Extent of hydrolysis of starches by amylases in the presence and absence of yeasts

Abstract

The extent of en-zymic conversion of corn starch, waxy maize starch, and potato amylose into materials fermentable by yeasts was studied for a number of different types of amylases. When the amylases are allowed to act on the starch substances, complete conversion to fermentable material may take place when the yeasts are allowed to act in the presence of the enzymes but not when the amylases and yeast act separately. The amylases that are capable of bring about complete conversion are the cereal [alpha]-amylases and the fungal amylases. Certain bacterial amylases, pancreatic amylases, and the cereal [beta]-amylases convert starch only partially to fermentable substances in the presence of yeasts. The expts. described in the present paper were carried out at starch concs. comparable to those employed in industrial grain-alcohol processes. With the notable exception of the malt amylases and the [beta]-amylases, all of the enzyme prepns. studied synthesize unfermentable substances from maltose and presumably from starch hydrolysis products. For certain of the enzyme prepns., this synthesizing action provides an explanation for the lack of complete conversion of the starches to fermentable materials; for other enzymes, other explanations are more probable. The nature of the actions of the amylases is considered in relation to the structures of starch substances. Improved procedures are given for the prepn. of soybean [beta]-amylase and of potato amylose. Methods are described for bringing starches into soln. without preliminary gel formation.