Effects of different drying methods on drying kinetics, quality characteristics and untargeted metabolomics of tiger nut.

To investigate suitable mechanized drying technologies for tiger nut, this study compared natural drying (ND), hot-air drying (HAD), heat-pump drying (HPD), infrared drying (ID), and radio-frequency drying (RFD) in terms of drying kinetics, microstructure, texture, rehydration ratio, relative electrical conductivity, major nutritional quality, and untargeted metabolomics. The results showed that mechanical drying significantly improved drying efficiency, with HPD requiring the shortest drying time (12 h). The Modified Page model provided the better fit for describing moisture changes during tiger nut drying. HAD and HPD were more effective in maintaining tissue continuity and resulted in higher hardness and chewiness, whereas RFD caused the most severe structural disruption. ID showed greater advantages in retaining protein, starch, and ash, while HAD was more favorable for lipid retention. HPD exhibited better performance in total dietary fiber retention and overall nutritional balance. Untargeted metabolomics analysis annotated 3977 metabolites and identified five key metabolic pathways. These findings provide a reference for optimizing tiger nut drying technologies and promoting postharvest processing and utilization.