Effects of Frying Time on Volatile Flavor Compounds in Fried Pepper (Zanthoxylum bungeanum) Oil as Analyzed by Gas Chromatography-Ion Mobility Spectrometry and Multivariate Statistical Analysis

In order to investigate the effect of frying time on the aroma of fried Hancheng pepper oil (HPO), four HPOs (HPOs 1, 2, 3 and 4) were prepared by frying Dahongpao pepper at 130 ℃ for 5, 15, 25 and 35 minutes with rapeseed oil as the carrier oil, respectively. Descriptive sensory analysis (DSA), an electronic nose (E-nose) system and gas chromatography-ion mobility spectrometry (GC-IMS) were employed to compare and analyze the volatile flavor compounds of the HPOs, and multivariate statistical analysis was used to explore differential volatile compounds between these four HPOs. Both DSA and E-nose results indicated that significant differences were observed between the HPOs; among them, HPO2 showed very strong herbal, lemon-like and pine-like aromas, with moderate fatty and green attributes and a very weak burnt. A total of 46 volatile compounds, including 19 aldehydes, 15 terpenes, 8 alcohols, 3 esters and 1 ketone, were identified from the four HPOs by GC-IMS. The types of volatile compounds in the HPOs were similar, in spite of significant differences in peak intensities. The contents of aldehydes including hexanal, heptanal and (E)-2-heptanal showed an increasing trend with increasing frying time; the contents of α-terpinene, phellandrene, 4-terpineol, ethyl 3-methylbutyrate and acetal showed an increasing and then decreasing trend, while a reverse trend was observed for alcohols and esters; however, the contents of terpenoids did not change so much. Principal component analysis (PCA) showed that the four HPOs were classified into two groups; one group contained HPO1 and HPO2, and another group contained HPO3 and HPO4, which was consistent with the results of linear discriminant analysis (LDA) from the E-nose data. The results of partial least square discriminant analysis (PLS-DA) showed that limonene, α-phellandrene, acetal, α-pinene and ethyl 3-methylbutyrate were the characteristic aroma compounds of HPO2, and 20 compounds were identified as differential markers, mainly including linalool, β-pinene, α-pinene, limonene, α-phellandrene, hexanal, heptanal, (E)-2-hexanal, (E)-2-heptenal, furfural, 2-methylbutanal, methylpropanal, 2-propenal, 1-propanol and ethyl-3-methylbutanoate.