In this study, six drying methods—vacuum freeze drying (VFD), hot air drying (HAD), heat pump drying (HPD), microwave vacuum drying (MVD), combined infrared-heat pump drying (IR-HPD), and combined microwave vacuum-hot air drying (MVD-HAD)—were comparatively investigated for their effects on the drying characteristics, nutritional content, antioxidant capacity, color, texture, and flavor of bird’s eye chili. The aim was to identify effective drying strategies for improving both the efficiency and quality of chili peppers. The results indicated that MVD and MVD-HAD achieved the highest drying efficiency, with drying times of only 26 and 170 min, respectively; their maximum drying rates were about 35 and 40 times that of HAD, respectively. VFD performed best in preserving heat-sensitive components such as vitamin C, polyphenols, and carotenoids, with retention rates all exceeding 84%. MVD and MVD-HAD significantly outperformed HAD and HPD in retaining vitamin C, capsaicin, polyphenols, and antioxidant capacity. VFD-dried peppers exhibited the highest lightness. Furthermore, MVD-HAD and MVD showed no significant difference in redness retention compared with the fresh samples. The hardness of chili peppers decreased significantly after drying, irrespective of the drying method used, while MVD-HAD best preserved their elasticity. A total of 54 chromatographic signal peaks were detected using gas chromatography-ion mobility spectrometry (GC-IMS), with aldehydes representing the largest proportion of the total, ranging from 30.89% to 41.05%. Drying reduced the contents of aldehydes and alcohols but increased those of ketones, esters, and heterocyclic compounds. This weakened the grassy aroma and enhanced the nutty, buttery, and caramel notes, imparting a characteristic roasted spicy flavor to the product. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) revealed significant differences in flavor composition of chili pepper subjected to different drying methods. Additionally, 19 key differential flavor compounds were identified. Taken together, MVD-HAD is an optimal drying strategy that balances both the efficiency and quality of chili peppers. The findings of this study provide a scientific basis for the optimization of chili drying processes.

The difference in the volatile composition of Toona sinensis from eight production areas was evaluated by gas chromatography-ion mobility spectrometry (GC-IMS). A total of 56 compounds were identified, the major ones being alcohols and aldehydes. Using principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA), T. sinensis samples from the eight production areas were well distinguished. A total of 12 volatile compounds with a variable importance in projection (VIP) score greater than one were selected as marker compounds, among which, (E)-2-hexenal-D, ethyl acetate-D, p-ethylphenol, furfural and benzeneethanol were found to be the major differential metabolites. The volatile composition of T. sinensis from different production areas was significantly different. GC-IMS could allow for the rapid identification of the differential volatile organic compounds in T. sinensis from different production regions, which provides a useful basis for the study of the difference in the volatile aroma composition of T. sinensis from different production areas.

The effects of different freezing temperatures (−20, −40 and −80 ℃) and freeze-thaw cycles (FTC; 1, 2 and 3) on the nutritional components, flavor compounds and enzyme activities of Toona sinensis shoots were examined, aiming to identify methods for improving its quality and flavor. The results showed that after different FTCs, the T₂ relaxation time was shortened, the area of peak M₂₁ decreased, and the bound water was transformed into weakly bound water and free water. The contents of soluble protein and vitamin C both significantly decreased (P < 0.05), while the content of reducing sugars significantly increased, reaching the highest value after two FTCs with a freezing temperature of −40 ℃. The activities of polyphenol oxidase (PPO), peroxidase (POD) and lipoxygenase (LOX) all significantly increased. The activity of γ-glutamyl-transpeptidase (GGT) initially increased and then decreased with increasing number of FTCs at different freezing temperatures. The activity of alcohol dehydrogenase (ADH) was the highest after two FTCs at −80 ℃, the content of umami amino acids increased by 42.5%, and the total amino acid content increased by 38.4%. In addition, the sensory scores for overall odor intensity, cooked onion/T. sinensis-like flavor, and cooked meat-like aroma were all higher than those of the untreated control group. A total of 54 volatile compounds were identified using gas chromatography-ion mobility spectrometry (GC-IMS), with aldehydes being the most abundant, followed by terpenes. Following FTC treatment, several new compounds emerged, accompanied by a 22.2% increase in the total content of volatile compounds. By partial least squares-discriminant analysis (PLS-DA), 11 volatile compounds were selected as potential biomarkers using the cutoff of variable importance in the projection (VIP) score > 1. Correlation analysis between enzyme activities and volatile compounds revealed that GGT, LOX, and ADH exhibited a strongly negative correlation with alcohols and esters, while a positive correlation was observed with aldehydes, acids, terpenes, ketones, and other compounds. Collectively, two FTCs at −40 ℃ can effectively preserve the nutritional quality and enhance the flavor profile of T. sinensis shoots.