Mechanistic effects of starch-lipid complexes formation on oat starch digestibility during roasting process

Roasting modifies the starch structure and inhibits lipid oxidation in oats; however, its role in regulating starch-lipid complexes (SLC) formation and starch digestibility remains unclear. Using a sealed ampoule system to simulate roasting, this study investigated the effects of initial moisture content, temperature and duration on SLC formation, structure, and digestibility of oat starch-lipid mixtures. Roasting significantly increased the complex index to above 35.00 % compared to unroasted sample (25.25 %, p < 0.05), indicating enhanced amount of SLC. An initial moisture content of 20.0 % promoted highly ordered type I crystallites, resulting in the highest enthalpy change (1.45 J/g), relative crystallinity (39.2 %), and resistant starch (RS) content (88.3 %). Roasting temperatures up to 120 °C further facilitated the formation of stable crystalline structures and significantly increased RS content (p < 0.05), whereas roasting durations had no significant effect on starch digestibility despite promoting SLC formation within 30-40 min. Multivariate analysis identified that starch digestion resistance was predominantly governed by the lamellar structural parameters (d_Bragg and D_m) and long-range molecular order of the mixture, both of which were strongly influenced by initial moisture content. These findings establish a structural and mechanistic basis for modulating starch digestibility in roasted oats.