Poly-γ-glutamic acid (γ- PGA) is a biodegradable, water-soluble, and non-toxic biopolymer produced by various Bacillus species. Its unique properties make it suitable for diverse applications in food, pharmaceuticals, agriculture, and water treatment (Figure 1). Also, various commercial Poly-γ-glutamic acids have been studied for their functional properties and further applied in diverse applications (Table 1).
| Source | Properties |
| Natto Biosciences (Montreal, QC, Canada) | Hydrophilicity, biodegradability, biocompatibility, immunogenicity, and ionic nature |
| Sigma Aldrich (St. Louis, MO, USA) | Detection of MCF-7 human breast cancer cells and MUC1 biomarker |
| VEDAN Co. (Taichung, Taiwan) | Polyelectrolyte complex formation |
| IRIS Biotech Gmbh (CAS No 26247-79-0, Marktredwitz, Germany) | Protective agent of protein aggregation, drug delivery, low physical stability |
| VEDAN Co. (Taichung, Taiwan) | Water-soluble properties, anti-cancer and antioxidant activties, increased biocompatible and biodegradable abilities, encapsulation efficiency |
| Bioshinking Company (Nanjing, China) | Biodegradability, physico-chemical characterization, and evaluation of PGA bioflocculant in coagulation flocculation and sedimentation processes |
| Sigma Aldrich | Antibacterial activity, low solubility in organic solvents, high positive potential, low sentivity |
| VEDAN Co. (Taichung, Taiwan) | Determination of swelling degree |
| New England BioLabs, Hitchin, Hertfordshire, UK | Biodegradable polymer; increased rigidity, porosity, and availailibity; rate of degradation |
Flocculation
γ-PGA can be used as a bio-flocculent in wastewater treatment, downstream processing in food industries, and pharmaceutical and medicine industries. γ-PGA is used for the flocculation of solid waste and metals in wastewater treatments. The flocculation efficiency has a direct relation with the molecular mass. γ-PGA from B. subtilis P-104 was shown to have good flocculating activity. It can be improved by the addition of cations by stimulating the flocculation activity by nullifying and alleviating the negative charge on the functional group of bio-flocculent by establishing bridges amid elements. Cations, temperature, and pH are the major factors that affect the flocculation efficiency of γ-PGA. A new organic approach for solving consequential environmental issues generated by the use of massive quantities of liquid fertilizer in agriculture: limiting surplus ammonia in soil and thus nitrogen translation into γ-PGA, has been reported. For cations like Fe2+, Fe3+, Mg2+, Ca2+, and Mn2+, which occur naturally, γ-PGA serves as a waste nitrogen transit base as well as an environmentally safe fertilizer/manure. γ-PGA (9.9 × 105 Da) could be used for the elimination of basic dyes from aqueous solution. The progression is a result of the electrostatic interface of γ-PGA and dyes, which initiates adsorption at pH > 5, and the exclusion of dyes from γ-PGA takes place at extremely acidic conditions (pH 1), facilitating the reuse of γ-PGA. In addition to its benefit as a flocculating agent, PGA, when used as an inorganic salt, may result into the production of raw sludge that has to be managed later.
γ-PGA is a flocculant as it can play an important role in effluent treatment, and downstream processing in foods, pharmaceuticals, and drug industries therefore can replace synthetic flocculants. γ-PGA can be used as a bio-flocculant in the food and fermentation industries to harvest microalgae. Reaping microalgae with PGA is lucrative, and during other harvesting techniques like centrifugation, loss of lipid is prevented due to algal cell breakage. γ-PGA from B. licheniformis CCRC 12826 revealed efficient flocculation of numerous organic and inorganic compounds.
Bioremediation
Pollutants in the environment, like heavy metals, radionuclides, and synthetic substances, endanger public health and upsurge universal lack of provisions because of contamination, which leads to polluted water, diminished agricultural output, and adverse effects like acid rain. The remediation of polluted soils, residues, and streams includes the interaction of these contaminations with γ-PGA to implement new remediation strategies.
Removal of heavy metals: γ-PGA covalently combined into microfiltration layers through membrane pore surface attachment has a super-high heavy metal sorption capability. γ-PGA muddles and effectively eliminates >99.8% of lead ions from water using a low-pressure ultra-filtration system.
Dye removal: γ-PGA (9.9 × 105 Da) is an efficient method for removing simple dyes from hydrated solutions. At pH 1, it was found that 98% of the adsorbed dye on γ-PGA might be retrieved, allowing γ-PGA to be reused.
