Engineering tannin functionality in food systems: a multiscale framework for balancing nutritional trade-offs and digestive modulation

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Tannins are traditionally regarded as antinutritional compounds due to their ability to reduce protein digestibility, inhibit digestive enzymes, and limit mineral bioavailability. However, this reductionist perspective fails to capture their emerging role as functional modulators in food systems. We propose a multiscale framework that integrates molecular interactions, food microstructure, processing-induced transformations, and digestive behavior to explain the complex functionality of tannins. This review synthesizes evidence indicating that tannin effects are inherently non-linear and context-dependent, governed by their molecular structure, concentration, and spatial distribution within food matrices. Importantly, this review introduces the concept of an optimal functional window, in which moderate tannin levels enable controlled modulation of digestion kinetics, improved glycemic response, and enhanced functional properties, without severely compromising nutritional quality. Within this framework, the apparent trade-off between antinutritional effects and health benefits is reinterpreted as a continuum arising from shared interaction mechanisms. By linking mechanistic insights to practical applications, this review proposes a shift in perspective from tannin reduction toward tannin engineering, where their multifunctional behavior can be strategically harnessed to design foods with targeted nutritional and potential physiological outcomes. This perspective provides a foundation for the rational development of next-generation food systems with controlled digestibility and optimized metabolic responses.