Study On The Properties Of Spanish Mackerel Surimi Gels Induced By Ultra-high Pressure

In this thesis, we have studied the effect of washing processes on gel properties of Spanish mackerel. The effect of high pressure treatment on gel properties of Spanish mackerel and compound Spanish mackerel surimi was also investigated. The mechanism of gel formation under high pressure was studied. Besides, the quality changes of the products during storage were also studied.It was observed that the gel strength of alkaline-saline washing process surimi (ASWPS) was 40.19% higher than that of unwashed surimi, and 26.74% higher than that of conventional washing process surimi (CWPS). These increases were associated with the lowered expressible moisture content. However, no differences were found in deformation of gels prepared by different washing processes. Electrophoretic studies revealed that ASWPS had the highest myosin heavy chain (MHC) and actin band intensity. Lightness (L*) and whiteness of ASWPS were significantly higher than those of other samples. From the above results, alkaline-saline washing surimi had the best gel strength and whiteness. Thus, we chose alkaline-saline washing for further study.Alkaline-saline washing process surimi was subjected to ultra-high pressures of 100,200, 300,400,500 MPa for 30 min. The effects of pressure on both springiness and cohesiveness were insignificant. Hardness and chewiness of samples treated at 300 and 400 MPa increased significantly when compared with the control, which increase by 2.68 and 2.40 times at 300 MPa and by 2.87 and 2.70 times at 400 MPa, respectively. However, these values slightly decreased after treatment at 500 MPa. In addition, pressure increased the whiteness of surimi.Actomyosin extracted from Spanish mackerel muscle was subjected to hydrostatic pressure treatment (100-500 MPa,30 min) to investigate the changes in sulfhydryl groups as well as its conformation. Total sulfhydryl group content of actomyosin decreased with the increase of pressure. However, surface sulfhydryl group content of actomyosin increased with increased pressure. Surface hydrophobicity content of actomyosin also increased with increased pressure.Using non-reducing SDS-PAGE analysis, the band intensity of myosin heavy chain and actin became weaken. At 300 MPa, they almost disappeared. Thus,300 MPa would be the critical pressure that induced actomyosin to form regular network structures.The effect of ultra high pressure (100-500 MPa) on gel properties and color of compound Spanish mackerel surimi adding 5%,10% and 15% of concentrated tomato juice was evluated. The results showed that the gel strength was significantly improved at 300-500 MPa. The hardness and chewiness was significantly enhanced and springiness and cohesive was slightly increased at 300-500 MPa. The ultra high pressure improved the whiteness of surimi. With the increase of concentrated tomato juice, the redness of surimi also increased.After high pressure treatment at 400 MPa/30 min, the shelf life of surimi and compound surimi at 4℃was investigated. The total number of bacteria and coliforms derived from the products met the national standards.The investigation on the products during 44 days storage period showed that moisture content, pH value, TBARS value,texture and color had all changed in a narrow range, and sensory evaluation of the products were within an acceptable range, especially the compound surimi product.