Microbial production of poly (γ-) glutamic acid and its use as an anti-thawing agent and as prebiotic

Abstract

Poly-γ-glutamic acid (γ-PGA) is a natural, edible, non-toxic, non-immunogenic, and an anionic homo-polyamide, produced by various microorganisms. At an industrial level, for preparing probiotic foods, probiotic cultures are added in powdered forms. Here, cultures are formerly freeze-dried. Freeze-drying process is itself very detrimental to the viability of such organisms as it utilizes very low temperatures of -80 °C. A bacterial strain was isolated from fertilized soil and was statistically optimized in this study. Upon optimization using Plackett-Burman model, a significant increase in the yield from 4.51 ± 0.32g/L to 19.0 ± 0.5g/L was observed. To investigate the cryoprotectant activity during freeze-drying process, Lactococcus lactis was freeze-dried and was subjected to a series of thawing temperatures. Cultures where then treated with a polyelectrolytic combination of γ-PGA (anionic polymer) and Gelatin (cationic polymer). This combination showed a synergistic effect in protecting Lactococcus lactis during freeze-drying wherein a log reduction of only 0.23 was noted, compared to unprotected cells, 2.85. In addition to this, the prebiotic activity of γ-PGA was also assessed in vitro. It was found that there was a significant increase in the growth of Lactococcus lactis (32.14%) considering the effect of γ-PGA alone. Thus, the combinatorial effect of this biopolymer i.e., as a cryoprotectant and as a prebiotic can definitely bring out a beneficial probiotic product into the market with improved health effects.