Abstract: Toona sinensis buds harvested in April through June of 2018 were separately used to prepare unfermented and fermented teas. The differences in the main bioactive ingredients, antioxidant activity, hypoglycemic activity and volatile components of the six tea samples were analyzed to reveal the quality change of fermented Toona sinensis tea with harvest time and to determine the optimal harvest time. Results demonstrated that significant variations were found among the six samples in the main bioactive ingredients, antioxidant activity and hypoglycemic activity and each had distinctive volatile components. The contents of total flavonoids, polysaccharides, tea polyphenols and tea pigments in both unfermented and fermented samples increased with later harvest date, the contents of saponin, free amino acid and caffeine showed fluctuating trends, and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and α-glucosidase inhibitory activity decreased gradually. For each harvest date, the contents of total flavonoids, polysaccharides, saponins, tea polyphenols and free amino acids in fermented tea samples were lower than those in the unfermented counterparts, while the contents of caffeine and tea pigment were higher. The DPPH radical scavenging activity decreased, whereas the α-glucosidase inhibitory activity increased after fermentation. Correlation analysis showed that total flavonoids were the main DPPH radical scavenger and α-glucosidase inhibitor in the six samples. A total of 7 classes of 90 volatile components were identified in these samples, among which, the number and amount of terpenes were the highest. A total of 42 and 49, 47 and 52, 50 and 51 volatile compounds were detected in unfermented and fermented T. sinensis teas in April, May and June, respectively. Principal component analysis (PCA) performed on the seven classes of volatile components generated 3 principal components, accounting for 88.01% of the total variance, which could reflect most of the information about these samples. Aldehydes, terpenes, alcohols, and terpene oxides were the main factors distinguishing the six samples. The fermented and unfermented T. sinensis teas in April and May gained higher scores. Comprehensive analysis showed that the quality of fermented T. sinensis tea made from T. sinensis buds in May was better.

Key words: fermented Toona sinensis tea; bioactive ingredients; antioxidant activity; hypoglycemic activity; volatile components