Abstract
AbstractChemical modifications in starch following heat treatment at low moisture content was studied in relation to enzymic availability of the starch. The samples, native wheat starch and a soluble starch (according to Zulkowsky), were heated with or without addition of levoglucosan (1,6‐anhydro‐β‐D‐glucopyranose), a highly reactive compound proposed to be active in transglycosidation reactions. The modifications induced by heat treatment significantly reduced the digestibility of starch in vitro. The decrease in available starch was not accompanied by any increase in dietary fibre, suggesting that the carbohydrate fragments remaining after enzymic digestion were of low molecular weight.The starch in the heated material was highly fragmented and chemical characterization by 1H‐nuclear magnetic resonance spectroscopy and methylation analysis revealed the formation of new non‐starch linkages mainly β‐(1→4) and β‐(1→6). It is probable that the introduction of non‐starch linkages reduces the enzymic access also of several adjacing α‐glucosidic bonds. Thus, it could explain the 7% decrease in in vitro availability after 4 h heat treatment of wheat starch.
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