| In order to explore the preservation effect of fresh leaves and processed products after frozen storage and the possibility of processing green tea,this study used young buds and leaves within one bud and one leaf in the spring of Mengshan No.9 as raw materials to study the changes in aroma substances during the processing of green tea.Fresh leaves,as well as pre green leaves,pre green leaves,pre green leaves,pre green leaves,pre green leaves,pre shaped leaves,and finished products made according to traditional green tea processing techniques,were used as raw materials,Using a freezing vacuum preservation technology at-18 ℃,experimental treatments were conducted with different freezing times such as 0d(CK),90 d,180d,270 d,and 360 d.The effects of different freezing times on the aroma,appearance,color,pigment composition,sensory quality,and taste components of green tea and its processed products were systematically studied.Based on this,the processed products with the best freezing effect were selected and used as raw materials to optimize the subsequent thawing and drying processes,Forming a new model for green tea processing.The main research findings are as follows:(1)During the processing of green tea,the types of new aroma substances increased,while the total amount(i.e.abundance)of aroma substances decreased.During the processing from "fresh leaves → green killing → initial kneading → second green → second kneading→ shaping → drying",the aroma abundance decreased by 58.02%,with the green killing process decreasing the most,with a decrease of 56.13%.Through green killing and other processes,the original aroma substances in fresh leaves were largely lost,and at the same time,dimethyl sulfide,linalool,and β-Fresh and refreshing aroma substances such as junipene and limonene make green tea present a pleasant aroma.In addition,after being refrigerated at 4 ℃ for 360 days,the aroma richness of finished green tea decreased by67.00%;The aroma richness of finished green tea stored for 180 days and frozen for 180 days decreased by 16.23% and 2.21% respectively compared to before storage.The traditional model of storing and selling green tea products made from fresh leaves is difficult to ensure the stability of tea aroma quality.(2)Study the changes in the "taste components" of various green tea products.The results showed that fresh leaves lost their value in processing green tea after being frozen,and after thawing,their color quickly turned brown,their odor disappeared,and they produced bad odors.The quality was severely damaged,while the quality of the processed green tea after being killed was relatively stable during frozen storage,and it could basically retain its pre frozen state.During the one-year frozen storage period,except for the significant decrease of 19.98% and 14.65% in the content of tea polyphenols in the fresh and freshly kneaded leaves,the changes in tea polyphenols in other products were not significant;The changes in amino acid content of all in-process products during frozen storage were not significant;The soluble sugar content of green tea in processed products(i.e.Erqing leaves,Errou leaves,and Shaping leaves)showed a significant increase trend during frozen storage,with increases of40.78%,79.04%,and 60.39%,respectively,while the changes in flavonoid content were not significant.It indicates that the frozen preservation effect of green tea products after being killed(especially after being green for two years)is better,and the non volatile flavor components contained in it can be stored for a long time through the freezing vacuum preservation technology at-18 ℃.(3)Study the changes in appearance,color,and pigment composition of green tea processed after blanching.The results showed that after treatment with different freezing times,the total chlorophyll content,chlorophyll a and chlorophyll b content of green tea in processed products were significantly reduced.Among them,the content of Erqing leaf decreased by 51.07%,31.84%,and 68.31%,respectively.The content of Errou leaf decreased by 54.64%,35.23%,and 71.48%,respectively,with the smallest decrease,and the difference between the two was not significant.And with the extension of frozen storage time,the comprehensive color difference(△ E *,△ L *,△ a *,△ b *)of Erqing leaf and Errou leaf also showed the smallest change.Although processed green tea can prolong its preservation time during frozen storage,it also experiences the phenomenon of greenness loss during normal temperature storage.As the frozen storage time prolongs,the degree of color deterioration worsens.Among them,the appearance,color,and pigment retention effects of Erqing leaf and Errou leaf are the best.(4)Study the "thawing" process of processed green tea with "two kneaded leaves" after blanching.The results indicate that low-temperature thawing is more effective in maintaining the freshness of green tea products than high-temperature thawing,and has a better retention effect on the appearance,color,pigment,and taste components.Compared with natural thawing(CK),ultrasonic thawing can shorten the thawing time to within 10 minutes.The water loss rate of green tea products in process after thawing by this method is only 1.38%.The change of main flavor components is basically insignificant,and the total color difference△ E * is less than 2.2.The visual perception of the color difference between the two is not obvious.Ultrasound thawing can accelerate the thawing process while maintaining the thawing quality,improve thawing efficiency,facilitate continuous production,and avoid uneven thawing or local overheating in other thawing methods.The comprehensive thawing effect is the best.(5)The "drying" process of green tea processed by ultrasonic thawing of the "two kneaded leaves" after blanching was studied.The results showed that infrared drying had a better effect than drum drying,effectively preserving the appearance,color,pigment,and taste components of green tea,and obtaining a fresher,mellow,and refreshing taste.Among them,the tea samples treated with two rounds of 8-minute three-stage infrared heating(110-125 ℃,100-110 ℃,100 ℃)showed the best color,aroma,taste,and shape.(6)On the basis of the above research,a new mode of green tea production has been formed: fresh leaves → blanching → initial kneading → second kneading → second kneading→ vacuum storage at-18 ℃ for 360 days → ultrasonic thawing → infrared drying → green tea finished products.Compared to the traditional production mode of green tea,which includes fresh leaves,blanching,initial kneading,second blanching,second kneading,shaping,drying,finished green tea,and vacuum freezing at-18 ℃ for 360 days.Comparative studies were conducted on the sensory quality,taste components,appearance,color,pigment components,amino acid components,polyphenol components,and aroma components of green tea processed using these two production modes.The results showed that compared to the traditional production mode of green tea,the amino acid content of green tea produced by the new mode significantly increased by 9.09%,with glutamine,arginine,and asparagine having the highest increase rate;The soluble sugar content significantly increased by 28.53%;The total chlorophyll content significantly increased by 44.59%;The content of ester type catechins decreased significantly by 10.36%,while the content of non ester type catechins increased significantly by 34.35%;The content of dimethyl sulfide significantly increased by89.60%.Compared to traditional production models,green tea produced under the new model has a fresher,more mellow and refreshing taste,a softer green color,and a higher content of aroma components belonging to the new tea,which can significantly extend the shelf life of green tea.This new model of green tea production has high promotion value. |
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