Brewer's spent grain biotransformation to produce lignocellulolytic enzymes and polyhydroxyalkanoates in a two-stage valorization scheme

Lignocellulolytic enzymes from low-cost sources are gaining attention as a tool to reduce production costs. Such enzymes can be obtained sustainably by diverse fungal strains via solid-state fermentation (SSF) of lignocellulosic-derived residues as substrates. Besides, these enzymes allow hydrolyzing the same residue, releasing fermentable sugars that can be transformed into value-added products. This study shows a two-stage valorization approach for the lignocellulosic leftover brewer's spent grain (BSG): first, by producing lignocellulolytic enzymes through the SSF of BSG using three fungal strains and, second, by using the self-produced enzymes to hydrolyze the same BSG and obtaining sugar-rich hydrolysates that serve as an alternative carbon source for polyhydroxyalkanoates (PHA) production. From the evaluated set,Aspergillus nigerandThermoascus aurantiacusproduced the highest xylanase activities compared withTrichoderma reesei(268 +/- 24, 241 +/- 10, and 150 +/- 24 U per gram of dry BSG, respectively).Also,A. nigerextracts resulted in the most effective for releasing sugars from BSG, obtaining up to 0.56 g per gram of dry BSG after 24 h without any pretreatment needed. Thus, the sugar-rich hydrolysate obtained withA. nigerwas used as a source for producing PHA by using two bacterial strains, namely,Burkholderia cepaciaandCupriavidus necator. Maximum PHA yield was achieved by usingC. necatorafter 48 h with 9.0 +/- 0.44 mg PHA center dot g(-1)dry BSG. These results show the significant potential of BSG as raw material for obtaining value-added bioproducts and the importance of multiple valorization schemes to improve the feasibility of similar residue-based systems.