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Gluconic acid
Gluconic acid
Gluconic acid
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d-Gluconic acid
Skeletal formula of gluconic acid
Skeletal formula of gluconic acid
Ball-and-stick model of gluconic acid
Ball-and-stick model of gluconic acid
Names
IUPAC name
d-Gluconic acid
Systematic IUPAC name
(2R,3S,4R,5R)-2,3,4,5,6-Pentahydroxyhexanoic acid
Other names
  • Dextronic acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.007.639 Edit this at Wikidata
EC Number
  • 208-401-4
E number E574 (acidity regulators, ...)
UNII
  • InChI=1S/C6H12O7/c7-1-2(8)3(9)4(10)5(11)6(12)13/h2-5,7-11H,1H2,(H,12,13)/t2-,3-,4+,5-/m1/s1 checkY
    Key: RGHNJXZEOKUKBD-SQOUGZDYSA-N checkY
  • InChI=1/C6H12O7/c7-1-2(8)3(9)4(10)5(11)6(12)13/h2-5,7-11H,1H2,(H,12,13)/t2-,3-,4+,5-/m1/s1
    Key: RGHNJXZEOKUKBD-SQOUGZDYBY
  • O=C(O)[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO
Properties
C6H12O7
Molar mass 196.155 g·mol−1
Appearance Colorless crystals
Density 1.23 g/cm3[1]
Melting point 131 °C (268 °F; 404 K)
316 g/L[2]
Acidity (pKa) 3.86[3]
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H315, H319
P264, P264+P265, P280, P302+P352, P305+P351+P338, P321, P332+P317, P337+P317, P362+P364
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Gluconic acid is an organic compound with molecular formula C6H12O7 and condensed structural formula HOCH2(CHOH)4CO2H. A white solid, it forms the gluconate anion in neutral aqueous solution. 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.

Chemical structure

[edit]

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. It is one of the 16 stereoisomers of 2,3,4,5,6-pentahydroxyhexanoic acid.

Production

[edit]

Gluconic acid is typically produced by the aerobic oxidation of glucose in the presence of the enzyme glucose oxidase. The conversion produces gluconolactone and hydrogen peroxide. The lactone spontaneously hydrolyzes to gluconic acid in water.[4]

C6H12O6 + O2 → C6H10O6 + H2O2
C6H10O6 + H2O → C6H12O7

Variations of glucose (or other carbohydrate-containing substrate) oxidation using fermentation.[5][6] or noble metal catalysis.[7][8]

Gluconic acid was first prepared by Hlasiwetz and Habermann in 1870[9] and involved the chemical oxidation of glucose. In 1880, Boutroux prepared and isolated gluconic acid using the glucose fermentation.[10]

Historical role in development of deep-tank fermentation

[edit]

The production of gluconic acid by deep-tank fermentation (aerated, pH controlled, and stirred >1000 L tanks) of the filamentous fungi Aspergillus niger in 1929, for use as a food acidity regulator and cleaning agent, was the first successful use of deep-tank fermentation by Pfizer.[11] This expertise later led to Pfizer's successful use of deep-tank fermentation of Penicillium fungi in February 1944,[11] to rapidly scale up penicillin production, resulting in sufficient penicillin to treat the American and British battle casualties of the June 6th Allied D-Day invasion of World War II.[12]

Occurrence and uses

[edit]

Gluconic acid occurs naturally in fruit, honey, and wine. As a food additive (E574[13]), it is now known as an acidity regulator.

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

Zinc gluconate injections are used to neuter male dogs.[14]

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.[15][16] 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.

Gluconic acid aqueous solution finds application as a medium for organic synthesis.[17]

Medicine

[edit]

In medicine, gluconate is used most commonly as a biologically neutral carrier of Zn2+, Ca2+, Cu2+, Fe2+, and K+ to treat electrolyte imbalance.[18]

Calcium gluconate, in the form of a gel, is used to treat burns from hydrofluoric acid;[19][20] 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.[21] Quinine gluconate is a salt of gluconic acid and quinine, which is used for intramuscular injection in the treatment of malaria.

