Real-time aroma monitoring of mint (Mentha spicata L.) leaves during the drying process using electronic nose system

Volatile compounds are important factors that affect the flavor quality of dried medicinal and aromatic plant products such as mint (Mentha spicata L.) leaves. This work aimed at capability evaluation of electronic nose as a complementary system for monitoring the dynamic changes of Volatile Organic Compounds (VOCs) of mint leaves during hot air drying process. The monitoring system includes a gas sensor array based on Metal Oxide Semiconductor (MOS) sensors, temperature and humidity sensors, a microcontroller device and laptop computer coupled with computational techniques. During the drying process aroma parameters, humidity, and temperature of the outlet air as well as sample weight were acquired at a given dryer setting. Results of Principal Component Analysis (PCA) showed that the fingerprints of VOCs for mint leaves are significantly altered during drying. Partial Least Squares (PLS), Multiple Linear Regression (MLR), and Principal Component Regression (PCR) were utilized to correlate the aroma parameters to mint leaf moisture content and to determine the termination time for the drying process. Performance of the models were approximately the same and showed high correlation coefficients of cross validation (RP2=0.94 and RMSEP = 5.79). The overall results demonstrated the effectiveness and feasibility of monitoring mint leaf drying conditions using electronic nose system to improve the final quality of the dried material, to decrease time of drying, and energy costs as well.