively versatile uses in the chemical, pharmaceutical, food, construction and other industries.

Gluconic acid, also known as dextronic acid, belongs to the class of organic compounds known as sugar acids and derivatives. 
Sugar acids and derivatives are compounds containing a saccharide unit which bears a carboxylic acid group. 
Gluconic acid is an extremely weak acid (based on its pKa). 
Gluconic acid exists in all living species, ranging from bacteria to humans. 
Gluconic acid is produced in particularly high abundance by certain fungi, such as Aspergillus niger (PMID: 24039465). 
Gluconic acid occurs naturally in fruit, honey, kombucha tea, and cow‚Äôs milk. 
Gluconic acid and its lactone have also been found in some table wines. 
The source of gluconic acid is most likely mold metabolism. 
Industrially, gluconate is used as a concrete admixture (retarder) to slow down the cement hydration reactions and to delay the cement setting time. 
It is also used in cleaning products where it helps cleaning up mineral deposits. 
In this regard, gluconic acid has been found to chelate the anions of calcium, iron, aluminium, copper, various rare earths and other heavy metals. 
The salts of gluconic acid are known as “gluconates”. 
Gluconic acid is also used to maintain the cation-anion balance on electrolyte solutions and is present in certain electrolye solutions, such as “plasmalyte A”, which is used for intravenous fluid resuscitation. 
Gluconate is also used in a variety of pharmaceutical applications. 
For instance, calcium gluconate is used to treat burns arising from hydrofluoric acid while quinine gluconate is a salt of gluconic acid and quinine, which is used for intramuscular injection in the treatment of malaria. 
In humans, altered levels of gluconic acid have been found in the metabolic disorder called the transaldolase deficiency.

Properties and Applications of Gluconic Acid
Gluconic acid is a white, odorless crystalline powder. 
Its melting point is below 12 °C, and the boiling point is 130–132 °C. 
The pKa value of gluconic acid is 3.72 (25 °C). 
It is readily soluble in water, but not in ethanol or ether.

The demands for gluconic acid, containing the forms of its δ-lactone and gluconates, worldwide are divided among the principal fields of use approximately as follows: construction (45%), food (35%), pharmaceutical (10%), and others (10%).

Due to low toxicity, low corrosivity, and the capability of forming water-soluble complexes with divalent and trivalent metal ions, gluconic acid is widely used in many industries. 
For example, the δ-lactone is used in the food industry as a mild acidulant. 
Calcium and iron gluconates are highly soluble in water and nontoxic, and are used in medical infusion preparations for the treatment of calcium or iron deficiencies. 
Various gluconates together with gluconic acid are used in the tanning and textile industry, and in the dairy industry either to prevent the deposition of milkstone or to remove it. 
The remarkable noncorrosiveness of gluconic acid may generally be utilized in gentle metal-cleaning operations, for example, in cleaning aluminum cans and other equipment. 
In beverages, it prevents cloudiness and scaling by calcium compounds. 
In various foods, it produces and improves a mild sour taste and complexes traces of heavy metals.

More than 80% of gluconic acid and gluconates is sold as sodium gluconate, which is the main product of commerce. 
This is due to the outstanding property of forming stable complexes with various metal ions, especially in alkaline solutions. 
Sodium gluconate is used to scale off oxides of heavy metals from metal surfaces, to remove zinc from metal surfaces, or to remove paints and lacquers from various objects. 
The sequestering action on calcium and similar ions may be used in alkaline glass washing preparations or in the textile industry to prevent iron deposition. 
Sodium gluconate is also recommended as an additive to concrete acting as a plastifier and retarding the setting process.

Gluconic acid (also known as gluconate) is an organic compound occurring widely in nature arising from the glucose oxidation. 
Gluconic acid is naturally found in fruit, honey and wine. 
Gluconic acid can also be used as a food additive to regulate acidity and a cleaning agent in alkaline solution. 
Its calcium salt, calcium gluconate can be used to treat burns from hydrofluoric acid and avoid necrosis of deep tissues as well as treating the verapamil poisoning and hypocalcemia in hospitalized patient. 
Some salts of gluconate can also be used to treat malaria (quinidine gluconate) and anemia (ferrous gluconate). 
In microbiology, gluconate is a common carbon source that can be supplemented to the medium for cell growth.

Gluconic acid is an organic compound with molecular formula C6H12O7 and condensed structural formula HOCH2(CHOH)4COOH. 
It is one of the 16 stereoisomers of 2,3,4,5,6-penta hydroxy hexanoic acid.
In aqueous solution at neutral pH, gluconic acid forms the gluconate ion. 
The salts of gluconic acid are known as “gluconates”. 
Gluconic acid, gluconate salts, and gluconate esters occur widely in nature because such species arise from the oxidation of glucose. 
Some drugs are injected in the form of gluconates.

d-Gluconic acid is an acid sugar composed of white crystals with a milk-acidic taste. 
In aqueous solutions, it is in equilibrium with gamma- and delta-gluconolactones. 
It is prepared by enzymatic oxidation of glucose and strains of the microorganisms used to supply the enzyme action are nonpathogenic and nontoxicogenic to man or other animals. 
This substance is used as a component of bottle rinsing formulations, at levels not to exceed good manufacturing practice.
An FDA letter to a trade association revoking affirmation of general recognition of safety in dietary supplements was dated April 9, 1970.

The chemical structure of gluconic acid consists of a six-carbon chain with five hydroxyl groups terminating in a carboxylic acid group. 
In aqueous solution, gluconic acid exists in equilibrium with the cyclic ester glucono delta-lactone.

Gluconic acid occurs naturally in fruit, honey, kombucha tea, and wine. As a food additive ( E574 ), it is an acidity regulator. 
It is also used in cleaning products where it dissolves mineral deposits especially in alkaline solution. 
The gluconate anion chelates Ca2+,Fe2+, Al3+, and other metals. 
In 1929 Horace Terhune Herrick developed a process for producing the salt by fermentation.
Calcium gluconate, in the form of a gel, is used to treat burns from hydrofluoric acid; calcium gluconate injections may be used for more severe cases to avoid necrosis of deep tissues.
Quinine gluconate is a salt between gluconic acid and quinine, which is used for intramuscular injection in the treatment of malaria. 
Zinc gluconate injections are used to neuter male dogs. 
Iron gluconate injections have been proposed in the past to treat anemia.

Gluconic Acid is an acidulant that is a mild organic acid which is the hydrolyzed form of glucono-delta-lactone. 
Gluconic Acid is prepared by the fermentation of dextrose, whereby the physiological d-form is produced. 
Gluconic Acid is soluble in water with a solubility of 100 g/100 ml at 20°c. it has a mild taste and at 1% has a ph of 2.8. 
Gluconic Acid functions as an antioxidant and enhances the function of other antioxidants. in beverages, syrups, and wine, it can eliminate calcium turbidities. 
Gluconic Acid is used as a leavening component in cake mixes, and as an acid component in dry-mix desserts and dry beverage mixes.

Currently, gluconic acid is commercially produced by submerged fed-batch cultivations of Aspergillus niger using glucose as substrate. 
A. niger produces citric acid and gluconic acid growing on glucose. 
The product concentration and yields of the product depend on the fermentation conditions. 
For optimal gluconic acid production, high glucose concentrations (110–250 g.L-1), low concentrations of nitrogen and phosphorus in the medium, a limitation of metal ion concentrations, a pH value in the range of 4.5–6.5, and high aeration rates for the oxygen supply are needed.
Much research has been carried out to find new ways for cheaper production. 
Different microorganisms have been studied (e.g. G. oxydans, Z. mobilis, A. methanolicous, and P. fluorescence. 
Moreover, new microbial strains have been developed by mutagenesis or genetic engineering. Additionally, the fermentation process and recovery have been optimized. New inexpensive substrates (e.g. cornstarch, grape or banana must, figs, and cheese whey) have been tested.
One example of a new and efficient production process of gluconic acid is the cultivation of Aureobasidium pullulans growing on glucose. 
Using a continuous process with biomass retention by crossover filtration, a product concentration of 375 g.L-1, a yield of 0.83 g of gluconic acid per gram of glucose, and a productivity of 17 g.L-1.h-1 could be achieved at a residence time of 22 h. 
In this process, 100 % of the glucose is converted. This process might be interesting for industrial applications. 
In continuous gluconic acid production with immobilized mycelia of A. niger, product concentrations of 120–140 g.L-1 have been achieved.

