چكيده فارسي :
Tea is the second most consumed drink after water, and black tea is the most abundant type of tea produced worldwide. Green and black tea are the most traditional styles of tea products representing 20–22% and 76–78% of the worldwide production, respectively [1]. Green tea comes from the unfermented, dried leaves, while black tea is a fully fermented product. The interest in tea and the analysis of its chemical compounds has increased significantly due to its nutritional, economic value, and the positive effects of tea on human health [2]. However, few studies have addressed the availability of these compounds associated with the infusion time of the black tea drink. For this purpose, machine learning methods were used in this study to investigate the effect of brewing time on its chemical composition. In this way, the following procedure was used: In a round-bottom glass flask, 1.0 g of black tea and 20.0 mL of methanol were added, and the mixture was refluxed at 60°C for 3 h. Sampling was done four times between 0 and 3 hours (once every hour). The GC-FID technique was employed for analysis of the extracts of 100 samples (25 samples for each time), and the peak areas were used to construct the machine learning models. Various pre-processing methods, such as mean centering (MC), auto-scaling, multiplicative scatter correction (MSC), and standard normal variate (SNV), were used to remove irrelevant variations. Machine learning methods, including principal component analysis-linear discriminant analysis (PCA-LDA), partial least square-discriminant analysis (PLS-DA), and support vector machine (SVM), were employed to characterize the phytochemical composition of the tea samples. The constructed models showed a distinct class separation between the tea samples that were analyzed immediately after adding methanol (0 hour) and the samples corresponding to 3 hours sampling. The samples corresponding to brewing time of 1 and 2 hours appear in one cluster. The obtained results showed that the brewing time may therefore be an important factor affecting the phytochemical composition of black tea.