Fertilizer
Plant growth and development are enhanced by adding fertilizers to the soil. To avoid environmental pollution, γ-PGA can be used as a bio-control agent and/or a synergist to chemical fertilizers in agriculture. It assists in enhancing growth by improving nutrient consumption, even in exhausted nutrient situations. The enzymes from soil such as urease, sucrase, and catalase show an augmented activity after the supplementation of γ-PGA, and nitrogen-immobilized microbes raise the total nitrogen accretion in soil. γ-PGA was found to promote the growth of Chinese cabbage and increase the total nitrogen, soluble protein, and soluble amino acid content in leaves. The addition of γ-PGA brings upon a surge in the activity of enzymes involved in the breakdown and acclimatization of nitrogen. It facilitates the Ca influx in the cytoplasm, which acts as a positive signal for nitrogen metabolism, thus promoting the growth of plants. Wang et al. (2024) reported the use of fermented grain broth BSG, which is a good source of live B. subtilis and other metabolites beneficial to soil and plants, and thus it tends to be used as a modern functional bioorganic fertilizer. B. subtilis B6-1 produces lipopeptides, and γ-PGA using soybean and sweet potato scums sufficiently repressed cucumber wilts, amplified the growth of cucumber seedlings, and also increased nutrient consumption.
Cryoprotectant
γ-PGA possesses a high anionic amino acid composition and thus exhibits an antifreeze activity. Polymers having acidic amino acids possess high antifreeze activity in comparison to other polymers. γ-PGA with lower molecular masses <20 kDa demonstrated significant antifreeze activities than very effective antifreeze agents like glucose, without interfering with the taste of foods. The antifreeze activity is reduced in the sequence Na salt = K salt > Ca salt > acidic form. During freeze drying, γ-PGA from B. subtilis has the potential to shield the probiotic bacteria Lactobacillus paracasei remarkably better than sucrose. The probiotic strains of Bifidobacteria (Bifidobacteria longum and Bifidobacteria breve) have been in use for proper operation of the gastrointestinal tract. γ-PGA helps protect these cells in fruit juices and prevents their survival from harsh environments of the digestive tract .
In Food and Medicine
γ-PGA is utilized as a food constituent due to its functional and physico-chemical features. Consumption of γ-PGA improves intestinal calcium absorption in post-menopausal women by inhibiting the formation of an insoluble calcium complex with phosphate and can potentially be used for the treatment of bone disorders. Supplementation of γ-PGA acts as a preventing agent for osteoporosis of bones by greatly improving in vitro and in vivo calcium solubility in rats and postmenopausal women, respectively, as well as the calcium content of their bones. γ-PGA conjugates to produce increased absorption of vanadyl sulphate, which is a mimetic insulin inorganic salt. γ-PGA has an anti-diabetic effect because it reduces the rate of intestinal absorption of glucose, as the γ-PGA vanadyl complex has a higher insulin-mimetic activity than free vanadyl sulfate. K-γ-PGA administration prevents a surge in blood pressure by tumbling sodium absorption and thus controls hypertension. γ-PGA was found to improve the gut microbiota by increasing the abundance of Lactobacillales in the gut.
γ-PGA has a significant antifreeze activity, which is why it acts as a cryoprotectant for frozen foods. As a cryoprotectant, during freeze-drying, the impact of γ-PGA probiotic microbes was found to be more effective than sucrose, sorbitol, and trehalose, and Acetobacter xylinum produces nata, bacterial cellulose. Also, it is used as a thickening agent in foods/beverages, which improves the texture of foods and also prevents aging. γ-PGA is demonstrated to have a positive effect in dropping oil uptake and moisture loss during deep fat frying of foods. γ-PGA is known to have water retention capacity and therefore it helps in controlling water loss and produces a dense matrix with improved integrity. Thus, γ-PGA can be utilized as a functional oil-reducing agent in deep-fat fried foods. During deep-fat frying, the impact of γ-PGA on the absorption of oil and loss of moisture content in doughnuts was found to be more effective and has preferred appearance and taste over ordinary doughnuts. Subsequently, in deep-fat fried foods, γ-PGA can be utilized as a functional oil-reductant.
Cosmetics
γ-PGA plays a significant role in cosmetics because γ-PGA improves the solubility of vitamin C when it forms the PGA-vitamin C complex. Vitamin C is crucial for collagen creation, which assists in skin repair. Due to its antioxidant activity, it acts as an anti-aging agent. Therefore, it is a dynamic component in cosmetic compositions, owing to its hygroscopic properties and skin compatibility. γ-PGA is a good hydrophilic humectant and has the potential to improve the production of urocanic acid, pyrrolidone carboxylic acid, and lactic acid compared to hyaluronic acid and soluble collagen as natural moisturizing agents. γ-PGA aids in enhancing the qualities of skincare and hair care products, such as exfoliating, nourishing, and taking away wrinkles. The cosmetic constituent with the γ-PGA-vitamin complex results in better firmness, enhanced absorption, and constant release of vitamins from the composite.
Biomedical Applications
γ-PGA gained its space in biomedical applications due to its glutamic acid composition, which are natural excerpts of the human body.
