Effects of tea varieties and turning over intensity on fatty acid content in Oolong tea

【Objective】By analyzing the effect of different varieties and different turning over intensities on the content of fatty acids in tea leaves, relationships between varieties, turning over intensity and quality of Oolong tea product could be better understood.【Method】The content of fatty acids in leaves was determined by gas chromatography-flame lonization detector(GC-FID). Huangdan, Tieguanyin, Rougui, Fujianshuixian, Jinguanyin, Fuding Dabaicha were used as experimental materials to screen out the suitable varieties for the study of turning over, and the effects of different turning over intensities on fatty acids were investigated by using Jinguanyin with different turning over intensities(fresh leaves, the first turning over leaves, the fifth turning over leaves, and the ninth turning over leaves) as materials.【Result】The results showed that the content of unsaturated fatty acids was more than 74.00% in all varieties, and the content of different types of fatty acids was the highest in Fujianshuixian and was the lowest in Tieguanyin. C18:3n3, C18:2n6c, C16:1 were the top three components of 10 fatty acids detected in 6 varieties. 75.00% of the unsaturated fatty acids content in each variety was composed of C18:3n3 and C18:2n6c, and 80.00% of the saturated fatty acids content was C16:1. The unsaturated fatty acids/total fatty acids ratio and C18:3n3 content in Jinguanyin was the highest, while in Fujianshuixian, the unsaturated fatty acids/total fatty acids ratio was the lowest, and C18:2n6c content was the highest. The content of different types of fatty acids in Jinguanyin showed an upward trend first and then a downward trend during turning over process. The content of unsaturated fatty acids(25962.15 μg/g) and total fatty acids(33249.16 μg/g) both reached the highest points in slightly turning over leaves(the first truning over leaves) while the content of unsaturated fatty acids in heavily turning over leaves(the ninth turning over leaves) dropped to 20731.28 μg/g, which was significantly lower than that in fresh leaves (P<0.05). A total of 8 fatty acids components were detected in Jinguanyin, among which 3 were 3 saturated fatty acids and 5 unsaturated fatty acids. The content of C18:3n3 increased to 18113.55 μg/g when it was slightly turning over, while the content decreased to the lowest point at 13621.25 μg/g when it was heavily turning over.【Conclusion】Unsaturated fatty acids are the main fatty acids in fresh tea leaves, while C18:3n3, C18:2n6c, C16:1 are the main components of fatty acids. The content of fatty acids in leaves decrease after turning over, the content of linolenic acids in unsaturated fatty acids increases first and then decreases with the increase of turning over intensity, for they might be the reaction substrates for the formation of tea aliphatic aroma components.