D-Gluconic acid [ACD/Index Name] [ACD/IUPAC Name]
157663-13-3 [RN]
1726055 [Beilstein]
2,3,4,5,6-Pentahydroxycaproic acid
208-401-4 [EINECS]
526-95-4 [RN]
Acide D-gluconique [French] [ACD/IUPAC Name]
D-Gluconsäure [German] [ACD/IUPAC Name]
Gluconic acid [Wiki]
Glyconic Acid
MFCD00004240 [MDL number]
R4R8J0Q44B
2,3,4,5,6-pentahydroxy-hexanoic acid
Dextronate
Glycogenate
Glyconate
Maltonate
(2R,3S,4R,5R)-2,3,4,5,6-pentahydroxyhexanoic acid
(3S,2R,4R,5R)-2,3,4,5,6-pentahydroxyhexanoic acid
[526-95-4]
2,3,4,5,6-pentahydroxyhexanoate
2,3,4,5,6-Pentahydroxyhexanoic acid
2-dehydro-3-deoxy-D-gluconate
2-keto-3-deoxy-D-gluconate
4-03-00-01255 [Beilstein]
4-03-00-01255 (Beilstein Handbook Reference) [Beilstein]
50% aqueous solution
50% gluconic acid solution
9025-70-1 [RN]
d-(+)-gluconic acid
Dextranase
Dextronic acid
D-gluco-Hexonic acid
D-Gluconic acid – 45-50% in water
D-Gluconic Acid (50per cent in Water)
D-Gluconic acid 50% in water
D-Gluconsaeure
D-GLUCOSONIC ACID
D-Glukonsaeure
d-葡萄糖酸溶液
Galactonic acid
GCO
Glosanto
Gluconic Acid (contains Gluconolactone)
Gluconic acid (VAN)
GLUCONIC ACID, D-
gluconicacid
Glycogenic acid
http://en.atomaxchem.com/526-95-4.html
http://www.hmdb.ca/metabolites/HMDB0000625
https://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:33198
ketogluconic acid
Maltonic acid
MFCD00066366
Pentahydroxycaproate
Pentahydroxycaproic acid
UNII:R4R8J0Q44B
UNII-R4R8J0Q44B
葡萄糖酸 [Chinese]

IUPAC name: d-Gluconic acid
Systematic IUPAC name: (2R,3S,4R,5R)-2,3,4,5,6-Pentahydroxyhexanoic acid

Dextronic acid

CAS Number    
526-95-4 (D) 
133-42-6 (racemate) 

Gluconic Acid is the carboxylic acid formed by the oxidation of the first carbon of glucose with antiseptic and chelating properties. 
Gluconic acid, found abundantly in plant, honey and wine, can be prepared by fungal fermentation process commercially. 
This agent and its derivatives can used in formulation of pharmaceuticals, cosmetics and food products as additive or buffer salts. 
Aqueous gluconic acid solution contains cyclic ester glucono delta lactone structure, which chelates metal ions and forms very stable complexes. 
In alkaline solution, this agent exhibits strong chelating activities towards anions, i.e. calcium, iron, aluminium, copper, and other heavy metals.

D-gluconate
D-gluconic acid
dextronic acid
gluconate
gluconic acid
gluconic acid, (113)indium-labeled
gluconic acid, (14)C-labeled
gluconic acid, (159)dysprosium-labeled salt
gluconic acid, (99)technecium (5+) salt
gluconic acid, 1-(14)C-labeled
gluconic acid, 6-(14)C-labeled
gluconic acid, aluminum (3:1) salt
gluconic acid, ammonium salt
gluconic acid, calcium salt
gluconic acid, cesium(+3) salt
gluconic acid, cobalt (2:1) salt
gluconic acid, copper salt
gluconic acid, Fe(+2) salt, dihydrate
gluconic acid, lanthanum(+3) salt
gluconic acid, magnesium (2:1) salt
gluconic acid, manganese (2:1) salt
gluconic acid, monolithium salt
gluconic acid, monopotassium salt
gluconic acid, monosodium salt
gluconic acid, potassium salt
gluconic acid, sodium salt
gluconic acid, strontium (2:1) salt
gluconic acid, tin(+2) salt
gluconic acid, zinc salt
lithium gluconate
magnerot
magnesium gluconate
maltonic acid
manganese gluconate
pentahydroxycaproic acid
sodium gluconate
zinc gluconate
gluconic acid
D-gluconic acid
526-95-4
dextronic acid
maltonic acid
Glycogenic acid
gluconate
Glosanto
Pentahydroxycaproic acid
(2R,3S,4R,5R)-2,3,4,5,6-pentahydroxyhexanoic acid
D-Gluco-hexonic acid
Gluconic acid, D-
Gluconic acid (VAN)
D-Gluconsaeure
D-Glukonsaeure
UNII-R4R8J0Q44B
BRN 1726055
Glyconic acid
Hexonic acid
R4R8J0Q44B
133-42-6
CHEBI:33198
Dextronate
Glycogenate
Glyconate
Maltonate
MFCD00004240
2,3,4,5,6-Pentahydroxycaproic acid
Gluconic Acid (contains Gluconolactone)
NSC 77381
GCO
Gluconic acid, 50 wt% solution in water
HSDB 487
C6H12O7
157663-13-3
19222-41-4
EINECS 208-401-4
ketogluconic acid
D-?Gluconic acid
Pentahydroxycaproate
D-Gluconic acid solution
DSSTox_CID_7169
SCHEMBL971
bmse000084
EC 208-401-4
DSSTox_RID_78332
DSSTox_GSID_27169
4-03-00-01255 (Beilstein Handbook Reference)
CHEMBL464345
D-Gluconic acid 50% in water
DTXSID8027169
DTXSID8042000
KS-00000UFG
HY-Y0569
ZINC1531008
2,3,4,5,6-pentahydroxy-hexanoate
Tox21_202745
SBB066208
AKOS015895892
Gluconic acid, 50% solution in water
D-Gluconic acid – 45-50% in water
DB13180
2,3,4,5,6-pentahydroxy-hexanoic acid
NCGC00260293-01
CAS-526-95-4
E574
CS-0015343
G0036
V2121
C00257
128393-EP2270002A1
128393-EP2295401A2
D-Gluconic acid solution, 49-53 wt. % in H2O
Q407569
W-109086
(3S,2R,4R,5R)-2,3,4,5,6-pentahydroxyhexanoic acid
D-Gluconic acid solution, SAJ first grade, 50% in H2O
6E52

Synonyms     
(2R,3S,4R,5R)-2,3,4,5,6-pentahydroxyhexanoic acid    
D-gluco-Hexonic acid    
D-Gluconic acid    K
D-Gluconsäure Deutsch    
D-Glukonsäure Deutsch    
Dextronic acid    
Gluconic acid    
GLUCONIC ACID    
Glycogenic acid    
Hexonic acid    
Maltonic acid

Gluconic Acid 50% is composed of an equilibrium between the free acid and the two lactones. 
This equilibrium is affected by the mixture’s concentration and temperature. 
A high concentration of the delta-lactone will favor the equilibrium to shift to the formation of gamma-lactone and vice versa. 
A low temperature favors formation of glucono-delta-lactone while high temperatures will increase formation of glucono-gamma-lactone. 
Under normal conditions, PMP Gluconic Acid 50% exhibits a stable equilibrium contributing to its clear to light yellow color with low level corrosiveness and toxicity.

Production
Gluconic acid is produced by oxidizing glucose. 
This can be accomplished in several ways:

Via hydrogen peroxide
Via bromine
In a fermentation bath

Occurrence and uses
Gluconic acid occurs naturally in fruit, honey, and wine. 
In 1929 Horace Terhune Herrick developed a process for producing the salt by fermentation.
As a food additive (E574), it is now known as an acidity regulator.

The gluconate anion chelates Ca2+, Fe2+, Al3+, and other metals, including lanthanides and actinides. 
It is also used in cleaning products, where it dissolves mineral deposits, especially in alkaline solution.

Calcium gluconate, in the form of a gel, is used to treat burns from hydrofluoric acid;calcium gluconate injections may be used for more severe cases to avoid necrosis of deep tissues, as well as to treat hypocalcemia in hospitalized patients. 
Gluconate is also an electrolyte present in certain solutions, such as “plasmalyte a”, used for intravenous fluid resuscitation.
Quinine gluconate is a salt of gluconic acid and quinine, which is used for intramuscular injection in the treatment of malaria.

Zinc gluconate injections are used to neuter male dogs.

Ferrous gluconate injections have been proposed in the past to treat anemia.

Gluconate is also used in building and construction as a concrete admixture (retarder) to slow down the cement hydration reactions, and to delay the cement setting time. 
It allows for a longer time to lay the concrete, or to spread the cement hydration heat over a longer period of time to avoid too high a temperature and the resulting cracking.
Retarders are mixed in to concrete when the weather temperature is high or to cast large and thick concrete slabs in successive and sufficiently well-mixed layers.

D-Gluconic acid is a water-soluble organic acid that belongs to the hydroxycarboxylic acid family. 
Gluconic acid is an oxidation product of glucose that occurs widely in nature, and is present in fruit, wine, honey, and other natural sources. 
The chemical structure of D-gluconic acid of a six-carbon chain with five hydroxyl (-OH) groups terminating in a carboxylic acid group. 
The close proximity of the oxygen atoms within the chemical structure lends to its function as a highly efficient chelating agent. 
Chelating agents bind to positively charged metal ions in solution and thereby prevent them from forming insoluble precipitates with other ions that may be present. 
D-Gluconic acid functions as a chelating agent over a wide pH range. 
It is efficient in forming stable chelates with divalent and trivalent metal ions such as calcium, copper, iron, aluminum, and other metals, reducing the adverse effects these metals can have on systems. 
D-Gluconic acid also acts as a humectant, which means that it attracts water and increases hydration in products. 
D-Gluconic acid is used as a high performing chelating agent, processing aid, and humectant in a variety of applications and product sectors

Gluconic acid is a mild organic acid derived from glucose by a simple oxidation reaction. 
The reaction is facilitated by the enzyme glucose oxidase (fungi) and glucose dehydrogenase (bacteria such as Gluconobacter). 
Microbial production of gluconic acid is thepreferred method and it dates back to several decades. 
The most studied and widely used fermentation process involves the fungus Aspergillus niger. 

