Recent developments in vibrational spectroscopic techniques for tea quality and safety analyses

Background: Tea is one of the most popular beverages around the world for its health benefit. The availability of rapid and reliable techniques for evaluating tea quality and safety is important for the tea industry. However, tea components and pesticide residues detection, sensory analysis, grading, and pricing are carried out by laborious, time-consuming, and destructive methods. Therefore, vibrational spectroscopy has emerged as an increasingly popular technology in tea quality and safety evaluation owing to its simple, nondestructive and rapid detection procedures. Scope and approach: The current review compares the employment of different vibrational spectroscopic techniques including near-infrared (NIR), mid-infrared (MIR), Raman, Terahertz (THz) spectroscopies and hyperspectral imaging (HSI) in tandem with regression and classification models in the quantitative and qualitative analyses of tea quality and safety. Furthermore, band assignments of tea components based on these spectroscopies are summarized. Key findings and conclusions: NIR spectroscopy dominates the applications of vibrational spectroscopy in the evaluation of tea quality, while only one study is related to THz spectroscopy. Raman technology is mainly applied to detect pesticide residues. HSI providing both spectral and spatial information has a potential in the optimization of the tea production process. Additionally, regression models find widespread use in the quantitative analysis of tea, such as phenolics, flavonoids, pigments, sensory evaluation, and pesticide residues, while classification models are useful for discriminating geographical origins, varieties, and fermentation degrees. The online detection of tea quality and safety by vibrational spectroscopy on the industrial scale is still an important and challenging task for future studies.