Changes in antioxidant phytochemicals and volatile composition of Camellia sinensis by oxidation during tea fermentation

• Published in: Food chemistry 2011-12, Vol.129 (4), p.1331-1342
• Main Authors: Kim, Youngmok, Goodner, Kevin L., Park, Jong-Dae, Choi, Jeong, Talcott, Stephen T.
• Format: Article
• Language: English
• Subjects: Absorbance; Antioxidant capacity; Biological and medical sciences; Black tea; Caffeine; Camellia sinensis; Catechins; Coffee, tea and other stimulative beverage industries; Flavonoids; Food industries; Fundamental and applied biological sciences. Psychology; Green tea; Oolong tea; Polyphenolics; Tea fermentation; Tea volatile compounds; Total soluble phenolics
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2011.05.012

► Catechins decreased during tea fermentation and it resulted in increase of tannins. ► Caffeine was higher in green tea due to the loss during tea fermentation. ► Total soluble phenolics and antioxidant capacity decreased during fermentation. ► Tea fermentation significantly changed the profile of volatile aroma compounds. Monomeric flavonoids (flavan 3-ols or tea catechins) present in Camellia sinensis leaf are transformed to polymeric theaflavin and thearubigin by oxidation occurring during tea fermentation. The distinctive colour, decreased bitterness and astringency, and characteristic flavour are derived from the fermentation process giving fermented teas a marked distinction from non-fermented green tea. Even though teas are available in many different fermentation levels from green to black, the difference in phytochemicals and volatile compounds in teas with different degrees of fermentation has not been fully investigated yet within the same tea leaf. The objective of this study was to observe non-volatile phytochemicals including polyphenolic and volatile compounds changes by oxidation under strict processing control and to evaluate the degree of fermentation for the maximum antioxidant capacity with the same tea material. Harvested tea leaf was immediately processed to different degrees of oxidative fermentation (0%, 20%, 40%, 60%, and 80%). Tea infusions brewed with each processed tea leaf were analysed for polyphenolic profile, total soluble phenolics, antioxidant capacity, and volatile profile using LC–MS, HPLC, Folin–Ciocalteu assay, Oxygen Radical Absorbance Capacity (ORAC), and GC–MS analyses. The flavonoids in non-fermented green tea were significantly lessened during the oxidative fermentation process and the decreased monomeric flavonoids were transformed to polymeric theaflavin and thearubigin as the leaves were more processed. Total soluble phenolics and antioxidant capacity were significantly higher as tea leaves were less processed with a high correlation with individual polyphenolic changes. Volatile compounds present in tea leaf were analysed by GC–MS to observe changes due to processing and were utilised to create a model to differentiate fermentation based on volatile composition. Twenty-four compounds were used to build an initial model which was optimised to 16 compounds with complete separation of the groups using discriminant function analysis. The data suggested that fermentation diminished antioxidant capacity of tea and