The aim of this work was to study the action of glucoamylase in the process of bioconversion of native starch in combination with amilolytic enzymes, that have a positive effect on the bioconversion of the pre-gelatinized starch. It was found that the use a composition of thermostable bacterial glucoamylase with α-amylase as catalyst, in contrast to the gelatinized starch, a positive effect is not observed. It was revealed a positive impact of composition the glucoamylase (Asp. niger) and pullulanase (Bac. licheniformis) with the dose of 0.4–0.5 units of ASPU/g DS of starch on the process. The studies revealed that the optimum рН of the reaction medium for the enzyme composition as well as of for glucoamylase at the action on native starch is in the range of 3.0–3.5, in contrast to the 4.0 to 4.5 for gelatinized starch.

The results showed that the optimum рН decrease for the action of glucoamylase in the process of bioconversion of native starch to 3.3 and 3.5 may be due to the synergistic action of glucoamylase and НСl. Pullulanase (Bac. licheniformis) retains the optimum рН (4,2) for gelatinized starch at independent action on native starch is partially inactivated while lowering рН. At a dose of 10 ASPU/g DS of starch under specified conditions pullulanase cleaves not more than 1% DS of starch at forming glucose (~ 45%), maltose (~ 13%), maltotriose (~ 12%) and HMS (~ 30%). That indicates to the ability of the test pullulanase in addition to the α-1,6-glycosidic linkages to break down starch and α-1,4 links. On the basis of the obtained data it is revealed that the use of the glucoamylase composition with α-amylase and/or pullulanase for low-temperature bioconversion of native starch, unlike gelatinized is ineffective.

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