Green tea catechins suppress xanthine oxidase activity in dairy products: An improved HPLC analysis

A new rapid isocratic HPLC method was developed to quantify xanthine oxidase activity in several dairy products by determining both substrate (xanthine) and product (urate) concentrations at short retention times (6.76 min and 4.92 min, respectively) with high values for linearity and reliability. The impact of added green tea catechins (1000 ppm) on xanthine oxidase activity was also examined in dairy products containing fat globules using the developed HPLC method. The addition of (+)-catechin, (−)-epigallocatechin gallate (EGCG), and green tea extract significantly (p ≤ 0.05) decreased the xanthine oxidase activity of these products. The effect of EGCG on decreasing xanthine oxidase activity of milk fat globules was stronger than for (+)-catechin, and can be attributed to different structures of green tea polyphenols, such as different numbers of OH groups in catechins. The results of this study suggest possible associations between milk fat globule surfaces and green tea catechins.