Spectral imaging approach to evaluate degree of tea fermentation by total catechins

Tea is one of the most widely consumed beverage in the world, only second to water. Different from black tea (fully fermented) and green tea (unfermented), partially fermented teas such as Oolong, Bouchong are popular in Taiwan, Japan, China and Asian countries. The quality assurance during the process of partially fermented tea is highly related to the fermentation degree of tea, which is the ratio of total catechins oxidized during tea fermentation. Spectral imaging system was developed in this study to evaluate the degree of tea fermentation, which consisted of lighting chamber, image acquisition modules, cameras, and liquid crystal tunable filter (LCTF, 400-1100 nm). Software programs of the system control and image processing were also developed. The spectra analyses were conducted; calibration models for the evaluation of total catechins were established by MPLSR (modified partial least square regression) and MLR (multiple linear regression) methods. The results showed that r (correlation coefficient), SEC (standard error of calibration), SEV (standard error of validation) were 0.99,4.56 mg/g, 5.67 mg/g for MPLSR model, and 0.99, 5.04 mg/g, 6.50 mg/g for MLR model respectively. Although MPLSR model has better prediction ability than MLR, MLR model has a potential to be integrated with multi-spectral image system to develop an on-line inspection system for monitoring fermentation degree of tea.