Abstract
Effects of the moisture content (MC) of tea on diffuse reflectance spectroscopy were investigated by integrated wavelet transform and multivariate analysis. A total of 738 representative samples, including fresh tea leaves, manufactured tea and partially processed tea were collected for spectral measurement in the 325–1,075 nm range with a field portable spectroradiometer. Then wavelet transform (WT) and multivariate analysis were adopted for quantitative determination of the relationship between MC and spectral data. Three feature extraction methods including WT, principal component analysis (PCA) and kernel principal component analysis (KPCA) were used to explore the internal structure of spectral data. Comparison of those three methods indicated that the variables generated by WT could efficiently discover structural information of spectral data. Calibration involving seeking the relationship between MC and spectral data was executed by using regression analysis, including partial least squares regression, multiple linear regression and least square support vector machine. Results showed that there was a significant correlation between MC and spectral data (r = 0.991, RMSEP = 0.034). Moreover, the effective wavelengths for MC measurement were detected at range of 888–1,007 nm by wavelet transform. The results indicated that the diffuse reflectance spectroscopy of tea is highly correlated with MC.
Highlights
Tea is produced from fresh burgeon of tea plant after a series of physical and chemical reactions in the various tea processing procedures
The tea processing procedures are always accompanied with great variations of moisture content (MC)
The total results indicate that visible/near infrared (Vis/NIR) diffuse reflectance spectroscopy data is significantly correlated to MC of tea, especially the wavelengths of 888–1,007 nm can be taken as fingerprint indicators of tea MC
Summary
Tea is produced from fresh burgeon of tea plant after a series of physical and chemical reactions in the various tea processing procedures. The tea processing procedures are always accompanied with great variations of moisture content (MC). There are three main processing procedures including fixation, rolling and drying for green tea. The fixation procedure is implemented by high temperature processing to reduce the activity of enzymes, to eliminate herbaceous odor components, and to evaporate some water. The drying procedure dehydrates tea to reduce MC and to improve tea’s smell and taste after thermochemical reactions under high temperature. The MC of tea determines the shelf life of tea, and affects the physical and chemical reactions in tea processing, so measurement of MC is an important task for producing high-quality tea [1]
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