Effect of pressure, temperature, time and storage on peroxidase and polyphenol oxidase from pineapple

摘要

The individual and combined effect of pressure, temperature, time and post-pressurisalion storage on pineapple polyphenol oxidase and peroxidase activity was evaluated in the study. The experiments were carried out according to a 27-basic treatments design using the following levels of the independent variables: temperature: 12, 40 and 60°C; pressure: 0, 100, 300, 500 and 600 MPa; time: 15, 30 and 45 min.; storage: 24 h storage at 5°C or absence of storage after pressure treatment, previously to the activity determination. Enzymatic extract including both peroxidase and polyphenol oxidase was obtained by blending internal part of the fruit with tris buffer (pH=6.5). After being filtrated the extract to be pressurised was divided into small portions in polietilene bags, which were then termosealed. The samples were frozen and kept in a freezer at -18°C and defrosted just before the pressurisation. Polyphenol oxidase activity was determined through an espectofometric method by measuring the absorbance resulted from the residual enzyme activity on catechol, used as substrate. Peroxidase was similarly determined but using in that case hydrogen peroxidc as substrate and p-phenylcnediamine as acceptor. A second-degree polynomial model was adjusted for each dependent variable polyphenol oxidase activity and peroxidase activity. Due to the restrictions in the aleatorisation procedure, a mixed model was adjusted, i.e., aleatory effects were used for the factor "day in which the experiment was carried out" and fixed effects for the polynomial coefficients. The aleatory effect for the day of treatment relates to the fact that the level of temperature was adjusted and maintained all day long for a set of three treatments carried out in each day of experiments. The statistical analysis for polyphenol oxidase has shown that there was a negative significant effect of storage factor on enzyme activity, i.e., the activity was lower for stored samples. No interaction among the independent variables was detected. Operational time presented a slight negative linear effect i.e., activity dropped linearly with time. Temperature and time did not result in linear and quadratic significant effects on polyphenol oxidase activity. The masimum polyphenol oxidase activity was verified for a temperature of 30.8 and pressure of 274 MPa. Change in temperature had a higher effect on polyphenol oxidase activity than change in pressure.