Optimizing Fermentation with Corynebacterium glutamicum to Enhance L-lysine in Corn-ethanol By-products: Distillers Dried Grains with Solubles, Whole Stillage, and Thin Stillage — 108a — Bhawana Khadka, Shishir Roka, and Bishnu Karki

Department of Biology and Microbiology, South Dakota State University, Brookings, SD, 57007

The corn-based ethanol industry generates considerable amount of by-product known as whole stillage. This nutrient-rich by-product is further processed into solids and liquid fractions, generating: Dried distillers’ grains (DDG) and thin stillage. The DDG is supplemented with concentrated thin stillage to produce dried distillers’ grains with solubles (DDGS), which is widely used animal feed additive, including aquaculture. However, due to unbalanced amino acids, low lysine content, higher phytate and fiber content, the inclusion of DDGS in animal diet is limited to only 30%. Fungal fermentation of DDGS has potential to increase its protein content and degrade antinutrients, however the low L-lysine content remains a challenge. Corynebacterium glutamicum is a GRAS approved bacterium, known for producing value-added essential amino acids, such as glutamate and L-lysine. Fermentation with a mutant strain of C. glutamicum can result in increased lysine availability in animal diet along with degradation of antinutrients. Therefore, optimizing fermentation with C. glutamicum could improve the nutritional quality of corn-ethanol by-products, making them more valuable feed additives. Hence, the objective this study was to determine if fermenting whole stillage, DDGS, and thin stillage with C. glutamicum would yield high levels of lysine and improve other desirable characteristics of these co-products during the submerged fermentation. Fermentation parameters such as pH, temperature, and solid loading rates were studied for all three substrates. The parameters measured included L-lysine content, crude protein, total sugars, and phytic acid content. Preliminary results showed 1.39 folds increase in L-lysine content of fermented thin stillage at pH 7.5 compared to the unfermented day 0 values. Similarly, L-lysine levels were increased in whole stillage samples fermented at pH 5 and pH 7.5. The experimental trials are currently underway, investigating the effect of C. glutamicum fermentation on the overall nutritional characteristics of whole stillage, DDGS, and thin stillage. 

South Dakota State University
Dr. Bishnu Karki