Ferrous gluconate injections have been proposed in the past to treat anemia.[22]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Gluconic acid

View on Grokipedia
from Grokipedia
Gluconic acid is an with the molecular C₆H₁₂O₇ and a molecular weight of 196.16 g/mol, representing the oxidized form of glucose where the group at the C-1 position is converted to a . It occurs naturally as a in various microorganisms, such as and species, and is commercially produced primarily through microbial of glucose using fungi like or bacteria like Gluconobacter oxydans. This mild, non-toxic acid exhibits key physical properties including a colorless to light yellow syrupy liquid or white crystalline powder appearance, a range of 113–131 °C, and high in (up to 316 mg/mL at 25 °C), with a pKa of 3.62 that contributes to its role as a chelating agent. Production methods emphasize submerged with A. niger at 6.0–6.5 and 34 °C, achieving yields of 0.97–1 g/g glucose, or bacterial processes with G. oxydans at pH below 4.5, reaching up to 148.5 g/L, often utilizing agro-industrial substrates like sugarcane molasses or for sustainability. Gluconic acid finds widespread applications across industries: in food as a nutrient supplement and acidulant (accounting for about 35% of use), in construction and metal cleaning as a non-corrosive chelator (45% of use), and in medicine for maintaining cation-anion balance in electrolyte solutions and parenteral nutrition (10% of use). Its derivatives, such as and glucono-δ-lactone, extend these roles to processing, , and pharmaceutical formulations like for treating biofilms or deficiencies. Overall, its biodegradable and environmentally friendly profile supports growing demand in sustainable chemical processes.

Chemical and physical properties

Molecular structure

Gluconic acid has the molecular \ceC6H12O7\ce{C6H12O7} and a molecular weight of 196.16 g/mol. It is an aldonic acid formed by the oxidation of D-glucose specifically at the group on carbon 1 (C1), converting it to a while preserving the rest of the sugar's carbon chain. This results in a straight-chain known as 2,3,4,5,6-pentahydroxyhexanoic acid, featuring a carboxyl group (-COOH) at C1 and a group (-CH2OH) at C6, with hydroxyl groups (-OH) attached to each of the intervening carbons 2 through 5. The open-chain form of gluconic acid can be represented as: \ceHOOC−CH(OH)−CH(OH)−CH(OH)−CH(OH)−CH2OH\ce{HOOC-CH(OH)-CH(OH)-CH(OH)-CH(OH)-CH2OH} This linear depiction highlights the six-carbon backbone, where the terminus at one end contrasts with the at the other, distinguishing it from the cyclic forms common in unmodified glucose./20%3A_Carbohydrates/20.03%3A_The_Structure_and_Properties_of_D-Glucose) Gluconic acid exhibits due to its retention of the D-configuration from D-glucose, with four stereocenters at carbons 2, 3, 4, and 5. These chiral centers maintain the specific spatial arrangement of hydroxyl groups as in the parent sugar, resulting in the naturally occurring D-gluconic acid . The molecule's optical activity arises from this , which is critical for its biological recognition and function. In comparison to other aldonic acids, gluconic acid is produced by single-end oxidation at C1, whereas glucaric acid (also known as ) results from oxidation at both the C1 and the C6 groups, yielding a with the \ceC6H10O8\ce{C6H10O8}. This difference in oxidation extent leads to distinct structural and chemical profiles, with gluconic acid retaining a terminal alcohol that glucaric acid lacks./20%3A_Carbohydrates/20.03%3A_The_Structure_and_Properties_of_D-Glucose)

Physical characteristics

Gluconic acid is typically encountered as a to off-white crystalline powder in its solid form, though it often appears as a colorless to pale yellow, viscous syrupy liquid when prepared as an . The compound exhibits high solubility in , approximately 100 g per 100 mL at 25°C, owing to its multiple hydroxyl groups; it is moderately soluble in alcohols such as and insoluble in non-polar solvents like . A 50% has a of about 1.23 g/cm³ and a ranging from 1.2 to 2.2. Upon heating, gluconic acid has a of 131°C, during which it decomposes to gluconolactone rather than forming a stable melt. The pure solid has a density of 1.24 g/cm³.

