Health promoting potential of black grains: Evaluation through in vitro gastrointestinal digestion and gut microbiota fermentation

This study systematically evaluated the nutritional composition, in vitro gastrointestinal digestion, and gut microbiota fermentation characteristics of six black grains: corn, millet, rice, buckwheat, quinoa, and wheat. The results indicated that, compared with their common grains, black grains contained higher levels of protein, dietary fiber, ash, fat, amylose, polyphenols, and flavonoids, but exhibited lower total starch (TS) contents and glycemic indices (GI). Black grains displayed significantly lower TS and protein hydrolysis rates, along with reduced insoluble dietary fiber digestibility and a smaller increase in soluble dietary fiber. Meanwhile, black grains exhibited higher content of both free and bound polyphenols and flavonoids at each stage of digestion. Subsequent fermentation revealed that polyphenols and flavonoids in insoluble black grains exhibited higher bioaccessibility. Furthermore, black grains favorably modulated gut microbiota composition by improving the abundance of beneficial genera ( Lactobacillus , Bifidobacterium , and Phascolarctobacterium ) and reducing the harmful ones ( Escherichia-Shigella and Desulfovibrio ). These changes promoted short-chain fatty acid production, thereby supporting a healthier gut microbial ecology. Overall, these results indicate that the high density of health-promoting components, lower GI, and favorable modulation of gut microbiota confer health benefits to black grains. Among these six grains, black buckwheat demonstrated the most favorable effects.