Platform chemical production from wheat-based biorefining strategy

Abstract

Development of biorefineries has attracted increasing attention around the world in the past decade. It focuses on alleviating pressure on fossil resources and the environmental burden of current fossil based processes, as well as facilitating sustainable development of the chemical industry. Many chemicals that used to be produced via chemical processes can now potentially be generated biologically from renewable raw materials. At the Satake Centre for Grain Process Engineering, a novel cost-competitive wheat-based biorefining strategy leading to the production of generic microbial feedstocks has been successfully developed (Webb and Wang, 1997 and Webb et al., 2004). These feedstocks are now being evaluated for the production of platform chemicals, biodegradable polymers and biofuels by bacterial fermentation. In the study reported here, succinic acid has been used as a model product for this biorefining strategy to convert wheat flour into fine chemicals. Another advantage of bio-synthesis of succinic acid is the fixation of CO2, which can help towards tackling the global warming challenge. Wheat is one of the predominant renewable resources in Europe. We aim to exploit all components of the wheat grain, producing both value-added end-products and precursors for chemical synthesis. In our process, whole wheat flour firstly undergoes fungal fermentation by Aspergillus awamori. The broth filtrate that is rich in glucoamylase is then used to hydrolyse flour components to generate a glucose-rich stream (flour hydrolysate) while the solid residue is used for fungal autolysis to produce a nutrient-rich stream (fungal autolysate). The possibility of replacing a commercial semi-defined medium by a combination of flour hydrolysate and fungal autolysate was investigated sequentially. Batch fermentations were performed using a complex medium containing wheat flour hydrolysate instead of commercial glucose. This resulted in a similar yield (0.64 g succinic acid per g glucose) and final succinic acid concentration (27 g/L) compared to fermentations with a semi-defined medium. The use of fungal autolysate instead of yeast extract as nitrogen source led to a succinic acid production of 23.2 g/L with a yield of 0.54 g/g. Even fermentations using the wheat-derived flour hydrolysate and fungal autolysate alone resulted in a succinic acid concentration of almost 16 g/L and an overall yield of 0.19 g succinic acid per g wheat flour. When fermentations were carried out with wheat-derived feedstock and an addition of 50 g/L MgCO3, 36.9 g/L succinic acid was produced from 50 g/L initial glucose with a productivity of 1.54 g/L h. The results of these studies demonstrate that a wheat-based biorefinery employing coupled fungal fermentation with subsequent flour hydrolysis and fungal autolysis can produce a suitable feedstock for efficient production of succinic acid.