Modelling the influence of storage time on the respiration rate of shredded carrots at different temperatures under ambient atmosphere

Measurement and modelling of the respiration rate of fresh-cut produce is vital for the engineering design of modified atmosphere packaging systems. In this work the closed system methodology was used to measure the respiration rate (O₂ consumption and CO₂ production) of shredded carrots as a function of time and temperature. The experiments were carried out at 4, 8, 12, 16 and 20°C for 144, 108, 90, 72 and 54 hours, respectively, during storage under ambient atmosphere. The effect of temperature on respiration rate was well described by an Arrhenius type equation. The respiratory quotient was approximately constant over time, but it showed a polynomial increase with temperature, ranging from 0.51 to 0.83. Under all the experimental conditions tested, respiration rate went through an initial lag phase before increasing sharply as storage time progressed. This effect was enhanced with increasing temperature and was well described by a Weibull model with a shape constant independent of temperature and with a time constant decreasing with temperature according to an Arrhenius type equation. The rate of O₂ consumption at time zero and at equilibrium, at a reference temperature of 12°C, were estimated to be 24±1 and 118±7 mL.kg^-1.h^-1, respectively. The time constant at the same temperature was 52±5 h and the shape constant was 1.6± 0.1. The activation energy, 79±1 kJ.mol^-1, was the same for both the dependence of the time constant and of respiration rate on temperature, and was within the normal range for fresh produce stored in ambient air.