Effects of Different Drying Methods on Nutritional Compositions, Bioactive Substances, and Volatile Compounds of Radish (Raphanus sativus L.) Leaves

Radish leaves are a nutrient-rich yet underutilized byproduct containing abundant fiber, minerals, and phytochemicals; however, their quality is highly affected by drying methods. This study systematically investigated the effects of three drying methods—hot-air drying (HD), microwave drying (MD), and freeze-vacuum drying (FD)—on the nutritional components, bioactive substances, and volatile compounds of radish leaves. A comparative analysis was conducted on their proximate composition, amino acid profiles, mineral contents, antioxidant capacities, glucosinolate profiles, and volatile profiles. Among the three methods, FD exhibited superior preservation of proteins, lipids, minerals (K, Mg, P, Fe, Zn, and Mn), and bioactive components, including polyphenols, flavonoids, glucosinolates, and vitamin C. In contrast, HD and MD led to significant reductions in these nutrients and bioactive compounds. A total of 33 glucosinolates and 779 volatile compounds, including 164 odor-active compounds, were identified collectively across the three treatments. The FD-treated samples exhibited distinct glucosinolate and volatile profiles, whereas HD- and MD-treated samples showed greater similarity. Multivariate analysis further revealed 12 key differential glucosinolates and 27 differential odor-active compounds among the three groups. This study provides a scientific basis for optimizing drying strategies to improve the nutritional quality and flavor characteristics of processed radish leaves.