Dynamic changes in volatile and non-volatile flavor compounds in lemon flavedo during freeze-drying and hot-air drying

This study investigated the effects of three drying methods, i.e., integrated freeze-drying, conventional freezedrying, and hot-air drying, on the dynamic changes in volatile and non-volatile flavor compounds in lemon flavedo. Compared with the fresh samples, the three drying methods resulted in significant loss in the types of volatile flavor compounds of the final dried samples (P < 0.05). Conventional freeze-drying resulted in the highest decrease in volatile compounds, followed by integrated freeze-drying and hot-air drying, however, integrated freeze-drying preserved more volatile flavor types than conventional freeze-drying and hot-air drying. The amount and types of amino acids of the final dried samples were found to be highest in integrated freezedrying followed by conventional freeze-drying and hot-air drying. The results of correlation analysis indicated positive and negative correlations between various amino acids, soluble sugars, and volatile flavor compounds. These variations in type and content of flavor compounds in lemon flavedo during drying processes may be attributed to physical diffusion of these compounds and biochemical reactions including enzymatic reactions, thermal degradation, Maillard reactions, heating oxidation etc.