Chemical properties

Gluconic acid is a mild characterized by a pKa value of 3.86 at 25°C, where it dissociates in to form the gluconate anion. This dissociation follows the equilibrium: \ceC6H12O7⇌C6H11O7−+H+\ce{C6H12O7 ⇌ C6H11O7^- + H^+} As a chelating agent, gluconic acid forms stable complexes with divalent and trivalent metal ions, such as Fe²⁺, Ca²⁺, and Cu²⁺, through coordination involving its multiple hydroxyl groups and the carboxylate moiety. These interactions typically occur via bidentate or multidentate binding, enhancing solubility and stability of the metal ions in aqueous solutions. Gluconic acid demonstrates resistance to oxidation owing to the absence of an group in its structure, which distinguishes it from its precursor glucose. It remains stable under neutral conditions, where the deprotonated gluconate form predominates, but in acidic media, it undergoes partial lactonization to form δ-gluconolactone and, to a lesser extent, γ-gluconolactone. Under aerobic conditions, gluconic acid is readily biodegradable, undergoing rapid microbial degradation within hours to days in environmental settings. Additionally, it exhibits negligible volatility, with a below 0.01 mmHg at ambient temperatures, consistent with its solid state and high .

History and production

Discovery and historical development

Gluconic acid was first synthesized in 1870 by Austrian chemists Franz Hlasiwetz and Joseph Habermann through the oxidation of glucose using chlorine gas, marking the initial chemical preparation of this compound. In 1880, French chemist Louis Boutroux isolated gluconic acid from the microbial oxidation of glucose by , such as , during studies on sugar fermentation; this discovery highlighted its natural formation in processes akin to those occurring in wine production. The commercialization of gluconic acid advanced significantly in 1929 when Chas. Pfizer & Co. developed a submerged fermentation process using the mold Aspergillus niger to oxidize glucose, enabling efficient microbial production on an industrial scale. During the 1940s, advancements in deep-tank fermentation—initially refined for gluconic acid production at Pfizer—facilitated large-scale output and were pivotal in scaling up penicillin manufacturing during World War II, as the aerated, stirred-tank systems supported high-yield fungal fermentations. Post-World War II, production shifted from costly chemical methods, such as hypobromite oxidation of , to biotechnological with due to improved efficiency, lower costs, and scalability in submerged processes.

Modern production methods

The primary industrial method for producing gluconic acid is submerged microbial , predominantly using the fungus as the biocatalyst, which oxidizes to gluconic acid via the enzyme . This process achieves high conversion yields of up to 95%, with serving as the main substrate in concentrations of 120–350 g/L, under controlled to maintain dissolved oxygen levels essential for the oxidation reaction. The reaction proceeds as follows: C6H12O6+O2+H2O→C6H12O7+H2O2\text{C}_6\text{H}_{12}\text{O}_6 + \text{O}_2 + \text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_7 + \text{H}_2\text{O}_2 where glucose is first converted to glucono-δ-lactone, which hydrolyzes to gluconic acid, and hydrogen peroxide is a byproduct often managed by co-produced catalase. Typical batch or fed-batch operations last 50–60 hours at temperatures around 30°C and pH 3–6, enabling titers up to 330 g/L. Bacterial fermentation, using organisms such as Gluconobacter oxydans, represents another key industrial approach. This method employs glucose dehydrogenase and operates at below 4.5 (optimally below 3.5), with substrates like or , achieving yields of 75–80% and titers up to 148.5 g/L. Enzymatic production represents an alternative biotechnological approach, employing isolated —sourced from or species—coupled with to decompose the byproduct and prevent inactivation. This method facilitates direct oxidation of glucose in bioreactors or immobilized systems, such as anion-exchange membranes or crosslinked aggregates, achieving conversions of 95–96% under mild conditions ( 4–7, 40–60°C) with oxygen-enriched . While scalable for high-purity applications, it is less dominant industrially than whole-cell due to enzyme production costs. Chemical synthesis methods, including electrochemical oxidation on electrodes or catalytic air oxidation with catalysts, offer selective glucose-to-gluconic acid conversion but are less common owing to higher demands, toxicity concerns, and overall production costs compared to . These approaches typically require alkaline conditions and elevated temperatures, limiting their adoption in favor of biological routes. Various feedstocks support these processes, including refined sources like (high-glucose syrup) and agro-industrial byproducts such as or rice bran hydrolysates, which provide cost-effective glucose equivalents while promoting . After or reaction completion, purification involves ion-exchange resins to remove impurities, followed by and to yield a 50% or powder, often achieving 98% purity for derivatives.

