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 degrees 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. (C) 2014 Society of Chemical Industry