A wheat biorefining strategy based on solid-state fermentation for fermentative production of succinic acid

In this study, a novel generic feedstock production strategy based on solid-state fermentation (SSF) has been developed and applied to the fermentative production of succinic acid. Wheat was fractionated into bran, gluten and gluten-free flour by milling and gluten extraction processes. The bran, which would normally be a waste product of the wheat milling industry, was used to produce glucoamylase and protease enzymes via SSF using Aspergillus awamori and Aspergillus oryzae, respectively. The resulting solutions were separately utilised for the hydrolysis of gluten-free flour and gluten to generate a glucose-rich stream of over 140 g l^-1 glucose and a nitrogen-rich stream of more than 3.5 g l^-1 free amino nitrogen. A microbial feedstock consisting of these two streams contained all the essential nutrients required for succinic acid fermentations using Actinobacillus succinogenes. In a fermentation using only the combined hydrolysate streams, around 22 g l^-1 succinic acid was produced. The addition of MgCO₃ into the wheat-derived medium improved the succinic acid production further to more than 64 g l^-1. These results demonstrate the SSF-based strategy is a successful approach for the production of a generic feedstock from wheat, and that this feedstock can be efficiently utilised for succinic acid production.