Comparison of Melting Frost Layers after 2 Frozen Methods in Pork Cuts (longissimus dorsi)

摘要

The frost formation and fusion of ice crystal on complex materials, such as meat, have a great importance, since they modify visible quality characteristics like color, and other important physical changes like thermal conductivity and diffusivity. Furthermore, changes take place in fibber morphology by formation of big ice crystal during freezing. Contribution to frost formation is also due by exchange of heat and humidity during the storage or transportation process due to doors opening and closing. Many authors report working researches over the effect of frost in cold plates, capillaries, or cylinders but not focused in food surfaces. In the food area, the researches was studied over commercial freezers evaluating food weigh lost, or over the compressor cycles efficiency. The aim of this work was to measure the frost formation and melting in meat cuts of 0.5 cm thickness without packaging. Thermal histories were made during freezing. A mechanical freeze chamber and cryogenic process by indirect contact with N_2 were used. After frozen, the meat cuts were observed in a microscope. The frost layer was measured and photographed every 30 seconds until the complete thawing. The thickness and fusion time were determined like an opposite process of frost formation. This is a different way to analysis the environmental effect over biochemical, microbiological and quality meat aspects. Morphological frost difference was found, and the fusion times were different too. The maximum thickness with mechanical freezing method was 1,187 mm and 1.788 mm with N_2. The melting time was 6.5 min, and 3 min respectively. All these results can be useful to complement and understand the complex thermal processes with phase change at low temperatures.