Bacteria produce poly (γ‐glutamic acid) (γ‐PGA), a polymer of l‐ or d‐glutamic acid, as a defense response and have gained importance due to their applications in food and pharmaceutical industry. In the present investigation, production of γ‐PGA using cost‐effective carbon substrate, characterization of the produced polymer, and its application as cryoprotectant for selected freeze‐dried probiotic bacteria were investigated. Central composite rotatable design of response surface methodology was used to study the main and the interactive effects of medium components: rice bran and casein peptone concentration. Rice bran at 35% (w/v) and casein peptone at 7.5% (w/v) were found to be optimal at an initial pH of 7.5, and incubation temperature of 37°C for 48 H produced 8.2 g/L γ‐PGA on dry weight basis. The thermal properties such as melting temperature, heat of fusion, and thermal stability were also studied. Ten percent (w/v) of γ‐PGA with 10 percent of sodium alginate (w/v) protected viability of Bifidiobacterium bifidum NCDC 235 and B. adolescentis NCDC 236 during freeze drying at –80 ˚C for 48 H. The γ‐PGA synthesized by the reported bacterium with GRAS status is suitable for food and biomedical applications.

Poly (γ-) glutamic acid (γ-PGA) is a polymer of L or D -glutamic acid units produced by microorganisms as a defense mechanism as an act of stress tolerance. Production of γ-PGA by microbial source has been gaining attention due to its low cost of production and varied application with high compatibility and high biodegradability. Its application ranges from food industry to waste water treatment. γ-PGA is a major constituent of Japanese foodnatto. γ-PGA has vast applications in food, pharmaceuticals, healthcare, water treatment and other fields. The high research interest that currently is developing for γ-PGA is due to its potential as a biomedical material with a high biocompatibility and a fair biodegradability. In fact, γ-PGA is extensively used as a food additive and it is known to be hydrolytically degradable by water with or without intervening of proteases. An incessant number of publications dealing with the use of γ-PGA as drug delivery system are appearing in these last few years and several processes have been developed at large scale which are able to afford great amounts of this compound for industrial uses.