Study on the Effects of Different Drying Methods on Nutritional Quality of Dictyophora rubrovalvata Soup Based on Metabolomics

This study investigated the effects of different drying methods on the quality and metabolic characteristics of Dictyophora rubrovalvata soup. Soups were prepared using D. rubrovalvata treated by means of vacuum freeze-drying (FDS), hot-air drying (HADS), far-infrared drying (FIDS), and combined hot-air and far-infrared drying (HAFIDS). The soups, referred to as FDS, HADS, FIDS, and HAFIDS, respectively, were evaluated using an electronic tongue, UV spectroscopy, fluorescence spectroscopy, and in vitro antioxidant and hypoglycaemic activity assays. By combining these evaluations with non-targeted metabolomics techniques, this study analysed the physicochemical properties, biological activities, and patterns of change in non-volatile metabolites. The spectral results indicated that the Maillard reaction occurred in all groups of D. rubrovalvata soup during the cooking process, with the reaction being more pronounced in the heat-dried group. Among the four soup samples, HAFIDS exhibited superior DPPH radical scavenging, FRAP, and α-amylase and α-glucosidase inhibitory activities, along with the highest abundance of umami-related metabolites, revealing that combined hot-air and far-infrared drying achieves a favourable balance between flavour and bioactivity. Metabolomics identified a total of 716 metabolites, with 238 differentially expressed metabolites screened, primarily enriched in pathways such as amino acid metabolism, the tricarboxylic acid cycle, glucose metabolism, and nucleotide metabolism. Twelve key taste-related amino acids were identified, with significant differences observed between the different drying groups in terms of umami, sweet, and bitter amino acids, as well as organic acids and sugar alcohols. This study systematically investigated the metabolic changes underlying the gustatory quality and bioactivity of D. rubrovalvata soup through a metabolomics analysis of drying methods. It demonstrated that combined hot-air and far-infrared drying is more suitable for the high-value processing of D. rubrovalvata soup, providing a theoretical basis and data support for the flavour optimisation and processing of edible fungus soups.