A commercial electronic nose system (product of FOX 3000, Alpha MOS, Toulouse, France) equipped with 12 metal oxide gas sensors (MOS sensors) based on different sensing materials available in our laboratory was used. Gas sensors were located in two temperature-controlled chambers under a high temperature and zero humidity, and a purified air generator was used to provide carrier gas for cleaning sensors. The sensors array was comprised of 12 metal oxide semiconductor (MOS) sensors, while the main applications of those sensors are depicted in Table 1 . Based on sensor coating materials, the LY sensors (LY2/G, LY2/AA, LY2/Gh, LY2/gCT1, LY2/gCT and LY2/LG) were p-type semiconductors, while the P and T sensors (T30/1, P10/1, P10/2, P40/1, T70/2 and PA2) were n-type semiconductors. Sensor response was recorded by Alpha Soft v.12 accompanying software (Alpha MOS, Toulouse, France). The sampling conditions (quantity, volume, temperature and headspace generating time) were optimized prior to data acquisition in order to improve the performance of the sensor.
Before data acquisition and downstream analysis, samples were cut into small pieces, while 1 g of each sample was placed in a 20 mL vial. Then, the samples were placed into a thermoblock at 50 °C for 20 min for headspace generation and 0.5 mL from the headspace was drawn off and injected into the electronic nose. Each sample was transferred to the detector at a constant rate over 120 s. Following that, a cleaning procedure of the detector chamber was carried out until the sensor signals returned to baseline. As sample gases flowed over the sensors, the sensors’ resistance (R) changed. Therefore, a ratio (R−R0)/R0 was used to estimate the changes in sensor resistance, where R0 is the sensor’s resistance baseline and R is the real-time resistance. Twelve maximum response values of each sample from each sensor (Table 1 ) were extracted and further analyzed. In total, 291 samples were analyzed with the e-nose sensor (177 from MI and 114 from SAMS, respectively)
Before data acquisition and downstream analysis, samples were cut into small pieces, while 1 g of each sample was placed in a 20 mL vial. Then, the samples were placed into a thermoblock at 50 °C for 20 min for headspace generation and 0.5 mL from the headspace was drawn off and injected into the electronic nose. Each sample was transferred to the detector at a constant rate over 120 s. Following that, a cleaning procedure of the detector chamber was carried out until the sensor signals returned to baseline. As sample gases flowed over the sensors, the sensors’ resistance (R) changed. Therefore, a ratio (R−R0)/R0 was used to estimate the changes in sensor resistance, where R0 is the sensor’s resistance baseline and R is the real-time resistance. Twelve maximum response values of each sample from each sensor (
