α-Amylase action on starch in chickpea flour following hydrothermal processing and different drying, cooling and storage conditions.

Starch is present in many prepared 'ready-meals' that have undergone processing and/or storage in frozen or chilled state. Hydrothermal processing greatly increases starch digestibility and postprandial glycaemia. Effects of different heating/drying and cooling regimes on amylolysis have received little attention. Hence, we examined the effects of different processing treatments on in vitro digestibility of starch in chickpea flour. Solid-state C NMR was used to estimate ordered double-helical structure in the starch. Native starch with 25 % double-helical content was the most resistant to digestion but hydrothermal processing (gelatinisation) resulted in >95 % loss of order and a large increase in starch digestibility. Air-drying of pre-treated flour produced slowly-digestible starch (C, 55.9 %). Refrigeration of gelatinised samples decreased ease of amylolysis coincident with increase in double-helical content. Freezing maintained the same degree of digestibility as freshly gelatinised material and produced negligible retrogradation. Chilling may be exploited to produce ready-meals with a lower glycaemic response.