Bioactive and nutritional properties of kilned whole-grain snacks: focus on buckwheat, oat, and rye

This study evaluated the effects of controlled heat treatment on the glycemic index (eGI), bile acid-binding capacity (BABC), total phenolics, antioxidant activity, and in vitro bioaccessibility of whole grain buckwheat (Fagopyrum esculentum), rye (Secale cereale L.), and oats (Avena sativa). Cereals were subjected to thermal processing at three temperatures (120, 150, and 180 °C) for 30 min. The eGI values increased in rye and oat following heat treatment but decreased in buckwheat at 150 and 180 °C. Thermal processing significantly affected BABC in all cereals (p ≤ 0.05), with the highest values observed at 180 °C for oats (6.56 µmol/g), buckwheat (6.65 µmol/g), and rye (5.77 µmol/g). The total phenolic content (TPC) increased with heat treatment. The highest TPC values were recorded at 180 °C for rye (9.33 mg GAE/g dw), 120 °C for buckwheat (15.39 mg GAE/g dw), and 150 °C for oats (10.04 mg GAE/g dw). Antioxidant capacities, measured using DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) assays, were enhanced in buckwheat and oats after thermal processing, while a significant decrease was observed in rye. The in vitro bioaccessibility of TPC significantly improved during the gastric phase for all samples except oat, with buckwheat showing the highest increase (86.56% at 180 °C). Oats maintained the highest bioaccessibility index (BI) for total antioxidant capacity (TAC) across all treatments, while rye peaked at 444.09% TAC during the intestinal phase at 120 °C. These findings underscore the influence of thermal processing on the functional and nutritional properties of these cereals, with notable variations based on their unique compositions. Overall, these findings demonstrate that controlled heat treatment can enhance the nutraceutical value and bioaccessibility of phenolics in whole grains, providing a promising strategy for developing minimally processed, functional cereal-based products with cardiometabolic and digestive health benefits. Heat treatment enhances dietary fiber content and bile acid binding capacity. Phenolic compounds and antioxidant activity increase with kilning. Buckwheat showed the highest improvement in TPC bioaccessibility. Thermal processing significantly enhanced rye’s TAC bioaccesibility.