THE ROLE OF OXYGEN PARTIAL PRESSURES ON CHEMICAL AND BIOCHEMICAL PROPERTIES OF RED MEATS

Meat is an essential component of a balanced diet, since it is a source of important nutrients totally or almost absent in all other foods. The distribution and sale of fresh meat products present many critical points, and a major concern is the product waste due to uncorrected practices at all levels (i.e. farmer, slaughter house, processor, distributor, retailer, consumer) and short shelf lives. In addition to good manufacturing practices and consumer education, meat packaging can help in prolonging the shelf life of meat products. In fact, the possibility to determine and control the oxygen partial pressure in the environment surrounding the product is the key factor which influence the maintenance of meat quality and safety. This PhD project aims to evaluate the effect of different oxygen partial pressures on chemical, biochemical and nutritional properties of a variety of fresh red meat products. We selected three specific products: ground beef patties, because their ease of degradation due to the grinding process and the presence of a high quantity of fats; slices from beef meat, because of the homogeneity of their surface; and slices from horse meat, because of its high oxygen sensitivity. As regarding ground beef patties, a low oxygen solution was studied in deep, inserting case ready units (i.e. foamed trays wrapped with a stretch film) in barrier master bags containing a low oxygen modified atmosphere and oxygen scavengers. After the storage at very low oxygen concentration, patties were exposed to atmospheric oxygen (around 20.7 %) and underwent a display life in air for 2 days. The evolution of chemical and biochemical quality of patties stored in anoxia was compared with that of patties exposed to air for the whole storage. Concerning the anoxic packaging solution, we proved the necessity to select proper primary package materials (i.e. tray, stretch film) to allow the correct gas exchanges between the internal and external side of the package. The selection of high permeable stretch films and open-cells trays allowed not only better reduction of patties’ surface pigments during the storage in low oxygen environment, but also better re-oxygenation and colour stability during the display life. Second, the combination of low oxygen storage and display life in air was optimized, and suitable storage and reoxygenation times were identified. The absence of oxygen during the storage resulted in the preservation of both the lipid and protein fraction from oxidation, and the products could be subsequently exposed to air undergoing a 2-days aerobic display life. Slices from beef meat were the second product selected for evaluation, since the muscle structure was not destroyed by the grinding process, and no evident fats were present. First, a comparison between chemical and biochemical quality evolution during low oxygen storage or traditional exposition to the air was carried out. All chemical, biochemical and microbiological indexes showed the benefits of the low oxygen solution, that contributes in the prolongation of meat shelf life, and especially preserves myoglobin functionality. Second, the optimized low oxygen system was compared with a high oxygen solution. In this case, we focused on the protein pattern evolution and their susceptibility to digestive enzymes. Meat stored in the presence of low oxygen partial pressure showed the higher colour stability for the longer storage time, as well as it registered better biochemical and nutritional properties. Finally, a preliminary study on slices from horse meat was carried out. This product requires very low oxygen concentration during the storage because its high myoglobin content makes it markedly sensitive to oxidation by free oxygen. Hence, we performed a comparison of different low oxygen solutions on the chemical and biochemical properties of horse meat. Further investigation is needed to evaluate the effects of this storage on protein pattern changes and digestibility.