The Application Of NMR And MRI In Surimi Processing And Storage

Freshwater surimi is a new aquatic food ingredients. A kind of elastic gel can be formed when the fish is grinded and smashed into thick fish paste and heated after adding salt and other ingredients. This process can improve the acceptance of the low-value fish by people and add significant economic value of the low-value fish, a promising aquatic food product. This objective of this study is to optimize the surimi production process, and obtain the best-quality surimi products with the least cost. Magnetic resonance imaging technology was used to study the whole process of surimi production process, the moisture changes during the storage process, and the impact of different processing parameters on the water binding capacity and the gel strength of the surimi. Primarily conclusions of the study are as follows:1. The grass carp fish was selected for the production of surimi since it has high protein content, low fat content, is rich in rare elements. The grass carp fish also has a neutral pH which is suitable for surimi gel formation.Therefore, it is a good raw material for the production of surimi.2. Rinsing is an important and indispensable step in the surimi production process. It can not only increase the strength of surimi gel, but also increase the water holding capacity of the surimi. Through the experiments the optimum process is to have two rinse with water and a saline rinse for a total of three rinsings. The changes of the water in the surimi during the rinsing process were studied using the NMR techniques. The results indicated that, the water, saline and alkaline rinse could all improve the water holding capacity of the surimi, and a certain concentration of salt water can dissolve and wash out a portion of the salt soluble protein, but it was not excessive.3. Antifreeze could be effective in preventing aggregation and denaturation of protein under freezing storage conditions, allowed surimi to maintain a good gel strength and texture after frozen preservation. Sucrose and sorbitol could also increase the gel strength of surimi, and sucrose addition of8%to10%or sorbitol addition of4%could achieve the maximum gel strength.4. Grind and smash is an indispensable step in the surimi process. Smash could distruct the fibrous tissue structure of the fish, salt addition could improve the dissolution of salt-soluble proteins, while could improve the penetration of the added seasoning into the fish. Smashing with3%salt concentration could achieve the maximum gel strength, and smashing without addition of salt for5minutes or with salt for20minutes could reach the maximum gel strength. The optimal combination obtained from the experiment was:2%salt content, smashing for5minutes without salt addition and then smashing for another20minutes with salt addition. The study on water movement during the smashing process by NMR indicated that water changes consistently as the surimi gel formation.5. We studied the NMR relaxation parameters, T2*, T11and Ti2,changes of the grass carb fish cake during the process of storage through NMR and MRI technology, and found the total water content of the surimi decreased during the storage, but the water content increased when the surimi asmple started to spoil, especially when the microbial activity was high, the total water content increased significantly. The moisture migrated from the interior to the exterior of the surimi cake during the storage indicating the gradual loss of water holding capacity of the surimi during storage. The experimental results showed that low freezing temperature was favorable to the long-term storage of surimi.