Effect of Relative Humidity on Quality and Metabolite Profiles of Perilla frutescens Seed Powder During Storage

This study investigated the effects of relative humidity (RH) and storage period on the quality and metabolite profiles of perilla seed powder (PSP). PSP was stored for 12 weeks at RH levels ranging from 11% to 93%, and quality changes were monitored by assessing microbial growth, lipid oxidation, color, and metabolite profiles. Visual deterioration occurred rapidly above RH 69% due to microbial proliferation, becoming apparent after four weeks at RH 69% and after one week above RH 81%. In contrast, lipid oxidation, measured by acid and peroxide values, was significantly delayed at RH levels below 43%, whereas at 53% RH, the acid value increased 14.8-fold after 12 weeks compared to the initial level. Multivariate statistical analysis showed distinct metabolite patterns dependent on RH and storage period. Unsaturated fatty acids, such as linoleic and linolenic acids, decreased, whereas lysophosphatidylethanolamines (LPEs) and their oxidized derivatives, including hydroxylinolenic acid, increased by up to 167-fold at RH 53% after 12 weeks. Rosmarinic acid declined, whereas glycosylated phenolics, including rosmarinyl glucoside, increased. Multi-output regression models based on metabolite and quality traits effectively predicted RH and storage duration (R² > 0.87, RMSE < 5.37), demonstrating their potential utility in monitoring storage conditions. These findings suggest that PSP should be stored under RH below 43% for no longer than four weeks to minimize quality degradation. This study provides new insights into RH-dependent metabolic responses in seed-based powders and offers a scientific basis for RH-controlled storage strategies to maintain product stability.