Physicochemical properties and in vitro digestibility of starch from naturally air-dried chestnut

Naturally air-dried chestnut is a type of traditionally processed chestnut in North China which has a pleasant flavor. After air drying at room temperature and low-air humidity for two wk, the moisture, total starch content and starch relative crystallinity decreased, while the content of water-soluble sugar and amylose increased because of the dehydration and the hydrolysis of endogenous amylase. The Fourier transform infrared (FTIR) spectroscopy ratio of 1047/1022 cm^-1 and the relative area of the Raman spectrum peak at 480/865 cm^-1 of air-dried chestnut starch decreased in the first two wk and then increased, while the full width at half-maximum height (FWHH) of the Raman spectrum peak at 480 cm^-1 showed the opposite tendency. Crystallinity had a positive correlation with the springiness and chewiness, and was negatively correlated with the estimated glycemic index (eGI). The eGI of air-dried starch was lower than those of roasted or boiled starch, which indicated that naturally air-dried chestnut with low digestibility is a good alternative to thermally processed chestnut.