Effect of poly-γ-glutamic acids (PGA) on oil uptake and sensory quality in doughnuts

Enhanced Production of Poly-γ-glutamic Acid by Bacillus subtilis Using Stage-controlled Fermentation and Viscosity Reduction Strategy

In this study, the production of poly-γ-glutamic acid (PGA) by Bacillus subtilis using stage-controlled fermentation and viscosity reduction strategy was investigated in detail. Based on the single-factor optimization experiment, temperature (42 °C and 37 °C), pH (7.0 and uncontrolled), aeration rate (1.2 vvm and 1.0 vvm), and agitation speed (700 rpm and 500 rpm) were selected for the two-stage controlled fermentation (TSCF). The time points for the TSCF of temperature, pH, aeration rate, and agitation speed were set at 18.52 h, 2.82 h, 5.92 h, and 3.62 h, respectively, based on the kinetic analysis. A PGA titer of 19.79 ~ 22.17 g/L was obtained from the TSCF, which did not increase significantly than that (21.25 ± 1.26 g/L) of non-stage controlled fermentation (NSCF). This may be due to the high viscosity and low dissolved oxygen of the PGA fermentation broth. Thus, the TSCF combined with a viscosity reduction strategy was developed to further improve the production of PGA. The PGA titer reached 25.00 ~ 30.67 g/L, which increased by 17.66 ~ 32.94% to that of NSCF. This study provided a valuable reference for the development of process control strategies for high-viscosity fermentation systems.

Poly (γ) glutamic acid: a unique microbial biopolymer with diverse commercial applicability

Microbial biopolymers have emerged as promising solutions for environmental pollution-related human health issues. Poly-γ-glutamic acid (γ-PGA), a natural anionic polymeric compound, is composed of highly viscous homo-polyamide of D and L-glutamic acid units. The extracellular water solubility of PGA biopolymer facilitates its complete biodegradation and makes it safe for humans. The unique properties have enabled its applications in healthcare, pharmaceuticals, water treatment, foods, and other domains. It is applied as a thickener, taste-masking agent, stabilizer, texture modifier, moisturizer, bitterness-reducing agent, probiotics cryoprotectant, and protein crystallization agent in food industries. γ-PGA is employed as a biological adhesive, drug carrier, and non-viral vector for safe gene delivery in tissue engineering, pharmaceuticals, and medicine. It is also used as a moisturizer to improve the quality of hair care and skincare cosmetic products. In agriculture, it serves as an ideal stabilizer, environment-friendly fertilizer synergist, plant-growth promoter, metal biosorbent in soil washing, and animal feed additive to reduce body fat and enhance egg-shell strength.

Minced Beef Meat Paste Characteristics: Gel Properties, Water Distribution, and Microstructures Regulated by Medium Molecular Mass of γ-Poly-Glutamic Acid

The influences of various m-γ-PGA (0.08-0.20%, w/w) concentrations on the properties of minced beef meat paste in terms of rheological properties, texture, moisture distribution, and microstructures were evaluated. The results indicated that m-γ-PGA enhanced the water-holding capacity, gel strength, texture, and whiteness of the minced beef meat paste. Based on the microstructural results, m-γ-PGA helped form a more organized and compact gel, thereby limiting the migration of water through the gel matrix. In contrast to the control group, the water-holding property, gel strength, and whiteness of minced meat paste gels with m-γ-PGA content of 0.12% increased from 75.89%, 584.51 g·cm, and 61.83 to 79.91%, 780.87 g·cm, and 62.54, respectively (p < 0.05), exhibiting the highest water-holding property and gel strength. Thus, m-γ-PGA exhibits great potential for minced meat paste products as a healthy gel water retainer and enhancer in low-fat meat products.

Antimicrobial activity of gamma-poly (glutamic acid), a preservative coating for cherries

We investigated the minimum inhibitory concentration (MIC), antibacterial activity, and preservation ability of four molar masses of γ-polyglutamic acid (PGA) against Escherichia coli, Bacillus subtilis, and yeast. The antibacterial mechanism was determined based on the cell structure, membrane permeability, and microscopic morphology of the microorganisms. We then measured the weight loss, decay rate, total acid, catalase activity, peroxidase activity, and malondialdehyde content toward the possible use of PGA as a preservative coating for cherries. When the molar mass was greater than 700 kDa, the MIC for Escherichia coli and Bacillus subtilis was less than 2.5 mg/mL. The mechanism of action of the four molar masses of PGA was different with respect to the three microbial species, but a higher molar mass of PGA corresponded to stronger inhibition against the microbes. PGA of 2000 kDa molar mass damaged the microbial cellular structure, resulting in excretion of alkaline phosphatase, but PGA of 1.5 kDa molar mass affected the membrane permeability and the amount of soluble sugar. Scanning electron microscopy indicated the inhibitory effect of PGA. The antibacterial mechanism of PGA was related to the molar mass of PGA and the microbial membrane structure. Compared with the control, a PGA coating effectively inhibit the spoilage rate, delay the ripening, and prolong the shelf life of cherries.

