Effects of different processing methods on the nutritional components and in vitro digestion and fermentation...

Foxtail millet (Setaria italica) is highly nutritious but has limited consumer acceptance due to its taste and low nutrient bioavailability. Adopting different processing methods may increase the nutritional components and bioavailability of whole grains. However, no study has systematically compared the different processing methods. Therefore, we systematically compared seven processing methods (raw grain, ultrafine pulverization, steaming, ultrasound, extrusion puffing, early sprouting (24 h), and sprouting (84 h) to evaluate their effects on foxtail millet nutritional quality and gut microbiota fermentation. In vitro simulated digestion and human fecal fermentation models were used to assess the release of nutrients, digestibility, and microbial metabolic response. The best effects were achieved using sprouting (84 h), which significantly increased the polyphenol content, γ-aminobutyric acid (GABA), and phenylalanine ammonia-lyase (PAL) activity. The digestion products had high concentrations of short-chain fatty acids (particularly propionate and butyrate) during fecal fermentation, indicating enhanced prebiotic potential. PAL activity transiently increased with extrusion puffing; however, effective GABA accumulation did not occur. Notably, the abundance of Proteobacteria increased with sprouting (84 h), suggesting a potential risk of opportunistic bacterial proliferation. Collectively, sprouting (84 h) is the optimal processing method for improving both the nutritional quality and prebiotic potential of foxtail millet, achieving primary nutrient enhancement and secondary metabolic regulation.