| Popis: |
In order to investigate the changes in the characteristic aroma components of sun-dried green tea during processing, the volatile substances in fresh, fixated, rolled and sun-dried leaves of Yunnan large leaf tea were determined using solvent flavor-assisted evaporation extraction (SAFE) combined with gas chromatography-mass spectrometry (GC-MS), and the aroma active components of sun-dried green tea were identified by odor activity value (OAV). The results showed that totally 67 volatile compounds were detected, the major ones being alcohols, esters and aldehydes, and the total amount of volatile substances increased from fresh leaves to the end of fixation. The total amount of volatile substances slightly decreased in sun-dried leaves compared to fresh leaves, but the number of volatile substances increased. A total of 23 aroma active compounds with OAV > 1 were found in sun-dried green tea, with the major ones being those contributing to floral and green aromas such as linalool, geraniol and nonanal. Aldehydes were the most prominent component in each processing stage. Using gas chromatography-flame ionization detector (GC-FID) and high performance liquid chromatography-photo-diode array (HPLC-PDA), a total of 7 fatty acids were detected, with saturated fatty acids being the major components; 13 carotenoids were detected, including lutein, whose content was the highest in all processing stages. During the processing of sun-dried green tea, the total amounts of fatty acids and carotenoids decreased continuously, especially linoleic acid and linolenic acid, and the content of hexanal as their major degradation product showed the opposite trend. The contents of terpene ketones, ionone and its oxidized derivatives such as β-ionone and 5,6-epoxy-β-ionone significantly increased as a result of the degradation and transformation of carotenoids. The trends of fatty acids and carotenoid precursors during the processing of sun-dried green tea were correlated with their associated aroma products. In conclusion, the results of this study may provide theoretical guidance for the targeted aroma improvement of sun-dried green tea. |
