Effect of temperature on saccharification and oligosaccharide production efficiency in koji amazake

Koji amazake, prepared from rice koji, is a traditional Japanese sweet beverage. The main source of sweetness is glucose derived from rice starch following digestion by enzymes of Aspergillus oryzae during saccharification. The temperature of this process was empirically determined as 45 degrees C-60 degrees C, but no studies have systematically investigated the effect of temperature on saccharification efficiency. We addressed this in the present study by evaluating saccharification efficiency at various temperatures. We found that glucose content was the highest at 50 degrees C (100%) and was reduced at temperatures of 40 degrees C (66.4%), 60 degrees C (91.9%), and 70 degrees C (76.6%). We previously reported that 12 types of oligosaccharides are present in koji amazake; the levels of eight of these, namely nigerose, kojibiose, trehalose, isomaltose, gentiobiose, raffinose, panose, and isomaltotriose, were the highest at 50 degrees C-60 degrees C, whereas sophorose production was maximal at 70 degrees C. Based on these findings, we initially performed saccharification at 50 degrees C and then switched the temperature to 70 degrees C. The maximum amount of each saccharide including sophorose that was produced was close to the values obtained at these two temperatures. Thus, oligosaccharide composition of koji amazake is dependent on saccharification temperature. These findings provide useful information for improving the consumer appeal of koji amazake by enhancing oligosaccharide content. (C) 2018, The Society for Biotechnology, Japan. All rights reserved.