Cryoprotection of probiotic bacteria with poly-γ-glutamic acid produced by Bacillus subtilis and Bacillus licheniformis

Effect of addition of γ-poly glutamic acid on bacterial nanocellulose production under agitated culture conditions

BACKGROUND

Bacterial nanocellulose (BNC), a natural polymer material, gained significant popularity among researchers and industry. It has great potential in areas, such as textile manufacturing, fiber-based paper, and packaging products, food industry, biomedical materials, and advanced functional bionanocomposites. The main current fermentation methods for BNC involved static culture, as the agitated culture methods had lower raw material conversion rates and resulted in non-uniform product formation. Currently, studies have shown that the production of BNC can be enhanced by incorporating specific additives into the culture medium. These additives included organic acids or polysaccharides. γ-Polyglutamic acid (γ-PGA), known for its high polymerization, excellent biodegradability, and environmental friendliness, has found extensive application in various industries including daily chemicals, medicine, food, and agriculture.

RESULTS

In this particular study, 0.15 g/L of γ-PGA was incorporated as a medium additive to cultivate BNC under agitated culture conditions of 120 rpm and 30 ℃. The BNC production increased remarkably by 209% in the medium with 0.15 g/L γ-PGA and initial pH of 5.0 compared to that in the standard medium, and BNC production increased by 7.3% in the medium with 0.06 g/L γ-PGA. The addition of γ-PGA as a medium additive resulted in significant improvements in BNC production. Similarly, at initial pH levels of 4.0 and 6.0, the BNC production also increased by 39.3% and 102.3%, respectively. To assess the characteristics of the BNC products, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis were used. The average diameter of BNC fibers, which was prepared from the medium adding 0.15 g/L γ-PGA, was twice thicker than that of BNC fibers prepared from the control culture medium. That might be because that polyglutamic acid relieved the BNC synthesis from the shear stress from the agitation.

CONCLUSIONS

This experiment held great significance as it explored the use of a novel medium additive, γ-PGA, to improve the production and the glucose conversion rate in BNC fermentation. And the BNC fibers became thicker, with better thermal stability, higher crystallinity, and higher degree of polymerization (DPv). These findings lay a solid foundation for future large-scale fermentation production of BNC using bioreactors.

Structural and genetic insights into a poly-γ-glutamic acid with in vitro antioxidant activity of Bacillus velezensis VCN56

Poly-γ‑glutamic acid (γ‑PGA) produced by Bacillus species is a natural biopolymer, which is widely used in various fields including food, pharmaceuticals, and cosmetics. In this study, the screening of 19 Bacillus isolates derived from traditionally fermented foods revealed that Bacillus velezensis VCN56 was the most potent γ‑PGA producer. The maximum concentration of crude γ‑PGA was 32.9 ± 1.5 g/L in the PGA-3 medium containing glycerol, citric acid, sodium glutamate, NH₄Cl, and starch. The resulting γ-PGA was purified and then characterized by HPLC, FTIR, and ¹H-NMR analyses. Molecular weight of purified γ‑PGA was estimated to be 98 kDa with a polydisperse index of 2.04. Notably, the pure γ‑PGA showed significant in vitro antioxidant scavenging activities against 1,1-diphenyl-2-picrylhydrazyl (72.0 ± 1.5%), hydroxyl (81.0 ± 0.6%), and superoxide (43.9 ± 0.8%) radicals at the concentration of 4 mg/mL. Using whole-genome sequencing, the genetic organization of pgs operon responsible for γ‑PGA biosynthesis in B. velezensis VCN56 differs from those in other Bacillus genomes. Further genome analysis revealed metabolic pathways for γ-PGA production and degradation. For the first time, the present study provides a better understanding of γ-PGA with a promising antioxidant activity produced by B. velezensis at the phenotypic, biochemical, and genomic levels, which hold potential applications in the foods, cosmetics, and pharmaceutical industries.

Probiotics in the dairy industry-Advances and opportunities

The past two decades have witnessed a global surge in the application of probiotics as functional ingredients in food, animal feed, and pharmaceutical products. Among food industries, the dairy industry is the largest sector where probiotics are employed in a number of dairy products including sour/fermented milk, yogurt, cheese, butter/cream, ice cream, and infant formula. These probiotics are either used as starter culture alone or in combination with traditional starters, or incorporated into dairy products following fermentation, where their presence imparts many functional characteristics to the product (for instance, improved aroma, taste, and textural characteristics), in addition to conferring many health-promoting properties. However, there are still many challenges related to the stability and functionality of probiotics in dairy products. This review highlights the advances, opportunities, and challenges of application of probiotics in dairy industries. Benefits imparted by probiotics to dairy products including their role in physicochemical characteristics and nutritional properties (clinical and functional perspective) are also discussed. We transcend the traditional concept of the application of probiotics in dairy products and discuss paraprobiotics and postbiotics as a newly emerged concept in the field of probiotics in a particular relation to the dairy industry. Some potential applications of paraprobiotics and postbiotics in dairy products as functional ingredients for the development of functional dairy products with health-promoting properties are briefly elucidated.

The Biotechnological Potential of Pediococcus spp. Isolated from Kombucha Microbial Consortium

In the past decade, the probiotic market has grown rapidly, both for foods and supplements intended to enhance wellness in healthy individuals. Different lactic acid bacteria (LAB), especially Lactobacillus spp., of different origins have already been used to develop commercial probiotic products. Nowadays, LAB new alternative sources, such as non-dairy fermented food products, are being exploited. One such source is Kombucha, a fermented low-alcohol beverage made of tea leaves. In this regard, we tested seven Pediococcus spp. strains isolated from a local industrial Kombucha for their biotechnological potential. Two, out of the seven isolates, identified as Pediococcus pentosaceus (L3) and Pediococcus acidiliactici (L5), were selected as successful candidates for the food industry, due to their probiotic and technological properties. In regard to their resistance in the gastro-intestinal tract, both selected strains were tolerant to a pH of 3.5, presence of 0.3% pepsin, and 0.5% bile salt concentration. On the antagonistic side, the fresh suspension of selected isolates had high inhibitory activity against pathogenic bacteria, such as Salmonella enterica Typhimurium, Listeria monocytogenes, Listeria ivanovii, Bacillus cereus, Proteus hauseri, and methicillin resistant Staphylococcus aureus. In addition, moderate to high inhibitory activity was noticed against foodborne molds (e.g., Penicillium expansum and Penicillium digitatum). These safety issues were supported by their negative hemolytic activity and good antioxidant potential (56-58%). Selected isolates were sensitive to ampicillin, penicillin, erythromycin, and lincomycin, while a broad range of other antibiotics were not effective inhibitors. On the technological side, both strains tolerated 5% NaCl and, during the freeze-drying process, had a good survival rate (86-92%). The selected Pediococcus strains have proven properties to be used for further development of functional products.

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.