Abstract
Potato starch granules were treated with heat-moisture, acid or 85% dimethylsulfoxide, respectively, and enzymatic digestibility of resulting starches were compared with those of intact potato and barley starch granules. Whereas digestibility of starches increased greatly after the heat-moisture treatment that of acid-treated and dimethylsulfoxide-treated starches remained essentially unchanged. It was suggested that crystalline structure of potato starch granules was most responsible to their low digestibility.
A bacterium was isolated that can utilize potato starch granules as a sole carbon source and identified as Bacillus circulans F-2. An extracellular α-amylase produced by this bacterium was purified and its digestive activity toward starch granules of various origins was compared to those of percine pancreatic and Streptococcus bovis α-amylases. The amylase from B. circulans F-2 proved to be most potent in digesting starch granules, especially, those of potato.
B. circulans F-2 produced amylase only when cultivated on starch granules. Other soluble (autoclavable) carbon sources, including maltose and gelatinized starches, have little or no activity in inducing amylase. Recently, starches crosslinked with epichlorohydrin were found to induce amylase as effectively as potato starch granules. These are autoclavable and, therefore, are very convenient carbon source for the production of B. circulans F-2 amylase.
