Study Of Tea Raw Materials Based On Near Infrared Spectrometry

In this study,a near-infrared identification model and a quantitative model of the main components of tea raw materials were established based on near-infrared spectroscopy,the chemical composition content of different leaves on the same branch was explored,and finally a new method for the rapid detection of chemical components related to tea raw materials was established.A theoretical foundation was laid for standardizing the selection of tea raw materials and improving the quality of tea leaves.The following are the main results:(1)A method was developed for the determination of gallic acid,theobromine,epigallocatechin(EGC),caffeine,epicatechin(EC),epigallocatechin gallate(EGCG),and epigallocatechin gallate(ECG)in tea raw materials.Epigallocatechin gallate(EGCG)and epigallocatechin gallate(ECG)were determined by high performance liquid chromatography(HPLC).The chromatographic conditions were optimized by examining the pretreatment method,column,column temperature and gradient elution.The methodological investigation of the established assay showed that the method could accurately determine the contents of these seven components in tea raw materials,with the contents of gallate ranging from 2.90 to 3.45 mg/g,theobromine from23.15 to 25.65 mg/g,EGC from 77.60 to 85.48mg/g,caffeine content365.90～378.55mg/g,EC content 52.78～61.25mg/g,EGCG content635.26～666.32mg/g,ECG content 187.26～198.56mg/g.(2)A HPLC method was developed for the determination of aspartic acid(Asp),glutamic acid(Glu),theanine(The),valine(Val),isoleucine(Ile),leucine(Leu)and phenylalanine(Phe)in tea raw materials.The chromatographic conditions were optimized by examining the pretreatment method,column,column temperature and gradient elution;the methodological investigation of the established assay showed that the method could accurately determine the contents of these seven amino acid components in tea raw materials,with the highest contents of theanine(3.6743～4.0644 mg/g)and aspartic acid(0.2338～0.2586 mg/g)in tea raw materials.0.2586 mg/g,glutamic acid content was0.1101～0.1218 mg/g,phenylalanine content was 0.1046～0.1157 mg/g,and leucine,isoleucine and valine content was less than 0.1 mg/g.(3)The effects of different NIR scanning parameters on the diffuse reflectance spectra and the quantitative model prediction results were investigated.Finally,the best processing method as well as scanning parameters were 8 cm-1 resolution and 64 scans,respectively.The 14 quantitative models of gallic acid,theobromine,EGC,caffeine,EC,EGCG,ECG,Asp,Glu,The,Val,Ile,Leu and Phe were developed by the best choice of spectral pre-treatment and the correction by regression method.The established models are more suitable for the prediction work of unknown samples of tea raw materials with a wide range of quality index components;the infrared spectra can reflect the linear relationship between the spectral absorption properties and chemical composition properties of the main components of tea raw materials.(4)Using the content of 14 chemical components of tea raw materials determined by HPLC as reference data,the reference data were corresponded to NIR one by one,and a rapid,real-time and nondestructive method for determining the content of 14 chemical components in tea raw materials was established through the optimization of model parameters such as spectral pre-processing and spectral range selection,which provides theoretical support for the prediction of the content of 14 chemical components in tea raw materials and lays the foundation for the quality control of tea raw materials.