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.

Roasted lamb chops were prepared by superheated steam roasting (SSR) and direct roasting (DR). To explore the formation mechanism of flavor substances, descriptive sensory analysis (DSA), an electronic nose (E-nose) system, head-space solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS), and gas chromatography-olfactometry (GC-O) were employed to analyze the sensory properties, fatty acid composition and volatile compounds of the SSR and DR samples. The DSA and E-nose results consistently revealed variations in aroma profiles between the two samples. The DR sample showed stronger roasted, fatty, and mutton-like aroma (P < 0.05). A total of 44 volatile compounds were identified from both samples. The contents of aldehydes, alcohols, and nitrogen-containing compounds in the DR sample were higher than those in the SSR sample. Totally 35 aroma-active compounds were identified by aroma extract dilution analysis (AEDA) combined with GC-O analysis, among which, decanal, hexanal, octanal, nonanal, (E,Z)-2,6-nonadienal, (E,E)-2,4-decadienal, (E,E)-2,4-nonadienal, 1-octen-3-one, 3-octen-2-one, 2-nonanone, heptanoic acid, 2-methylpyrazine, 3-(methylthio)propanal, benzothiazole, and 2-pentylfuran were the major ones. The types of aroma-active compounds in the two samples were similar, but their flavor dilution (FD) factors were different. Compared with the SSR sample, the content of total fatty acids in the DR sample significantly increased (P < 0.05). The content ratio of polyunsaturated fatty acids to saturated fatty acids (PUFA/SFA) in the DR sample was 40.66%, indicating higher nutritional value. Pearson’s correlation analysis showed that the oxidative degradation of unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, and eicosenoic acid was closely related to the formation of the characteristic flavor in roasted lamb chops.

To investigate the effects of thyme (Thymus vulgaris L.) addition on the flavor modification of mutton broth during boiling, three mutton-broth samples with various thyme contents 0.06% (S1), 0.30% (S2), and 1.50% (S3) were analyzed and compared, without thyme as control (0.00%, S0). The meaty, fatty, pastoral flavor and spicy were chosen as sensory attributes to evaluate the flavor of the mutton-broth samples. Sensory results were significantly different (P < 0.001), with S2 having the optimum overall acceptability. A total of 99 volatile compounds were identified by gas chromatography-mass spectrometry, among which 19 compounds were considered as the odor-active compounds according to their odor activity values. Significant changes (P < 0.05) appeared in most volatiles in S0 with thyme addition, especially aldehydes. Free fatty acids (FFAs) were also identified, and all of them significantly increased with increased thyme (P < 0.05). Correlation analysis of odor-active compounds, FFAs, and sensory attributes through partial least squares regression (PLSR) indicated the important volatiles and FFAs remarkably contributed to the mutton broth samples, and further confirmed that the 0.30% of thyme may be a desirable addition amount for the sensory characteristics of mutton broth.