Process optimization and characterization of polyhydroxyalkanoate copolymers produced by marine Pichia kudriavzevii VIT-NNO2 using banana peels and chicken feather hydrolysate

The present study was focused on the production of polyhydroxyalkanoates (PHA) by halophilic yeast using biowaste materials. The yeast strain was isolated from marine seaweeds and identified as Pichia kudriavzevii VIT-NN02 based on partial 18SrDNA sequencing and phylogenetic analysis. PHA granules were observed by Sudan Black B and Nile Red staining methods. Banana peels and chicken feathers hydrolysate were screened as potential carbon and nitrogen sources for PHA content in biomass (%) by P. kudriavzevii. Process parameters were optimized using 3-level, six variables, Box-Behnken design showing significant improvement in PHA content in biomass from 40.00 +/- 0.1 to 79.68 +/- 0.2% under optimized growth conditions viz. banana peel extract (40%), salt (16.6gL(-1)), incubation time (96 h), pH (10), temperature (37 degrees C) and chicken feather hydrolysate (0.80%). The statistical significance of the model equation was calculated by F-test and R-2 values of the respective responses were found to be 0.9904 and 0.9926, indicating a realistic fit of the model to the experimental data. The actual values of the PHA content in biomass (79.68 +/- 0.2%) was in close agreement to the predicted value (79.68 +/- 1.5%), confirmed the validity of the model. The biopolymer was identified as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] copolymer based on Gas Chromatography-Mass Spectrometry (GC-MS), Fourier Transform Infrared (FTIR) spectroscopy and Nuclear Magnetic Resonance spectroscopy (NMR) analysis. The [P(3HB-co-3HV)] copolymer was found to be highly crystalline and thermally stable through X-Ray Diffraction (XRD), Thermogravimetric analysis (TGA) and Differential scanning calorimetric (DSC) analysis. The Scanning Electron Microscopic (SEM) images of [P(3HB-co-3HV)] copolymer showed porous, smooth and spherical surface morphology.