Elucidation of the impact of four different drying methods on the phenolics, volatiles, and color properties of the peels of four types of citrus fruits

BACKGROUND: Citrus fruit peels are considered to be process waste in the fruit juice industry but they are a valuable raw material due to their volatile and bioactive components. Drying is one of the most common methods to preserve this material. In this study, four drying processes were applied to the peels of four kinds of citrus fruits. The drying processes were convective drying (CD), microwave drying (MD), conductive hydro drying (CHD), and freeze drying (FD). The citrus fruits used were orange, bitter orange, grapefruit, and lemon. RESULTS: The influence of dehydration on the aroma and phenolic composition, microstructure, and color properties were studied in detail. It was determined that drying increased the amount of both phenolics and volatiles in the dried samples. The MD and FD methods better preserved the color and phenolics of the samples, and the MD and CD processes increased the amount of aroma substances. CONCLUSION: The MD method would be more suitable for drying citrus peels due to its shorter duration and its positive effects on the phenolic and aroma components.