Gluconic acid and its derivatives, the principal being sodium gluconate, have wide applications in food and pharmaceutical industry. 

Gluconic acid is produced from glucose through a simple dehydrogenation reaction catalysed by glucose oxidase. 
Oxidation of the aldehyde group on the C-1 of b-D-glucose to a carboxyl group results in the production of glucono-d-lactone and hydrogen peroxide. 
Glucono- -d-lactone is further hydrolysed to gluconic acid either spontaneously or by lactone hydrolysing enzyme, while hydrogen peroxide is decomposed to water and oxygen by peroxidase. 
The conversion process could be purely chemical too, but the most commonly involved method is the fermentation process. 
The enzymatic process could also be conducted, where the conversion takes place in the absence of cells with glucose oxidase and catalase derived from A. niger. 
Nearly 100 % of the glucose is converted to gluconic acid under the appropriate conditions. 
This method is an FDA approved process. 
Production of gluconic acid using the enzyme has the potential advantage that no product purification steps are required if the enzyme is immobilised, e.g. the use of a polymer membrane adjacent to anion-exchange membrane of low- -density polyethylene grafted with 4-vinylpyridine.

Gluconic acid production dates back to 1870 when Hlasiwetz and Habermann discovered gluconic acid. 
In 1880 Boutroux found for the first time that acetic acid bacteria are capable of producing sugar acid. 
In 1922 Molliard detected gluconic acid in the Sterigmatocystis nigra, now known as Aspergillus niger. 
Later, production of gluconic acid was demonstrated in bacterial species such as Pseudomonas, Gluconobacter, Acetobacter, and various fungal species. 
Studies of Bernhauer showed that A. niger produced high yields of gluconic acid when it was neutralised by calcium carbonate and the production was found to be highly pH dependent. 
However, it was found that with Penicillium sp., the pH dependence is not as critical when compared to A. niger, indicating that there was some correlation between the amount and time-dependent appearance of organic acids, such as gluconic acid, citric acid, oxalic acid, which are formed under different conditions. 
Gluconic acid production has been extensively studied by May et al., Moyer, Wells et al., and Stubbs et al. using A. niger. Using Penicillium luteum and A. niger Currie et al. filed a patent employing submerged culture, giving yields of gluconic acid up to 90 % in 48–60 h. 
Later Moyer et al. used A. niger in pilot plant studies and produced as high as 95 % of theoretical yields in glucose solution of 150 to 200 g/L in 24 h. 
Porges et al. found that the process could be run semicontinuously, by the reuse of the mycelium for nine times repeatedly where the inoculum was recovered either by filtration or centrifugation. 
Findings of Moyer et al. showed that efficiency of more than 95 % could be achieved by the addition of glucose at 250 g/L and boron compounds at later stages of the fungal growth with the reuse of mycelium in cycles of 24 h each. 
Current commercial production of sodium gluconate uses submerged fermentation with A. niger and is based on the modified process developed by Blom et al. 
It involves fed-batch cultivation with intermittent glucose feedings and the use of sodium hydroxide as neutralising agent. 
pH is held at 6.0–6.5 and the temperature at about 34 °C. 
The productivity of this process is very high, since glucose is converted at a rate of 15 g/ (L·h.)

Properties 
Physicochemical behaviour Gluconic acid is a noncorrosive, nonvolatile, nontoxic, mild organic acid. 
It imparts a refreshing sour taste in many food items such as wine, fruit juices, etc. 
Sodium gluconate has a high sequestering power. 
It is a good chelator at alkaline pH; its action is comparatively better than EDTA, NTA and other chelators. 
Aqueous solutions of sodium gluconate are resistant to oxidation and reduction at high temperatures. 
It is an efficient plasticizer and a highly efficient set retarder. 
It is easily biodegradable (98 % at 48 h). 
It has an interesting property of inhibiting bitterness in foodstuffs. 
Concentrated gluconic acid solution contains certain lactone structures (neutral cyclic ester) showing antiseptic property

The
characterisitics are described in Table 1.
In the European Parliament and Council Directive
No. 95/2/EC, gluconic acid is listed as a generally permitted food additive (E 574). 
The US FDA (Food and rug Administration) has assigned sodium gluconate a GRAS (generally recognized as safe) status and its use in foodstuff is permitted without limitation.

Gluconic acid
Nature 
Noncorrosive, mildly acidic,less irritating, nonodorous,nontoxic, easily biodegradable, nonvolatile organic acid
Relative molecular mass: 196.16
Chemical formula: C6H12O7
Synonym 2,3,4,5,6-pentahydroxyhexanoic acid
pKa 3.7
Melting point (50 % solution): Lower than 12 °C
Boiling point (50 % solution): Higher than 100 °C
Density:  1.24 g/mL
Appearance:  Clear to brown
Solubility:  Soluble in water
Sourness Degree of sourness (sourness of citric acid is regarded as 100): Mild, soft, refreshing taste : 29–35

Occurrence
Gluconic acid is abundantly available in plants, fruits and other foodstuffs such as rice, meat, dairy products, wine (up to 0.25 %), honey (up to 1 %), and vinegar. 
It is produced by different microorganisms as well, which include bacteria such as Pseudomonas ovalis, Acetobacter methanolicus, Zymomonas mobilis, Acetobacter diazotrophicus, Gluconobacter oxydans, Gluconobacter suboxydans, Azospirillum brasiliense, fungi such as Aspergillus niger, Penicillium funiculosum, P. variabile, P. amagasakiense, and various other species such as Gliocladium, Scopulariopsis, Gonatobotrys, Endomycopsis and yeasts such as Aureobasidium pullulans (formerly known as Dematium or Pullularia pullulans). 
Ectomycorrhizal fungus Tricholoma robustum, which is associated with the roots of Pinus densiflora, was found to synthesise gluconic acid. 
Applications Gluconic acid is a mild organic acid, which finds applications in the food industry. 
As stated above, it is a natural constituent in fruit juices and honey and is used in the pickling of foods. 
Its inner ester, glucono-d-lactone imparts an initially sweet taste which later becomes slightly acidic. 
Gluconic acid is used in meat and dairy products, particularly in baked goods as a component of leavening agent for preleavened products. 
Gluconic acid is used as a flavouring agent (for example, in sherbets) and it also finds application in reducing fat absorption in doughnuts and cones. 
Foodstuffs containing D-glucono-d-lactone include bean curd, yoghurt, cottage cheese, bread, confectionery and meat.

Generally speaking, gluconic acid and its salts are used in the formulation of food, pharmaceutical and hygienic products (Table 2)

Components 

Applications
Gluconic acid Prevention of milkstone in dairy industry
Cleaning of aluminium cans

Glucono-d–lactone
Latent acid in baking powders for use in dry cakes and instantly leavened bread mixes
Slow acting acidulant in meat processing such as sausages
Coagulation of soybean protein in the manufacture of tofu
In dairy industry for cheese curd formation and for improvement of heat stability of milk

Sodium salt of gluconic acid
Detergent in bottle washing
Metallurgy (alkaline derusting)
Additive in cement
Derusting agent
Textile (iron deposits prevention)
Paper industry

Calcium salt of gluconic acid
Calcium therapy
Animal nutrition

Iron salt of gluconic acid
Treatment of anaemia
Foliar feed formulations in horticulture

Calcium gluconate is used in pharmaceutical industry as a source of calcium for treating calcium deficiency by oral or intravenous administration. 
It also finds a place in animal nutrition. 
Iron gluconate and iron phosphogluconate are used in iron therapy. 
Zinc gluconate is used as an ingredient for treating common cold, wound healing and various diseases caused by zinc deficiencies such as delayed sexual maturation, mental lethargy, skin changes, and susceptibility to infections.

The main product among the gluconic acid derivatives is the sodium gluconate due to its properties and applications.

Calcium gluconate is also an important product among the derivatives of gluconic acid and it is available as tablets, powder, and liquid for dietary supplements

Production of Gluconic Acid 
Introduction There are different approaches available for the production of gluconic acid, namely, chemical, electrochemical, biochemical and bioelectrochemical. 
There are several different oxidising agents available, but still the process appears to be costlier and less efficient compared to the fermentation processes. 
Although the conversion is a simple one-step process, the chemical method is not favoured. 
Thus, fermentation has been one of the efficient and dominant techniques for manufacturing gluconic acid. 
Among various microbial fermentation processes, the method utilising the fungus A. niger is one of the most widely used ones. 
However, the process using G. oxydans has also gained significant importance. 

