晒青绿茶加工过程香气物质及其部分前体变化分析

Changes in Aroma Compounds and Selected Precursors of Sun-Dried Green Tea during Processing

为探究晒青绿茶特征香气成分在加工过程中的变化规律,以云南大叶种为原料制作晒青绿茶,利用溶剂风味辅助蒸发萃取和气相色谱-质谱联用技术测定鲜叶、杀青叶、揉捻叶和晒青叶的挥发性物质,并结合气味活度值(odor activity value,OAV)表征晒青绿茶活性香气。结果显示,共检测出67种挥发性化合物,以醇类、酯类、醛类物质为主,从鲜叶至杀青结束后挥发物总量增加,晒青叶挥发物质总量较鲜叶略有下降,但种类数增加。晒青绿茶中OAV>1的活性香气成分共计23种,主要为芳樟醇、香叶醇、壬醛等呈花香型和青香型的化合物,各加工工序中以醛类最为突出。采用气相色谱-火焰离子化检测器和高效液相色谱-二极管阵列检测器分别测定其香气前体脂肪酸和类胡萝卜素组分含量,共检测出7种脂肪酸,以饱和脂肪酸为主。共检测出13种类胡萝卜素,其中黄体素在各加工工序中含量都为最高。在晒青绿茶加工过程中,脂肪酸和类胡萝卜素总量持续下降,亚油酸、亚麻酸尤为明显,与其主要降解产物己醛含量变化趋势相反;类胡萝卜素降解转化生成的萜烯酮、紫罗酮及其衍生氧化物,如β-紫罗酮、5,6-环氧-β-紫罗兰酮等含量显著上升。晒青绿茶加工过程中脂肪酸和类胡萝卜素前体变化趋势与其关联香气产物均有一定相关性。本研究结果可为定向改良晒青绿茶香气提供理论指导。

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 asβ-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.