Bioethanol production from germinated grain by inherent enzymes

Summary

The malting in brewing process develops enzymes that are required to hydrolyze the complex starch in grain into simple fermentable sugars. These proceed the three following steps: Steeping encourages germination to start, germination prepares the conversion of the starch to sugars, and kilning stops the germination.
In this study, a method for bioethanol production from rye grain was developed by utilizing the inherent amylase activity from germination of the seed. Grain germination was performed in two steps (steeping, germination) under different conditions, where the effect of temperature, duration and humidity was examined on amylase activity and final ethanol yield. Commercial enzymes were used for reference experiments.
Simultaneous Saccharification and Fermentation (SSF) was performed to reduce end-product inhibition of the amylases during ethanol fermentation. Using cheap nutrient source (cheese whey) minimized the use of water and chemicals with reducing process costs. Whey is a by-product from the dairy industry, which represents a disposal problem. However it containing valuable sugars (lactose) which can be used for bioethanol production. Thermotolerant Kluyveromyces marxianus DSMZ 7239 was used in the SSF process since it is able to convert all C6 sugars including lactose to ethanol,
The process was proved successfully. The results showed that germination phase was strongly affecting the final ethanol yield, which could be increased with up to >90% of theoretical. Contaminated grains which can not be used either as food or feed were also involved in our research.