Study On The Authentication Technology Of Tea Products Based On The Characteristics Of Multi Element Stable Isotopes And Their Ratios

Food certification has attracted the attention worldwide.Brand protection,wrong labeling and origin mismatch are important parameters of food certification.Tea is one of the most common beverages worldwide,people have been interested in the confirmation of tea products.The formula,production year and origin of tea products are the most concerned aspects of tea certification.There is an urgent need to strengthen the detection and certification of tea products,and use discriminatory science and technology to manage and verify.ICP-MS,ICP-OES,EA-IRMS and GC-C-IRMS were used to quantify analyse the mineral elements and their stable isotopes,multiple stable isotope ratios,?¹³C and?¹⁵N of caffeine and six main free amino acids in Chongqing Tuo tea products with different formulas,Pu'er tea samples from 2014 to 2018 and tea samples from Yongchuan,Xiushan,Wanzhou,Jiangjin,Rongchang and Yibin.The change rules and mechanism of these indexes in tea products were analyzed,and the feasibility and effect of confirming tea products(formula,production year and geographical traceability)by combining fingerprints of mineral elements and their stable isotopes,multiple stable isotope ratios,?¹³C and?¹⁵N of caffeine and six main free amino acids were studied.Then the technical system and index system of tea product validation were established.The four methods have high applicability,high sensitivity,wide linear range,good precision and accuracy in tea.There were significant differences(P<0.05)in mineral elements and their stable isotopes in tea with different formulas,different production years and different producing areas.It is feasible to use the fingerprint technology of mineral elements and their stable isotopes for tea products.The prediction accuracy of each model is more than 90%,and the verification accuracy is more than 88%.LDA and BP-ANN showed the best performance.¹¹⁴Cd,⁹⁵Mo and ⁸⁵Rb are the most important chemical markers to confirm tea samples with different formulas;Mn,⁶⁸Zn and ²⁰³Tl are the most important chemical markers to confirm tea samples with different production years;⁸⁶Sr and ¹¹²Cd are the most important chemical markers to confirm tea samples from different producing areas;they can be used as an effective index system to confirm tea products.Different formula,different production years and different producing areas of tea have different characteristics of multi stable isotope ratio fingerprints.It is feasible to use stable isotope ratio fingerprint technology to verify tea products.The prediction accuracy of each model is more than 90%,and the verification accuracy is more than85%.LDA and BP-ANN showed the best performance.Therefore,the discriminant model based on the combination of multiple stable isotope ratios can effectively identify the tea products.The results showed that the most important chemical markers for the confirmation of tea samples of different formulas were?²H,?¹⁸O,⁹⁸Mo/⁹⁵Mo,⁹⁶Mo/⁹⁵Mo and ⁹⁸Mo^/96Mo;?²H,?¹³C and ¹⁵⁴Sm/¹⁵²Sm were the most important chemical markers for the confirmation of tea samples of different production years;?²H,¹³⁸Ba/¹³⁷Ba,²⁰⁵Tl/²⁰³Tl,?¹⁵N,⁸⁸Sr/⁸⁶Sr and ¹⁵⁴Sm/¹⁵²Sm are the most important chemical markers for the confirmation of tea samples from different producing areas,and they are the effective index system for the confirmation of tea products.The analytical method of?¹³C and?¹⁵N of caffeine and six main free amino acids in tea was proved to be effective and suitable for the analysis of caffeine in tea.The?¹³C and?¹⁵N fingerprints of caffeine and six main free amino acids were different in tea with different formula,different production years and different producing areas.It is feasible to confirm tea products with?¹³C and?¹⁵N fingerprints of caffeine and six main free amino acids.The prediction accuracy of each model is more than 85%,and the verification accuracy is more than 85%.BP-ANN proved the best performance.Therefore,the discriminant model based on the combination of?¹³C and?¹⁵N of caffeine and six major free amino acids can effectively identify the tea products.The results showed that the most important chemical markers of Chongqing Tuo tea samples with different formulas were?¹³C_Ser and?¹⁵N_Ser;the most important chemical markers of tea samples with different production years were?¹⁵N_Thea,?¹³C_Glu and?¹⁵N_Glu;the most important chemical markers of tea samples from different producing areas were?¹⁵N_Ala and?¹³C_Thea;they can be used as an effective index system for tea product validation.Through the comparison of different fingerprint characteristics,it was found that the combination of mineral elements and their stable isotopes,multi-element stable isotope ratio,?¹³C and?¹⁵N of caffeine and six main free amino acids>mineral elements and their stable isotope value>multi stable isotope ratio index>?¹³C and?¹⁵N of caffeine and six main free amino acids.The combination of mineral elements and their stable isotopes,multi-element stable isotope ratios,?¹³C and?¹⁵N of caffeine and six main free amino acids has advantages in tea product validation.The validation performance of each model is equal and excellent,which can improve the overall correct validation rate.⁹⁵Mo,?¹⁵N_Ser,¹³³Cs,?¹³C_Ser,Co,⁸⁵Rb,P,La,¹⁷²Yb,⁴⁷Ti/⁴⁶Ti,¹¹²Cd and ⁸⁸Sr/⁸⁶Sr were selected as the most important chemical markers to confirm the tea products of different formulations by combining 136 variables,K and ⁸⁵Rb were the most important chemical markers to confirm the tea products from different production years by combining 110 variables,and?²H was the most important chemical marker to confirm the tea products from different producing areas by combining 134 variables,and the index system of tea products confirmation were further screened and established.Chemometrics methods(HCA,PCA,PLS-DA,BP-ANN and LDA)are indispensable mathematical tools for the screening of tea product validation indexes and the establishment of discrimination model.Different methods have different validation effects on tea products,and the preconditions need to be carefully investigated.The results of this study provide technical support for the confirmation of tea products.At the same time,the methods and results of this study also have important reference significance for the confirmation of other food products,especially the botanical products.