Impact of drying technologies on bioactive composition of fruit pomace: a critical review and future perspectives

Fruit pomaces are major underutilized by-products of the juice and wine industries, rich in polyphenols, including flavonoids, anthocyanins, and tannins, as well as functional polysaccharides such as dietary fiber and pectin. Their valorization as food ingredients depends critically on drying, which stabilizes the material while strongly influencing bioactive retention. This review synthesizes recent findings on the effects of conventional (hot-air) and emerging (vacuum, microwave-assisted, infrared, refractance window, and hybrid) drying technologies applied to apple, grape, blueberry, cherry, pear, citrus, kiwi, peach, apricot, and other berry pomaces. Across matrices, oxygen exposure and residence time emerged as more decisive than temperature alone in governing bioactive stability. Optimized hot-air drying at 60-70 °C can preserve phenolics and antioxidant activity, whereas extended or high-temperature treatments accelerate oxidative degradation. Low-oxygen and rapid-transfer techniques, particularly vacuum-based and hybrid systems, consistently enhanced retention of phenolics, anthocyanins, and antioxidant activity while maintaining fiber and pectin integrity. Overall, the findings highlight the need for matrix-specific, energy-aware drying strategies to support scalable and sustainable pomace valorization.