Effect of agitation on the efficiency of enzymatic hydrolysis of highly concentrated media of extruded corn starch

Abstract

The influence of the mixing factor and its intensity was investigated at the stage of developing a technology for processing highly concentrated hydrolysates (50% solids) of extruded corn starch. The starch was extruded using a twin-screw extruder at a temperature of 185 °C and a pressure at the die of 2 MPa. Extruded substrate was hydrolyzed with enzyme preparations of ?-amylase and glucoamylase for 4 hours with different stirring modes. The significance of the stirring speed on the degree of hydrolysis of extruded starch, especially in the first 2 hours of enzymatic treatment, has been established. As a result of 4-hour exposure, the dextrose equivalent of the hydrolyzate incubated without stirring was 52.2. Dextrose equivalent of the hydrolysates stirred at speed of 100, 200 and 500 rpm was 54.5, 59.3, and 59.8, respectively. The study of rheological properties showed that the dynamic viscosity of a medium without stirring significantly differed from the viscosity of a medium with stirring throughout the entire hydrolysis period. As a result, the dynamic viscosity of the sample without stirring and with stirring decreased from 3 Pa?s to 0.35 Pa?s and from 2.5-2.8 Pa?s to 0.145-0.221 Pa?s, respectively. An double increase of the glucoamylase dosage made the mixing factor after 4 hours of hydrolysis insignificant and increased the dextrose equivalent value by 18-35%. The dextrose equivalents of samples without stirring and with stirring at a frequency of 200 rpm were 70 and 71, respectively. But in the first 2 hours of hydrolysis, the stirring factor for samples with an increased dosage of glucoamylase was also statistically significant. The study showed that hydrolysis of highly concentrated media of extruded starch under the condition of high-quality homogenization with the enzymes provides a high degree of bioconversion without the requirement for continuous mixing,