Natural occurrence and biological role

Sources in nature

Gluconic acid occurs naturally in various , where it contributes to their profile. In apples, concentrations can reach up to approximately 0.3% on a dry weight basis, as identified in analyses of fruit samples. It is also present in grapes and fruits, though typically at lower levels, often resulting from metabolic processes or microbial interactions during growth. Honey serves as a significant natural source of gluconic acid, which is the predominant in this product, arising from the enzymatic activity of bees. Concentrations in range from 0.18% to 1.27%, with variations depending on floral origin and processing. In wine, gluconic acid appears primarily through microbial action on grapes, particularly from fungal infections like , with levels up to 0.25% in affected batches. Gluconic acid is produced in fermented foods through bacterial and fungal metabolism during the fermentation process. In tea, it accumulates as a key metabolite from the oxidation of glucose by , contributing to the beverage's acidity. In environmental contexts, gluconic acid is generated in and around roots by rhizosphere bacteria, such as species of , which secrete it to solubilize nutrients like and iron. This production enhances growth by improving availability in the root zone. Trace amounts are also found in rice bran, various vegetables, and meats as metabolic byproducts of glucose oxidation. Overall, gluconic acid concentrations in these natural matrices typically range from 0.01% to 1%, though they can be higher in processed ferments where microbial activity is concentrated.

Role in biology

In mammals, gluconic acid, in its deprotonated form as gluconate, serves as a metabolic intermediate that can enter the (PPP) through by gluconokinase to form 6-phosphogluconate, which is then further metabolized to generate NADPH and ribose-5-phosphate for biosynthetic needs. This pathway supports cellular redox balance and nucleotide synthesis, with human gluconokinase exhibiting a dimeric structure and ATP-dependent activity optimized for gluconate utilization under physiological conditions. Although the primary entry to the oxidative PPP occurs via acting on glucose-6-phosphate, the gluconate shunt provides an alternative route for gluconate assimilation, particularly in response to extracellular glucose oxidation products. In plants, gluconic acid contributes to rhizosphere acidification, lowering the pH to around 4-5, which facilitates mineral nutrient uptake such as phosphorus and iron by solubilizing insoluble phosphates and chelating metals. This acidification also aids in cell wall loosening during root growth and expansion by promoting the activity of expansins and other wall-modifying enzymes in an acidic environment. Microbial symbionts in the rhizosphere, including plant growth-promoting bacteria, enhance this process by excreting gluconic acid, thereby improving overall plant nutrient acquisition and stress tolerance. Microorganisms, particularly fungi like Aspergillus species and bacteria such as Pseudomonas and Gluconobacter, produce gluconic acid as a key strategy for adapting to nutrient-poor environments, where it enhances organic acid tolerance by buffering intracellular pH and facilitates metal chelation to mobilize essential trace elements like iron and . In metal-contaminated soils, this production allows fungi to tolerate high heavy metal concentrations through extracellular , preventing toxicity while enabling for nutrient recovery. Bacterial production similarly supports survival by lowering local pH to deter predators like and to solubilize minerals in oligotrophic habitats. Gluconic acid participates in biological detoxification and systems by chelating and reactive species, thereby mitigating in cellular environments. In certain microbial pathways, particularly those engineered for industrial production, it can be converted through sequential oxidations to intermediates like 2-keto-gluconic acid and 2,5-diketo-D-gluconic acid, which serve as precursors to ascorbic acid () in bioprocesses supporting applications. The D-enantiomer of gluconic acid predominates in natural biological systems, derived from D-glucose oxidation, and exhibits the primary bioactivity in metabolic and ecological roles, while the L-form is rare and shows reduced enzymatic recognition and physiological impact. This enantiomeric specificity ensures efficient integration into chiral-dependent pathways like the PPP and processes.

