Fast nondestructive identification of steamed green tea powder adulterations in matcha by visible spectroscopy combined with chemometrics

摘要

Compared with green tea powder, whether enzyme-deactivated by steam or pan-fire, matcha is rich in nutrients, but is more expensive. Using steamed green tea powder to adulterate matcha often occurs and this study provided an effective method to identify steamed green tea powder adulterations in matcha rapidly and nondestructively with the combination of visible spectroscopy and chemometrics. Thirty pure matcha samples, 30 100% steamed green tea powder samples and 120 adulterated samples with steamed green tea powder's concentration from 20% to 80% (w/w) were prepared and their spectra of 500-700nm were acquired and applied for the qualitative classification and quantitative prediction. The principal component analysis-linear discriminant analysis model and the soft independent modeling of class analogy model in the qualitative classification as well as the partial least squares model in the quantitative analysis performed well with the accuracy of 100% and R-2 of 0.9815 in their corresponding prediction sets. Because of the covering step during its longer growth period, matcha contained more contents of chlorophyll b than steamed green tea powder, which made the absorption band of chlorophyll b at 645nm become the major contributing band both in discriminant and quantification models.