Characterization of changes of sago starch components during hydrolysis by a thermostable alpha-amylase

Abstract

Apparent molecular weight profiles of native and hydrolysed sago starch were investigated. Components of sago starch were characterized by high-performance size-exclusion chromatography (HPSEC) and the relative peak areas of amylose and amylopectin calculated as 27·2 and 61·8%, respectively. Techniques to disperse molecularly the components of sago starch with minimal degradation were developed. Storage of samples at −20°C prior to analysis resulted in depolymerization. Polymer integrity was, however, maintained if samples were stored at 40°C in the presence of a suitable antimicrobial agent. The hydrolysis pattern of Termamyl 120L on sago starch was monitored using kinetic, HPSEC and scanning electron microscopy (SEM) studies. Kinetic studies showed that both K m and V max were temperature dependent; K m at 90°C was lower than that at 40°C and the activity of 1 ml of Termamyl 120L solution on solubilized sago starch at 90°C, pH 6·0 and 30 ppm of Ca 2+ was determined and found to hydrolyse an average of 7716 μequivalent glycosidic bonds of the starch per minute. Product spectra from HPSEC showed that the amylolysis was dependent on temperature, enzyme concentration, chain length and nature of substrate. SEM studies appeared to suggest that the enzyme tunnelled into the granular interior and then hydrolysed from within, along concentric rings.