Effect of sequential hydrothermal treatments on the physicochemical properties and in vitro digestibility of bitter vetch (vicia ervilia) starch

This study evaluated the effects of single (heat-moisture treatment (HMT, 120 °C/24 h, 30 % moisture) and annealing (ANN, 50 °C/24 h, 70 % moisture)) and sequential (HMT-ANN and ANN-HMT) hydrothermal modifications on the physicochemical and digestibility properties of bitter vetch starch (BVS). The most significant reduction in peak and setback viscosities was observed in HMT sample, decreasing from 3278 ± 33 cP to 1467 ± 47 cP and from 3199 ± 79 cP to 406 ± 10 cP, respectively, compared to the native starch. DSC experiment confirmed elevated gelatinization temperatures, with onset (T_o) increasing from 59.54 ± 0.08 °C (native) to 69.35 ± 0.01 °C (HMT-ANN), accompanied by higher enthalpy (ΔH) values, from 7.12 ± 0.05 J/g to 11.40 ± 0.13 J/g. XRD and FTIR analyses indicated increased crystallinity (from 33.51 to 41.78 %) and short-range molecular order (1047/1022 ratio from 0.9812 to 0.9885), whereas SEM images of starch gels revealed primarily morphological changes. Gel hardness was notably reduced following HMT (222.1 ± 9.1 g) and HMT-ANN (253.6 ± 9.3 g), suggesting that dense crystallinity and limited chain mobility hindered the formation of firm gels. Importantly, in vitro digestibility assays showed that HMT and HMT-ANN treatments increased resistant and slowly digestible starch fractions by approximately 1.5- and 4-fold, respectively, indicating potential for low-glycemic food applications. These findings highlight the promising role of hydrothermal treatments in tailoring the functionality of BVS for clean-label, health-promoting food systems.