Kinetic modeling of ascorbic acid degradation of pineapple juice subjected to combined pressure-thermal treatment

A study was conducted to investigate and model kinetic degradation of ascorbic acid in freshly prepared pineapple juice subjected to various pressure (0.1, 300,450 and 600 MPa)-thermal (30, 75, 85 and 95 degrees C) treatment combinations. Experiments were conducted using a semi-custom made high pressure kinetic tester as well as an aluminum thermal kinetic tester. Thermal degradation of ascorbic acid was described with simple first order kinetics. The thermal rate constants (k (75 _95 degrees c, 0.1 MPa)) and activation energy (E-a) for ascorbic acid degradation reaction varied in the range of 0.004-0.006 per min and 14.22-29.78 kJ/mol, respectively. Within the experimental conditions of the study (300-600 MPa at 30 degrees C for holding times up to 15 min) high pressure processing did not alter ascorbic acid content (535.5-564.5 mg/kg). Combined pressure-thermal treatment (300-600 MPa at 75-95 degrees C) degraded ascorbic acid with increasing thermal intensity and was modeled using first order fractional conversion kinetics model. The lower asymptote value ([A](infinity)/[A](0))rate constants (k(75 _95 degrees c, 0.1 MPa)) and Ea were in the range of 77-85%, 0.108 to 0.138 per min and 17.4-43.8 kJ/mol, respectively. Similarly, pressure sensitivity (Delta V-not equal) was similar to 0 and -2.99 cm(3)/mol at 30 and 95 degrees C, respectively. Knowledge gained from the study can be useful for food processors to optimize high pressure treatment conditions for pineapple juice products. (C) 2017 Elsevier Ltd. All rights reserved.