Hydrogels
Hydrogel is a bioabsorbable product known to have the ability to swell in water and retain it inside its structure. It has paved the way for immense applications in the field of drug delivery and tissue engineering. Hydrogel preparation has various approaches, including γ-irradiation, chemical, or physical cross-linking. Microbial γ-PGA and L-lysine were cross-linked to prepare biodegradable hydrogels by amide bond in the presence of DMT-MM in water. Using no chemical treatment, γ-PGA reacted with polyvinyl alcohol (PVA) in aqueous solution to form hydrogel. The elongation and water retention ability of the hydrogels is increased with an increase in γ-PGA concentration. Protein adsorption and platelet adhesion on hydrogel have an inverse relation with γ-PGA concentration and thus help in improving the blood compatibility of the hydrogel. Due to its water resistance, mechanical properties, and blood compatibility, PGA-PVA hydrogel functions as a good biomaterial for medical devices that are used to carry blood. The combination formed with bacterial cellulose and γ-PGA was found to have promising applications as a bio-degradable structural high-performance materials, construction material, and tissue engineering scaffold (tendon, ligament, and skin) due to its biodegradability and good tensile toughness. γ-PGA hydrogel showed a promising result as an edible coating material in shiitake mushrooms, preserving its nutrient quality and extending the shelf-life.
Nanoparticles
Gene and drug delivery could be made possible by nanoparticles. Due to the smaller size of the nanoparticle, it can easily escape from the reticuloendothelial system, resulting in increased circulation time in blood. γ-PGA, being hydrophilic and water soluble, is used as a carrier for anti-cancer drugs. The γ-PGA and chitosan nanoparticles have been widely used for the oral conveyance of hydrophobic drugs and proteins. PGA-chitosan nanoparticles act as an efficient system for the delivery of insulin to diabetic patients for treatment.
Tissue Engineering
Tissue engineering is the process by which biological substitutes are developed to reinstate and sustain the functions of tissue. Due to its hydrophilic and cytocompatible nature, γ-PGA/chitosan composite biomaterial exhibits latent application in tissue engineering than traditional chitosan matrices. A PEC (poly electrolyte complex) of chitosan and γ-PGA shows a potential application in wound dressing. The complex holds the required moisture and has good mechanical properties, which allows for the easy removal of the dressing from the surface of the wound without destroying the renewed tissues.
Drug Carrier/Deliverer
As a drug delivery agent, the factor determining the drug delivery properties involves the molecular mass of γ-PGA, which helps to regulate the rate of drug discharge. γ-PGA with covalently attached cisplatin reduces cisplatin toxicity, improves tumor size retention in naked mice with xenografted human breast tumors, and extends the survival of bare mice with Bcap-37 tumor cells.
Metal Chelators
Heavy metals and radionuclides may be removed using metal chelators. PGA-coated super paramagnetic iron oxide NPs had a high efficiency in removing heavy metal from activated gastrointestinal fluid and a metal solution [100]. For instance, γ-PGA molecular mass or sub-atomic mass of ~3-6 × 104 Da was utilized to deliver Paclitaxel poliglumex (a macromolecular form of paclitaxel and γ-l-PGA), exhibiting advantages over ordinary paclitaxel. The active agent paclitaxel was eventually released from paclitaxel poliglumex as it accumulated in tumor tissue.
Biological Adhesive
A hydrogel formed by a mixture of γ-PGA aqueous solution and gelatin in the presence of water-soluble carbodiimide helped in lung adhesion and air-leak sealing over regular fibrin glue.
Humectant
The physical properties of γ-PGA that makes it valuable as a food humectant include its exceptional ability to absorb and retain moisture. With a capacity to hold water up to 5000 times its weight, γ-PGA significantly outperforms other common humectants used in the food industry. In wheat gluten, γ-PGA has been shown to contribute to its functionality as a food humectant, revealing that γ-PGA addition gradually weakens elastic properties while enhancing viscous characteristics. This redistribution of water molecules within the food matrix creates a more stable hydration state that resists dehydration under various environmental conditions. The rheological modification creates a more uniform microstructure with smaller pore sizes, which further restricts moisture migration and promotes water retention. Baked goods are susceptible to staling, a complex phenomenon involving moisture redistribution and starch retrogradation that leads to textural hardening and quality deterioration. When incorporated into bakery formulations, γ-PGA significantly impairs starch aging by 20 to 30 %, effectively maintaining product softness and freshness for extended periods. This anti-staling effect provides considerable economic advantages for both producers and retailers by extending shelf life and reducing food waste.
Conclusions
Dora PolyGlutamic Acid (γ-PGA) is produced through fermentation by Bacillus subtilis. γ-PGA is a homo-polymer of glutamic acid, it has excellent hydrophilic and high water absorption capacity. It can chelate trace elements in the soil, induce endogenous hormones and enhance plant resistance ability. Dora PolyGlutamic Acid also contains microbes, NPK, glucose, organic matter, etc. It is a great fertilizer synergist and a natural, organic, and environment-friendly plant nutrition enhancer.
