Properties of Polyglutamic Acid Produced by Bacillus subtilis ATCC 6633 in Rehydrated Whey Powder Supplemented with Different Carbon Sources

Abstract

In this study, the use of rehydrated whey powder (RWP) solutions containing different carbon sources (citric acid, ammonium sulfate, or glutamic acid) for gamma-poly(glutamic acid) (gamma-PGA) by Bacillus subtilis ATCC 6633 was explored. After 72 h of fermentation at 30 degrees C, cell growth, gamma-PGA production, molecular weight by SDS-PAGE, rheological properties and NMR analysis of gamma-PGA were determined. The growth of B. subtilis was significantly different during 72 h of fermentation in RWP, medium E, and RWP containing citric acid or glutamic acid. These results showed the dynamic viscosity of the 1% polymer solution was 2.5 Pa-s at 10 1/sec shear rate. The maximum gamma-PGA concentration was 1.57 g/100 mL in RWP containing glutamic acid, citric acid and ammonium sulfate. Therefore, RWP as a waste product with being efficient and more economic fermentation medium to produce gamma-PGA can be ideal for the industrial production.