Reducing retrogradation of gelatinized rice starch and rice meal under low temperature storage by addition of extremely thermostable maltogenic amylase during their cooking

Abstract

Most of anti-retrogradation amylases could not be used in rice cooking due to their low optimal temperature. To overcome this disadvantage, an extremely thermostable maltogenic amylase from Thermofilum pendens at 3.5, 35 or 80U/g substrate was incubated at 90, 95, or 100°C with rice starch at 0.5% (w/v) or 5% (w/v), or polished rice grains at 50% (w/w), respectively. Its hydrolytic patterns and anti-retrogradation roles were evaluated. The amylose content of rice starch decreased from 16.6 to 8.6% after incubation of 120min, while the amylopectin content remained almost constant with a somewhat increase in ratio of short-to-long branch-chains. Substrate specificity analysis of the enzyme showed that its kcat/Km value on amylose was 0.98s−1mLmg−1, whereas that for amylopectin was 0.30s−1mLmg−1, indicating an exceptionally high preference toward amylose. Retrogradation rates of gelatinized rice starch and rice meal decreased significantly during storage of 4°C.