Cereal Chem 60:46 - 50. | VIEW
Comparison of Nephelometric and Phadebas Methods of Determining Alpha-Amylase Activity in Wheat Flour Supplemented with Barley Malt.
E. Hsu and E. Varriano-Marston. Copyright 1983 by the American Association of Cereal Chemists, Inc.
Alpha-amylase activity in wheat flour supplemented with different levels of barley malt was determined by nephelometric and Phadebas methods. The methods were highly correlated with each other, indicating that one method can be used to predict the other. At low levels of malt supplementation (0.05-0.2%), the nephelometric method, which had greater variations among replicates, was more sensitive in detecting alpha-amylase activity than was the Phadebas method. However, the relationship between alpha-amylase activity and Amylase 1 readings was linear only to about 660 Amylase 1 units. This contrasted with the linearity shown by the Phadebas method that existed at absorbances as high as 1.6. A biochemical study showed that the beta-limit dextrin substrate contained a high concentration of reducing sugars (2.5 mg/ml), which may have decreased alpha-amylase activity (via product inhibition) and accounted for the lack of linearity for Amylase 1 readings above 660. The average chain length of the high molecular weight fraction of the beta-limit dextrin varied among bottles but ranged from 26 to 32 glucose units. The beta-amylolysis limits for the 24-hr digestion of beta-limit dextrin by sweet potato beta-amylase averaged 22%; thus, the commercial substrate was not entirely specific for alpha-amylase.