Abstract:

158 non-comminuted and comminuted green tea samples were scanned by NIR Systems 6500 and InfraXact NIR analyzers. An analysis model for quantitation of polyphenols in green tea was developed through orthogonal test design and validated with principle component regression (PCR), partial least square (PLS) and modified PLS. The models were evaluated by the objective function method and the applicability of the optimal models was validated. The optimal model was obtained by using the NIR Systems 6500 analyzer with comminuted samples by modified PLS and the optimum analytic conditions for spectral data preprocessing were standard normal variate (SNV)/detrend scatter, second derivative treatment (the interval for one point), smoothing interval for four points and the secondary-smoothing interval for eight points. This optimal condition leaded to the objective function value of 95.74% and RSD and RPD of validation of 4.52% and 2.52, respectively. The results showed that orthogonal experiment design could comprehensively evaluate the effect of methods for validation and spectral data preprocessing on the models. Quantitative analysis of polyphenols could be realized by NIRS and this optimal NIRS model had very good precision and applicability.

Key words: near infrared spectroscopy, green tea, polyphenols content, quantitative analysis model, optimization