Parametric Study on the Solid Substrate Fermentation of Poly-γ-Glutamic Acid by a Locally Isolated Bacillus subtilis

Author : Tenorio, Aileene Collantes
Major Adviser : Valencia, Jeanne Michelle T.
Major Co-Adviser : Mercado, Margarita A.
Committee Members : Arocena, Rhebner E.; Movillon, Jovita A.
Year : 2016
Month : December
Type : Thesis
Degree: BS
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The study was conducted to determine the effects of initial moisture content, initial pH, incubation temperature, and incubation period on the solid substrate fermentation of poly-γ-glutamic acid (γ-PGA) by a locally isolated Bacillus subtilis. In the time profile experiment, soybean curd residue and coconut paring cake were used as substrates for fermentation, and the substrate that produced the highest γ-PGA yield was chosen for the factorial experiment. It was found that soybean curd residue achieved the highest γ-PGA yield (11.70 g/kg). A two-level factorial experiment was done to determine the effects of the initial moisture content (50 and 70%), initial pH (6.0 and 8.0), incubation temperature (30 and 40°C), and incubation period (48 and 60 hours). From the Analysis of Variance, it was found that initial moisture content, initial pH, and incubation temperature significantly increased the γ-PGA yield of the strain using soybean curd residue. The best condition from the factorial experiment, which was at 70% initial moisture content, an initial pH of 8, and an incubation temperature of 40°C, was used for the time profile experiment of the growth and γ-PGA yield of the strain. The results showed that the lag phase of the bacteria using the best condition occurred from 0 to 18 hours, the exponential phase took place from 18 to 36 hours, and the stationary phase was from 36 to 72 hours. At the stationary phase, a maximum γ-PGA yield of 9.65 g/kg was found at 60 hours.

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