| Ultra-high pressure technology(UHP) is now widely used in the food industry, because compared with the traditional heat treatment sterilization technology, it is a cold sterilization technique that can extent the shelf life of food with fewer damage on the color, fragrance, taste, and nutritional components of foods. But now the application of ultra-high pressure technology in meat products is limited due to the increased lipid oxidation resulted from high pressure treatment. The reasons for the increased lipid oxidation under high pressure in meat still remain not very clear now. According to some reports which may be associated with the release of metal ions, damages to cell membranes or cooperative actions of denatured proteins under high pressure. There are some antioxidant enzymes in meat, such as superoxide dismutase, catalase, and glutathione oxidase which may play an important role in anti-oxidation or inhibit of lipid oxidation in meat. High pressure treatment will inevitably affect the activity of antioxidant enzymes in meat, considering that antioxidant enzymes are very important for lipid oxidation in meat, the change of their activities would certainly lead to corresponding changes in meat quality. However, to date, studies on these effects have not been reported. In order to study the relations between antioxidant enzyme activity and lipid oxidation in meat after high pressure treatment, first of all it is necessary to study kinetics changes of antioxidant enzymes under high pressure treatment; in addition, now it is a trend that high pressure in combination with certain temperature treatment is mostly applied in meat products. Therefore, the longsissimus muscles were treated under different pressure, temperature, and time, then the activity changes of three antioxidant enzymes were studied. Thus laying a theoretical foundation for the further application of high-pressure technology in meat processing.1. The glutathione peroxidase(GSH-Px) activity of pork under different pressure(100 ~ 750MPa) combined with different tempreture(25 ~ 55 ℃) were determined, and the ultrahigh-pressure inactivation kinetics of GSH-Px was researched in the further study. The results showed that the deactivation constants of GSH-Px in pork was increased with the increasing of pressure when treatment tempreture was at a certain range(25℃≤T≤40℃ or 55℃). Under these treatment temperatures the reaction activation volume was negative in the various temperature conditions and the absolute value of the reaction activation volume was increased with the increasing of tempreture. The GSH-Px has the minimum inactivation constants(the highest pressure stability) at 400 and 300 MPa when treated at 45 and 50℃ respectively. The inactivation constants of GSH-Px had minimum value at 40℃(the highest tempreture stability) when treated at 400MPa~650MPa. The inactivation constants of GSH-Px increased with the increasing of tempreture when treated at 700 MPa and 750 MPa. The activation energy values were all positive when pressure and tempreture ranged in 550~750MPa and 25~35℃ respectively. The activation energy increased with the increasing of pressure at the range of 550~700MPa while had the minimum value at 750 MPa.2.The superoxide dismutase(SOD) activity of pork under different pressure(400 ~ 750MPa) combined with different tempreture(20 ~ 60 ℃) were determined, and the ultrahigh-pressure inactivation kinetics of SOD was researched in the further study. The results showed that at a constant temperature(20℃≤T≤60℃), the deactivation constants of SOD in the pork was increased with the increasing of pressure. The reaction activation volume Va was negative in the various temperature conditions, which showed that the inactivation constants of SOD increased with the increasing of pressure. The absolute value of SOD reaction activation volume was minimum at 40℃ and 60℃, which showed that the pressure had the minimal effect on ultrahigh-pressure inactivation of SOD and SOD had a high pressure stability in these temperature conditions. Throughout the test pressure range(400MPa≤P≤750MPa), the activation energy Ea values were decreased generally, which indicated that the influence of temperature on SOD inactivation constants were weakening with the increasing of pressure.3.In order to study the effect of different test conditions(200~600MPa, 10~30 min and 30~50℃) on the catalase(CAT) activity of pork. Use longissimus muscle as experimental materials and a response surface method(RSM) was applied on the basis of the analysis of the single factor experimental results. The results of RSM showed that pressure and temperature were the most significant factors on the CAT activity. Pressure and temperature as well as pressure and holding time had significant(p<0.05) interactive on CAT activity, while the critical temperatures influencing the activity of CAT linearly decreased with pressure increasing and the critical holding time influencing the activity of CAT linearly increased with pressure increasing. The highest CAT activity processing conditions was 600 MPa, 30℃, 10 min and its activity was 1.679U/mgprot. |
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