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.

In order to study the dynamic changes of major active substances and volatile components in Toona sinensis at different growth stages, the contents of total flavonoids, total polysaccharides, total saponins and total alkaloids in the leaves of T. sinensis collected from April to October, 2019 were determined by conventional methods, and the volatile compounds by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-ion mobility spectrometry (GC-IMS). Additionally, the volatile components in the leaves of T. sinensis in different growth periods were distinguished by cluster analysis (CA) and principal component analysis (PCA). The results showed that the major active substances in the leaves of T. sinensis exhibited an obvious accumulation tendency during the growth process; the contents of total flavonoids, total polysaccharides and total alkaloids reached the highest levels in October, while the content of total saponins reached the highest level in September. The volatile components changed significantly during the growth period, and 109 and 49 volatile components were identified by GC-MS and GC-IMS, respectively, mainly including terpenes, aldehydes, sulfur-containing compounds and alcohols. Most of the volatile components detected by GC-MS were larger molecules (C₆–C₂₀) at high levels, while most of the volatile components detected by GC-IMS were smaller molecules (C₄–C₁₀) at low levels. The combination of the two techniques can expand the scope of detection of volatile components in T. sinensis leaves. The results of this study can provide a scientific basis for the planting, quality evaluation, and comprehensive development and utilization of T. sinensis.

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.

To extend its shelf life, vacuum freeze-dried Toona sinensis (VFDTS) powder was packaged in sealed polyethylene (PE) bags, sealed aluminum foil bags, composite vacuum bags, or aluminum foil vacuum bags. Changes in the sensory quality, moisture content, color, flavor components and total bacterial count of VFDTS powder were monitored during storage under accelerated conditions at (55 ± 1) ℃ and (40 ± 3)% relative humidity (RH). The results showed that VFDTS powder packaged in sealed PE bags exhibited severe moisture absorption and browning with prolonged storage time, and the total bacterial count significantly increased. On the other hand, the moisture content, color and total bacterial count of the powder stored in aluminum foil vacuum bags remained substantially unchanged. A total of 56 volatile compounds were identified in VFDTS powder stored in the different packaging systems, including 13 alcohols, 11 aldehydes, 3 acids, 3 terpenes, 7 ketones, 9 esters, one ether, 2 sulfur compounds, 3 alkanes, and 4 heterocycles. Principal component analysis (PCA) of the volatile compounds showed clear separation among VFDTS powder samples stored in the 4 packaging systems. Based on variable importance in projection (VIP > 1) from orthogonal partial least squares discriminant analysis (OPLS-DA), a total of 14 differential volatile compounds were selected, and their clustering heatmaps could be used to effectively classify the samples in different packaging systems. The samples in aluminum foil vacuum bags had the best quality, followed by sealed aluminum foil bags and composite vacuum bags, while the greatest changes in moisture, color, flavor and microbiological quality were observed in VFDTS powder in sealed PE bags during storage.