| Bluefin tuna (Thunnus orientalis) is one of the biggest also the most precious tuna species. Under the low-temperature freezing storage, meat color would become brown with the extension of storage time, and have a undesirable influence on its commercial value. Color change was primarily caused by the formation of metmyoglobin, and this phenomenon was effected by lots of factors, among which muscle parts, storage temperature and fat oxidation were the three most important. This thesis took three muscle parts of bluefin tuna (Ce-DOM; Ca-VOM; Ce-VOM) as the experimental materials. Firstly, analyze their nutritional compositions and make a further evaluation of essential amino acid. Secondly, explore the optimum operation conditions of chromatic meter. Thirdly, observe the change rule of meat color in three bluefin parts under different freezing storage conditions. Results would be helpful to the storage and preservation of bluefin tuna. The main results obtained in this study were as follows:(1)Analyze the nutritional compositions of three bluefin parts. Results showed that:three muscle parts showed significant differences in contents of each chemical composition (P<0.05), and fat contents for three parts were:Ce-DOM0.24%, Ca-VOM2.32%, Ce-VOM13.81%, respectively. Three parts contained abundant macro elements and micro elements, so did poly-unsaturated fatty acids (PUFA). The contents of PUFA were29.44%,27.14%and30.46%, respectively, DHA and EPA were the two predominant. The ratios of essential to non-essential amino acids for three parts were95.12%,81.45%and88.67%, and EAAI were92.87,86.37and86.37, respectively. Generally, bluefin tuna were proved to be high quality raw materials with high nutritional value.(2)Confirm the best color observation time for three parts, and find the best background for the using of chromatic meter. Results showed that:the best color observation time was:Ce-DOM20-30min, Ca-VOM15-25min, Ce-VOM10-20min, respectively. Taking white paper (L*was93.03) as the background could perfectly avoid the influence of meat thickness on color determination, while white plastic, white ceramic, white paper (L*was90.21) and white paper (L*was95.87) could not reach this requirement. In addition, white paper (L*was93.03) all applied to three bluefin parts.(3)Analyze the change rule of fat oxidation and meat color for three parts storing at the same freezing temperature (-18℃). Results showed that:the extent of fat oxidation (TBA value) was getting higher with the extended storage time, and they all showed the trend to become brown. Higher the fat content, more significant brown. After180-day storage, metMb%for Ce-DOM increased from the initial4.76%to42.45%, still maroon, and a*/b*was0.91; Ca-VOM increased from9.58%to63.64%, becoming a bit deep, a*/b*was0.62; while for Ce-VOM, it increased from25.41%to79.73%, having been totally brown, and a*/b*was0.38. metMb%and TBA value showed highly significant positive correlation (R=0.914, P<0.01), metMb%and a*/b*showed highly significant inverse difference (R=-0.943, P<0.01).(4)Research on the the kinetics of fat oxidation and myoglobin oxidation under different freezing conditions (18℃,-30℃,-40℃,-50℃). Results showed that:with the rise of temperature, the extended storage time, TBA value and metMb%both increased gradually, higher the freezing temperature, worse the results of storage, and higher the oxidation rate of both lipid and myoglobin. The change rule of fat oxidation and myoglobin oxidation for three bluefin parts at different freezing temperature fitted to the zero order kinetic model well, and it could be expressed as "A-Ao=kit". The constant of reaction rate for two chemical reactions in three bluefin parts at different freezing temperature corresponded to Arrhenius equation well, and the fitting coefficient were all very high (R2>0.9). |
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