Study On Quality Changes Of Tuna During Steam Cooking Processes

Tuna meat is tender,delicious,high protein content,rich in DHA and EPA and other biologicially active polyunsaturated fatty acids,is recommended one of the three fish nutrition by the International Nutrition Association.Steam cooking is a very important process in tuna industry,control of the unit operation of atmospheric steam cooking is critically important to producing cooked muscle for tuna industry.The thermal change and mass and moisture loss which occur during this processing step significantly impact final products yields and quality.First of all,the heat transfer characteristics of tuna meat in the atmospheric pressure steam heating have been studied.Determination the 4cm thick pieces of tuna in the center temperature heating process changes over time.The results showed that:the center of tuna meat temperature with heating time and increasing the initial heating up faster rate than the latter.Secondly,the thesis study on the protein thermal denaturation temperature.of tuna back muscle by DSC.The results showed that:the myosin thermal denaturation temperature is 48.09℃,the thermal denaturation of collagen temperature is 54.53℃,and the actin thermal denaturation temperature is 64.70℃.Third,the physical and chemical characteristics in tuna meat during the cooking process have been studied.Tuna meat heated to the center temperature at 4,10,20,30,40,50,60,70 and 80℃,and measure the weight,moisture content, size,pH,protein components,the actomyosin's Ca2 +-ATPase activity, surface hydrophobicity,reactive and total sulfhydryl base as well as its solubility,the process of inspection in the heated center of the indicators with the temperature change trend.The results showed that:the cooking loss and moisture loss rate as the heating time and the center temperature increasing, and growth in the early heating faster,the weight loss rate and moisture loss rates at 80℃is respectivelye:19.86% and 14.43%;the size of fish has a lot of changes in the heating process,the tuna fillet skrinkaged in the length,and the shrinkage rate is 24.62%,but the width and thickness has occurred in varying degrees of expansion,the expansion rates are as follows:12.27% and 22.03%; pH value increases with the center temperature rising,rising from an initial 5.97 to 6.53 at the end of the heating;the composition of muscle protein is changed distinctly,water-soluble protein and salt-solube protein distinctly decreases with the temperature increases,however the alkali-soluble protein is increased,in addition,the alkali-insoluble protein is decreased above 50℃and the non-protein-nitrogen is increased slightly;the actomyosin's Ca2+-ATPase activity increased continuously,and above at 50℃the enzyme activity could not be detected,the total sulfhydryl base steady decline as the center temperature,the activity of sulfhydryl decrease and then increase the base first and then decrease,the overall is still downward trend, the surface hydrophobicity increased first and then decline in the content of actomyosin was a downward trend.Finally,the texture changes of meat tuna in the heating process have been researched.The results show that:the texture of the tuna changed dramatically in the heating process.The hardness,chewiness and cohensiveness show an increasing trend in both,but when the center temperature reaches 70℃, the values of these three all decline.The springiness has a downward trend during the heating process,and decline faster in the early stage,above 50℃the change is not obvious.Combination of these factors,under the product achieve the purpose of thermal processing,the endpoint temperature should be controlled at 65~70℃in order to ensure product quality and yield, and to avoid unnecessary energy consumption.