Study On The Taste Quality Of Yichang Congou Black Tea Based On Electronic Tongue Technology

The congou black tea is characteristic of high aroma,mellow taste,warm stomach,health care,fashion and convenient,with rapid growth domestic production and sales in recent years.Brewing technique is very important for obtaining the best quality infusion.This paper took the Yichang congou black tea as the research object,combining the specificity electronic tongue technology and the quality characteristics of tea infusion under different brewing water temperature and brewing time were systematically studied,the quantitative models of the methods of manual review,chemical composition and electronic tongue detection were established to determine the application of electronic tongue technology in the taste quality detection.And finally the changes of sensory flavor and quality components of tea infusion under different brewing conditions were explored,the suitable brewing method of tea was obtained.The main findings are as follows:1.Study on electronic tongue evaluation tea infusion quality: The electronic tongue detection showed good stability and high repeatability,the response signal curve was approximate to the smooth line when 100 s to 120s;the relative standard deviation value of the repeated detection value of the seven-root sensor were less than 4.5%.The tea infusion of the same brewing mode of different kinds of tea and different brewing modes of the same tea sample were detected by the electronic tongue,the results showed that the use of electronic tongue technology combined with principal component analysis,clustering analysis,discriminant factor analysis can be a good classification of different tea infusions,of which qualitative classification results was the same as that of the the artificial sensory taste.225 kinds of tea infusions were detected and SVM method was used to establish the model between the electronic tongue responses with the sensory taste scores.The results showed that the prediction effect of the quantitative model was good.The optimum penalty coefficient of modeling parameters and the radial basis kernel function were 0.25,9.18 respectively,the selected principal component factor was 3 showed a best model,the training set and the forecast set correlation coefficient were 0.97,0.73,the smallest mutual authentication mean square root error and the forecast mean square root error were 0.92,2.51.56 kinds of tea infusions were predicted the taste scores by the model,the result showed that the relative error of the predicted results were not more than 9%,showed a good predictive function of the model.Thus the electronic tongue combined with the quantitative model could effectively evaluate the taste quality of tea.2.Effects of different brewing conditions on the quality and chemical constituents of tea infusion research: Two factors brewing temperature(70?,80?,90?),brewing time(1min,3min,5min,7min,9min)were studied combined with sensory review and electronic tongue detection,chemical composition determination.The results showed that different brewing temperatures and brewing times had significant effects on the taste value and chemical compositions,sensory taste quality and electronic tongue taste of tea infusion.(1)The taste score at the same temperature increased to the highest and then decreased as the brewing time prolonged.At the same time(t <3min),the taste score were 90?> 80?> 70?,time more than 5min,the taste score were 80?> 70?> 90?.Temperature * time interaction had significant effects on sourness,umami;the umami strength increased over time,staying stable after 7min at 70 ? and 3min at 80?,90?.The same period of time,with temperature up to 80 ?from 70 ?,the umami was significantly increased,no significant change with temperature up to 90 from ?80?.(2)70?,80?,the tea infusion color grading gradually increased as the time prolonged;at 90?,the color score increased to the highest and then declined with the time prolonged;short brewing time(t ? 5min),the infusion color score increased as the temperature rise,but time long(t ? 7min),the infusion color score from high to low were 80?> 70?> 90?.With the prolongation of time and the rising of the temperature,the brightness L decreased gradually,and the red value(a)and the yellow value(b)gradually increased.The leaching rate of water extract,tea polyphenols,total flavonoids,soluble sugar and 8 kinds of catechin were affected by the brewing temperatures and brewing times.Soluble sugar,EC,GCG,EGC were time-sensitive ingredients;water leaching,tea polyphenols,total flavonoids,GC,C,EGCG,ECG,CG,CAF,GA were the time * temperature-dependent ingredients.The leaching rate of GC and CG of single bud was larger than that of one bud and two leaves on the whole and the leaching rate of C,EGCG,ECG of single bud were smaller than that of one bud two leaves.The leaching of chemical constituents such as tea polyphenols,total flavonoids,GA,GC and CG of single bud were faster than that of one bud two leaves,and the leaching rate of CAF,C,EGCG and ECG were the opposite of which the leaching rate of one bud two leaves was faster than that of single bud.The leaching rate of the ingredients of all leaves were 90 >80 > 70? ? ?.The leaching rate of two kinds of tender teas were CAF> water extract>tea polyphenols.(4)Appropriate brewing condition of the congou black tea of one bud and one bud two leaves were 80?5min?90?5min.3.The relationship between the electronic tongue response and the color value or the contents of the chemical composition were studied by using the support vector machine(SVM)method to establish models.The results showed that the quantitative prediction models of the water extract,tea polyphenol,total flavonoids and soluble sugars were better,and the coefficients of the calibration set and the prediction set were higher than 0.89 and 0.81 respectively.The quantitative prediction model of the color value was better and the coefficients of the calibration set and the prediction set were 0.94,081 respectively.