The application of response surface methodology in studying the effect of heat and high hydrostatic pressure on anthocyanins, polyphenol oxidase, and peroxidase of mulberry ( Morus nigra ) juice

BACKGROUND Mulberry juice is an excellent source of phytochemicals with medicinal properties. The effects of four independent variables (temperature, heating time, pressure, and pressurising time) on three response variables [% anthocyanin retained, and % residual activities of the enzymes polyphenol oxidase ( PPO ), and peroxidase ( POD )] of mulberry juice were studied using response surface methodology. Mathematical models and optimum levels of the response variables were generated . RESULTS Temperature had the greatest effect on all the response variables. The synergistic effect of temperature and pressure had significant effect ( P < 0.05) on anthocyanin retained and residual PPO activity. The prediction of the desirability model, based on 95% confidence in the range of the independent variables, gave optimal treatment conditions of 83.39°C, 2.38 min, 480.00 MPa , and 21.67 min, respectively for temperature, heating time, pressure, and pressurising time. At these levels, the corresponding response variables were 91.68%, 44.69% and 20.17% for the amounts of anthocyanin retained, and residual activities of PPO and POD , respectively. The desirability index obtained was 0.741 . CONCLUSION The results were desirable and the mathematical models developed could be used to predict the outcome of the response variables to a high degree of accuracy. © 2014 Society of Chemical Industry