Determination of the respiration rate parameters of cherry tomatoes and their joint confidence regions using closed systems

Measuring the respiration rate of fresh produce is essential to design modified atmosphere packaging systems to extend their shelf life. A simple and common way of determining the rates of consumption of oxygen and production of carbon dioxide is to measure their variation in a closed system. In this work the respiration rate of cherry tomatoes was measured in a closed system at 5, 10, 15 and 20 °C. The results could be explained by a constant and temperature independent respiratory quotient (1.20 ± 0.01) and a Michaelis-Menten (M-M) model. The analysis of the joint confidence region showed that the two M-M parameters have a very high collinearity, where data of one single temperature set can provide misleading values. The results showed that parameter K_M could be considered independent of temperature but only has statistical significance at higher temperatures, while V_M varied with temperature with a stronger curvature than an Arrhenius model would suggest, with a parabolic functionality giving excellent results, albeit with no linear term, thus having the same number of parameters as an Arrhenius equation. This was due to a small increase in the rate between 5 and 10 °C. The data analysis clearly showed the importance of assessing the joint confidence region to ensure robust respiration rate model parameters.