牛奶对茶汤纳米聚集体茶多酚分布特性的影响

茶汤纳米聚集体是茶多酚和蛋白质等自组装而成的纳米胶粒,是各组分介于游离分子与沉淀颗粒的中间状态。为探究牛奶对茶汤茶多酚分布特性的影响,本研究以云南大叶种蒸青绿茶、红茶为原料,以1:50茶水比浸提茶汤,按不同比例添加全脂、半脱脂和脱脂牛奶,利用超滤离心技术分离茶汤纳米聚集体,采用动态光散射技术分析各组茶汤纳米聚集体的总光强和平均直径,采用福林酚法分析其茶多酚浓度和分布率,比较研究牛奶添加比例、脂肪含量和茶类等因素对纳米聚集体物理化学特性和茶多酚分布特性的影响。结果表明:添加不同脂肪含量的牛奶均会促使部分牛奶纳米胶粒与茶汤纳米聚集体结合,导致茶汤超过90%的茶多酚富集于纳米聚集体,使绿茶和红茶的游离茶多酚比例分别降低78%和67%。初步证实:添加牛奶会促进绿茶、红茶的茶多酚参与分子聚集,使游离茶多酚比例大幅降低。

Effects of Milks on the Distribution of Tea Polyphenols in Nano-aggregates from Green Tea and Black Tea Infusions

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.