Derivatives

Gluconolactone

Gluconolactone, particularly in its δ-form (also known as glucono-δ-lactone or glucono-1,5-lactone), is the cyclic internal of gluconic acid. It forms through an intramolecular esterification reaction where the carboxyl group at carbon 1 reacts with the hydroxyl group at carbon 5 of gluconic acid, creating a stable six-membered ring . This lactonization process involves the elimination of from the parent acid and is reversible under appropriate conditions. The equilibrium for this transformation is represented by the equation: \ceC6H12O7⇌C6H10O6+H2O\ce{C6H12O7 ⇌ C6H10O6 + H2O} where \ceC6H12O7\ce{C6H12O7} denotes gluconic acid and \ceC6H10O6\ce{C6H10O6} is δ-gluconolactone. Physically, δ-gluconolactone presents as a white to off-white crystalline powder with a melting point of 153 °C. It exhibits good solubility in water, approximately 50 g per 100 mL at 20 °C, and is also soluble in alcohols such as methanol and ethanol, though insoluble in most organic solvents. These properties make it suitable for applications requiring gradual dissolution and reactivity in aqueous environments. In water, δ-gluconolactone undergoes slow back to gluconic acid, with the rate depending on temperature, , and concentration; for instance, the half-life is about 10 minutes at 6.6. This controlled hydrolysis distinguishes it from the free acid, enabling its use as a slow-release acidulant that provides progressive acidification rather than immediate pH drop. The slower release profile is particularly advantageous in processes where rapid acidity could disrupt structure or flavor development. A key application unique to the lactone form is its role as a in , designated as food additive E575 in the . When combined with , it acts as a , releasing gradually due to its hydrolysis kinetics, which promotes dough relaxation, enhances texture, and improves overall volume without excessive stickiness or rapid souring. This slower acidification compared to direct gluconic acid addition helps maintain optimal during and , contributing to softer, more uniform baked goods.

Metal gluconates

Metal gluconates are salts formed from gluconic acid and various metal ions, valued for their chelating capabilities that enable applications in and industry. These compounds typically exhibit the gluconate anion (C₆H₁₁O₇⁻) coordinating with metal cations, forming stable complexes that enhance and prevent of metal ions in aqueous environments. Common metal gluconates include , which serves as a sequestrant to bind and stabilize di- and trivalent metal ions in solutions. acts as a to provide bioavailable calcium. Ferrous gluconate is employed in iron therapy to address deficiencies. appears in lozenge formulations for oral delivery. These salts are generally prepared by neutralizing gluconic acid with the corresponding or , yielding the desired gluconate through acid-base reaction. For instance, results from reacting gluconic acid with or lime. This method ensures high purity and for commercial production. Key properties of metal gluconates include high water solubility and stability at neutral pH, facilitating their use in diverse formulations. Calcium gluconate, for example, dissolves at approximately 3.5 g per 100 mL of water at 25°C. Their chelating nature promotes bioavailability enhancement of the associated metal ions in biological systems. Chelating stoichiometry varies by metal ion valence: monovalent salts like sodium gluconate adopt a 1:1 metal-to-gluconate ratio (NaC₆H₁₁O₇), while divalent salts such as calcium or ferrous gluconate follow a 1:2 ratio. A specific example is ferrous gluconate, with the formula Fe(C₆H₁₁O₇)₂, utilized in treatments for due to its iron content. This compound demonstrates the typical 1:2 , where the ferrous ion (Fe²⁺) binds two gluconate ligands, contributing to its in (with slight heating) and overall stability.

