Recycling of yeast cells for simultaneous saccharification and fermentation of liquefied starch of rice flour

Different concentrations (150, 200, 280 and 300 gL-1) of rice flour were hydrolysed either by one-step (simultaneous) or two-steps liquefaction and saccharification with α-amylase (2.5 KNU g DS-1) and glucoamylase (2.3 AGU g DS-1) for 4h. Hydrolysis of rice flour suspension (10L) by two-steps process led to better starch hydrolysis than the single step process. The hydrolysate (DE 88.2) obtained by the hydrolysis of 280 gL-1 rice flour fermented by bakers yeast led 25.3 gL-1 ethanol at 48h. Addition of glucoamylase (0.53 AGU mL-1) increased ethanol production to 64 gL-1 at 96h. When 280 gL-1 rice flour liquefied with 2.5 KNU g DS-1 was subjected to simultaneous saccharification with different amounts of glucoamylase at 48h, 95.3 gL-1 ethanol was obtained with 2.3 AGU g DS-1. Replacing the commercial glucoamylase with that produced in the lab gave similar ethanol yield and efficiency. With yeast cell recycling, the efficiency and yield of ethanol production were decreased. Intermittent addition of nutrient medium improved the ethanol production by yeast recycling