Hydrolytic action of α‐amylase on high‐amylose starch of low molecular mass

Abstract

High‐amylose starches of low average degree of polymerization (đp 61–71), formed as fine granules by interaction of Bacillus macerans cyclodextrin glucanotransferase with α‐cyclodextrin (CD) at 2–70 °C, are highly insoluble in water and not gelatinizable under normal cooking conditions (100 °C). Samples of CD‐derived starches, both cooked and uncooked, were subjected to hydrolysis in vitro by human salivary α‐amylase at 37 °C under conditions chosen to resemble those in the human intestinal lumen. Released low‐molecular‐mass saccharides were determined quantitatively by HPLC and the results compared with those from similar studies with natural starches. Among uncooked starches, CD‐derived starch showed very low reactivity towards α‐amylase, along with potato starch and a high‐amylose hybrid corn starch (64% amylose). Cooking greatly enhanced reactivity of natural starches, but only moderately increased reactivity of CD‐derived starches. Susceptibility to hydrolysis of cooked starches increased in the following general order: CD‐derived starch (≈100% amylose)<100% corn amylose (isolated by the butan‐1‐ol method)<hybrid high‐amylose corn starch (64–66% amylose)<waxy maize starch (99–100% amylopectin)∼ordinary corn starch (≈25% amylose)<potato starch (≈25% amylose).