Properties of tea-polyphenol-complexed bromelain

Tea polyphenols extracted from Chinese green tea were used to complex and s eparate bromelain from pineapple juice. The antioxidant activity of tea pol yphenols and their effects on the properties of bromelain were studied. The thermal stability of bromelain was enhanced after complexing with tea poly phenols. By complexing, the activity half-life of bromelain at 60 degrees C was lengthened from 60 to 105 min. The improved thermal stability of the t ea-polyphenol-complexed (TPC) bromelain is attributed to the antioxidant ac tivity of tea polyphenols. Iso-electric focusing showed that six iso-enzyme s fractions of bromelain could complex tea polyphenols with no change in th eir iso-electric points. Complexing with tea polyphenols did not change the optimum temperature (60 degrees C) for the enzyme activity but the optimum pH value range was narrowed down from pH 6.8-9.0 to around 7.8. The Michae lis constant (K) of the TPC bromelain for casein substrate was determined t o be 1.42x10(-5) mol/l, higher than that of free bromelain (8.06x 10(-6) mo l/l). Tea polyphenols were found to act as a competitive inhibitor on brome lain in the hydrolysis of casein. (C) 2000 Canadian Institute of Food Scien ce and Technology. Published by Elsevier Science Ltd. All rights reserved.