Determination Of Tea Polyphenols In Tea Milk And Their Interaction With Milk Protein

Tea polyphenols are antioxidants and the active ingredients of the tea, which showed activity for anti-aging, anti-radiation, elimination of free radicals produced in human body, lowering serum glucose, prevention and treatment of cardiovascular diseases, antibacteria and precipitation of heavy metals, etc. Thus, they have a wide range of applications in food, medicine, health care, and chemical industry. However, when they are added into cow milk to produce tea milk, two problems aroused. Firstly, it's difficult to analyze them because of the turbidity; Secondly, the interaction between of tea polyphenols and cow milk proteins may influence the polyphenols'bioactivity and nutrition of the milk protein. In order to guide the tea milk production and application of tea polyphenol, an accurancy and simple method was devoloped to test tea polyphenols in tea milk and their interaction with milk protein was investigated in this research. The main resulths were as follows:1. Derermination of tea polyphenos in tea milkAcid acetone was used to destroy the emusifying system and precipitate protein to obtain clarified filtrates, tea polyphenold were determined spectrophotometrically by iron tartrate method, which significantly increased detection accuracy. The result showed that the recovery ratio reached 99.6%-102.2%, and RSD kept as low as 0.21%-0.26%(n=6), indicating its perspective application in measurement of tea polyphenols in milk tea.2. Application of the determination methodThe content of tea polyphenols in 4 types of tea beverage, including black tea, green tea, milk tea and milk-flavor tea (36 products in total), and the effect of production technolgy on the content and stability of tea polyphenols was investigated. The results indicated that 86.1% of the products was qualified according to the natinal standard. In addition, it was found that the content of tea polythenols was influenced by sterilization temperature time and storage length.3. Interaction of tea polyphenos with milk proteinAccording to the processing technology conditions of milk tea and the consumption of milk and tea, change in in vitro protein digestibility and contents of several major catchins after the interaction of tea polyphenol with milk protein was invetigated. The results showed that, in the model milk tea which contains 0.5% of milk protein and 0-10.0g/kg tea polyphenols, the in vitro digestibility of the protein decreased as addition of tea polyphenols increased. It decreased significantly after the contents of tea polyphenols were more than 2.0 g/kg; Indicating that the milk protein digestibility would decreased significantly when isopyknic pure milk and tea which contains tea polyphenols more than 2.5 g/L were eaten at the same time. The further research showed that the interaction of tea polyphenols with milk protein was mainly physical association under the edible condition. And the two catechins, EGCG and ECG, which had high affinity for milk protein and had major effects on the in vitro digestibility of milk protein.