Effects Of Ultra High Pressure On The Conformational Transitions Of Pure Enzymes And Activity Inactivation Of Three Enzymes In Cantaloupe Juice

This article studied the influence of Ultra High Pressure (UHP) on the pure peroxydase (POD), polyphenoloxidase (PPO) and lipoxygenase (LOX) activities, and the primary structure, secondary structure and tertiary structure of POD, PPO and LOX were also studied by SDS-PAGE, Circular Dichrism and Fluorescence Spectra methods. The activity changes of POD, PPO, LOX and some quality indexes of Hami melon juice were also detected. The main conclusions were summarized as follows:(1) The inactivation effect of POD, PPO and LOX was enhanced significantly by UHP-temperature synergistic treatment. The three enzymes were activated after lower pressure(<400MPa) treatment at common temperature. The residual activity of POD, PPO and LOX were 86.8%,85.7% and 29.9% after 500MPa/30min treatment at common temperature, but after 500MPa/30min treatment at 55℃, the residual activity were 75.3%, 14.0% and 8.0%.(2) The primary structures of POD, PPO and LOX were not changed after UHP treatment, but the secondary and tertiary structures were changed significantly, Thea-helix contents raised andβ-sheet contents decreased with increasing of temperature and pressure, the enzyme activities showed direct correlation with a-helix contents, and showed inverse correlation withβ-sheet contents. The fluorescence intensity, peak position and peak types also changed under different temperature and pressure, but not well corresponded with enzyme activities.(3) At common temperature, the POD,PPO and LOX were not inactivated by UHP treatment, but it can be significantly inactivated by UHP-temperature synergistic treatment.(4) UHP treatment has a good inactive effects to POD, PPO and LOX in Hami melon juice, the analysis of first-order reaction kinetic data showed that D values of POD, PPO and LOX in Hami melon juice were closely to the pressure and temperature of UHP treatment. Higher pressures and higher temperatures resulted in lower D values and higher k values. The activity of POD, PPO and LOX in cantaloupe juice had different degree recovery during storage at 4℃for 4 weeks, and the degree of the changing had a relation with treatment condition such as pressure. The changing degree of the activity of POD, PPO and LOX in Hami melon juice had a relationship with treatment condition such as pressure, the samples with higher pressure and longer treatment time had less recovery degree.(5) The inactivation reciprocity of POD, PPO and LOX were different from each other, the residual activity of POD raised significantly, but the residual activity of PPO and LOX were decreased with extending of holding time, but not significant (p<0.05).(6) pH value in coordination with high pressure can improve the sterilization effect of UHP, the UHP treatment can diminish the loss of some nutrient substances and amend some quality indexes compared with thermization.