Properties of tea-polyphenol-complexed bromelain

Tea polyphenols extracted from Chinese green tea were used to complex and separate bromelain from pineapple juice. The antioxidant activity of tea polyphenols and their effects on the properties of bromelain were studied. The thermal stability of bromelain was enhanced after complexing with tea polyphenols. By complexing, the activity half-life of bromelain at 60°C was lengthened from 60 to 105 min. The improved thermal stability of the tea-polyphenol-complexed (TPC) bromelain is attributed to the antioxidant activity of tea polyphenols. Iso-electric focusing showed that six iso-enzymes fractions of bromelain could complex tea polyphenols with no change in their iso-electric points. Complexing with tea polyphenols did not change the optimum temperature (60°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 Michaelis constant (K) of the TPC bromelain for casein substrate was determined to be 1.42 x 10-5mol/l, higher than that of free bromelain (8.06 x 10-6mol/l). Tea polyphenols were found to act as a competitive inhibitor on bromelain in the hydrolysis of casein.