Headspace gas chromatography–ion mobility spectrometry and partial-least-squares discriminant analysis (PLS-DA) were adopted to analyze the rule of change in flavor substances for different varieties of green plums at different levels of maturity (S1—immature, S2—commercially mature, and S3—fully mature). The results showed that 68 kinds of volatile flavor substances were identified in all green plum samples. The types and contents of such volatile substances experienced a V-shaped trend with an increasing degree of green plum maturity. During the S1 and S2 stages, aldehydes, ketones, and a small amount of alcohols were the main volatile flavor substances in the green plum samples. During the S3 stage, esters and alcohols were the most important volatile flavor components in the green plum pulp samples, followed by terpenes and ketones. YS had the most types and highest contents of volatile flavor substances in three stages, followed by GC and DZ. By using the PLS-DA method, this study revealed the differences in flavor of the different varieties of green plums at different maturity stages, and it identified eight common characteristic volatile flavor substances, such as ethyl acetate, 3-methylbutan-1-ol, and 2-propanone, produced by the different green plum samples during the ripening process, as well as the characteristic flavor substances of green plums at each maturity stage (S1–S3).

In this study, the physicochemical properties, antioxidant capacity, and volatile compounds of the juices of different guava cultivars before and after pectinase treatment were evaluated. The results showed that the guava juice of the small fragrant (SF) cultivar exhibited the highest ascorbic acid concentration (1761.09 mg/L), and the highest contents of total phenolics (329.52 mg GAE/L) and total flavonoids (411.13 mg RE/L) were both found in the juice of the watermelon red (WR) cultivar. After pectinase treatment, the juice yield and the titratable acid, sugar components, total phenolics and total flavonoids, and antioxidant capacity levels of the guava juices were all higher than those of the non-pectinase group. However, lower sensory evaluation scores were obtained in the pectinase-treated guava juices. Aldehydes and terpenoids were the main flavor components in the guava juices, which were responsible for the aroma of the juice, while their relative contents were different in the four cultivar guava juices. Furthermore, pectinase treatment could change the amounts and relative contents of volatile compounds in the guava juice. During the pectinase treatment process, the relative contents of the main aroma constituents in the guava juices were significantly decreased. The findings of this research provide valuable information for the processing of guava juice.

The aim of this study was to evaluate the effect of high hydrostatic pressure (HHP) and co-fermentation by Lactobacillus rhamnosus and Gluconacetobacter xylinus on the quality of yacon-litchi-longan (YLL) juice. The carbohydrates, organic acids, free amino acids (FAAs), and volatile compounds in YLL juice were analyzed. Thermal processing (TP) increased the content of total carbohydrates, organic acids and FAAs, and destroyed the aroma components, whereas HHP treatment had a negligible effect. Carbohydrate content was lower, and content of lactic acid, acetic acid, and exopolysaccharide (EPS) were higher in co-fermented juice than in unfermented juice. Furthermore, the content of bitter FAAs in fermented TP and HHP-treated YLL juices decreased by 88.7% and 86.9%, respectively. Co-fermentation also increased ketones and the sum of individual volatile constituents, and improved the overall flavor of juice. Taken together, HHP treatment prior to co-fermentation can be used to improve the quality of YLL juice, especially the flavor thereof.