Sustainable utilization of food waste: Production and characterization of polyhydroxybutyrate (PHB) from damaged wheat grains

Abstract

Sizeable quantities of wheat grains are wasted or damaged every year either due to improper storage in warehouses or adverse environmental conditions that trigger insect and rodent infestations. As a result damaged wheat grain (DWG) is generated in substantial quantities which, if left alone, could cause environmental pollution. This work focuses on utilizing DWGs for the production of polyhydroxybutyrate (PHB), a biodegradable plastic, with ‘green’ applications. A two-step process involving acid hydrolysis followed by bacterial fermentation by Bacillus sp. NII2 was used at optimum hydrolysis conditions: 3 % acid concentration, 15 % substrate loading and 15 min hydrolysis time, which resulted in 102.47 mg/mL reducing sugars in the hydrolysate. Morphological analysis of the hydrolysis residue displayed pore formation in the substrate as seen in scanning electron micrographs, indicating localized release of sugars. Under optimal conditions, the bacterial culture exhibited 4.33 g/L biomass that accumulated 1.41 mg/L PHB. Produced PHB was characterized through nuclear magnetic resonance imaging (1H-NMR, 13C-NMR) and Fourier transform infrared spectroscopy to confirm the presence of the functional groups (–CH, –CH2, –CH3, –C=O, –C–O–C–) that are innate to the structure of PHB. Thermogravimetric analysis of PHB demonstrated the stability of the biopolymer up to a temperature of 256 °C. The PHB produced from DWG opens up a new opportunity for its sustainable utilization and application in the development of biodegradable biopolymer which could find applications in food packaging.