The Effect Of Ultrasound On Rehydration Quality Of Sea Cucumber And Mechanism Research

Sea cucumber (Holothurian) is rich in nutrients, and has the functions of anti-tumor, anti fatigue, anti coagulation and enhance immune, so it is deeply loved by the consumers in China, Japan, South Korea and other Asian countries. Since sea cucumber is prone to autolysis after capture, the traditional hot processing or cold processing are unable to inhibit the enzyme activity and easy to destroy its edible quality, so dried sea cucumber is the main products in market currently. However, dried sea cucumber needs to be soaked for a long time (2-3 d), difficult to grasp the soaking degree, so that cooking sea cucumber at home is difficult, which restricts the further development of sea cucumber industry. Therefore, ultrasonic was adopted to assist sea cucumber rehydration in this study, to explore the effect of ultrasonic on the quality of sea cucumber after rehydration. And the low-field nuclear magnetic resonance (LF-NMR) and its magnetic resonance imaging (MRI) were used to study the water distribution and status of sea cucumber before and after rehydration under ultrasonic, then the complex microstructure changes of that were combined to explore the mechanism of ultrasonic promoting rehydration of dry sea cucumber, to provide theoretical data for rehydration of dry sea cucumber, further to promote the development of sea cucumber processing industry. The main research contents as follows:(1) Effect of ultrasonic treatment on rehydration of sea cucumber and its kinetic modelThe ultrasonic could significantly improve the rehydration rate of dried sea cucumber, which soaking time by 2-3 d was shortened to less than 6 h. With ultrasonic power increasing or ultrasonic frequency decreasing, rehydration rate and water holding rate of sea cucumber were increasing. The sea cucumber rehydration was fitting by four models include Fickian diffusion law, Peleg equation, Weibull model and First Order equations, to establish kinetics model of sea cucumber rehydration. According to the fitting results of Fickian diffusion law, the effective moisture diffusion coefficient of sea cucumber rehydration assisted by ultrasonic was 0.182 mm2/min-0.197 mm2/min. Comparing the fitting coefficient and fitting curve, fitness of Peleg equation was the highest, could be used to predict the process of sea cucumber rehydration assisted by ultrasonic.(2) Research on edible quality of sea cucumber after rehydration assisted by ultrasonic Dried sea cucumber was treated by different ultrasonic conditions. The results showed that the ultrasonic would not lead to the great loss of sea cucumber nutrients or edible quality decreased greatly. Compared with traditional sea cucumber rehydration, nutrient loss of sea cucumber rehydration assisted by ultrasonic was lower, collagen content was higher, and textural properties was much better. With ultrasonic power increasing or ultrasonic frequency decreasing, the effect of ultrasonic on nutritional characteristics and textural properties of sea cucumber was more significant.(3) The mechanism of sea cucumber rehydration promoted by ultrasonicThis study showed that the ultrasonic could promote the dried sea cucumber rehydration, immobilized water and free water of sea cucumber after rehydration by ultrasonic were increasing with bound water decreasing, rehydration process accompanied by intermigration among three states of water molecules (bound water, immobilized water and free water), the main migration accumulation form was free water. And ultrasonic could change the organic structure of sea cucumber by cavitation and mechanical effect, lead the collagen of sea cucumber to form spatial network structure with small and dense hole, increased the the rate of external water into sea cucumber. The rehydration rate, water holding rate and ratio of free water to total water were increasing with ultrasonic intensity increasing. The micro aperture of sea cucumber increased first and then decreased with the increase of ultrasonic strength, the minimum was 8.127 μm, while the fractal dimension is increasing with ultrasonic strength increasing, in the range of 2.682～2.864. Ultrasonic could promote the sea cucumber collagen form spatial network structure, for which exposing more hydrophilic groups than before, promoting free water from external water exchanged into sea cucumber to transfer into immobilized water more faster, and water holding rate was improved.