Comprehensive analysis of changes in the drying characteristics, quality, and metabolome of peanuts by different drying methods

To investigate suitable mechanical drying methods for peanuts, this study employed natural drying (ND), hot-air drying (HAD), heat pump drying (HPD), infrared drying (ID), radio frequency drying (RFD) and microwave drying (MD) and evaluated their effects on drying characteristics, hardness, microstructure, nutritional qualities (proteins, fats and amino acids), oil qualities (acid value, peroxide value and fatty acids) and metabolome level. The results indicated that MD had the highest drying efficiency but caused more damage to the microstructure, resulting in lower hardness and higher chewiness; HPD was superior in terms of colour and oil quality retention; and ID offered certain benefits in nutrient quality preservation. The two-term model was identified as the most suitable for predicting moisture changes during peanut drying. Non-targeted metabolomics analysis revealed that the different drying methods markedly altered the metabolite composition and pathways of peanuts. It also identified 1720 metabolites and 8 key metabolic pathways, among which the tricarboxylic acid cycle and glycine, serine and threonine metabolism were the principal metabolic pathways governing peanut drying. These findings establish a theoretical foundation for the enhancement of peanut-drying technologies and post-harvest processing and usage.