Study On The Effect Of Drying Process On The Formation Of Chestnut-Like Aroma Of Green Tea

As one of the typical aroma of high-grade green tea,the chestnut-like aroma is deeply loved by consumers because of its harmonious and pleasant flavor.Although the chestnut-like aroma type has been subdivided and some key components have been explored,the influencing factors of the formation of chestnut-like aroma have not been investigated based on the processing technology.Particularly,the influences of drying process and related parameters on the formation of chestnut-like aroma have not been studied specifically and systematically.Moreover,the formation mechanism of chestnut-like aroma of green tea is still unclear,which partly prevents the directional processing and quality control of chestnut-like aroma of green tea.Therefore,the effects of different drying process on the formation of chestnut-like aroma were investigated in this study.Based on the optimal drying method,the drying parameters on the formation of chestnut-like aroma of green tea were explored subsequently.Furthermore,the formation factors and mechanism of chestnut-like flavor of green tea were investigated by adding the exogenous substances into the tea samples during the final firing process.The main results are as follows:1.The effects on the formation of chestnut-like aroma obtained from six drying methods including tunnel-type far infrared radiation drying,box-type hot air convection drying,chain-plate hot air convection drying,bucket-type hot air convection drying,vibration strip-type conduction drying and roller-type conduction drying were investigated.Infrared-assisted extraction coupled to headspace solid-phase microextraction(IRAE-HS-SPME)and gas chromatography-mass spectrometry(GC-MS)was developed to analyze the volatile components in green tea.And the sensory evaluation,physicochemical compositions as well as multivariate statistical analysis were combined for further analysis.The results showed that,the chestnut-like aroma of tea sample obtained by box-type hot air convection drying was the strongest according to the comparison of sensory evaluation.The aroma score was significantly higher than other methods 3-5 points,and the overall quality was also better,reaching up to 90 points or more.Based on the comparison of manufacturing process,obvious regional distribution characteristic was observed before vs after drying.The well-explained variance(R2X = 0.822,R2 Y = 0.982)and cross-validated predictive capability(Q2 = 0.856)indicated the model’s good feasibility,which confirmed the important influence of drying methods on the formation of chestnut-like aroma.In addition,it was found that the heat transfer modes of convection and conduction were more favorable for producing chestnut-like aroma than the radiation mode.What is more,the electromagnetic roller-hot air coupling drying method,possessing the advantages of box-type hot air convection and roller-type conduction,could also obtain tea sample with high qulity of chestnut-like aroma,which verified the above results.2.Based on the optimal drying method of box-type hot air convection,the effects of different drying temperatures(80 ℃,95 ℃,110 ℃,125 ℃)and drying time(10-90 min)on the quality of chestnut-like aroma of green tea were studied.The results indicated that,a higher quality of chestnut-like aroma of green tea was obtained under the condition of drying at 95 ℃ for 40 min.Besides,the effects of electromagnetic roller-hot air coupling drying method on the formation of chestnut-like aroma were investigated from the aspects of drum temperature,hot air temperature,fan speed(air volume)and drying time.It was found that the tea sample presented a stronger chestnut-like aroma under the condition of the roll temperatures(front/180 ℃,middle/170 ℃ and back/160 ℃),and the hot air temperature of 110 ℃ for 6-min-drying.In addition,the results of multivariate statistical analysis were well consistent with sensory evaluation,and many key components of chestnut-like aroma detected also provided a theoretical basis for the above results.3.Based on the final firing process,the effect of exogenous additives on the formation of chestnut-like flavor was investigated by the addition experiments of adding different amounts of theanine and sucrose into green tea.The aroma of green tea was detected by IRAE-HS-SPME combined with GC-MS.The influence of exogenous additives on the formation of chestnut-like flavor of green tea was analyzed by combining the sensory evaluation and physicochemical components.It showed that the types and contents of exogenous additives have different effects on the quality of chestnut-like aroma,and the single addition of exogenous substance had better effect than the simultaneous addition of theanine/sucrose,among which the chestnut-like aroma quality and comprehensive quality of green tea were significantly improved by the addition of theanine/dry tea(5‰ w/w).In addition,the effect of different drying time(15-75 min)was investigated and the chestnuts-like aroma was significantly improved when the drying time reached at 45 min.Particularly,the change trends of two key chestnut-like aroma compounds(α-ionone and methyl salicylate)were well consistent with the sensory evaluation,which can be regarded as the pivotal components in the regulation of chestnut-like aroma.This paper combines the practical process with the basic theoretical research.The results would further enrich the basic theoretical system of chestnut-like fragrance and also provide a reference for the processing of chestnut-like aroma of green tea.