Enzymatic hydrolysis of high gravity extruded corn starch media

Increase of solubles concentration in processable liquid media is one of the trends of technological development of starchy materials bioconversion. It promotes the reduction in operating costs, in heat and energy consumption and increases the efficiency of using capacitive equipment. The use of thermoplastic extrusion in the bioconversion processes as a pretreatment stage is perspective. Extrusion provides intensive gelatinization of starch with a moisture content of 15-30 % that has become a prerequisite for the development of extrusion-hydrolytic technology for obtaining of concentrated hydrolysates from starch-containing raw materials. As a part of the technology development, the effect of the key factors of biocatalysis on the formation of hydrolysis products and the rheological properties of highly concentrated hydrolysates of corn starch has been studied. The dosage of thermostable α-amylase and the concentration of the medium were taken as independent variables. The ranges of variation of the factors were set in the range of 5-13 units of amylolytic activity per 1 g of starch and 40- 60 % soluble concentration in accordance with the central orthogonal second-order design of the experiment. The value of dextrose equivalent in the area of the studied factor space varied from 23 to 40. Dynamic viscosity values were in the range from 89 to 2219 mPa·s. The analysis of the results and the mathematical model showed that an increase in the dextrose equivalent in the hydrolysis products was facilitated by a decrease of the concentration of the medium and an increase in the dosage of α-amylase. The growth dynamics of the dextrose equivalent value decreased with an excess of the dosage of the enzyme preparation of 9 units of amylolytic activity per 1 g of starch. Rheological studies have shown that a dosage of α-amylase of 1- 13 units of amylolytic activity per gram of starch at 40 % concentration of the medium provided dynamic viscosity values in the range 89-780 mPa·s, which is sufficient for the subsequent stages of hydrolyzate processing. Increasing the concentration to 50-60 % requires the introduction of α-amylase at a dosage of more than 5 units of amylolytic activity to ensure a rheologically safe process.