Irrespective of the use of fungi or bacteria, the importance lies on the product which is produced, for example, sodium gluconate or calcium gluconate, etc. 
As the reaction leads to an acidic product, it is required that it is neutralised by the addition of neutralising agents, otherwise the acidity inactivates the glucose oxidase, resulting in the arrest of gluconic acid production. 
The conditions for the fermentation processes in the production of calcium gluconate and sodium gluconate differ in many aspects such as glucose concentration (initial and final) and pH control. 
In the process involving calcium gluconate production, the control of pH results from the addition of calcium carbonate slurry.
Another important point to be noted is about the solubility of calcium gluconate in water (4 % at 30 °C). 
At high glucose concentration, above 15 %, supersaturation occurs, and if it exceeds the limit, the calcium salt precipitates on the mycelia and inhibits the oxygen transfer. 

The neutralising agent should also be sterilized separately from the glucose solution to avoid Lobry de Bruyn-van Ekenstein reaction, which alters the conformation of glucose, which results in the reduction of yield for about 30 %. 
On the contrary, the process for sodium gluconate is highly preferable as the glucose concentration of up to 350 g/L can be used without any such problems. 

pH is controlled by the automatic addition of NaOH solution. 
Sodium gluconate is readily soluble in water (39.6 % at 30 °C). 

Gluconic acid production by filamentous fungi Glucose oxidase 
The reaction involving the conversion of glucose to gluconic acid by filamentous fungi is catalysed by the enzyme glucose oxidase (b-D-glucose: oxygen 1-oxidoreductase, E.C. 1.1.3.4). 
The enzyme was first isolated from a press juice obtained from Penicillium glaucum by Müller. 
The enzyme was crystallised by Kusai et al. from P. amagasakiense. 
The enzyme was previously known as notatin. 
Glucose oxidase is a flavoprotein which contains one very tightly but noncovalently bound FAD cofactor per monomer and is a homodimer with a molecular mass of 130–320 kDa depending on the extent of glycosylation. 
It catalyses the reaction where glucose is dehydrated to glucono-d-lactone, while hydrogen is transferred to FAD. 
The resulting FADH2 is regenerated to FAD by transmission of the hydrogen to oxygen to form hydrogen peroxide. 
Glucose oxidase is a glycoprotein. 
The native enzyme is glycosylated, with a carbohydrate mass percentage of 16–25 %. 
The enzyme from A. niger contains 10.5 % carbohydrate, which is believed to contribute to the stability without affecting the overall mechanism 

Aspergillus niger A. niger produces all the enzymes required for the conversion of glucose into gluconic acid, which include glucose oxidase, catalase, lactonase and mutarotase. 
Although crystalline glucose monohydrate, which is in the alpha form, is converted spontaneously into beta form in the solution, A. niger produces the enzyme mutarotase, which serves to accelerate the reaction. 
During the process of glucose conversion, glucose oxidase present in A. niger undergoes self-reduction by the removal of two hydrogens. 
The reduced form of the enzyme is further oxidised by the molecular oxygen, which results in the formation of hydrogen peroxide, a by-product in the reaction. 
A. niger produces catalase which acts on hydrogen peroxide releasing water and oxygen. 
Hydrolysis of glucono-d-lactone to gluconic acid is facilitated by lactonase. 
The reaction can be carried out spontaneously as the cleavage of lactone occurs rapidly at pH near neutral, which are brought about by the addition of calcium carbonate, or sodium hydroxide. 
Removal of lactone from the medium is recommended as its accumulation in the media has a negative effect on the rate of glucose oxidation and the production of gluconic acid and its salt. 
There are reports stating that the enzyme gluconolactonase is also present in A. niger, which increases the rate of conversion of glucono-d-lactone to gluconic acid. 
Production of gluconic acid is directly linked with the glucose oxidase activity. 
Depending on the application, the fermentation broths containing sodium gluconate or calcium gluconate are produced by the addition of solutions of sodium hydroxide or calcium carbonate respectively, for neutralisation. 
The general optimal condition for gluconic acid production is as follows: 
¿ Glucose at concentrations between 110–250 g/L 
¿ Nitrogen and phosphorus sources at a very low concentration (20 mM) 
¿ pH value of medium around 4.5 to 6.5 
¿ Very high aeration rate by the application of elevated air pressure (4 bar). 

There are two key parameters which influence the gluconic acid production. 
These are oxygen availability and pH of the culture medium. 
Oxygen is one of the key substrates in the oxidation of glucose as glucose oxidase uses molecular oxygen in the bioconversion of glucose. 
The concentration of oxygen gradient and the volumetric oxygen transfer coefficient are the critical factors, which monitor the availability of oxygen in the medium. 
These two factors highly influence the rate of the transfer of oxygen from gaseous to aqueous phase. 
Several reports are available on this particular aspect. 
The aeration rate and the speed of agitation are the two parameters which affect the availability of the oxygen in the medium. 
Gluconic acid production is an extremely oxygen-consuming process with a high oxygen demand for the bioconversion reaction, which is strongly influenced by the dissolved oxygen concentration. 
Oxygen is generally supplied in the form of atmospheric air; however, in some studies high-pressure pure oxygen has also been provided. 

For example, Sakurai et al. supplied high-pressure oxygen at approx. 6 bar and maintained dissolved oxygen at 150 ppm. 

They found that immobilised mycelium of A. niger grown using pure oxygen produced high titres of gluconic acid in comparison with mycelium grown in air. 
Kapat et al.found that at an agitation speed of 420 rpm and aeration of 0.25 vvm, the dissolved oxygen concentration was optimal for glucose oxidase production. 
The Km value of glucose oxidase for oxygen lies in the range of air saturation in water . 
Lee et al. (58) obtained high volumetric productivity of gluconic acid using relatively high pressure (2–6 bar), resulting in an increase in dissolved oxygen up to 150 mg/L. 
Generally, during the course of fungal growth, the distribution of oxygen becomes uneven, as the size of gas bubbles increases, resulting in insufficient oxygen supply. 
The oxygen absorption rate is also influenced by the viscosity of the culture. 
A rapid decrease is observed in the absorption rate of oxygen with an increase in mycelial concentration. 
pH is another important parameter that influences the gluconic acid production. 
A. niger produces weak organic acids such as citric acid, gluconic acid and oxalic acid, and their accumulation depends on the pH of the nutritive medium. 
pH below 3.5 triggers the TCA cycle and facilitates the citric acid formation. 
The pH range of the fungi for the production of gluconic acid is around 4.5 to 7.0. pH=5.5 is generally considered as optimum for Aspergillus niger. 
Franke collected some data concerning the relative activity of glucose oxidase at different pH levels and reported 5 and 35 % activity at pH=2.0 and 3.0, respectively, based on 100 % activity at pH=5.6. 
Report by Heinrich and Rehm states that gluconic acid production occurs even at pH=2.5 in the presence of manganese in fixed bed and stirred bed reactors, possibly because of the difference in intracellular and extracellular pH.

Cheaper raw materials as substrates Glucose is generally used as carbon source for microbial production of gluconic acid. 
However, hydrolysates of various raw materials such as agro-industrial waste have also been used as substrate. 
Kundu and Das obtained a high yield of gluconic acid in media containing glucose or starch hydrolysate as the sole carbon source. 
Vassilev et al. used hydrol (corn starch hydrolysate) as the fermentable sugar to produce gluconic acid by immobilized A. niger. 
Rao and Panda used Indian cane molasses as a source of glucose. 
The cane molasses was subjected to different pre-treatments such as acid treatment, potassium ferrocyanide treatment, salt treatment, etc. Potassium ferrocyanide treatment gave a promising result. 

Gluconic acid synthesis was influenced by various metal ions such as copper, zinc, magnesium, calcium, iron, etc. Mukhopadhyay et al. (68) used deproteinised whey as a nutritive medium for gluconic acid production. 
Lactose was used as a substrate and 92 g of gluconic acid was produced from 1 L of whey containing 0.5 % glucose and 9.5 % lactose by A. niger immobilized on polyurethane foam. 
Ikeda et al. used saccharified solution of waste paper with glucose concentration adjusted to 50–100 g/L for bioconversion with A. niger. 
The yields were 92 % in Erlenmeyer flasks and 60 % in repeated batch cultures in the turbine blade reactor with 800 mL of working volume. 
Another striking feature in the study was when xylose and cellobiose were used as the sole carbon sources, yields of gluconic acid obtained were 83 and 56 %, respectively. 
Singh et al.observed that grape must and banana must resulted in significant levels of gluconic acid production, i.e. 63 and 55 g/L respectively. 
The purification of grape and banana must leads to a 20–21 % increase in gluconic acid yield. 
They also used molasses, where the gluconate production was 12 g/L, but a significant increase in production of 60 g/L with a yield of 61 % was observed following treatment of the molasses with hexacyanoferrate. 
Rectified grape must appeared to be the best suited substrate, which after 144 h resulted in 73 g/L of gluconic acid with 81 % yield when compared to the value of 72 % obtained from the rectified banana must. Buzzini et al.  also used grape must and rectified grape must and they found that the latter substrate was better, with a production of 67 g/L and a yield of 96 % in 72 h. 

