Effects of two microwave heating treatments on gel properties of silver carp surimi
The gel properties of surimi products are the comprehensive expression of gel strength, water holding capacity and whiteness, and are also important indicators to measure their quality. The gel properties depend on the formation and processing methods of surimi gel. The formation process of the surimi gel mainly consists of three stages: gelation stage before 50 degree, and the myofibrillar protein dissolved under the action of salt, forming a loose network structure, that is, sol becomes gel.
At 50~70 C, the gelatinization network structure was gradually broken due to the gel degradation stage. This is because the endogenous proteolytic enzymes in fish are most active at this temperature range, resulting in the degradation of peptide bonds in myofibrillar proteins, resulting in a decrease in the gel properties of surimi and seriously affecting the commercial value of surimi. After 70 degrees Celsius, the gel became orderly and non transparent, and the gel strength of surimi increased significantly. Therefore, the heating method directly affects the formation process of surimi gel. At present, the main methods of processing surimi products by microwave heating equipment are water bath heating, steam heating, microwave heating, ohmic heating and so on. The method of water bath heating is often used in actual production, and its heat is slowly transferred from the outside to the interior of the surimi. It not only has high energy consumption and slow temperature rise, but also the temperature of the gel at 50~70 C.
Too long residence time increases the degree of gel deterioration. Microwave heating is the use of polar molecules in materials, in the rapidly changing electromagnetic field to produce violent rotation, friction effect with adjacent molecules, so as to make the material temperature rise. Compared with water bath heating, microwave heating has the advantages of fast heat transfer speed, short heating time, uniform heating and high thermal efficiency. It can quickly pass through the temperature range of 50-70 C, and quickly lose endogenous proteolytic enzymes. Live to avoid the deterioration of surimi gel.
Therefore, microwave heating has a significant advantage in the formation of surimi gel. However, because of the fast heating rate of microwave, the gelation process is not enough enough before 50 degree. The myofibrillar protein molecules can not fully extend, and the stability of the network structure formed by cross-linking is poor, which affects the gel properties of surimi. Therefore, the heating method combining the advantages of water bath and microwave will be more attractive in the processing of surimi products in the future.
Through single factor test, the best microwave heating conditions were microwave power 600 W and microwave time 60 s. At this time, the strength of surimi gel was 608.64 G. Cm, water holding capacity 83.64% and whiteness 75.79. On the basis of single factor and orthogonal test, the best technology of water bath microwave combined heating was obtained by comprehensive scoring method. The components are microwave power 450 W, microwave time 60 s, water bath temperature 40 centigrade.
At this time, the gel strength of surimi gel was 627.37 g.cm, water holding capacity was 85.37%, whiteness was 74.37. Under the two stage heating process of conventional water bath, the strength of surimi gel was 578.22 g cm, water holding capacity was 83.10%, whiteness was 72.67. The results showed that the surimi gel heated by water bath and microwave heating was superior to the surimi cooked by microwave heating alone, while the surimi gel prepared by microwave heating alone was better than that in the two stage heated surimi.