Production of green biodegradable plastics of poly(3-hydroxybutyrate) from renewable resources of agricultural residues.

This work describes potential opportunities for utilization of agro-industrial residues to produce green biodegradable plastics of poly(3-hydroxybutyrate) (PHB). Wheat straws were examined with good efficacy of carbon substrates using Cupriavidus necator. Production was examined in separate hydrolysis and fermentation (SHF) in the presence and absence of WS hydrolysis enzymes, and in simultaneous saccharification and fermentation (SSF) with enzymes. Results showed that production of PHB in SSF was more efficient in terms of viable cell count, cell dry weight, and PHB production and yield compared to those of SHF and glucose-control cultures. While glucose control experiment produced 4.6 g/L PHB; SSF produced 10.0 g/L compared to 7.1 g/L in SHF when utilizing enzymes during WS hydrolysis. Results showed that most of sugars produced during the hydrolysis were consumed in SHF (~98 %) compared to 89.2 % in SSF. Results also demonstrated that a combination of glucose and xylose can compensate for the excess carbon required for enhancing PHB production by C. necator. However, higher concentration of sugars at the beginning of fermentation in SHF can lead to cell inhibition and consequently catabolite repressions. Accordingly, results demonstrated that the gradual release of sugars in SSF enhanced PHB production. Moreover, the presence of sugars other than glucose and xylose can eliminate PHB degradation in medium of low carbon substrate concentrations in SSF.