Citric acid was also observed as a by-product. 
Use of solid-state fermentation (SSF) SSF has been widely described for the production of industrial enzymes and organic acids. 
However, for the production of gluconic acid, there are only a few reports using SSF. 
Roukas reported the production of gluconic acid by solid-state fermentation on figs. 
The maximal gluconic acid concentration was 490 g/kg of dry fig with 63 % yield. 
The addition of 6 % methanol into the substrate helped to increase the production of gluconic acid from 490 to 685 g/kg. 
Singh et al. performed SSF by using HCl pretreated sugarcane bagasse and the highest level of gluconic acid (107 g/L) with 95 % yield was obtained. 
In comparison with the submerged culture, the degree of conversion was higher in SSF. 
The increased rate of product formation might be due to the variations of osmotic pressure, water content and dissolved oxygen. 
A study by Moksia et al. used a two- -step process, the first being the production of spores of A. niger by SSF on buckwheat seeds, and the second step, the bioconversion of glucose to gluconic acid by the spores recovered from the SSF medium. 
The interesting aspect about this work was that the spores were not allowed to germinate as the bioconversion medium did not contain any nitrogen source. 
The spores acted as a biocatalyst, producing 200 g/L of gluconic acid with a yield of 1.06 g per mass of glucose, very close to the stoichiometric value. 
Production of gluconic acid by bacteria Acetic acid bacteria and Pseudomonas savastanoi were the cultures initially observed to produce gluconic acid. 
Unlike in fungi, in bacteria the reaction is carried out by glucose dehydrogenase (GDH, E.C. 1.1.99.17) that oxidises glucose to gluconic acid, which is further oxidised to 2-ketogluconate by gluconic acid dehydrogenase (GADH). 
The final oxidation step to 2,5-diketogluconic acid (DKG) is mediated by 2-ketogluconate dehydrogenase (KGDH). 
The reaction steps are shown in Fig. 4. 
All three enzymes are localised in the membranes of the cells and are induced by high glucose concentrations (>15 mM). 
GDH is an extracellular protein and has PQQ (pyrroloquinoline quinine) as a coenzyme. 
Also, there is an intracellular enzyme, an NADP+-dependent glucose dehydrogenase, which is less involved in the gluconic acid formation when compared to the extracellular enzyme. 
Gluconic acid produced is exported to the cell and further catabolised via the reactions in pentose phosphate pathway. 
When the glucose concentration in the medium is greater than 15 mM, pentose phosphate pathway is repressed and thus gluconic acid accumulation takes place.

Conclusions 
Although the production of gluconic acid is a simple oxidation process that can be carried out by electrochemical, biochemical or bioelectrochemical methods, production by fermentation process involving fungi and bacteria is well established commercially. 
Considerable progress has been made in understanding the mechanism of fermentation process by different microorganisms, and highly efficient production process, which dates back to five decades, has been developed. 
However, development of novel, more economical process for the conversion of glucose to gluconic acid with longer shelf life would be promising. 
These requirements could be met by enzymatic system. 
Another way of improvement is to use cheap substrates, such as methanol instead of glucose.

Production of gluconic acid by microorganisms was discovered in 1880 by Boutroux [4], who observed the formation of a ‘sugar acid’ in the course of studies on the lactic acid fermentation and was verified by several authors as the action of acetic acid bacteria. 
In 1922, Molliard first detected gluconic acid in the cultivation broth of the filamentous fungus, Sterigmatocystis nigra, now known as A. niger. 
Subsequently, the formation of gluconic acid was demonstrated with various strains of Pseudomonas and related genera, Gluconobacter, Acetobacter, and Zymomonas.

In 1924, Bernhauer revealed that A. niger can convert glucose to gluconic acid with high yield when the acid produced is neutralized. 
Large-scale utilization of fungal gluconic acid production was first performed in the USA following the pioneering studies of Currie on citric acid fermentation in 1917, and technological research on gluconic acid production started in the US Department of Agriculture in 1926. 
In 1933, Currie et al. obtained a patent covering the production of gluconic acid by Aspergillus or Penicillium employing the submerged fermentation process: Yields as high as 90% in 48–60 h were achieved for both A. niger and P. luteum. Finally, a strain of A. niger (strain 67) was obtained by selection through fermentative production tests, which could easily be handled. 
In pilot plant studies, yield of up to 95% of the theoretical one was obtained with 150–200 g l−1 glucose solutions within 24 h. Elevated air pressure (2–4 bar) and neutralization with calcium carbonate were applied. Furthermore, it was found that the process could be run semicontinuously by reuse of the mycelia recovered by filtration or centrifugation up to 9 times.

In the 1940s, it was discovered that the concentration of glucose could be increased up to 350 g l−1 by the addition of boron compounds as complexing agents, which prevented the precipitation of calcium gluconate, but was detrimental to the growth of A. niger. 
It was necessary to overcome this effect by selecting particularly resistant strains and by adding the borates only during a later phase of the fungal growth. 
On a technical scale, 250 g l−1 glucose solutions were converted with an efficiency of more than 95% with the reuse of mycelia in cycles of 24 h each. 
However, these techniques have never been allowed to date because borates are recognized to be harmful to human beings.

In 1952, Blom et al. developed a process for the production of sodium gluconate, in which the acid produced during fermentation was neutralized by aqueous NaOH to pH 6.5. 
Today, based on these studies, the submerged fermentation process utilizing mainly A. niger is operating for the production of gluconic acid and gluconates. 
In parallel, several attempts have also been performed to transfer bacterial gluconic acid production into industrial production processes.

Gluconic acid
Gluconic acid is a non-corrosive, non-toxic, biodegradable, weak (pKa =3.86) organic acid. Gluconic acid mainly occurs in plants, fruits, wine, and honey. 
Gluconic acid is produced from D-glucose by the oxidation of its aldehyde group (C1) to a carboxyl group. 
It is not to be confused with other glucose-derived acids such as glucuronic acid, where C6 is oxidized to a carboxyl group, or glucaric acid, where both C1 and C6 are carboxylic groups. 
In aqueous solution at neutral pH, gluconic acid forms gluconate ion that is in equilibrium with its cyclic ester D-glucono delta-lactone (1, 5-gluconolactone). 
The equilibrium is dependent on pH and temperature; heat and high pH increase the rate of D-glucono-delta-lactone hydrolysis. 
Together with its salts and the delta-lactone form, gluconic acid is included as a flavoring agent in a variety of food items such as meat, wine, and dairy products. 
Due to its ability to form water-soluble complexes (chelates) with di- and trivalent metal ions, it is frequently applied as counterion during therapeutic calcium and/or iron administration. 
For the same reason, Gluconic acid is also used to remove calcareous and rust deposits from metals or other surfaces. 

In contrast to bacterial gluconic acid formation, which is a one-step process typically catalyzed by a membrane-bound D-glucose dehydrogenase, fungal gluconic acid formation consists of two steps. 
The first is the direct dehydrogenation of ß-D-glucose to D-glucono-delta-lactone by glucose oxidase. 
This enzyme is a flavoprotein containing a FAD-cofactor which takes up two hydrogen atoms from D-glucose during catalysis and releases hydrogen peroxide. 
However, D-glucono-delta-lactone is unstable in aqueous solution. 
The second step – the hydrolysis of the lactone to its free form, gluconic acid – can therefore be either spontaneous or catalyzed by lactonase. 
Depending on the fungal genera, glucose oxidase is either a fully extracellular enzyme or partially cell wall-bound. 
In all cases, however, it requires molecular oxygen to regenerate FADH2 and is inactivated at pH <3. 
Therefore, the fermentation has to be carefully kept above this pH value. 
The goxA gene encoding glucose oxidase is induced by high glucose concentrations and high dissolved oxygen levels, but the enzyme is competitively inhibited by the hydrogen peroxide formed during FAD recycling. 
To prevent this, A. niger also secretes several catalases that catalyze the decomposition of hydrogen peroxide to water and oxygen. 
Sufficient catalase activity is in fact critical during gluconic acid fermentation. 
The ability of A. niger to form glucose oxidase may be an evolutionary advantage related to competition with other micro-organisms, as the produced hydrogen peroxide has been shown to be the causal agent in combatting other fungi. 
However, due to the necessity of high glucose concentrations, this mechanism only applies at special conditions. 

In addition, glucose oxidase activity depletes the available glucose pool in exchange for the formation gluconic acid. 
Gluconic acid is usually a poor carbon source for micro-organisms, but happens to be a good one for A. niger.

At technical scale, gluconic acid is prepared by microbial fermentation of the various bacterial and fungal strains that were shown to be capable of accumulating gluconic acid, A. niger is the most widely used platform organism. 
Gluconic acid accumulation in A. niger cultures was first observed in 1922. 
The traditional gluconic acid production with A. niger is named “calcium gluconate process”, which stems from the use of calcium carbonate for neutralization of the fermentation broth, a critical technological step to keep the extracellular glucose oxidase active. 
The production medium contains up to 150 g L−1 glucose (most frequently derived from corn or rice); further increase in the glucose concentration is hampered by the limited solubility of calcium gluconate, which would precipitate on the mycelia and inhibit oxygen and substrate uptake. 
Other components of the nutrient medium – particularly phosphorus and nitrogen – are kept at low levels to prevent fungal growth (= loss of carbon source). 
The stoichiometry of the reaction leading to gluconic acid formation shows that on a molar basis, identical amounts of oxygen and D-glucose are needed, despite of the former being much less soluble in water. 
Applying overpressure (up to 3 bars) in the fermentor – which, according to Henry’s law, will increase the saturation level of oxygen in the medium through increasing its partial pressure – has therefore been shown to be highly beneficial. 
The fermentations with almost quantitative yields (Yp/s >95% on a molar basis) are short, between 24 and 48 h. 
In fact, the process resembles to an enzymatic conversion rather than a microbial fermentation.

