The role of drying methods in determining the in vitro digestibility of starch in whole chestnut flour

Since high temperature facilitates the gelatinization of starch, temperature is generally recognized to play a key factor in the digestibility of starch during the drying process. However, the food matrix is complex and other factors may influence the digestibility of starch in dried whole flour. In this study, the drying temperature varied depending on the drying method used, i.e., freeze drying (−45 °C), natural drying (25 °C), vacuum drying (40 °C), hot-air drying (50 °C) and roasting (200 °C), and a pretreatment with ascorbic acid or salicylic acid was used to produce whole chestnut flour. The estimated glycemic index was higher for hot-air dried and freeze-dried chestnut flour, while that for vacuum-dried, roasted and phenolics-pretreated hot-air dried chestnut flour was lower than that for naturally-dried chestnut flour. During the drying process, the digestibility of starch was correlated with the drying temperature, long- and short-range molecular order, and other compounds in the chestnut.