Applications

Food and beverage industry

In the , gluconic acid is approved as a under the designation E574, functioning primarily as an acidity regulator and sequestrant. In the United States, it holds (GRAS) status from the , permitting its use in food products without specific quantitative limitations when employed as intended. Gluconic acid plays a key role in pH adjustment across various food categories, particularly in dairy products where it acts as a sequestrant to bind metal ions and prevent protein precipitation, thereby maintaining product stability and texture. In beverages, its mild sour taste profile helps replicate natural acidity, such as in wines and fruit juices, contributing to a balanced flavor without overpowering sharpness. For baking applications, gluconic acid is often utilized indirectly through its derivative gluconolactone, which serves as a slow-acting leavening agent; upon hydration, it gradually releases acid to react with baking soda, producing carbon dioxide for dough expansion in products like refrigerated or frozen baked goods. Beyond control, , a derivative of gluconic acid, inhibits bitterness in foodstuffs. It also improves mineral absorption in fortified foods; for instance, as ferrous gluconate, it enhances iron compared to other iron salts, making it suitable for nutrient-enriched products like cereals and beverages. Typical usage levels of gluconic acid range from 0.1% to 0.5% in final products such as fruit juices, jams, and meat preservatives, where it stabilizes formulations and extends without altering sensory qualities significantly. It exhibits synergy with other acids like for flavor balance, combining citric acid's initial sharp sourness with gluconic acid's prolonged mild acidity to achieve a more rounded in and beverages.

Pharmaceutical and medical uses

Gluconic acid derivatives, particularly its metal salts, play a significant role in pharmaceutical applications due to their and ability to deliver essential ions in therapeutic forms. is widely used for the treatment of , where it is administered via intravenous injection or to rapidly restore serum calcium levels in acute symptomatic cases. For instance, a typical regimen involves infusing 1 to 2 grams of diluted in dextrose solution over 10 to 20 minutes, with continuous infusions of 5 to 20 mg/kg/hour for persistent . Additionally, serves as an adjunct therapy in envenomation, particularly for neurotoxic bites such as those from kraits, where it helps stabilize the and alleviate muscle spasms when given intravenously at doses of 10 mL of 10% solution. Ferrous gluconate is a common oral employed in the management of , providing approximately 12% elemental iron by weight, which enhances production and formation. Its allows for up to 20% absorption of the elemental iron in iron-deficient individuals, making it a gentler alternative to other ferrous salts with fewer gastrointestinal side effects. Zinc gluconate, another key derivative, is incorporated into cold remedies such as lozenges to support immune function and reduce the duration of symptoms by inhibiting in the upper . Clinical trials indicate that zinc gluconate lozenges, taken at doses exceeding 75 mg daily, can shorten cold duration by 28% compared to . In , gluconate salts like and are utilized in intravenous solutions to maintain balance, ensuring stable cation-anion ratios and preventing imbalances in patients unable to receive enteral feeding. These salts contribute to the formulation of total parenteral nutrition admixtures by providing bioavailable ions without causing precipitation issues common in other salt forms. In dental care, chlorhexidine gluconate mouthwashes leverage the mild acidity of the gluconate component (pH around 5-7) alongside the action to control plaque accumulation and reduce , with twice-daily rinses demonstrating significant plaque reduction over 21 days in clinical studies.

Industrial uses

Gluconic acid and its salts, particularly sodium gluconate, serve as versatile chelating agents in various industrial processes due to their ability to bind metal ions such as calcium and magnesium, preventing precipitation and scaling without causing corrosion. In detergents and industrial cleaners, sodium gluconate is widely employed to enhance cleaning efficiency in hard water environments by sequestering divalent metal ions, which otherwise form insoluble deposits that reduce detergent performance. For instance, it is commonly used in bottle washing formulations to remove scale and residues from glass surfaces, allowing for more effective rinsing and reduced water consumption. Typical concentrations in such cleaning formulations range from 0.5% to 2%, providing optimal chelation while maintaining cost-effectiveness. In water treatment applications, gluconic acid derivatives act as scale inhibitors in systems and cooling towers by forming stable complexes with Ca²⁺ and Mg²⁺ ions, thereby preventing the formation of deposits that can impair and equipment longevity. This chelating action also mitigates in industrial water circuits, offering a non-toxic alternative to traditional phosphate-based treatments, as is readily biodegradable and does not contribute to in effluents. Usage levels in formulations typically fall within 0.5-2%, ensuring effective sequestration at operational ranges without excessive dosing. Within metalworking, gluconic acid is utilized in baths and operations for its mild properties, which facilitate surface preparation without aggressive material removal. Specifically, in aluminum processing, enhances the efficiency of caustic etch baths by inhibiting the formation of hydrated aluminum , leading to uniform surface roughening suitable for subsequent coatings or . It is also applied in acidic solutions for removal prior to , where concentrations around 1% promote controlled and improve adhesion of metal layers. In the textile and leather industries, gluconic acid functions as a pH buffer and dye fixative, stabilizing processing baths to ensure even dye uptake and color fastness by chelating interfering metal ions from or fabrics. For leather tanning, it aids in softening hides and uniform metal salt distribution, reducing defects while operating at typical levels of 0.5-2%. Additionally, as a concrete admixture, acts as a set retarder, extending workability time in hot climates or large pours by delaying hydration of , which improves placement and reduces cracking; it constitutes over 80% of gluconic acid derivatives used in globally.

