Effects Of Tea Cultivar,Growing Season And Processing Method On Volatiles Of Tea Leaves

Volatile compounds are components of tea aroma and they are the key compositions affecting sensory quality of tea. There are many factors affecting tea aroma or volatiles, including tea cultivar, agronomic techniques, processing methods and storage conditions. The present paper was set to investigate the effects of tea cultivar, growing season, organic fertilizing and processing methods on volatile composition and levels of tea. The major results are as follows:1. Tea cultivars ’Jiukengzhong’, ’Fudingdabai’,’Jinxuan’ and ’Xiangshanzao’ were used in the experiment. It shows that there were great differences in total content of volatiles between tea cultivars. The total content of volatile compounds in the 4 tested cultivars changed with growing seasons in two different forms:1) The total volatile compounds in cultivars ’Xiangshanzao’ and ’Jinxuan’ changed as:summer> autumn> spring; 2) The total content of volatile compounds in cultivars ’Jiukengzhong’ and ’Fudingdabaicha’ changed as:autumn> summer> spring. Spring green tea usually has better aroma than the summer tea. However, the present study shows that total contents of volatile compounds in the summer or autumn tea leaves were higher than that in spring tea. These suggest that total content of volatile compounds in fresh leaves are not correlated to the aroma sensory quality of finished tea products. There may be many other factors influencing the tea aroma, such as conversion, degradation or loss of the volatile compounds in the fresh leaf or the release of the bound volatile compounds by enzymic hydrolysis during tea processing.2. There were significant differences in composition and concentration level of volatile compounds in spring, summer and autumn fresh leaves of the four tested cultivars. Alcohol volatiles were the most abundant volatile compounds, being more than 50% of total volatiles in fresh leaf; followed by esters, ketones and aldehydes.Fatty acid volatiles were detected exclusively in leaves of summer or autumn seasons, but not in spring leaf. Twenty-eight volatile compounds were identified in the fresh tea leaves, among which 3,7-dimethyl-1,6-octadien-3-ol was the most abundant volatile, accounting for more than 10% of total volatile compounds, followed by methyl 2-hydroxybenzoate and 1-hexen-3-ol.3. Volatile composition showed obvious specific characteristics related to cultivar, geographical location and growing season.2-Ethyl-l-hexanol was detected exclusively in cultivars ’Jiukengzhong’ and ’Xiangshanzao’, the two cultivars originated from Zhejiang Province, but it was not detected in cultivars’ Fudingdabaicha’ and ’Jinxuan’ which were introduced from Fujian and Taiwan respectively. Geraniol,cis-linalool oxide and decanoicacid were detected in summer and/or autumn leaves, but not in spring tea. Butyl acetate was detected in spring and summer teas, but not in autumn tea. These suggest that composition and concentration level of volatile compounds can be improved by planting improved tea cultivars, introducing good cultivation method and improving environmental growing conditions, which will results in improvement of tea quality.4. Application of organic fertilizer had positive effect on improvement of volatile compounds in tea leaves. This effect was the most obvious in summer tea, followed by autumn tea. The least effect was observed in spring tea. The effect of organic fertilizer on volatiles varied with tea cultivars and growing season, and a positive effect was observed in spring, summer and autumn leaves in cultivars ’Shuchazao’ and ’Bixiangzao’. Positive effect was observed in spring and autumn leaves in cultivar ’Yinshuang’, but observed only in summer tea in cultivar ’Fudingdabai’. These suggest that the effect of organic fertilizer on volatiles depended on tea cultivars and growing seasons. A good fertilizing method should be suitable for specific cultivars and growing environmental conditions.5. During processing of green tea, black tea and oolong tea,total volatiles level decreased in the tea leaves. Although total content of volatiles in the leaves changed with cultivars, there was no significant difference in total concentration of volatiles in the final tea products prepared from various tea cultivars, suggesting that tea aroma characteristics of various tea cultivars were not determined by the total content level of volatiles, but determined by its volatile composition or key volatile individuals. When black tea, green tea and oolong tea were processed using a same batch of fresh tea leaves, the black tea had the highest level of total volatiles, followed by oolong tea, and green tea had the lowest level of total volatiles. These suggest that processing techniques had great impact on volatile compounds.6. Volatiles 3,7-dimethyl-1,6-octadien-3-ol (with molecular weight 154.25 and boiling point 199℃) and 2-hexenal (with molecular weight 98.14 and boiling point 150℃) were greatly lost during processing of green tea, black tea and oolong tea, among which volatiles in green tea was lost the most, and black tea least, with oolong tea in between. It is considered that the fixation process in green tea and oolong tea manufacture, which was carried out at temperature 220℃ or more, had great impact on the loss of volatiles. There was no fixation procedure in black tea processing, and it was dried at 120℃ or below, resulting in more residues of volatiles in black tea leaf. However,3,7-dimethyl-1,5,7-octatriene-3-ol was significantly increased by almost 8 times during processing of green tea, black tea and oolong tea, of which oolong tea was the highest.2-Methylbutyraldehyde was not detected in fresh leaf of cultivar ’Jinxuan’, but a high level of 2-methylbutyraldehyde was detected in the green tea, black tea and oolong tea prepared from its fresh leaf. These suggest that the increased volatiles might be released from their bound types during tea processing. Concentrations of benzaldehyde and 2-ethyl furan were increased during black tea and oolong tea processing, but decreased during green tea processing. These illustrate that tea processing methods had different effects on release of the bound types of volatiles.7. Black tea, oolong tea and green tea which were prepared from a same batch of fresh leaves had specific volatiles. The characteristic volatiles were 2-hexenal,1-hexanol, geraniol, benzene ethanol and methyl 2-hydroxybenzoate for black tea, and indole for green tea, while 1-octen-3-ol for oolong tea.8. During green tea processing, fixation process had great impact on volatiles. Leaves fixed by drum-fixation method and its dry tea (roasted green tea) had higher total content of volatiles than fixed leaves and dry tea (steamed green tea) by steam-fixation method. The changes were more obvious in alcohol volatiles and ester volatiles. Concentrations of 3,7-dimethyl-1,6-octadien-3-ol, methyl 2-hydroxybenzoate and geraniol in roasted green tea were higher than those in steamed green tea. Steamed green teas prepared from cultivars ’Jiukengzhong’ and’ Fudingdabai’ had higher levels of indole and dimethylbutyraldehyde than roasted green tea prepared from the same fresh leaves. These suggest that a quality green tea should be prepared using suitable cultivars and processing method.