The Effect of Thermal Modifications on the Physicochemical, Structural, Functional Properties and In Vitro Digestibility of Black Wheat Kernel and Whole-Grain Flour

Whole grains, due to their intact structure, retain more nutrients and offer significant health benefits. Thermal modification is commonly applied to modify cereal grains. This study aimed to investigate the effects of thermal treatments (microwaving (abbreviation MW-BW), roasting (RST-BW), and an emerging technology, heat fluidization (HFL-BW)) on whole-grain black wheat flour. The results showed minimal loss in proximate composition and increased anthocyanin content (from 38.78 mg/kg (BW) to 39.57 (HFL-BW) and 46.06 mg/kg (MW-BW)) relative to the control. Analysis of physical properties and microstructure revealed that all thermal treatments caused kernel swelling, darkened the flour color, decreased the kernel hardness, and disrupted the starch microstructure. All thermal treatments disrupted starch short-range order and reduced crystallinity (from 26.75% (BW) to 2.56 (HFL-BW) and 15.74% (RST-BW)), resulting in a transformation to a V-type structure. The protein secondary structure (mainly for <i>α</i>-helix) was disrupted, and gluten was denatured and aggregated in all thermal-treatment groups. Thermal treatments decreased gelatinization enthalpy (from 4.76 J/g (BW) to 0.59 (HFL-BW) and 4.44 J/g (RST-BW)) and altered pasting viscosity. The viscoelasticity of pastes made from thermal treatments was improved. In vitro digestibility results showed that thermal treatments decreased starch digestibility, decreased the protein bioavailability, and increased resistant starch content (from 20.1% (BW) to 30.9 (MW-BW) and 39.6% (RST-BW)). Altogether, heat fluidization had the most pronounced effect among the treatments. Thermal modifications-particularly heat fluidization-are promising technologies for enhancing the quality of whole-grain black wheat flour and developing functional foods.