Poly-gamma-glutamic acid biopolymer: a sleeping giant with diverse applications and unique opportunities for commercialization

Poly-gamma-glutamic acid (γ-PGA) is a biodegradable, non-toxic, ecofriendly, and non-immunogenic biopolymer. Its phenomenal properties have gained immense attention in the field of regenerative medicine, the food industry, wastewater treatment, and even in 3D printing bio-ink. The γ-PGA has the potential to replace synthetic non-degradable counterparts, but the main obstacle is the high production cost and lower productivity. Extensive research has been carried out to reduce the production cost by using different waste; however, it is unable to match the commercialization needs. This review focuses on the biosynthetic mechanism of γ-PGA, its production using the synthetic medium as well as different wastes by L-glutamic acid-dependent and independent microbial strains. Furthermore, various metabolic engineering strategies and the recovery processes for γ-PGA and their possible applications are discussed. Finally, highlights on the challenges and unique approaches to reduce the production cost and to increase the productivity for commercialization of γ-PGA are also summarized.

Recent Advances in Microbial Synthesis of Poly-γ-Glutamic Acid: A Review

Poly-γ-glutamic acid (γ-PGA) is a natural, safe, non-immunogenic, biodegradable, and environmentally friendly glutamic biopolymer. γ-PGA has been regarded as a promising bio-based materials in the food field, medical field, even in environmental engineering field, and other industrial fields. Microbial synthesis is an economical and effective way to synthesize γ-PGA. Bacillus species are the most widely studied producing strains. γ-PGA biosynthesis involves metabolic pathway of racemization, polymerization, transfer, and catabolism. Although microbial synthesis of γ-PGA has already been used extensively, productivity and yield remain the major constraints for its industrial application. Metabolic regulation is an attempt to solve the above bottleneck problems and meet the demands of commercialization. Therefore, it is important to understand critical factors that influence γ-PGA microbial synthesis in depth. This review focuses on production strains, biosynthetic pathway, and metabolic regulation. Moreover, it systematically summarizes the functional properties, purification procedure, and industrial application of γ-PGA.

Optimization of fermentation conditions, purification and rheological properties of poly (γ-glutamic acid) produced by Bacillus subtilis 1006-3

This study aimed to investigate the optimal fermentation condition, purification and rheological properties of extracellular polymers produced by Bacillus subtilis 1006-3. An optimum temperature of 30.2 °C, inoculation amount of 6.1%, and pH of 8.2 were determined via Response Surface Methodology. The result of amino acid analysis and gel electrophoresis indicated that the obtained polymer contained only glutamic acid, with a wide molecular weight range. This polymer was finally determined as γ-PGA by infrared spectroscopy. The γ-PGA solution displayed a behavior of pseudoplastic non-Newtonian fluid with shear thinning properties, which can be described by the Ostward-de Waele power law model. The apparent viscosity of γ-PGA solution increased with the increase in its concentration from 1% to 10%. The deviation in pH from neutral value, and the addition of NaCl or MgCl₂ can reduce the apparent viscosity of γ-PGA solution, and it was more sensitive to Mg²⁺ than to Na⁺ addition. At the concentration of 4, 6, and 8%, γ-PGA solution showed predominantly viscous response in the range of 0.1-100 rad/s angular frequency (G″>G'). These results indicated the potential application of the γ-PGA as a thickening agent.

Study on the mechanism of production of γ-PGA and nattokinase in Bacillus subtilis natto based on RNA-seq analysis

Poly-γ-glutamic acid (γ-PGA) and nattokinase (NK) are the main substances produced by Bacillus subtilis natto in solid-state fermentation and have wide application prospects. We found that our strains had higher activity of nattokinase when soybeans were used as substrate to increase the yield of γ-PGA. Commercial production of γ-PGA and nattokinase requires an understanding of the mechanism of co-production. Here, we obtained the maximum γ-PGA yield (358.5 g/kg, w/w) and highest activity of NK during fermentation and analyzed the transcriptome of Bacillus subtilis natto during co-production of γ-PGA and NK. By comparing changes in expression of genes encoding key enzymes and the metabolic pathways associated with the products in genetic engineering, the mechanism of co-production of γ-PGA and nattokinase can be summarized based on RNA-seq analysis. This study firstly provides new insights into the mechanism of co-production of γ-PGA and nattokinase by Bacillus subtilis natto and reveals potential molecular targets to promote the co-production of γ-PGA and nattokinase.

