Cereal-based biorefinery development: Utilisation of wheat milling by-products for the production of succinic acid

Abstract

A novel wheat-based bioprocess for the production of a nutrient-complete feedstock for the fermentative succinic acid production by Actinobacillus succinogenes has been developed. Wheat was fractionated into bran, middlings and flour. The bran fraction, which would normally be a waste product of the wheat milling industry, was used as the sole medium in two solid-state fermentations (SSF) of Aspergillus awamori and Aspergillus oryzae that produce enzyme complexes rich in amylolytic and proteolytic enzymes, respectively. The resulting fermentation solids were then used as crude enzyme sources, by adding directly to an aqueous suspension of milled bran and middlings fractions (wheat flour milling by-products) to generate a hydrolysate containing over 95 g/L glucose, 25 g/L maltose and 300 mg/L free amino nitrogen (FAN). This hydrolysate was then used as the sole medium for A. succinogenes fermentations, which led to the production of 50.6 g/L succinic acid. Supplementation of the medium with yeast extract did not significantly improve succinic acid production though increasing the inoculum concentration to 20% did result in the production of 62.1 g/L succinic acid. Results indicated that A. succinogenes cells were able to utilise glucose and maltose in the wheat hydrolysate for cell growth and succinic acid production. The proposed process could be potentially integrated into a wheat-milling process to upgrade the wheat flour milling by-products (WFMB) into succinic acid, one of the future platform chemicals of a sustainable chemical industry.