Sodium gluconate has been used as a superior alternative to the calcium gluconate process, as it enables to use even higher glucose concentrations (up to 350 g L−1). 
Here, the pH is maintained at 6.5 by external control with NaOH, but otherwise, the process is similar to the previous one. 
Based on this technology a continuous process was developed, converting 35% (w v−1) glucose solutions with 95% yield. 
Another continuous fermentation method employing the osmotolerant yeast Aureobasidium pullulans was also described, with the advantage of enabling extremely high (>350 g L−1) initial glucose concentrations in the medium

Gluconic acid and sorbitol are chemical commodities with many applications in food and chemical industries. 
Both compounds are industrially produced from glucose whereby gluconic acid is derived by chemical or microbial oxidation and sorbitol is obtained by chemical reduction

Gluconic acid is a mild organic acid, neither caustic nor corrosive and with an excellent sequestering power. 
Non-toxic and readily biodegradable (98 % after 2 days), it occurs naturally in plants, fruits and other foodstuffs such as wine (up to 0.25 %) and honey (up to 1 %). 
Gluconic acid is prepared by fermentation of glucose, whereby the physiological d-form is produced.

In all recipes where gluconic acid is used together with sodium hydroxide, we recommend the direct use of sodium gluconate, the dry sodium salt of gluconic acid or the special product NAGLUSOL®.

Gluconic acid has versatile properties through being a polyhydroxycarboxylic acid, with both hydroxyl and carboxyl groups which can react.

Concentrated solutions of gluconic acid contain some lactone (GdL), the neutral cyclic ester, which is less soluble in the cold and possesses no actual acid properties. 
About 5 % of GdL are present in the 50 % gluconic acid solution at room temperature.

The outstanding property of gluconic acid is its excellent chelating power, especially in alkaline and concentrated alkaline solutions. 
In this respect, it surpasses all other chelating agents, such as EDTA, NTA and related compounds. 
Calcium, iron, copper, aluminium and other heavy metals are firmly chelated in alkaline solution and masked in such a way that their interferences are eliminated.

Gluconic acid is stable at the boiling point even of concentrated alkaline solutions. 
However, it is easily and totally degraded in waste water treatment plants (98 % after 2 days).

Outgoing    
D-gluconic acid  has role Penicillium metabolite (CHEBI:76964)
D-gluconic acid  has role chelator (CHEBI:38161)
D-gluconic acid  is a gluconic acid (CHEBI:24266)
D-gluconic acid  is conjugate acid of D-gluconate (CHEBI:18391)
D-gluconic acid  is enantiomer of L-gluconic acid (CHEBI:86359)

Incoming    
2,5-didehydro-D-gluconic acid (CHEBI:18281) has functional parent D-gluconic acid 
2-amino-2-deoxy-D-gluconic acid (CHEBI:17784) has functional parent D-gluconic acid 
2-dehydro-3-deoxy-D-gluconic acid (CHEBI:17032) has functional parent D-gluconic acid 
2-dehydro-D-gluconic acid (CHEBI:27469) has functional parent D-gluconic acid 
3-dehydro-2-deoxy-D-gluconic acid (CHEBI:16622) has functional parent D-gluconic acid 
3-dehydro-D-gluconic acid (CHEBI:85257) has functional parent D-gluconic acid 
5-dehydro-D-gluconic acid (CHEBI:17426) has functional parent D-gluconic acid 
6-deoxy-6-sulfo-D-gluconic acid (CHEBI:88270) has functional parent D-gluconic acid 
N-acetyl-D-glucosaminic acid (CHEBI:16948) has functional parent D-gluconic acid 
D-glucono-1,4-lactone (CHEBI:16165) has functional parent D-gluconic acid 
D-glucono-1,5-lactone (CHEBI:16217) has functional parent D-gluconic acid 
D-gluconate (CHEBI:18391) is conjugate base of D-gluconic acid 
L-gluconic acid (CHEBI:86359) is enantiomer of D-gluconic acid 

Gluconates are readily biodegradable both in aerobic and anaerobic conditions. 
As the sequestering tendency of gluconates decreases rapidly upon dilution or lowering pH, their chelated metal complexes are destroyed effectively and quickly by biological waste water treatment as well. 
A closed bottle test for sodium D-gluconate showed that the Theoretical Oxygen Demand (ThOD) was 89% after 28 days which predicts 100% degradation; and an anaerobic study showed that 100% of sodium Dgluconate was degraded after 35 days. 
Gluconic acid, its salts of sodium, potassium and calcium as well as glucono-delta-lactone are all characterised by a low vapour pressure (from 2.41e-009 hPa to 1.58e-022 hPa, estimated from the modified Grain Method), and a low octanol/water partition coefficient (estimated as -5.99 for the sodium salt, -7.51 for the calcium salt, – 5.99 for the potassium salt, -1.87 for the free acid and -1.98 for GDL). 
The dissociation constant of gluconic acid is in the range of 3.5 to 3.8. 
Because of their good water solubility (from 30 g/L for calcium gluconate to 590 g/L for sodium gluconate) and low Log Ko/w, no bioaccumulation effects are to be expected, the substances were also shown to be readily metabolised. 
Estimations from a level II/III fugacity model

Anhydrous gluconic acid is a white, odorless, crystalline powder. 
It is a mild organic acid. The commercial form is a 50 % aqueous solution, which is a colorless to brownish liquid. 
Glucono-delta-lactone is also a white solid, which in aqueous solution slowly hydrolyses to gluconic acid until equilibrium is reached. 
The other members of the category are mineral salts of gluconic acid; i.e. sodium gluconate, potassium gluconate (anhydrous) and calcium gluconate (both anhydrous and the monohydrate). 
Gluconic acid and its derivatives are naturally occurring substances. 
Besides being naturally present at a level up to 1% in wine, honey and other foods and drinks, sodium gluconate (E 576), potassium gluconate (E 577), calcium gluconate (E 578), gluconic acid (E 574) and glucono-delta-lactone (E 575) are all listed as permitted food additives, which may be added to all foodstuffs, following the “quantum satis” principle, as long as no special regulations restrict their use. (European Parliament and Council Directive 95/2/EC). 
The US Food and Drug Administration (FDA) assigned sodium gluconate, potassium gluconate, calcium gluconate and glucono-delta-lactone the “generally recognised as safe” (GRAS) status and permits their use in food without limitation other than good manufacturing practice. 
The Select Committee on GRAS substances has also concluded that there is no evidence in the available information on potassium gluconate that demonstrates or suggests reasonable grounds to suspect a hazard to the public, should it be used as a food ingredient at levels now used for sodium gluconate, or that might be expected in the future.

The purity of the marketed substances may vary depending on the intended uses, but it is generally above 97%. 
For food and/or medical applications the level of impurities complies with the restrictions laid down in the corresponding EU Directives.
Purity (%) of :
Gluconic acid 50% solution : 49-52%
Glucono-delta-lactone: 99-101%
Sodium gluconate: 98-102%
Calcium gluconate: 98-104%
Potassium gluconate: 97-103% 

Gluconic acid and its salts have been used in various applications in the food industry. 
As a sequestrant, sodium gluconate finds broad application in cleaning solutions for the food industry. 
Also, sodium gluconate has been used in indirect application in washing solutions for eggs, denuding tripe, and for preventing the staining of the exteriors of canned goods by cooling and retort water. 
Sodium and calcium gluconate are used as nutritional supplements in sausage products and to increase the water binding properties of the products. 
Over the past ten years, there has been considerable research conducted in Japan using sodium gluconate in order to complement sodium chloride in the proteins extraction from fish muscles. 
Sodium gluconate is used as a replacement for phosphates in the processing of Surimi (minced fish meat) to improve the whiteness and elasticity of the fish product.

In metal surface treatment, sodium gluconate is an effective sequestering agent in alkaline solutions where it forms chelates with earth metals such as calcium and magnesium. 
In this case, as well as in other industrial applications, the product finally flows into the wastewater treatment plant of the user’s site. 
Also in industrial cleaning formulations, where gluconates are valuable complexing agents for di- or trivalent metal cations in alkaline solutions, they are washed out with clean water during the cleaning process. The washing water most likely flows into the wastewater treatment plant of the site. 
These applications  represent about half of the estimated production volumes for sodium gluconate.

In wide-dispersive applications as well, however, the environmental impact is quite limited. 
When used as sequestering agents in the building industry (concrete and mortar), the gluconate ions react with calcium ions present in the cement to form an insoluble and impermeable layer of calcium gluconate. 
Therefore, the gluconate is bound within the microcrystalline fibers of cement and is not free to migrate to cause any environmental pollution.

