Crescimento de cristais de gelo em tilápia congelada sob diferentes flutuações de temperatura na estocagem

Abstract

There are several studies in the literature, that explain how the freezing rate determines the number, distribution and size of ice crystals in frozen foods; Meanwhile the degenerative effect of temperature oscillations over the shelf life becomes a critical condition that needs to be quantitatively characterized in products of high demand such as fish meat where losses by exudation are appreciable. To reproduce real storage conditions under controlled temperature fluctuations, it is possible to predict the behavior of recrystallization in the food during storage, as well as to subsidize technical information that helps to estimate the shelf life of these products. In this work, Tilapia (Oreochromis niloticus) was chosen as a case study to quantify the relationship between the development of ice crystals and different levels of temperature oscillation.The measurements performed on the micrographs showed that the growth of the crystals still in the first days of storage follows an asymptote whose final value is conditioned only by the level of temperature oscillation imposed on the product, regardless of the initial diameter with which the stock is started. It has also been observed that the growth of the crystals formed during the rapid freezing also evolves rapidly, due to the temperature fluctuations to which they were subjected. This behavior disagrees with some authors who present the theory of a final boundary diameter. In this work, this single level was not identified, but it was verified that the growth of the crystals during the storage reaches different final limit diameters. Thus, statistically significant differences were demonstrated between the four levels of oscillation proposed in this work with a level of significance of p <0.05. Additionally, an empirical model was developed to predict the growth of ice crystals during recrystallization in the samples. The correlation coefficient R 2 = 0.917 indicated that the model provides a satisfactory description of crystal growth when evaluated at temperatures from -18 to -11 °C.