FUNGAL HYDROLYSIS AND YEAST FERMENTATION OF STARCH IN RAW WHOLE CORN (ETHANOL, KOJI).

摘要

In a liquid fermentation, hydrolysis of the raw starch in ground corn to fermentable sugars which are simultaneously fermented to ethanol by yeast in a non-sterile environment was investigated. This showed the conventional cooking step can be eliminated for energy conservation. A koji of Aspergillus niger grown on whole corn for three days was the crude enzyme source. A ratio of 0.2 g dry koji per g total solids was found sufficient. Optimum pH was 4.2. Ethanol concentration was 7.7% (w/w) in the aqueous phase with 92% raw starch conversion. Agitation increased rate. Saccharification was the rate limiting step. The initial ethanol concentration preventing fermentation was estimated to be 8.3% by weight.; Solid-state fermentation of raw corn to ethanol was also investigated. At 40% koji solids, 12% ethanol (w/w) in the aqueous phase was obtained with 59% starch conversion; this represents an energy savings of 43% in distillation and 84% in stillage drying. When the mash was diluted to 7.7% ethanol after 48 hours and fermentation continued, starch conversion was increased to 74% without lowering ethanol concentration.; Substrate comparisons were made in a liquid to solid-state fermentation among dent corn (DC), high lysine corn (HLC), dent corn starch (DCS), and high lysine corn starch (HLCS) in simultaneous raw starch hydrolysis and fermentation with koji as enzyme source. HLC and HLCS showed higher ethanol concentration and starch conversion than DC and DCS. A water extract of koji gave a slower initial fermentation but the same results as koji after 90 hours. Sake yeast at 24% starch and 30 deg C for three days increased final ethanol concentration to about 14% with 92% starch conversion while 11.8% ethanol with 75% conversion was obtained with commercial yeast. At 20 deg C and 29% starch, final ethanol concentration was increased to 17% with 91% conversion in 13 days.