Starches from Different Tiger Nut Varieties: A Comparative Study of Multi-Scale Structural Characteristics, Functional Properties, and In Vitro Digestibility

Tiger nuts are rich in various nutrients, with starch being a key component that holds potential for applications in foods with lower digestibility. However, the varietal dependence of their functional properties has not yet been comprehensively characterized. In this study, starches from different tiger nut varieties—Yunnan Large-seeded Tiger Nut (YLL), Yunnan Small-seeded Tiger Nut (YSL), and Zhongyousha No.1 (ZYS)—were systematically analyzed to investigate differences in their multi-scale structures, functional properties, and digestibility. The results revealed significant varietal differences in amylose content (22.82–26.99%), granule size (D50 8.66–10.23 μm), and short-range molecular order. All starches exhibited A-type crystalline structures, though their relative crystallinity (25.40–30.60%) differed significantly. In vitro digestion profiles demonstrated a two-phase hydrolysis pattern across all varieties, a rapid digestion phase (0–30 min) followed by a slow digestion phase (30–120 min), with resistant starch content ranging from 33.55% to 38.31%. Among the three varieties, higher amylose content and crystallinity were generally associated with enhanced digestive resistance and lower peak viscosity, while gelatinization temperature appeared to be more closely related to granule size than to crystallinity. Peak gelatinization temperature (TP) ranged from 67.40 to 68.16 °C and peak viscosity (PV) from 7030.0 to 7749.5 mPa·s, with YSL, which had a relatively broad granule size distribution and the lowest crystallinity, exhibiting the highest TP and PV. This study provides a reference for understanding the structure–property relationships of tiger nut starches across different varieties and their potential application in functional foods.