Effects of Milks on the Distribution of Tea Polyphenols in Nano-aggregates from Green Tea and Black Tea Infusions
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Abstract:
Tea nano-aggregates were colloidal particles spontaneously assembled by tea polyphenols, proteins and other components in natural tea infusions. These peculiar particles were the intermediate states of tea components between free molecules and precipitates. To primarily explore the effects of milks on the distribution of tea polyphenols in tea infusions, tea infusions extracted from green tea and black tea at tea-water ratio of 1:50, and then mixed with whole milk, semi-skimmed milk and skimmed milk of various percentages, respectively. Tea nano-aggregates in these milk teas were subsequently separated by ultrafiltration centrifugal technology. In addition, total intensity and average diameter of tea nano-aggregates were analyzed by dynamic light scattering; meanwhile, the concentration and distribution of tea polyphenols in tea nano-aggregates were evaluated by Folin-Ciocalteu method. The effect of milk addition ratio, fat content and variety of tea on the physical and chemical characteristics of nano-aggregates, as well as the distribution characteristics of tea polyphenols was studied. The results showed that the addition of milk with different fat content would promote the combination of some milk nanometer micelles and tea nano-aggregates, resulting in more than 90% of tea polyphenols in original tea infusions enriched in tea nano-aggregates, and the ratio of free tea polyphenols in green tea and black tea infusions reduced by 78% and 67%, respectively. In conclusion, adding milks to green tea and black tea infusions would strengthen the aggregation of tea polyphenols and remarkably reduce the ratio of free tea polyphenols.
