| Green tea is considered to be a vital part of the Chinese tea industry,particularly the famous green tea.Conventionally,domestic green tea quality is equivalent to approval of sensory evaluation.However,the sensory review is subjective,vulnerable to environmental disturbances,and needs historical standards etc.Maintaining consistency in quality judgment for international trade and establishing a standardized quality discrimination system as well as a shelf life prediction model still remains a great problem in the tea industry.Hence,Longjing,a Qiantang production tea was used as the research object whose physical and chemical data were collected from different grades of Longjing green tea.A combination of traditional sensory scores with chemometric analysis and intelligent sensory techniques,a quality discriminant model that can characterize sensory scores using physicochemical data were obtained,and then a predictive model was established for shelf life prediction model to compensate for the subjective and standard missing of traditional sensory reviews and realize the quality judgment of the green tea industry and the scale of the shelf life determination.The standardization and digitization are the inevitable trends in the future development of the tea industry with broad application prospects.So as the change law of physical and chemical components during storage,the corresponding quality discrimination model and shelf life prediction model were established,and two kinds of application were applied.The model screening package material that effectively prolongs the shelf life of green tea provided a stable and reliable evaluation method for green tea quality judgment.(1)Six different grades of Longjing green tea were carried out for sensory scores;the changes of main physical,chemical indicators,intelligent sensory analysis results,and the correlation between the latter two and green tea sensory scores were studied.The results showed that there were significant differences in the sensory evaluation scores of different grades of green tea,which were suitable for correlation analysis and model establishment.The main physical and chemical components were determined by instrumental analysis and stoichiometry.There were significant differences in tea polyphenols,free amino acids,ascorbic acid,chlorophyll and tea catechins(P<0.05).It was found via the intelligent sensory analysis:b/a value the difference between the grades was significant(P<0.05).The electronic nose obtained complex aroma components,but through DFA analysis,the effective correlation,sensory score and physical and chemical indicators correlation analysis showed:tea polyphenols,free amino acids,phenol The ratio of ammonia,ascorbic acid,soluble sugar,catechins,and the ratio of ester to non-ester catechins in catechins were significantly correlated with sensory scores;Correlation analysis of the differences revealed that the a value and the b/a value were significantly correlated with the sensory score.Among them,ascorbic acid has a significant linear correlation with the sensory score.(2)Establishment of Longjing green tea quality discrimination model was based on the research on the physical and chemical indicators of different grades of green tea and the changes of intelligent sensory analysis results,through PCA principal component analysis,six main components with a high contribution rate to the sensory quality of green tea were extracted:tea polyphenols,free amino acids,ratio of phenol to ammonia,ascorbic acid,ester/non-ester catechins,and b/a value.The PLS-DA quality discriminant model was established.The correlation coefficient between the actual score of each sample and the model prediction was 0.9909,and the root mean square error(RMSECV)was at 0.230.The performance of the model was verified by 60 independent prediction sets.The correlation coefficient between the actual score and the model prediction was 0.9930,and the prediction mean square error(RMSEP)was at 0.208,the model predicts good results.(3)The establishment of Longjing green tea shelf life prediction model was studied,the storage temperature(20?~70?),humidity(20%~80%RH)and time(30 d~180 d)for the main components of prepackaged green tea through accelerated experiments.The results showed that with the increase of temperature and time,tea polyphenols,phenol to ammonia ratio,ascorbic acid,and non-ester catechins showed a downward trend,and the free amino acids fluctuated in stages,and the fluctuation range was between 15 mg/g~25 mg/g.The catechins,ester/non-ester catechins,and b/a showed an upward trend,which increased by 2~3times compared with the room temperature conditions.The analysis of the aroma components by DFA,the influence of temperature and time on the aroma and the cumulative contribution rate was at 89.04%and 94.72%.Therefore,the storage temperature and time were selected as the key control points of green tea shelf life.Furthermore,it was observed via the accelerated experiments that the storage temperature,humidity and time had an effect on the main chemical components in pre-packaged green tea.The Arrhenius model was used to study the shelf life of green tea,based on PLS-DA.The model obtained the acceleration equation ln?=6081/T-16.665(R~2=0.9968);based on the artificial sensory evaluation,the acceleration equation ln?=6325.8/T-17.455(R~2=0.9990)was obtained,the shelf life of pre-packaged green tea at room temperature was 42 days and 43 days,the predicted values of the two are only one day apart,which is basically consistent.Therefore,the sensory score obtained based on PLS-DA can effectively predict the shelf life of green tea.(4)The shelf life prediction model based on the PLS-DA model was carried out to compare the effect of Composite Kraft paper and tinplate packaging on extending the shelf life of green tea through the influence of different packaging materials on the six main ingredients,it was preliminarily determined that the green tea shelf life of the two packaging materials was about 180 days(Kraft paper was greater than 180 days,tinplate cans was less than 180 days),and the Arrhenius shelf life based on PLS-DA was obtained,respectively.The prediction model showed that the shelf life acceleration equation of green tea wrapped in Kraft paper was ln?=7405.1/T-19.62(R~2=0.9982)whereas for canned green tea was ln?=4909.5/T-11.448(R~2=0.9985).Kraft packaging had a shelf life of 184 days at room temperature(25?)and 151 days in cans,which were 142 days and 119 days longer than pre-packaged green tea,respectively,extending the shelf life of green tea. |
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