The objective of the paper was to determine the effect of brewing time, fragmentation degree, and brand of black tea on the colour of infusion and its antioxidant properties. The content of total polyphenols and antioxidant activity as well as the colour components using an CIE L*, a*, b* system were determined in the infusions of black tea (leaf, granular, and dust tea – teabags) purchased in the area of TriCity (Poland) and in England. With the use of the analysis results of principal components, it was attempted to qualitatively classify the teas analyzed. It was found that the brewing time was a significant factor that determined the content of polyphenols in the studied samples of tea infusions. An average content of polyphenols in all the samples of tea infusions ranged from 67.70 mg GAE / 100 ml (brewing time of 3 minutes) to 239.57 mg GAE / 100 ml (brewing time of 15 minutes). An important factor to determine whether or not the tea infusion would be accepted is its colour. The infusions made of leaf tea brewed for 3 minutes are characterized by higher brightness (36.15 ÷ 37.85) than the infusions made of granulated tea (32.68 ÷ 34.32) and of dust tea (29.95 ÷ 36.73). A similar tendency was observed in the case of the infusions brewed for 15 minutes. It was also found that the ratio between the absolute values of a* and b* colour parameters changed along with the prolonged brewing time. No significant effect (p ≤ 0.05) was proved of the fragmentation degree and tea brand on the values of the parameters analyzed. The principal components were analyzed and the analysis results did not show any clear differences in the quality of the tea samples analyzed; this fact could prove that the quality attributes of the raw materials used to produce the teas analyzed were comparable. The results of the research studies performed prove that the colour parameters could be significant physical parameters for the discrimination analysis and the determination of tea quality.
black tea, infusion, polyphenols, antioxidant activities, colour, quality