Properties and Application of Multifunctional Composite Polypropylene-Based Films Incorporating a Combination of BHT, BHA and Sorbic Acid in Extending Donut Shelf-Life

To extend the shelf-life of packaged donut without the addition of preservative, polypropylene-based active composite films loaded with a combination of sorbic acid, BHA and BHT were prepared by the extrusion moulding method: T1 (Control-pure PP-film), T2 (PP-BHT1%-SA2%), T3 (PP-BHA3%-SA2%) and T4 (PP-BHT1%-BHA1%-SA2%). The incorporation of active additives enhanced water vapour permeability (WVP) and increased oxygen permeability of films. Active films had higher antioxidant activity than pure PP in the order T4 > T2 > T3 (89.11, 83.40 and 79.16%). In vitro examinations demonstrated a significant antibacterial effect on Escherichia coli and S. aureus growth. Overall migration was not significantly different for watery food simulants, while in acidic and fatty foods increased it significantly. The effect of the active films on the fried and packaged donut samples showed significantly higher moisture contents and peroxide values, while acidity was lower. T2 film is proposed due to the preservation of the intrinsic properties of the film, increasing the storage period up to 25 to 50 days.

Improving enzyme activity, thermostability and storage stability of β-1,3-1,4-glucanase with poly-γ-glutamic acid produced by Bacillus sp. SJ-10

β-1,3-1,4-glucanase (BG) is an industrially important enzyme owing to its stringent specificity for β-glucan cleavage. In this study, poly-γ-glutamic acid (γ-PGA) was added to BG to investigate its effect on improving the activity and stability of the enzyme. The effect of γ-PGA was investigated by analyzing kinetic and thermodynamic parameters. Compared to control, significant differences (P < .05) in enzyme activity were observed when 1.0 %, 1.5 %, and 2.0 % γ-PGA was added, and the activities were increased 1.23 ± 0.05, 1.23 ± 0.07, and 1.31 ± 0.07-fold, respectively. Regarding thermostability, residual BG activity after a 1 h incubation at 60 °C was 12.53 ± 0.06 % without γ-PGA and 79.02 ± 5.76 % with 1% γ-PGA. The storage stability at 25 °C and 50 °C also increased when γ-PGA was present. The kinetics and thermodynamic investigations indicated that the increased activity and stability of BG when γ-PGA was added were due to increased values of the V_max, K_cat, and activation energy for denaturation. The findings of this study suggest that adding γ-PGA to BG increases the application value of this enzyme in the food and feed industries.

Effect of poly-γ-glutamic acid on hydration and structure of wheat gluten

In recent years, hydrocolloids have been used extensively as enhancers in dough products. However, studies on the effect of hydrophilic polymers on wheat gluten (WG) within the dough are scarce. In the present study, poly-γ-glutamic acid (γ-PGA), a new and healthy food additive, was added to the WG to investigate its effect on hydration, rheological properties, and structures of WG. Results showed that with the addition of γ-PGA, the water-holding capacity (WHC) of WG and the content of bound water increased, whereas the content of immobilized water decreased. In addition, γ-PGA changed the rheological properties of WG. The elastic properties of WG gradually weakened and the viscous properties gradually increased. Furthermore, scanning electron microscopy (SEM) results showed that with the addition of γ-PGA, the structure of the WG network became more uniform and the pore size was smaller. A change also occurred in the secondary structure of WG, in which the α-helix content was significantly reduced while the contents of β-turn angles were significantly increased, thereby suggesting that γ-PGA not only functions as a filler in the WG system, but also interacts with WG. From the present study, we conclude that γ-PGA can interact with WG and water to change the WG secondary structure. γ-PGA can also restrict moisture migration and enhance the WHC of WG, thereby changing the WG microstructure and improving its functional properties. This condition provides the basis for γ-PGA to be recommended as WG enhancer for addition in WG-containing products such as bread, seitan (meat replacement), and others. PRACTICAL APPLICATION: WG performance plays a key role in the quality of flour products. Thus, many studies have been conducted to improve the WG quality to produce highly popular flour products. The results of this study showed that γ-PGA can interact with WG and water, and had a good effect on improving the WHC of WG, which means that γ-PGA has potential usefulness in improving the quality of WG and WG-containing products such as bread, seitan (meat replacement), and others.

