Effects of intermittent mechanical mixing on solid-state fermentation of wet corn distillers grain with Trichoderma reesei

• The effects of mechanical mixing on SSF of wet distillers grain were investigated.
• Mixing increased spore production by approximately one order of magnitude.
• Cellulase production decreased between 5 and 10% for mechanically mixed fermentations.
• Moisture content and substrate weight loss were unaffected by mixing.
• Results indicate mixing can be incorporated into bioreactor design for this system.

The influence of mixing on microorganism integrity and product formation is a critical design parameter for solid-state fermentation bioreactors. The effects of intermittent mechanical mixing on the solid-state fermentation of wet corn distillers grain with Trichoderma reesei NRRL 11460 for the production of cellulase were investigated. Experiments were conducted using the unbuffered media at mixing frequencies of 0, 1, 2, 3, and 6 d−1 at 27.5 °C with an initial moisture content of 50%. The results indicate that mixing caused about a tenfold increase in spore production compared to fermentations at static conditions. The cellulase enzyme activity produced was minimally affected by mixing with only a 5–10% decrease in filter paper activity for mechanically mixed fermentations compared to static fermentations. Mixing at lower frequencies of 1, 2, and 3 d−1 caused an increase in CO2 evolution compared to static conditions and higher mixing frequencies of 6 d−1. A correlation between substrate weight loss and cumulative CO2 evolution was established. The ability to intermittently mix a solid-state fermentation bioreactor with minimal detrimental effects increases the feasibility of onsite production of enzymes at biofuel facilities to lower the overall production costs of cellulosic biofuels.