Enzymatic, antioxidant activities and stability of bromelain-polyphenol precipitate in pineapple juice

Abstract

Bromelain, a cysteine protease derived from pineapple, is highly susceptible to denaturation. To stabilize its enzymatic activity, polyphenols from cashew leaf extract with antioxidant activity and protein-binding characteristic was used to precipitate bromelain in pineapple juice and formed bromelain-polyphenol precipitate subsequently. Nutraceutical properties (bromelain and antioxidant activities) and effect of temperature and pH on free and precipitated bromelain w'ere evaluated and compared. Bromelain from pineapple juice was successfully precipitated with cashew polyphenols. The bromelain activity of bromelainpolyphenol precipitate was retained at about 65 %, 63 % and 40 % of its original activities by precipitating w'ith 1.5 %, 1.0 % and 0.5 % cashew polyphenols respectively. 1.5 % and 1.0 % bromelain-polyphenol precipitates were found to have 15 % greater antioxidant activity than pineapple juice. 1.5 % and 1.0 % precipitates were shown to have good heat resistance by displaying 7 and 3.5 times lower denaturation rate constants respectively as compared to free bromelain. All bromelain-polyphenol precipitates exhibited stable bromelain activity and antioxidant activity at temperature range of 25 °C - 85 °C, whereas free bromelain showed an activity declination. Kinetics of thermal inactivation (E, AH*, AG* and AS ) showed that the precipitate was more thermostable than free bromelain. Bromelain-polyphenol precipitate exhibited an increased bromelain activity over alkaline pH whereas free bromelain was stable at acidic and neutral pH. Besides, the precipitate displayed a high and stable antioxidant activity at acidic region. The study showed that precipitating of bromelain with cashew polyphenols could stabilize bromelain activity, increase antioxidant capacity and improve stability in response to temperature and pH. These results suggested that precipitating of bromelain with polyphenols could be a new method for enhancing the nutraceutical properties of enzyme.