| The chemical compositions in tea leaves are influenced by their growing surroundings,and the provenance soil is an important contributor to the trace element composition of the tea leaves.The content of the chemical components are related to the quality of tea.The composition of chemical substances in tea can be used as ranking evaluation standard and geographical origin identification index.This study takes three major tea growing areas in Jiangsu Province(Ningzhenyang tea growing area,Taihu Lake tea growing area and Lianyungang tea growing area)as the research areas,with soil and tea shoots with one bud and two leaves as the research materials,which collected from 66 randomly selected in the three major tea growing areas.The contents of 11 mineral elements(Zn,Ni,Fe,Mn,Cr,Cu,Al,Cd,As,Hg,Pb)in soil and tea leaves were determined by ICP-MS and ICP-OES.In this paper,the content differences of 11 mineral elements among the three tea growing areas,the correlation of mineral elements in soil and tea leaves,and the regional distribution characteristics were analyzed.Multiple logistic regression analysis and multiple linear regression analysis were carried out for 11 mineral elements in leaves,and the geographical origin discrimination model of tea was established to provide a theoretical basis for the traceability of tea.The specific results are as follows:1.The order of average contents of 11 mineral elements(mg/kg)in soil is as follows:Al>Fe>Mn>Zn>Cr>Cu>Ni>Pb>As>Hg>Cd.The order of average contents of 11 mineral elements(mg/kg)in tea leaves is as follows: Mn>Al> Fe>Zn>Cu>Ni>Cr>Pb>As>Cd>Hg.The contents of Mn and Al in tea leaves are the highest.The order of the coefficient of variation of 11 mineral elements in the soil is as follows: Hg>Cd>Ni>Mn>Cu>Al>Cr>Fe>Pb>Zn>As,the range is between 29.89%～135.50%.The variation coefficients of Hg and Cd in soil are the largest.The order of the coefficient of variation of 11 mineral elements in the tea leaves is as follows: Hg>As>Cd>Cr>Mn>Pb>Al>Cu>Ni>Fe>Zn,the range is between 17.49%～157.94%.The variation coefficients of Hg and As in tea leaves are the largest.2.Correlation analysis results of 11 mineral elements in soil and tea leaves in the research areas shows that the three elements(Cr,Al,Hg)present significant positive correlation between the soil and tea leaves.In addition,in this study,the increase of Hg content in soil can significantly reduce the content of Zn and Cu in tea leaves,while the increase of the content of Pb in soil can significantly reduce the content of Al in tea leaves.3.Through the multiple logistic regression analysis of 11 mineral elements in tea leaves,we could found that the five mineral elements(Zn,Ni,Cr,Al,Hg)are significantly related to the classification of three tea growing areas.The Bayes discriminant function was used to build a prediction model to predict the tea growing area of the tea leaves samples.The results showed that the accuracy of back-substitution test reached 87.7%,and the accuracy of cross-validation reached 78.9%,which shows that the established discriminant function can be used to distinguish Lianyungang tea growing area and Ningzhenyang tea growing area.This study continues to take the tea leaves samples in Ningzhenyang tea growing area as an example,and establishes a discriminant function through stepwise discriminant regression.The 33 tea leaves samples from different sources in the Ningzhenyang tea growing area are discriminated correctly.The results showed that the accuracy rate of back-substitution test reached 100%,and the accuracy rate of cross-validation reached 93.9%.In this study,the multiple linear regression model is established by stepwise regression,and the predicted value is fits well with the actual value,and the equation alsofits well.In this study,the above three kinds of analysis have achieved good results,indicating that it is possible to determine the origin of tea by measuring the content of mineral elements in tea and combining with stoichiometric analysis method. |
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