Changes and correlation analysis of volatile compounds, key enzymes, and fatty acids in lemon flavedo under different drying methods

Lemon flavedo is distinguished by their unique and abundant volatile flavor compounds that can undergo complex changes during drying. In this study, integrated freeze drying (IFD), conventional freeze drying (CFD), and hot-air drying (AD) were employed to dry lemon flavedo to investigate the changes and correlations of volatile compounds, fatty acids, and key enzymatic activities during the drying process. The results showed that IFD retained the most volatile compound types, followed by CFD and AD. Furthermore, after drying, IFD, CFD, and AD had lost 47.92 mg/g, 56.07 mg/g, and 13.22 mg/g of total volatile compounds, respectively, compared with fresh samples, and the content loss rates of total fatty acids were 77.38% in AD > 72.95% in CFD > 56.54% in IFD, respectively. During the three drying processes, IFD retained relatively higher enzyme activity in the samples. Lots of positive and negative correlations (P < 0.05) were observed among the key enzyme activities, fatty acids, and volatile compounds, showing close associations. The current work provides important information for selecting suitable drying techniques of lemon flavedo and shows lights on how to control its flavor during drying process.