Microbial production and functional assessment of γ-polyglutamic acid isolated from Bacillus sp. M-E6

This study describes the production and functional evaluation of <i>γ</i>-polyglutamic acid (<i>γ</i>-PGA) synthesized by <i>Bacillus</i> sp. M-E6, isolated from a traditional fermented food. Among 103 isolates screened, strain <i>Bacillus</i> sp. M-E6 exhibited the highest <i>γ</i>-PGA yield (4.9 g/L) and was taxonomically identified through 16S rRNA gene sequencing. The <i>γ</i>-PGA was extracted and characterized for the physicochemical and techno-functional properties. The <i>γ</i>-PGA was purified using ion-exchange column chromatography, and its molecular mass was determined by Electrospray Ionization-Mass Spectrometry (ESI-MS), which found it to be 60.42 kDa. Fourier-transform infrared spectroscopy and nuclear magnetic resonance analysis confirmed the polymer's structure as <i>γ</i>-PGA. Thermogravimetric analysis revealed high thermal stability (>600 °C), while scanning electron microscopy showed a porous and granular morphology. The <i>γ</i>-PGA showed potent functional properties such as water holding capacity (196.21%), water solubility index (96.64%), water contact angle (26°), oil binding capacity (104.78%), flocculation activity (29.32%), emulsifying activity (79.33%), and antioxidant activity. Further, the <i>γ</i>-PGA showed an excellent cryoprotectant activity with probiotic bacteria <i>Lacticaseibacillus rhamnosus</i> (97.57%), <i>Streptococcus thermophilus</i> (93.47%), and <i>Limosilactobacillus fermentum</i> (84.53%) as evaluated by flow cytometric analysis and direct plate count. These findings highlight the multifunctional potential of <i>γ</i>-PGA from <i>Bacillus</i> sp. M-E6 as a natural, biocompatible cryoprotectant with promising applications in the food, cosmetic, and biomedical industries.