Abstract
This study investigates the use of brewer's spent grains (BSG), a major waste stream from the brewing process, for its potential as a carbon source for the fermentative production of polyhydroxyalkanoates (PHAs), biodegradable polyesters. The sugars obtained from hydrolysis of raw and hot water-pretreated BSG were fermented using a recombinant Escherichia coli LSBJ harboring genes for biosynthesis of either homopolymer polyhydroxybutyrate (PHB) or PHB-co-medium chain length copolymer (PHB-co-MCL). The highest biopolymer titers obtained from the BSG hydrolysate were 3.53 g/L and 3.32 g/L for PHB and PHB-co-MCL, respectively, which corresponded to process yields of 0.353 g PHB/g sugar and 0.32 g PHB-co-MCL/g sugar. Titers obtained from the BSG hydrolysate were higher compared to titers from native PHA producers observed in previous works, which was likely due to the metabolic advantages inherent to using a recombinant organism. These results demonstrate both the viability of BSG as a feedstock for production of PHB-co-MCL copolymer and the feasibility of reducing the manufacturing cost of biodegradable biopolymers by using upgraded (valorized) waste resources.