Food applications could potentially contribute to spreading gluconates and glucono-delta-lactone in the environment, as these products are added in their crystalline or powder forms to food components such as meat, milk or soja at levels below 5 %w/w. 
However, since the final food is meant for human consumption and mostly gets ingested, there is no real potential for environmental distribution of gluconates from this application either. 
If dispersed into the environment, the substances of the category will be found predominantly in the aquatic compartment. 
Indeed, on the basis of the fugacity Level II/III Fugacity Model from US EPA, the main target compartments of gluconates are water and soil but their good water solubility and low vapor pressure designate water as a major target compartment for these substances. 
For sodium gluconate the vapor pressure at 20°C is estimated (on the basis of the modified Grain Method) as 4.53e-017 hPa, which is negligible; the estimated values for the other members of the category are of the same order of magnitude (2.41e-009 hPa for glucono-delta-lactone, 10.87e-010 hPa for gluconic acid, 1.58e-022 hPa for calcium gluconate and 11.89e-017 hPa for potassium gluconate). 
Gluconic acid is a weak acid; its dissociation in water is characterized by the pKa in the range of 3.5 to 3.8. 
Thus, dissociation of gluconates in water is expected to be complete (Ullman’s Encyclopedia, 1999). 
Glucono-delta-lactone slowly hydrolyses in aqueous solution until a balance is reached between gluconic acid and its lactone ester. 
Equilibrium of a 1 % glucono-delta-lactone solution is reached after 2 hours. 
At an initial concentration of 10 % glucono-delta-lactone, the equilibrium gluconatelactone is 80/20. 
The dilution and lowering of pH decrease the stability of metal complexes and the metal ions released during the complex degradation can be removed by precipitation or absorption by the sludge

Other names: D-Gluconic acid; Gluconic acid, D-; 2,3,4,5,6-Pentahydroxyhexanoic acid; Dextronic acid; Glycogenic acid; Glyconic acid; Maltonic acid; Pentahydroxycaproic acid; NSC 77381 a lactones.

DESCRIPTION:
Gluconic Acid 50% is composed of an equilibrium between the free acid and the two lactones. 
This equilibrium is affected by the mixture’s concentration and temperature. 
A high concentration of the delta-lactone will favor the equilibrium to shift to the formation of gamma-lactone and vice versa. 
A low temperature favors formation of glucono-delta-lactone while high temperatures will increase formation of glucono-gamma-lactone. 
Under normal conditions, PMP Gluconic Acid 50% exhibits a stable equilibrium contributing to its clear to light yellow color with low level corrosiveness and toxicity.

GENERAL CHARACTERISTICS:

Chemical Name: Gluconic Acid    

Molecular Weight:196.16

Formula:
C6H12O7    Other Names:Dextronic acid; Pentahydroxycaproic acid

APPLICATION:
Gluconic acid has versatile properties through being a polyhydroxycarboxylic acid, with both hydroxyl and carboxyl groups which can react.

Concentrated solutions of gluconic acid contain some lactone (GDL), the neutral cyclic ester, which is less soluble in the cold and possesses no actual acid properties. 
About 5 % of GdL are present in the 50 % gluconic acid solution at room temperature.

The outstanding property of gluconic acid is its excellent chelating power, especially in alkaline and concentrated alkaline solutions. 
In this respect, it surpasses all other chelating agents, such as EDTA, NTA and related compounds. 
Calcium, iron, copper, aluminum and other heavy metals are firmly chelated in alkaline solution and masked in such a way that their interferences are eliminated.

Gluconic acid is stable at the boiling point even of concentrated alkaline solutions. 
However, it is easily and totally degraded in waste water treatment plants (98% after 2 days).

STANDARD PACKAGING & AVAILABILITY:
PMP Gluconic Acid 50%, Technical is packaged in 55 gallon, 555 lb. net weight plastic drums and is also available in 2500lb totes.

STORAGE & HANDLING:
This product should be stored above 60°F since lactones may crystallize at lower temperatures. 
This product is a slightly corrosive organic acid solution. 
It is recommended that material of construction and handling be stainless steel, rubber lined steel, epoxy resin coated steel, plastic or glass. 
The use of aluminum, mild steel, and iron as equipment for materials of construction is not recommended.

Gluconic acid is an organic compound with a molecular formula of C6H12O7 and condensed structural formula HOCH2 (CHOH)4 COOH. 
It is one of the 16 stereoisomers of 2, 3, 4, 5, 6-pentahydroxyhexanoic acid commonly known as dextronic acid.

 

In aqueous solution at neutral pH, gluconic acid forms the Gluconate ion. 
The salts of gluconic acid are known as “Gluconates”. 
Gluconic acid, gluconate salts, and gluconate esters occur widely in nature as these compounds arise from the oxidation of glucose. 
Some drugs are injected in the form of gluconates.

The chemical structure of gluconic acid consists of a six-carbon chain with five hydroxyl groups terminating in a carboxylic acid group. 
In aqueous solution, gluconic acid exists in equilibrium with its cyclic ester glucono delta-lactone. 
Gluconic acid occurs naturally in fruits, honey, Kombucha tea, and wine.
 

Production

Gluconic acid can be obtained by chemical synthesis, on account of its superior selectively; however microbial production is highly preferred. 
A series of microorganisms under the genus of Aspergillus, Penicillin, Gluconobacter, Pseudomonas, Phytomonas, Achromobacter, Klebsiella, Zymomonas, and Acetobacter have already been used for microbial production of gluconic acid. A yeast-like fungal culture, Aureobasidium pullulans was also known for the production of small amounts of gluconic acid.

For microbial production of gluconic acid, predominantly, Aspergillus niger or Gluconobacter suboxidans are in industrial use. 
Aspergillus niger is difficult to handle, as it causes clogging and unsuitable for the continuous production. 
This is mainly due to the drawback that cell growth and gluconic formation would not be possible simultaneously. 
On the other hand, Gluconobacter has been found to produce a relatively large quantity of keto acids during production. 
These keto acids complicate the processing and isolation of the pure gluconic acid.

Applications

Gluconic acid is a multifunction carbonic acid and it is used extensively in various applications with its physiological and chemical characteristics.

As a food additive, it acts as an acidity regulator.
In metal cleaning formulations for rust and stains (mineral deposits) removal on metal surfaces.
Used in metal finishing baths for aluminum etching and in metal plating processing baths.
In high-performance metal degreasers.
In textile industries as stabilizers for dye baths and bleach baths.
In leather tanning and dyeing processes.
Mixed in mortar and concrete admixes as a retarder as well as a plasticizer (after neutralization with alkali).
 

Used as a raw material for the manufacturing of gluconate salts with minerals like Calcium, Sodium, Potassium, and Manganese etc.

Different Salts of Gluconic acid

 

The gluconate anion chelates with Ca2+, Fe2+, Al3+ as well as other metals and forms salts. 
In 1929, Horace Terhune Herric first developed a process for producing the salt by fermentation. 
Various gluconate salts with their applications are as follows.    

 

Calcium Gluconate
Calcium is an essential element of tissues and blood, which constitutes approximately 10 mg/ 100 mL. 
The average daily requirement of calcium is 500 mg, however higher amounts are necessary during the periods of growth. 
Calcium Gluconate has the molecular formula of C12H22CaO14.H2O with 448.40 g/mol of molecular weight.

 Calcium Gluconate has various applications in pharmaceutical, food, and feed industries

It is used to treat acid burns caused by hydrofluoric acid.
Used as a cardioprotective agent in hyperkalemia and in magnesium toxicity.
As an emulsifier, stabilizer, or thickener, or to control pH levels of some foods.
Added to foods for its health value. E.g. baby foods, juices, biscuits, and health foods etc.
Incorporated in pudding preparation for preventing the sour taste obtained by other salts.
In the treatment of hypocalcemia in cases of milk fever and gross tetany in cattle.
 

Potassium Gluconate
Potassium Gluconate is administered in all cases of potassium deficiencies or in danger of potassium depletion in conditions like diabetic acidosis, diarrhea, and vomiting etc. 
Potassium chloride is also used but potassium gluconate is highly preferred because of its slight saline taste.

To stabilize blood pressure
In Regulation of heart rhythms
To control the nervous system and muscle contractions
Regulates water balance and alkalinity of body fluids
As a nutrition enhancer in dairy products
 

Sodium Gluconate
It is a sodium salt of gluconic acid with a molecular formula of C6H11O7Na. 
It has a molar mass of 218.14 g/mole. Sodium gluconate has many applications in as below

As a detergent in bottle washing to control heavy metals and harness ions.
In alkaline derusting.
As an additive in the construction industry in cement retarder and water reducer for concrete.
In the textile industry as a sequestering agent for heavy metal ions and to remove iron deposits.
In the paper industry.
 

Manganese Gluconate
Manganese gluconate can be readily formulated into tablets for the treatment of manganese deficiency. 
It is primarily added to vitamins and mineral dietary preparations to supplement the normal intake in the case of inadequate levels. 
In feed Stuff Manganese Gluconate is added to animals feed to assure adequate manganese ions for balanced diet development.
Manganese gluconate has applications in Pharma, Food, and Feed sectors.

 
Various other gluconates of Zn, Fe, Quinine also have important pharma applications as below

 
Zinc Gluconate injections are used to neuter male dogs.
Iron Gluconate injections have been in use to treat anemia.
Quinine Gluconate is a salt of gluconic acid and quinine. It is used as an intramuscular injection in the treatment of malaria.

