Modelling the influence of storage temperature and time after cutting on respiration rate of diced red onions (Allium cepa L. cv. Vermelha da Povoa)

Ready-to-use diced onions are very convenient to final consumers and food service companies due to unpleasant pungency and lacrimation effects during bulb cutting. Nevertheless maintaining freshness and functional quality of diced onions is a challenge in the food industry. Thus it is important to know and model the influence of external factors on the product respiration phenomena in order to better control product deterioration. The respiration rate (RR) of diced red onions (Allium cepa L., cv. Vermelha da Povoa) was studied over a period of storage time after dicing at different temperatures (4, 8, 12, 16 and 20 degrees C) under a normal atmosphere. At each of the tested temperatures, RR for both O-2 and CO2 showed an exponential increase over time. This effect was enhanced with temperature. It was further observed that both the initial RR and reaction rate constants changed with temperature according to an Arrhenius-type equation with identical activation energy. This effect was incorporated in the primary model and the fit of the global model to experimental data was good (R-2 = 0.94), with normal distribution of the residuals and correlation coefficients between the model constants below 0.85. Results helped establish a global mathematical model describing RR dependency on temperature over a period of storage time after dicing onions that will allow for a proper package design of this product.