Quality Analysis Of Pu'er Tea Based On Near Infrared Spectroscopy

Pu'er tea is a unique tea species in China and has an important part in China's long history of tea drinking.Pu'er tea is widely welcomed by consumers due to its antibacterial and fat-suppressing effects,but the quality issue has always been the focus of the majority of tea consumers.Pu'er tea tree's age,storage time,tea appearance and taste play a key role in its quality certification and market price.Some Pu'er tea manufacturers can obtain greater profits by confusing storage time,blending ancient and tableland pu'er tea or adulterating flavors.Therefore,it is of great significance to study the quality testing methods of Pu'er tea to protect consumers' rights and interests,NIR spectroscopy is a fast,simple,and efficient technique that combines chemometric methods in a wide range of detection and analysis fields.In this paper,near-infrared spectroscopy and chemometric methods were used to analyze qualitatively and quantitatively three aspects of Pu'er tea's storage year,blended tea,and flavored adulterated tea.The main research results obtained are as follows:1)Identification of Pu'er tea storage years:In this paper,five different storage years of Pu'er tea from Wuliang Mountain in Yunnan Province were selected,and the near-infrared spectroscopy analysis technology was used to discriminate the storage year of Pu'er tea.First,principal component analysis(PCA)was used to observe the clustering of Pu'er tea in different storage years and the results showed that there was no obvious clustering in Pu'er tea in different storage years.Second,partial least squares discrimination(PLS-DA)and support vectors Machine(SVM)were selected to establish two qualitative discriminant models along with different spectral pre-processing.Nearly 100%qualitative discriminant accuracy of Pu'er tea was achieved in different storage years.2)Analysis of blended tea of ancient Pu'er tea and tableland Pu'er tea:The near-infrared spectroscopy technique was used in this paper for qualitative and quantitative analysis of blended tea.Establishing PLS-DA model can realize 100%discrimination of blended tea.Partial least squares regression(PLSR)and backward interval partial least squares(FiPLS)methods were used to establish a quantitative analysis model for blended Pu'er tea.The prediction determination coefficient(Rp2)and root mean square error(RMSEP)of the PLS quantitative analysis model combined with different spectral pretreatments are 0.992 and 0.0313.respectively.The Rp2 and RMSEP of the FiPLS quantitative analysis model are 0.9948 and 0.0262,respectively.3)Analysis of flavor adulterated Pu'er tea:This paper qualitatively and quantitatively analyzes the three common flavor components coumarin,vanillin and ethyl maltol in Pu'er tea.The three flavor components were blended into Pu'er tea at a certain ratio to prepare flavor adulterated Pu'er tea samples.First,a PLS-DA qualitative discriminant model of adulterated Pu'er tea was established,which could achieve 100%of flavor adulterated Pu'er tea and pure Pu'er tea Identification;Secondly,the establishment of PLSR and FiPLS quantitative analysis models,combined with different spectral pretreatment methods,can achieve quantitative detection of adulterated flavors in Pu'er tea.The Rp2 of the three adulterated fragrance verification set samples were up to 0.7989,07697 and 0.6253.The RMSEP of the three adulterated fragrance verification set samples were up to 0.1461,0.1573 and 0.1976,respectively.In short,there are practical application needs to develop a simple and rapid method for testing the quality of Pu'er tea to provide a guarantee for the quality monitoring of Pu'er tea.Among them,NIR spectroscopy has been widely used in the detection and analysis of food safety issues.This article mainly studies the application of NIR spectroscopy in the identification and detection of Pu'er tea.