Effects of different drying treatments on the structural, functional and in vitro digestive characteristics of isolated starch from tiger nut

Abstract

Drying treatment can significantly increase the oil yield of tiger nuts, and the full utilization of starch by-products in tiger nut meal is an important aspect of improving its industrial value. Consequently, the effects of roasting, microwave and roasting treatments on the structure, functional properties and in vitro digestive characteristics of tiger nut starch were investigated. The results showed that compared to that of CS (untreated control starch), samples of BS (baked starch), MS (microwaved starch), and RS (roasted starch) showed deeper color, surface cracks, partial aggregation on the granules, and larger particle size. In addition, baking, microwave and roasting treatments all decreased the relative crystallinity and short-range ordering of the tiger nut starch, explaining the decrease in enthalpy in the DSC results, the increase in the stability of the freeze-thaw, the solubility and the swelling. From the rheological analysis of starch, it was found that the gel structure of tiger nut starch decreased after the aforementioned treatments. This indicates that the branched chain starch was damaged, which impacing the digestibility of the starch. Further in vitro digestion tests demonstrated that three drying treatments increased slow-digestible starch and resistant starch content. Among them, microwave drying treatment had a significant effect on the structural and functional properties of the isolated starch of tiger nut. This study aimed to provide theoretical guidance for the comeplete utilization of tiger nut starch.