Qualitative and quantitative quality evaluation of black tea fermentation through noncontact chemical imaging

Fermentation is the most critical step in black tea processing and contributes to the taste and appearance of black tea. Conventionally, the degree of fermentation is evaluated through sensory reviews by experts. However, this method has low accuracy and is subject to reviewers’ experience. In this study, the fermentation quality of black tea was qualitatively and quantitatively evaluated through near-infrared hyperspectral imaging (HSI). The spectral information of samples of four fermentation degrees was collected and preprocessed using standard normal variate. The developed qualitative model could discriminate fermentation degrees, with a correct classification rate of 83.33 % for the prediction set. The quantitative prediction model achieved excellent prediction accuracy for the catechin content, with a residual prediction deviation of 2.18. Finally, the spatial distribution of catechins during fermentation was mapped through chemical imaging. Our study confirmed the feasibility of HSI for monitoring the fermentation quality of black tea.