91E-8 |
Processing of orange and apple juice by a combination of high hydrostatic pressure and mild heat treatment: Inactivation of enzymes and quality factor changes |
A. BAYINDIRLI1, H. Alpas1, and F. Bozoglu. (1) Food Engineering Dept., Middle East Technical Univ., Ankara, 06531, Turkey Polyphenoloxidase (PPO) is responsible for enzymatic browning and pectinesterase (PE) causes undesired cloud instability in fruit juices. High hydrostatic pressure (HHP) processing (100-900 MPa) is an alternative to thermal treatment for the inactivation of enzymes. The purpose of this research was to determine the effects of HHP treatments at different pressures and times combined with mild heat treatment (<50°C) on PPO in apple juice and PE in orange juice. HHP treatments were performed in a designed and constructed lab-scale unit with a maximum pressure 600 MPa and a maximum possible temperature of 95°C. Time to reach the desired pressure and also decompression was approximately 5-10 seconds. PE activity was determined by a modified titrimetric method. PPO activity was measured spectrophotometrically by using catechol as substrate and by observing the increase in A420. Response surface methodology was applied for simultaneous analysis of the effects of variables. The residual PPO activity in apple juice (pH=3.67) and PE activity in orange juice (pH=3.76) after treatment at 440 MPa and 50°C for 60 min were obtained as 9±2.25% and 7±0.18%, respectively. A synergistic effect of pressure and temperature is noted according to the statistical analysis. PE is more pressure-sensitive and temperature sensitive than PPO.Inactivation of PPO and PE can be accurately described by a first order decay. The inactivation studies were limited at pressures between 300 and 600 MPa, since this range was sufficient for the microbial inactivation. For the complete inactivation of the enzyme, instead of using pressures higher than 600 MPa, the use of HHP treatment together with a mild thermal treatment was possible to accelerate enzyme inactivation. After HHP processing, significant changes in appearance, color and nutrients of the fruit juices were not determined if compared with that of the fresh juices.
Session 91E, Nonthermal Processing: Nonthermal processing of foods
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