Abstract/Summary

Wheat Dried Distiller’s Grains with Solubles (DDGS) is a by-product of bioethanol and distillery industries, currently marketed as animal feed. However, DDGS is a carbohydrate- and protein-rich material that could be converted into an alternative feedstock for microbial fermentations. The present study focused on exploiting DDGS as a starting material for the production of the biodegradable polymer, polylatic acid (PLA). DDGS was firstly subjected to alkaline pretreatment to facilitate enzymatic hydrolysis (Accellerase® 1500) of carbohydrate polymers to monosaccharides by removing hemicellulose and increased the surface area inside the DDGS matrix. Improved hydrolysis yields were observed in alkaline treated DDGS compared to untreated DDGS. Secondly, the hydrolysates of DDGS were used as carbon sources for lactic acid fermentation. Here, three Lactobacillus sp. were evaluated for their lactic acid production using DDGS hydrolysates in Separate Hydrolysis and Fermentation (SHF). Among the tested strains, L. coryniformis subsp. torquens showed promising characteristics producing D-lactic acid with 99.9% of optical purity and at high conversion yields. D-Lactic acid production from alkaline treated DDGS was also evaluated using Simultaneous Saccharification and Fermentation (SSF) approach, where high concentrations, yields and productivities of D- lactic acid were achieved. Furthermore, D-lactic was subjected to broth decolorisation with activated carbon, followed by acidification and D-lactic acid separation using ion exchange chromatography. High recovery and purity of D-lactic acid with complete removal of sugars and protein from the fermentation broth was obtained at the end of the process. The purified D-lactic acid was then concentrated and used as monomer to synthesise poly-D-lactic acid (PDLA). Azeotropic polycondensation process was used to polymerise purified D-lactic acid leading into a clear, solid PDLA with 3010 Da molecular size at the end of polymerisation process.