Effects Of Baking Technics On The Quality Of Wuyi Rock-essence Tea

Oolong tea is one of the six major tea types in China and Wuyi rock-essence tea is also the representative tea of the northern Oolong tea,which is deeply loved by consumers.Baking process is very important for the tea color,aroma,taste and shape of Wuyi rock-essence tea.In this paper,the effects of different baking degrees and different baking conditions on the quality of Wuyi Shuixian tea and Wuyi Rougui tea were studied.Optimizing baking conditions is on the basis of the response surface methodology(RSM)design experiment.Analysis and detection of biochemical components by using gas chromatography-mass spectrometer(GCMS),high performance liquid chromatography(HPLC),amino acid automatic analyzer.The quality changes of Wuyi rock-essence tea in different baking processes were analyzed by means of statistical methods to find out the optimum conditions for the baking of Wuyi rock-essence tea.The main research contents and results are as follows:1.Aiming at exploring the effects of different baking technics on the volatile components and aroma characteristics of Wuyi rock-essence tea,two cultivars of Wuyi rock-essence tea named Shuixian and Rougui were processed with different baking technics.The GC-MS results showed that there were 88 kinds of aroma components detected,including 14 kinds of alcohols,14 nitrogen compounds,7 hydrocarbon compounds,19 esters,18 aldehydes,12 ketones,1 acid,2 heterocyclic oxygen compounds and 1 sulfocompound.As the baking degree increased,the contents of alcohols showed a decreasing trend while the contents of esters and aldehydes showed an increasing trend.Additionally,the aroma components of Wuyi rock-essence tea made from Shuixian and Rougui were significantly different.The aroma components of Shuixian were mainly alcohols and nitrogen compounds while in Rougui,there were mainly alcohols and aldehydes.Moreover,along with the increasing of baking degree,the changing trend of the main aroma components,such as nitrogen compounds,aldehydes,nerolidol,linalool,geraniol,in Shuixian and Rougui were significantly different.According to the sensory evaluation,Shuixian(degree 3,130℃、2 h→130℃、2 h→125℃、2 h→140℃、2 h→145℃、1 h→150℃、1 h)and Rougui(degree2,130℃、2 h→130℃、2 h→125℃、2 h)had the best aroma quality.2.On the basis of single factor results,CCD design was carried out on the baking conditions of Wuyi Rougui tea,and the main biochemical components of tea samples under different baking conditions were tested.The results showed that the biochemical components of Wuyi Rougui tea,tea polyphenol,flavonoids and soluble sugar were lower than those of unbaked tea,while the free amino acids were not changed.The fuzzy comprehensive evaluation method was applied to evaluate the main biochemical quality of the baking process,and the fuzzy comprehensive evaluation result was used as the Y value of the response surface to optimize the baking conditions.The best baking process conditions is:95.06℃,13.92 h,8.8 kg/m~2 leaf thickness.The confirmatory test results show that the difference between the predicted value and the actual value is not significant.3.The correlation analysis results between biochemical components and tea soup color and flavor showed that EGC,EC,kaempferol,gallic acid,salicylic acid,malic acid,citric acid,ascorbic acid and TB affected the color of the tea soup.EGC、EC、ECG and most of the amino acid monomers were positively correlated with the taste score of tea soup,gallic acid were significantly negatively correlated with tea flavor.The path analysis of the taste of tea soup showed that EGC,aspartic acid and arginine have a direct effect on flavor properties,but ECG and leucine have indirect effects on flavor properties.4.Different baking conditions of Wuyi Rougui tea and unbaked tea were detected128 kinds of aroma components detected,including 11 kinds of alcohols,16 kinds of nitrogen compounds,11 kinds of hydrocarbons,28 kinds of esters,38 kinds of aldehydes,16 kinds of ketone,6 kinds of acids,2 kinds of heterocyclic oxygen.Nitrogen compounds and aldehydes are the main aromatic components of Wuyi Rougui tea with baking.The PCA results of aroma show that the main aroma components of Wuyi Rougui tea with baking are nerolidol,dehydrogenation linalool,β-ionone,hexanal,β-cyclocitral,hyacinthin,2-heptanone,methyl-2-furoate,heptanal,α-farnesene,2-ethyl-3-methyl-pyrazin,2-ethyl-3,5-dimethylpyrazine,linalool,indole,benzaldehyde,1-ethyl-1-H-pyrrole,2-phenyl-2-butenal,benzene acetone.5.On the basis of PCA results,the samples of Wuyi Rougui tea were evaluated by the comprehensive evaluation model of aroma.Based on the evaluation index of aroma quality and the Y value of the response surface,the best baking conditions for the aroma quality of Wuyi rock-essence were:93.71℃,11.92 h,6.82 kg/m~2 leaf thickness.