Tannin in foods: Classification, Dietary Sources, and Processing Strategies to Minimize Anti-Nutrient Effects

Abstract Anti-nutrients are naturally occurring compounds that negatively affect nutrient intake, absorption, and utilisation, ultimately impairing human and animal growth and development. These include various phytochemicals such as tannins, cyanogenic glycosides, glucosinolates, alkaloids, phytic acid, saponins, and certain oligosaccharides. Among them, tannins are widely distributed in plant-derived foods and play a significant role in food flavour and health effects. However, tannins also hinder the absorption of essential minerals, vitamins, and proteins, reducing the overall nutritional value of foods. To mitigate these effects, various food processing techniques have been employed to lower tannin content. These methods include conventional approaches (e.g., boiling, roasting, and drying), modern technologies (e.g., microwave-assisted processing, irradiation, and pulsed electric fields), biological treatments (e.g., fermentation, enzyme-assisted degradation, and germination), and combined strategies (e.g., boiling-fermentation and soaking-microwave). Each technique has its advantages and limitations, with some requiring specialized equipment and others being more practical for household use. Potentially, combining different processing methods has shown promise in effectively reducing tannin levels while preserving the nutritional integrity of foods. This study provides a comprehensive overview of tannins in the context of their phytochemical dietary sources, types, and physiological effects. Additionally, a comparison of the various processing techniques to reduce tannin content is presented, aiming to optimize food quality and nutritional benefits. By comparing these approaches, insights into optimizing tannin reduction while preserving food quality can be applied, which is an area of great interest to researchers and food technologists. Graphical Abstract