Thermally induced structural and digestive modifications of endosperm starch in whole highland barley kernels: A closer insight from in situ cell wall permeability

This study investigated the effects of thermal treatment (100 °C–200 °C, 5 min–50 min) on in-kernel highland barley (HB) starch at the molecular, structural, and physicochemical levels, along with the underlying digestion mechanisms. In situ observations using fluorescent dextran probes revealed variable permeability in thermally damaged kernel cells, where the composite network of the cell wall matrix and expanded starch impeded probe diffusion. Thermal processing induced the formation of dark rings and disrupted Maltese crosses, with these morphological alterations correlating with starch surface damage. Multi-scale structural analysis showed that thermal treatment reduced both the molecular weight (from 155.40 × 10 6 to 27.15 × 10 6  g/mol) and relative crystallinity (27.02 %–15.61 %), but increased the amylose/amylopectin ratio (0.29–0.61) and degree of gelatinisation. These changes also led to a reduction in the viscoelastic moduli (G′ and G″) of HB starch gels. Prolonged processing time exerted stronger destructive effects than shorter treatments at the same temperature. Notably, heat treatment promoted the formation of short-range ordered structures and enhanced entanglement between cell wall fibres and gelatinised starch, thereby converting rapidly digestible starch into slowly digestible starch. The 150-25-HBS and 150-50-HBS samples exhibited the lowest equilibrium digestibility (C ∞ , 84.39 ± 2.6 % and 82.73 ± 0.19 %, respectively). These findings offer valuable insights for the design of HB-based products with improved slow-digesting properties.