| Green bud tea belongs to the bud shaped tea.It is processed with tea bud(single bud)in Sichuan.According to the color of products,green bud tea can be classified as ‘green type' and half yellow green type'.The ‘green type' lowers temperature and shorter time during preparation process in order to maintain the green color.It's steaming and frying processing use low temperature in a long period.Its flavor often is with different degrees of green smell and poor aroma quality.In the process of green tea,green color and fragrance keep improve is always a process of contradiction.This is due to the low temperature frying can keep chlorophyll,prevent browning;high temperature frying easy loss of grass gas substances,improve the flavor,but the color of tea was turn out to be yellow.To solve this contradiction,the process needs to have a balance point.How to effectively protect the color and remove the smell of green is of great concern to the researchers.Therefore,theoretically study of ‘green bud tea' in composition and the process of heat dissipation rule,discusses the relations between maintaining green color and loss of green aroma material basis,technology parameters,analysis of the formation mechanism of the green tea quality has theoretical research value.At the same time,the study is also important for solving the basic problems of Green Tea production practices.Therefore,on the basis of experiments,the following conclusions have been drawn:(1)This study established a gas chromatographic method for the detection of the characteristic green aroma compounds of emerald green tea,including the use of SDE extraction and GC-FID detection.The sample volume is 1?L and the inlet temperature is 230?.The GC condition should be as follows: the initial column box temperature is set at 40? to keep 2min,the temperature increase to 230?,and keep 8min,and enter the detector for analysis,and the temperature of the detector mouth is 230?.The working curve of cis-3-hexenol is y=2×10-7x-0.0008,and the linearity is good.(2)In this study,the threshold intensity evaluation test of the smell threshold of cis-3-hexenol aqueous solution and the tea sample with cis-3-hexenol was evaluated.The results showed that the detection threshold value of cis-3-hexenol was 0.26mg/kg,the recognition threshold value was 0.96mg/kg,the maximum threshold was 7.31mg/kg,and the water bath 10 min at 50? at the temperature of 25?.With the addition of cis-3-hexenol to the green tea sample,the recognition threshold was 0.03mg/kg.(3)In this study,the processing parameters of green bud tea were measured.The results showed that the setting temperature of green bud tea was 105?,the leaf temperature was 69.30(±0.39)?,with 10 min sustained.At the same time,the strip,pressure strip,denuding and drying process were all carried out in the strip machine,and the temperature setting of the strip machine was not more than 70? in these processes.The measured leaf temperature is not more than 50?,and it is 405 min in the strip mill.The processing shows an exactly characteristic of ‘low temperature and long time'.(4)In this study,the intensity of green bud tea was evaluated by the threshold strength evaluation method.The results showed that the green gas intensity score(50mL group)decreased from 4.2 of the fresh leaf to 2.3 of the dry tea.It showed that the green bud tea was gradually reduced in the process of processing,among which the fried leaves had a strong green odor.It turns to green odor in striped leaves,and start to show green aroma in pressure strip leaves.Finally,it turns out to be nice green aroma in dried tea.(5)In this study,the RGB color channel was used to analyze the digital photos of green bud tea.The results showed that the color and luster change of green bud tea was divided into two segments,one is from the green leaf(G=145)to the press leaf(G=98),and the color gradually becomes shallow,and the decolorization(G =127)is changed because of less moisture.The emerald green tea deepened to dry 1(G =156)reached its peak and then continued to decline.The grey correlation analysis showed that the color and luster change of green bud tea was influenced by the content of chlorophyll a(correlation degree 0.81)and the content of chlorophyll b(correlation degree 0.80),as well as the water content(correlation degree 0.69).(6)In this study,the content of cis-3-hexenol in the processing of green bud tea was quantitatively analyzed by gas chromatography.The results showed that when the content of cis-3-hexenol in tea was 7.27mg/kg,that is,the fresh leaf presented strong green odor,and when the content of cis-3-hexenol was 2.25 mg /kg in tea,the leaves showed green odor;when the content of cis-3-hexenol in tea is 0.54mg/kg,that is strip leaves 3 started to show green aroma;when the content of the cis-3-hexenol of tea is 0.52mg/kg,that is,the pressure strip leaves appears clear green aroma,and when the content of cis-3-hexenol is 0.04mg/kg in tea,the dry tea presents a clear green fragrance.(7)The content of the main flavors in the processing of green bud tea was determined in this study.The results showed that the content of tea polyphenols,catechin and caffeine decreased continuously during the processing of green bud tea,while the content of soluble sugar and free amino acid showed fluctuation,and the chlorophyll content in the processing of green bud tea was detected.It was found that the chlorophyll a decreased significantly from the spreading leaves to the strip,and the decrease was not significant between the other processes.The chlorophyll b was not changed significantly during the processing,and the green bud tea processing technology could effectively protect the chlorophyll in the tea leaves.(8)In this study,the GC-MS method was used to detect the aroma components in the key process of aroma transformation of green bud tea,and the characteristic components of green bud tea were determined,including(E)-2-hexenal,(Z)-2-hexenal,hexaldehyde,(E)-3-hexenol,(Z)-3-hexenol,(E)-2-hexenol,linalool,methyl salicylate,nerol,and geraniol.Combined with the active value of aroma,suggest that linalool(OAV=460.35)and cis-3-hexenol(OAV=249.24)have a great influence on the odors of green bud tea.Using grey correlation analysis,it is considered that the linalool(correlation degree 0.99)influence the green aroma the most.An electronic nose was used to determine the key process of aroma transformation in the process of green bud tea,and the main component analysis showed that the response range of the fried leaves inductor was more extensive,so its unique aroma characteristics were not prominent,and the response range of the dry tea inductor was narrower,indicating that the sense of the aroma should be more concentrated and its aroma characteristics were more outstanding. |
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