Detection of Type, Blended Ratio, and Mixed Ratio of Pu'er Tea by Using Electronic Nose and Visible/Near Infrared Spectrometer.

Sai Xu,Xiuxiu Sun,Huazhong Lu,Qianqian Zhang

doi:10.3390/s19102359

Abstract

The objective of this study was to find an intelligent and fast method to detect the type, blended ratio, and mixed ratio of ancient Pu’er tea, which is significant in maintaining order in the Pu’er tea industry. An electronic nose (E-nose) and a visible near infrared spectrometer (VIS/NIR spectrometer) were applied for tea sampling. Feature extraction was conducted using both the traditional method and a convolutional neural network (CNN) technique. Linear discriminant analysis (LDA) and partial least square regression (PLSR) were applied for pattern recognition. After sampling while using the traditional method, the analysis of variance (ANOVA) results showed that the mean differential value of each sensor should be selected as the optimal feature extraction method for E-nose data, and raw data comparison results showed that 19 peak/valley values and two slope values were extracted. While the format of E-nose data was in accord with the input format for CNN, the VIS/NIR spectrometer data required matrixing to meet the format requirements. The LDA and PLSR analysis results showed that CNN has superior detection ability, being able to acquire more local features than the traditional method, but it has the risk of mixing in redundant information, which can act to reduce the detection ability. Multi-source information fusion (E-nose and VIS/NIR spectrometer fusion) can collect more features from different angles to improve the detection ability, but it also contains the risk of adding redundant information, which reduces the detection ability. For practical detection, the type of Pu’er tea should be recognizable using a VIS/NIR spectrometer and the traditional feature extraction method. The blended ratio of Pu’er tea should also be identifiable by using a VIS/NIR spectrometer with traditional feature extraction. Multi-source information fusion with traditional feature extraction should be used if the accuracy requirement is extremely high; otherwise, a VIS/NIR spectrometer with traditional feature extraction is preferred.

Highlights

Yunnan province of China is the heartland and presumed sourceof tea in the world [1]
The Linear discriminant analysis (LDA) classification results of ancient Pu’er tea type based on multi-source information fusion (E-nose and visible/near Infrared (VIS/NIR) spectrometer data fusion) and traditional feature extraction is shown in Figure 3c; all types can be classified
(1) For E-nose and VIS/NIR spectrometer data of Pu’er tea that was extracted using the traditional method, the mean differential value of each sensor should be selected as the optimal feature extraction method for E-nose data

Summary

Introduction

Yunnan province of China is the heartland and presumed sourceof tea in the world [1]. Pu’er tea leaves are plucked from the trees, named Daye in Pu’er city of Yunnan province, and put through a processing procedure before finishing [2]. Due to its unique soil and climate, tea plants will only develop the flavor in Pu’er city (aroma, liquor color, and taste), which is traditionally considered to be correct As a consequence, Yunnan Pu’er tea has been awarded a national Geographic Indication. Pu’er tea is loved by consumers all around the world because to the first-class flavor and special health efficacy, with vast market demand [3]. The problem of developing an accurate tea type detection technique is important in order to maintain the integrity of the Pu’er tea industry While Pu’er tea has a much higher market price than most other teas and different types of Pu’er tea vary considerably in price, the various types of Pu’er tea (as well as some non-Pu’er teas) are similar in appearance and hard to discriminate between by ordinary consumers.

Objectives

Methods

Results

Discussion

Conclusion