| Kuruma prawn was cultured widely around the world, had characteristics of high yield and abundant nutrition. It could be the materials of sushi after heat treatment. As the major component of kuruma prawn, protein thermal denaturation is an important factor affected the quality of products. In order to improve product quality, it was necessary to research protein denaturation law. There are many literature about physical or chemical changes during heating process, meanwhile the protein denaturation rate could be calculated by the method of food engineering, however the correlation between the rate of protein denaturation and physico-chemical indexes is unclear. The related factor affected protein denaturation were not only heating temperature and time but also heating methods. Forecast and control the protein denaturation degree is a hot topic.Taking the kuruma prawn as raw materials, prawn meat protein denaturation dynamics model and three dimensional distribution were researched. Changes of physico-chemical during boiled and microwave heating were studied. Relationship between protein denaturation rate and the physico-chemical changes under boiled heating were analyzed. The main research contents and results were shown as follows:(1) DSC was used to measure the protein heat absorption curve. Thermodynamic parameters such as activation energy and pre-exponential factor were calculated by DSC-dynamic method. Protein denaturation kinetic model was established with primary chemical kinetic equation. Arrhenius equation and temperature distribution model was combined to establish a three-dimensional model of the protein denaturation. Internal protein denaturation distribution and visualization were studied.The result showed that three discernible peaks were seen at 48.62±1.89, 65.45±1.32 and 81.29±1.86℃. Peaks 1 and 2 correspond to myosin and sarcoplasmic denaturation,and peak 3 was associated with actin denaturation. Activation energies and pre-exponential factor for the denaturation of myosin(183.17 k J/mol, 1.05×1030/min),sarcoplasmic(178.75 k J/mol, 3.58×1026/min) and actin(380.50 k J/mol, 1.78×1059/min)were calculated by DSC-dynamic. Simulated and measured temperature curve had great goodness of fit. The accuracy of the model was verified. At low temperatures51 ℃ heating, myosin gradual denatured, while sarcoplasmic protein and actin was not degeneration. Myosin was denatured faster under the higher heating temperature,while sarcoplasmic protein and actin gradually denatured.(2) Samples were taken out when the non-denaturation ratio of myosin(51℃),sarcoplasmic(68℃) and actin(85℃) were 1.00, 0.75, 0.50, 0.25, 0.00 and the end-point. The effects of protein non-denaturation ratio on weight loss, mass loss,stress, color, protein components, ATPase activity, total sulfhydryl content and protein solubility were investigated. The relationship between physicochemical changes and total protein non-denaturatio ratio were explored.With the decreasing of protein non-denaturation ratio, weight loss, stress and colour changed significantly(p<0.05) at the beginning of heating process. SDS-PAGE electrophoresis showed that changes in protein fractions relatively slowly under 51℃,myofibrillar proteins and sarcoplasmic protein bands continued to decline with temperature rise, which indicating that myofibrillar proteins and sarcoplasmic aggregates and formed insoluble macromolecular. The total sulfhydryl content was significantly reduced in the early heating(p<0.05). ATPase activity mainly trend to descend with the increasing protein denaturation degree. But changes of Mg2+-ATPase activity during 51℃ heating showed no apparently, it needs continue studying. During heating treatment, the protein structure was damaged, ionic bonds reduced while hydrophobic interaction enhanced with the increasing protein denaturation. However, hydrogen content need explored. There was a high relative coefficient(-0.9) between stress, color values, hydrophobic interactions and protein non-denaturation. Mg2+-ATPase activity, total sulfhydryl, ionic bond and total protein non-denaturation rate had higher correlation under 68℃ and 85℃ heating.(3) Under microwave constant power heating, the temperature at the center of the shrimp was maintained at actin and myosin denaturation temperature, changes of physical and chemical properties of prawn were studied.The results showed compared to the boiled heating, microwave heating was more rapidly to achieve protein denaturation temperature. The weight loss, stress and color values were rose with the prolonging of the microwave heating time. Although the trend was the similar under two heating methods, Changes of stress were relatively flat. Under high temperature conditions, a*, b*changed significantly(p<0.05). With the extension of heating time, myosin heavy chain and actin disappeared while sarcoplasmic protein bands decreased, changes were more obviously. There was no significant difference in total sulfhydryl content(p>0.05) under both temperature heating end-point; Ca2+-ATPase activity decreased first, then leveled off(p>0.05),Mg2+-ATPase activity continued to decrease. Ionic bond was reduced, hydrophobic interactions was enhanced, this was similar to that in boiled heating. Changes in hydrogen bonds still different with the previous research. |