Poly(N-Isopropyl-Acrylamide)/Poly(γ-Glutamic Acid) Thermo-Sensitive Hydrogels Loaded with Superoxide Dismutase for Wound Dressing Application

INTRODUCTION

Chronic trauma repair is an important issue affecting people's healthy lives. Thermo-sensitive hydrogel is injectable in situ and can be used to treat large-area wounds. In addition, antioxidants play important roles in promoting wound repair.

METHODS

The purpose of this research was to prepare a novel thermo-sensitive hydrogel-poly(N-isopropyl-acrylamide)/poly(γ-glutamic acid) (PP) loaded with superoxide dismutase (SOD) to improve the effect for trauma treatment. The micromorphology of the hydrogel was observed by scanning electron microscope and the physical properties were measured. The biocompatibility of hydrogel was evaluated by MTT experiment, and the effect of hydrogel on skin wound healing was evaluated by in vivo histological staining.

RESULTS

Gelling behavior and differential scanning calorimeter outcomes showed that the PP hydrogels possessed thermo-sensitivity at physiological temperature and the phase transformation temperature was 28.2°C. The high swelling rate and good water retention were conducive to wound healing. The activity of SOD in vitro was up to 85% at 10 h, which was advantageous to eliminate the superoxide anion. MTT assay revealed that this hydrogel possessed good biocompatibility. Dressings of PP loaded with SOD (SOD-PP) had a higher wound closure rate than other treatments in vivo in diabetic rat model.

DISCUSSION

The SOD-PP thermo-sensitive hydrogels can effectively promote wound healing and have good application prospects for wound repair.

Poly-γ-glutamic Acid Synthesis, Gene Regulation, Phylogenetic Relationships, and Role in Fermentation

Poly-γ-glutamic acid (γ-PGA) is a biodegradable biopolymer produced by several bacteria, including Bacillus subtilis and other Bacillus species; it has good biocompatibility, is non-toxic, and has various potential biological applications in the food, pharmaceutical, cosmetic, and other industries. In this review, we have described the mechanisms of γ-PGA synthesis and gene regulation, its role in fermentation, and the phylogenetic relationships among various pgsBCAE, a biosynthesis gene cluster of γ-PGA, and pgdS, a degradation gene of γ-PGA. We also discuss potential applications of γ-PGA and highlight the established genetic recombinant bacterial strains that produce high levels of γ-PGA, which can be useful for large-scale γ-PGA production.

Microbial synthesis of poly-γ-glutamic acid: current progress, challenges, and future perspectives

Poly-γ-glutamic acid (γ-PGA) is a naturally occurring biopolymer made from repeating units of l-glutamic acid, d-glutamic acid, or both. Since some bacteria are capable of vigorous γ-PGA biosynthesis from renewable biomass, γ-PGA is considered a promising bio-based chemical and is already widely used in the food, medical, and wastewater industries due to its biodegradable, non-toxic, and non-immunogenic properties. In this review, we consider the properties, biosynthetic pathway, production strategies, and applications of γ-PGA. Microbial biosynthesis of γ-PGA and the molecular mechanisms regulating production are covered in particular detail. Genetic engineering and optimization of the growth medium, process control, and downstream processing have proved to be effective strategies for lowering the cost of production, as well as manipulating the molecular mass and conformational/enantiomeric properties that facilitate screening of competitive γ-PGA producers. Finally, future prospects of microbial γ-PGA production are discussed in light of recent progress, challenges, and trends in this field.

Poly-γ-glutamic acid: production, properties and applications

Poly-γ-glutamic acid (γ-PGA) is a naturally occurring biopolymer made up of repeating units of l-glutamic acid, d-glutamic acid or both. γ-PGA can exhibit different properties (conformational states, enantiomeric properties and molecular mass). Owing to its biodegradable, non-toxic and non-immunogenic properties, it has been used successfully in the food, medical and wastewater industries. Amongst other novel applications, it has the potential to be used for protein crystallization, as a soft tissue adhesive and a non-viral vector for safe gene delivery. This review focuses on the production, properties and applications of γ-PGA. Each application of γ-PGA utilizes specific properties attributed to various forms of γ-PGA. As a result of its growing applications, more strains of bacteria need to be investigated for γ-PGA production to obtain high yields of γ-PGA with different properties. Many medical applications (especially drug delivery) have exploited α-PGA. As γ-PGA is essentially different from α-PGA (i.e. it does not involve a chemical modification step and is not susceptible to proteases), it could be better utilized for such medical applications. Optimization of γ-PGA with respect to cost of production, molecular mass and conformational/enantiomeric properties is a major step in making its application practical. Analyses of γ-PGA production and knowledge of the enzymes and genes involved in γ-PGA production will not only help increase productivity whilst reducing the cost of production, but also help to understand the mechanism by which γ-PGA is effective in numerous applications.