Safety and environmental impact

Toxicity profile

Gluconic acid exhibits low , with an oral LD50 greater than 2000 mg/kg in rats, indicating minimal risk from single high-dose ingestion. Dermal LD50 values exceed 2000 mg/kg in rats, and the compound is non-irritating to in rabbits. Eye irritation is mild and reversible within 72 hours at typical exposure levels, with no severe damage reported. In applications such as preservatives in baby wipes, plant-derived gluconic acid serves as a mild chelator and pH balancer, offering a gentler alternative to traditional preservatives. The Environmental Working Group (EWG) rates gluconic acid with low hazard scores across all concerns, including cancer, allergies and immunotoxicity, developmental and reproductive toxicity, use restrictions, and non-reproductive organ system toxicity. It is considered safe for use in baby wipes, with no reported risks associated with its application in such products. Gluconic acid shows no evidence of carcinogenicity, mutagenicity, or based on OECD guideline studies, including negative results in Ames bacterial mutation assays ( 471), chromosomal aberration tests ( 473), and combined repeated dose/reproduction screening ( 422). It is recognized as safe for use in food by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), with no genotoxic or oncogenic concerns identified in long-term evaluations, and is affirmed as (GRAS) by the U.S. FDA. As of 2024, the (EFSA) is re-evaluating gluconic acid (E 574) and related additives. No specific occupational exposure limits have been established for gluconic acid by regulatory bodies such as OSHA, reflecting its low hazard profile; however, general ventilation is recommended to control during handling to prevent respiratory . Chronic dietary studies in rats demonstrate no adverse effects at levels up to 5% in feed over 24 months, with NOAELs exceeding 340 mg/kg-day and no impacts on organ function or survival.

Biodegradability and environmental effects

Gluconic acid is readily biodegradable under aerobic conditions, with 88.9% degradation in 28 days as demonstrated in an 301D study, and rapid breakdown in . This occurs through natural microbial processes, similar to those observed in biological systems where gluconic acid serves as an intermediate in glucose . Due to its hydrophilic nature, gluconic acid exhibits low bioaccumulation potential, with a log Kow value below 1, preventing significant uptake and sequestration in fatty tissues of organisms. It is also non-toxic to aquatic life, with LC50 >100 mg/L for fish (e.g., Oryzias latipes) and >1000 mg/L for invertebrates (e.g., Daphnia magna) and algae in standard toxicity assays, indicating minimal ecological risk in water bodies. Gluconic acid is primarily produced via microbial of renewable glucose sources, such as those derived from , which supports principles by reducing reliance on fossil fuel-based feedstocks. In wastewater treatment, it is easily mineralized by processes, ensuring complete conversion to harmless byproducts like and water without persistent residues. Additionally, gluconic acid has no ozone-depleting potential, as its chemical structure and low atmospheric reactivity preclude contributions to stratospheric loss. Life-cycle assessments of gluconic acid production through reveal a low , typically ranging from 1 to 2 kg CO2 equivalents per kg of acid, attributable to efficient microbial conversion and minimal energy inputs compared to synthetic alternatives.

References

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