The aim of this work was to study the production of polyhydroxybutyrate (PHB) using agro-industrial residues as the carbon source. Seven substrates, viz., wheat bran, potato starch, sesame oil cake, groundnut oil cake, cassava powder, jackfruit seed powder and corn flour were hydrolyzed using commercial enzymes and the hydrolyzates assessed for selecting the best substrate for PHB production. Jackfruit seed powder gave the maximum production of PHB under submerged fermentation using Bacillus sphaericus (19%) at the initial pH of 7.5.

The aim of this work was to statistically optimize the cultural and nutritional parameters for the production of polyhydroxybutyrate (PHB) under submerged fermentation using jackfruit seed hydrolysate as the sole carbon source. On the basis of results obtained from "one variable at a time" experiment, inoculum age, jackfruit seed hydrolysate concentration, and pH were selected for response surface methodology studies. A central composite design (CCD) was employed to get the optimum level of these three factors to maximize the PHB production. The CCD results predicted that jackfruit seed hydrolysates containing 2.5% reducing sugar, inoculum age of 18 h, and initial medium pH 6 could enhance the production of PHB to reach 49% of the biomass (biomass 4.5 g/l and PHB concentration 2.2 g/l). Analysis of variance exhibited a high coefficient of determination (R(2)) value of 0.910 and 0.928 for biomass and PHB concentration, respectively, and ensured that the quadratic model with the experimental data was a satisfactory one. This is the first report on PHB production by Bacillus sphaericus using statistical experimental design and RSM in submerged fermentation with jackfruit seed hydrolysate as the sole source of carbon.

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