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American Journal of Food Technology
Year: 2006  |  Volume: 1  |  Issue: 1  |  Page No.: 43 - 51

In vitro Hydrolysis of Starches by α-amylase in Comparison to That by Acid

V. Singh and S.Z. Ali    

Abstract: Starches from cereals (maize, wheat, rice, sorghum, finger millet, waxy rice), pulses (green gram, chick pea) tuber (potato and root (tapioca) were converted to non-granular form and hydrolysed in a homogenous phase. In vitro hydrolysis by α-amylase at 37 °C for 5 to 30 min was carried out and the same starches were also modified with 0.5 N HCl at 37°C for 0.75 to 3 h. Molecular weight of the starches decreased to 7-35% of the respective initial values at the end of 5 min and down further to 3-15% at the end of 30 min. Acid hydrolysis in comparison was very slow. At the end of 3 h, of the resultant starches was still 18-70% of their initial . Degradative pattern of 20 min enzyme hydrolysed starches was studied by gel permeation chromatography on Sepharose CL-6B column. The carbohydrate content of the Fraction-I (void volume, Fr-I) decreased from 81 to 21% after hydrolysis and that of Fraction-II (Fr-IIA and Fr-IIB) increased. The increase was more (from 4.9 to 43.4%) in Fr-IIB (towards total volume). The in the peak of this fraction had a range of 2 x 103 to 9 x 103 indicating that the enzyme hydrolysis in non-granular state produced very low molecular weight dextrins in comparison to granular hydrolysis. The resistance for enzyme hydrolysis, in descending order was found to be finger millet, potato, chickpea, rice, sorghum, green gram, wheat, tapioca, waxy rice and maize. The λmax of iodine complex of enzyme hydrolysed fractions was low in comparison to their respective native fractions. Maximum drop of >100 nm was noted in Fr-IIA, which had comparatively higher values for their respective native fractions indicating that hydrolysed product had many branch points. The higher λmax for peak of Fr-IIB indicated that carbohydrate content corresponding to this peak represented long linear chain fraction probably coming from external chains of the amylopectin molecule.

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