What are Gluconates?
Gluconates usually refer to the salts of gluconic acid that are commonly made from the reaction between gluconic acid and the corresponding metal carbonate salts.
The following are six common types of gluconates and their uses/functions in food: 

Calcium gluconate: functions as a firming agent, formulation aid, sequestrant, stabilizer or thickener and texturizer that can be used in baked goods, dairy products, gelatins, puddings and sugar substitutes. 
Sodium gluconate: a sequestrant.
Copper gluconate: works as a nutrient supplement and a synergist, may be used in infant formula.
Ferrous gluconate: a nutrient supplement that may be used in infant formula, also can be acted as a food color.
Manganese gluconate: a nutrient supplement that can be used in baked goods, dairy and meat products, poultry products, and infant formulas. 
Zinc gluconate:  nutrient. 

Solubility
In water

Freely soluble in water with the solubility 100g/100ml at 25°C. (14)

In organic solvents

Slightly soluble in alcohol, insoluble in ether and most other organic solvents.

PKa & PH
Gluconic acid is a weak carboxylic acid with a dissociation constant pKa 3.6. It dissociates a proton and a gluconate ion (conjugation). Its aqueous solution has a neutral pH. (15)

What’re the Uses of Gluconic Acid?
Mainly used for its leavening and acidity properties in food; chelating and perfuming agents in cosmetics products; also it can be used in industrial uses for chelating heavy metals.

Food
The following food may contain with gluconic acid:

Bakery goods: as a leavening acid in leavening agent to increase dough volume by producing gas by the reaction with baking soda.
Dairy products: as a chelating agent and prevent milkstone.
Some food and beverage: as an acidity regulator to impart a mild organic acid and adjust pH level and also as a preservative and an antifungal agent. Also, it can be used to clean aluminium cans.
Animal Nutrition
Gluconic acid functions as a weak acid in piglet feed, poultry feed and aquaculture to comfort digestive and promote growth, also to increase the production of butyric acid and SCFA (Short-chain fatty acid). (16)

Cosmetics
It can be used as a chelating and perfuming agent in cosmetic and personal care products. (17)

Industrial uses 
The power of chelating heavy metals is stronger than that of EDTA, such as the chelation of calcium, iron, copper, and aluminium in alkaline conditions. This property can be utilized in detergents, electroplating, textiles and so on.

Is Gluconic Acid Safe to Eat?
Yes, this acid has been approved safe by the U.S. Food and Drug Administration (FDA) and European Food Safety Authority (EFSA), as well as the Joint FAO/WHO Expert Committee on Food Additives (JECFA).

FDA
D-gluconic acid can be added to food as a nutrient supplement. (18)

EFSA
Gluconic acid (E574) is listed in Commission Regulation (EU) No 231/2012 as an authorised food additive and categorized in “ additives other than colours and sweeteners” (19).

Approved uses
The food application of gluconic acid is classified in “Group I”, which means the usage is “quantum satis”, also the same use levels in nutrients. (22)

Food Standards Australia New Zealand 
It is approved ingredient in Australia and New Zealand with the code number 574. (23)

Frequently asked questions of Gluconic Acid
What is it made of?
Generally, it is a mixed aqueous solution of gluconic acid and glucono-delta-lactone. (24)

Is it Vegan?
Yes, it is vegan as the raw material is from the plant sources and the manufacturing process without the use of animal matter or products derived from animal origin. So that it is suitable to be added in the diet of vegetarians.

Is it Natural?
Yes, it is natural if obtained by microbial oxidation of glucose.

Is it Gluten free? 
Yes, it is gluten free or without gluten as it does not contain wheat, rye, barley, or crossbreeds of these grains, therefore can be used for people with celiac disease.

Is it the same with Glucuronic acid?
No, it is different with Glucuronic acid (C6H10O7), which is also a derivative of glucose.

Conclusion
Now you may have a knowledge of the acidulant – gluconic acid (E574), from the following aspects:

Production process
Gluconates
Uses in food, animal and others
Safety

Gluconic acid, or pentahydroxycaproic acid (C6H12O7), naturally occurs in plants, fruits, wine, honey, rice, meat, vinegar, and other natural sources. 
The alkali salt of gluconic acid such as calcium gluconate or sodium gluconate has multiple applications used in chemical, pharmaceutical, food, beverage, and construction industries. 
Due to its low toxicity, low corrosiveness, and high capability of forming water-soluble complexes with divalent and trivalent metal ions, sodium gluconate has been designated as GRAS by the US FDA. 
This acid is also recognized as a generally permitted food additive (E574) in the European Parliament and the Council Directive No. 95/2/EC. 
Like other organic acids, gluconic acid has diverse uses that range widely depending on their particular structure. 
Thus, gluconic acid and its derivatives (except glucono-lactone) are used mainly as additives by food, pharmaceutical, hygiene, and building industries

Gluconic acid (2,3,4,5,6-pentahydroxy caproic acid, C6H12O7) is a noncorrosive, nontoxic, mild organic acid with a brown clear appearance. 
It is very soluble in water and has a mild and refreshing taste. 
It is a good chelator at high pH, with better activity than commonly used chelators.
 
Gluconic acid.
Gluconic acid was discovered in 1870 by Hlasiwetz and Habermann, when glucose was oxidized with chlorine. 
In 1922 it was isolated from a strain of A. niger. 
Later, other filamentous fungi, such as Penicillium, Scopulariopsis, Gonatobotrys, and Gliocladium, and also oxidative bacteria, such as strains of Pseudomonas, Gluconobacter (Acetobacter), Moraxella, Micrococcus, Enterobacter, and Zymomonas were found to produce gluconic acid. 
Already in the 1940s it was possible to obtain good yields of gluconic acid using A. niger by fermentation, neutralizing the accumulating acid with calcium carbonate.
The physiological functions of gluconic acid accumulation for these organisms are not clear; one possibility is its contribution to the competitiveness of the organism, removing glucose from the close environment. 
In the case of P. expansum (a phytopathogenic fungus), it was demonstrated that secreted gluconic acid contributed to the colonization and disease development of apple tissues by this fungus.
Gluconic acid is used in the manufacture of metal, leather, and food. 
It has been accredited with the capability of inhibiting bitterness in foods. 
Sodium gluconate is permitted in food and it has GRAS (generally recognized as safe) status. 
This salt is also utilized as a sequestering agent in many detergents, and added to cement to improve the hardening process.

The formation of gluconic acid is different from most other organic acids, since it is formed outside the cytoplasmic membrane, by the enzyme glucose oxidase. 
This enzyme has been shown to be localized in the cell wall, at least for fungi known to accumulate gluconic acid. 
Glucose in the medium is oxidized in a two-step reaction to gluconic acid; first glucose oxidase oxidizes β-d-glucopyranose to d-glucono-1,5 lactone with the formation of hydrogen peroxide, acted upon by catalase to form water and oxygen

Gluconic acid is a non-corrosive, non-toxic, biodegradable, weak (pKa =3.86) organic acid. 
It mainly occurs in plants, fruits, wine, and honey.
Gluconic acid is produced from D-glucose by the oxidation of its aldehyde group (C1) to a carboxyl group. 
It is not to be confused with other glucose-derived acids such as glucuronic acid, where C6 is oxidized to a carboxyl group, or glucaric acid, where both C1 and C6 are carboxylic groups. 
In aqueous solution at neutral pH, gluconic acid forms gluconate ion that is in equilibrium with its cyclic ester D-glucono delta-lactone (1, 5-gluconolactone). 
The equilibrium is dependent on pH and temperature; heat and high pH increase the rate of D-glucono-delta-lactone hydrolysis. 
Together with its salts and the delta-lactone form, gluconic acid is included as a flavoring agent in a variety of food items such as meat, wine, and dairy products. 
Due to its ability to form water-soluble complexes (chelates) with di- and trivalent metal ions, it is frequently applied as counterion during therapeutic calcium and/or iron administration. 
For the same reason, it is also used to remove calcareous and rust deposits from metals or other surfaces.

Gluconic acid is produced from glucose. In this glucose oxidase catalysis process, the dehydrogenation reaction leads to its production. 
It had already been produced in 1870. 
Being found later by Molliard (1922) in A. niger. 
Since then many researchers have studied the conditions and processes that would lead to better yields.
Gluconic acid production by fermentation of glucose using A. niger is a mature bioprocess with literature reporting highly efficient processes dating back to 1940.
Gluconic acid has applications in the food industry, as in meat and dairy products, baked goods, flavoring agent, and reducing fat absorption in doughnuts. 
Although with a market smaller than that of citric acid, gluconic acid finds its place, as well as its derivatives, such as sodium, calcium, and iron gluconate, which is used for dietary supplements, in the pharmaceutical and textile industries (Ramachandran et al., 2006).
Nowadays, despite having access to a variety of methods to produce gluconic acid, microbial fermentation remains the chosen approach since other methods are more expensive and less efficient compared to fermentation (Ramachandran et al., 2006). 
For that the microorganism most commonly used is A. niger. 
Even though several factors influence microbial fermentation, it is believed that oxygen availability and the pH of the medium are key parameters to be addressed. 
Studies concentrate in exploring the fermentation processes, as well as alternatives such as cheaper raw materials, enzymatic immobilization, molecular biology tools, so that production can be optimal and the results the best possible