Simultaneous liquefaction, saccharification and fermentation at very high gravity of rice at pilot scale for potable ethanol production and distillers dried grains composition

• We studied a very high gravity (311.5 g/l) process to produce ethanol from rice.
• We reached 17.6% v/v ethanol (corresponding to a yield of 86.3%) at lab scale.
• We reached 17.0% v/v (corresponding to a yield of 83.2%) at pilot scale (25 l).
• Rice-based distillers dried grains with high protein content (47.5%) were obtained.

In this work, a simultaneous liquefaction, saccharification, and fermentation (SLSF) process at very high gravity (VHG) of broken rice for potable ethanol production was developed at pilot scale. The SLSF–VHG process was performed in a unique fermenter, at 30 °C. Rice flour (RF) was dissolved in tap water to reach 311.5 g/l dry matter and then the mixture was simultaneousely liquefied, saccharified, and fermented. Thanks to the addition of a raw starch hydrolyzing enzyme containing a mixture of alpha-amylase and gluco-amylase (Stargen 002 at 991.8 GAU/kg RF), gluco-amylase (Amigase Mega L at 0.035% w/w), protease (Fermgen at 600 SAPU/kg RF), active dry yeast Saccharomyces cerevisiae (Red Ethanol at 3.5 × 107 cells/ml), KH2PO4 (4.8 mM), and urea (16.0 mM). Under these conditions, the SLSF–VHG process finished after 120 h and achieved an ethanol content of 17.6% v/v corresponding to 86.3% of the theoretical ethanol yield. We scaled up this SLSF process at very high gravity at pilot scale (25 l) and achieved an ethanol content of 17.0% v/v corresponding to a yield of 83.2% of the theoretical ethanol yield. Rice-based distillers dried grains (DDG) was produced from the whole stillage of SLSF process at very high gravity by being plate-filtered and dried. The obtained DDG had high contents of crude protein (47.5%) and fibers (15.8%). Our results suggest, the SLSF under VHG condition of broken rice as well as the recovery of protein-rich DDG could have a great potential for the ethanol and animal feeding industry in Vietnam.