| Green tea is the largest consumption and export tea of China and the demand has been rising. However, in the production of green tea, the typical flavor ills including bitter flavor of summer green tea and grassy aroma of bud green tea are widespread, which seriously-restricting the overall benefits of tea industry. On the one hand, old summer green tea showed flavor ills with low short aroma and bitter taste due to growth environment, processing technology and so other factors. Thus formed a status quo that "high-grade tea best-selling, low-grade tea unmarketable" and many places only pick spring tea expect summer-autumnal tea. a lot of summer-autumnal tea raw materials are waste and serious unmarketable. On the other hand. In recent years, famous green tea because consumers pay more attention on appearance, producers devotion to tenderness to pick single bud to produce bud green tea so as to meet market demand. Most bud green tea showed flavor ills with grass heavy aroma and astringent weak taste without rolling and with low tea making temperature. Attractive does not taste good has become a common phenomenon on the bud green tea, which seriously reduced tea drinking value. Aim at vintage summer common green tea and present spring bud green tea with above flavor ills, this test was conducted by using dry-heat post-treatment to study the effects of dry heat factors on flavor quality change rule, explore the optimum process parameters and overall evaluate flavor quality improving effect. In order to achieve the goal of improve flavor quality and enhance drinking value, and provide theoretical basis and technology references for green tea with flavor ills. The results showed that:(1) Dry-heat post-treatment had a significant effect on the flavor quality of green tea with flavor ills. In sensory, aroma, taste and comprehensive sensory score of all treatments were increased significantly (P<0.05). summer green tea aroma showed chen smell faded and chestnut smell present, taste showed chen taste disappeared, bitterness decreased and become mellow. Bud green tea aroma showed grass smell disappeared and fragrance and floral smell appeared, taste showed bitterness and weak taste decreased and become mellow. But two kinds of teas both showed dry tea color and soup quality slightly declined. The optimum process of summer green tea was A1B4C4 (temperature 55?. moisture 9%. time 6 h). The optimum process of bud green tea was A1B3C3 (temperature 55?. moisture 7.5%, time 150min).(2) Factors (summer green tea expect time factor) all had significant impact on test results (P<0.05). Influence order of summer green tea was:A (temperature)> AŚ B (temperatureŚmoisture)> Ar C (temperatureŚmoisture)> B Ś C (moistureŚtime)> B (moisture)> C (time). Influence order of bud green tea was:A (temperature)> AŚ B (temperatureŚmoisture)> A Ś C (temperatureŚmoisture)> B (moisture)> BŚC (moistureŚ time)> C (time). Obviously temperature was the dominant factor and relatively low temperature was more conducive to tea flavor quality. Time was the secondary factor.(3) Based on the optimum technological temperature and moisture, flavor quality dynamic variation with time of green tea with flavor ills were:in sensory, aroma, taste and comprehensive sensory score of all treatments were increased first and then decreased extend with time while dry tea and liquor color score were decreased. In taste ingredient, the content of water extract, polyphenols, amino acids, soluble sugar and phenol ratio to ammonia increased first and then decreased. The content of caffeine, chlorophyll a. chlorophyll b and total chlorophyll decreased gradua-lly.(4) Ills green tea by dry-heat post-treatment. It's taste ingredients, amino acid components, catechin components and aroma components were changed greatly. In taste ingredients of summer green tea, the content of amino acids significantly increased (P<0.05). The content of water extract, polyphenols, and soluble sugar slightly increased but not significantly (P>0.05). The content of caffeine and phenol ratio to ammonia slightly decreased but not significantly (P>0.05). In taste ingredient of bud green tea, the content of water extract and amino acids significantly increased but caffeine significantly decreased (P<0.05). The content of polyphenols slightly increased but not significantly (P>0.05). The content of soluble sugar and phenol ratio to ammonia slightly decreased but not significantly (P>0.05). The content of chlorophyll a, chlorophyll b and total chlorophyll of two kinds of green teas significantly decreased (P<0.05). In amino acid composition, two kinds of green teas both had the highest content of theanine and slightly decreased compared with original sample. To summer green tea. the content of glycine. threonine, alanine and total sweet taste amino acids significantly increased (P<0.05).The content of tyrosine, phenylalanine and total bitter taste amino acids significantly decreased (P<0.05). The content of flavor amino acid slightly decreased. To bud green tea, the content of total flavor and sweet taste amino acids both increased. And the content of glycine, proline and alanine significantly increased (P<0.05). The content of tyrosine, phenylalanine and total bitter taste amino acids significantly decreased (P<0.05). Besides, the content of arginine of two kinds of green teas increased and cysteine decreased. Bud type green tea reached significant level. In catechin components, the content of ETC and TC decreased but NETC significantly increased (P<0.05). The content of EGCG and ECG of summer green tea slightly decreased. while GC and EC significantly increased (P<0.05). The content of GC of bud green tea significantly increased but GCG and ECG significantly decreased (P<0.05). The content of EC and C slightly increased while EGCG slightly decreased but had no significant difference (P>0.05). The CAI. CAF+ETC of two kinds of green teas decreased but CAF+NETC increased. In aroma components, aroma substances were invariable but composition ratio and relative content showed a large variation. To summer green tea. chen smell main aroma substance including 1-pentene-3-alcohol.2.4-heptyl diene formaldehyde,3,5-symplectic diene-2-ketone,5.6-epoxy-?-ionone decreased dramatically. Sweet and fragrant fruit smell substance including benzyl alcohol, phenethyl alcohol, beta ring citral, geranyl acetone.6-methyl hept-5-en-2-one. dimethyl methyl valerate, limonene besides baking, nuts and burnt smell substance including 2-amyl furan. 1-ethyl-2-formyl pyrrole and benzene acetonitrile increased dramatically. To bud green tea. chen smell main aroma substance including 1-pentene-3-alcohol,3,5-symplectic diene-2-ketone and grass smell substance liking 3-hexene-1-alcohol decreased dramatically. Fragrant fruit and fresh sweet smell substance including a-cedar alcohol, nerolidol. 6-methyl-5-heptene-2-one, ?-ring citral, geranyl acetone, (3-ionone, baking smell substance including 1-ethyl-2-formyl pyrrole and benzene acetonitrile, and new tea smell main composition Dimethyl sulfur increased dramatically.In summary, dry-heat post-treatment had a significant effect on the flavor quality of vintage summer green tea and bud green tea, which could effectively remove chen and grass smell, improve tea aroma and decrease bitterness. |
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