Structural Organization, Processing Transformations, and Bioaccessibility of Cereal Phytochemicals: From Grain Matrix to Gut Microbiota and Artificial Intelligence Applications

Cereal grains are rich in bioactive phytochemicals, including phenolic acids, flavonoids, and carotenoids, which are known for their antioxidant and anti-inflammatory properties. However, their bioaccessibility and bioactivity depend on their chemical form and association with the cereal matrix. Many phytochemicals are bound to cell wall structures, limiting their release during digestion; consequently, their bioavailability relies on processing and microbial biotransformation, particularly in the colon. This review examines the various phytochemical forms (free, conjugated, and insoluble-bound) and their distribution across grain tissues. It highlights the role of advanced processing techniques, such as ultrasound-assisted processing, high-pressure processing, and fermentation, in enhancing phytochemical release and bioaccessibility by disrupting the cereal matrix, improving solubility, and promoting microbial conversion. The role of gastrointestinal (GI) digestion and microbial metabolism in transforming bound compounds into bioactive metabolites is also discussed. Understanding the interactions among grain structure, processing, and microbial activity is essential for the optimizing health benefits of cereal-based foods. Furthermore, the integration of artificial intelligence (AI) with metabolomics and spectroscopy enables accurate prediction, classification, and enhancement of cereal phytochemicals. Future research should focus on refining processing strategies to maximize bioaccessibility while preserving nutritional quality.