چكيده فارسي :
Camellia sinensis is an evergreen shrub that produces the plant materials used to prepare tea. East Asia constitutes the largest tea-producing area represented by China, which accounts for 38% of world tea production, followed by South Asian countries, India and Sri Lanka. Nowadays, green tea has received increasing attention for its potential health benefits. The health benefits of green tea are mainly due to its polyphenol content; around 60–80% of polyphenols are flavan-3-ols, commonly known as catechins [1]. Catechins are major constituents of the tea leaf (approximately 30% of the dry weight of green tea and 9% of the dry weight of black tea) and of considerable importance because of these compounds are responsible for astringency in the tea infusion [2]. The phytochemical composition, sensory qualities, and antioxidant activity of green tea infusion are significantly affected by brewing conditions [3]. This study aimed to investigate the effect of brewing time on the phytochemical composition of green tea infusion using machine-learning methods. For this purpose, the following procedure was used: In a round-bottom glass flask, 1.0 g of tea and 20.0 mL of methanol were added, and the mixture was refluxed at 80°C for 3 h. Sampling was accomplished at different time intervals including, 0 (immediately after addition of methanol), 1, 2, and 3 hours. The resultant was injected into GC-FID, the chromatograms were obtained, and the peak areas were used for model construction. Several pre-processing methods, such as mean centering (MC), auto-scaling, multiplicative scatter correction (MSC), standard normal variate (SNV), and their combinations, were employed to improve the quality of the data. 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 other samples (1, 2, and 3 hours). The results showed that the brewing time after 1 hour did not significantly affect the phytochemical composition of green tea.
