Effects Of Ultra-high Pressure Treatment On The Quality Of Grass Carp Meat And Surimi

The aquaculture production of grass carp is the largest in China.Surimi is one of aquatic food that very popular among consumers. Ultra-high Pressure(UHP) technology has many advantages, such as bactericidal action, inhibitive enzyme activity, extend shelf-life, keep nutrients, improve the quality of surimi gel. So UHP has broad application prospects in food processing and preservation. In this study, the effects of UHP on the quality of grass carp and gel properties of grass carp surimi were investigated.The effects of ultra-high pressure(UHP)(0.1,100,200,300,400 and 500 MPa for 10 min) on the quality of grass carp were investigated by examining the total viable counts, TVB-N value, TBA value, texture, color, microstructure, volatile odor and taste. The results showed that total viable counts of grass carp were reduced significantly by UHP treatment. Meanwhile, TVB-N value showed a trend of decrease with the pressure enhancing, while TBA value showed a trend of increase. After the process of 300 MPa, TVB-N value was decreased by 12.09% and TBA value was increased 0.7 times. Hardness and chewiness increased with the pressure enhancing, and could be improved significantly(p<0.05) when pressure exceeded 200 MPa. An increase in pressure resulted in an increase in total color difference,meanwhile L* value and whiteness were markedly improved with pressure beyond 200 MPa. Scanning electron microscopic(SEM) demonstrated that structure of grass carp muscle with UHP treatment were different obviously from that of control. Lipoxygenase activity of grass carp was inhibited significantly by high pressure treatment, cathepsin D and lipase activity did not change evident, cathepsin B activity was restrained significantly when pressure exceeded 300 MPa. The increase of TVB-N value was delayed by 300 MPa treatment during cold storage, and the shelf life was extended from 10 days to 16 days.The changes in flavor compounds of grass carp with different pressure treatment were investigated. The results showed that the content of IMP in the samples treated by 100 and 300 MPa was markedly improved. The effects of different pressure on free amino acids were various, indicating that after treated with 100, 300 and 400 MPa, the changes in free amino acid content of grass carp was not obvious(p>0.05), while the total amount of free amino acids in the samples treated by 200 and 500 MPa was decreased significantly. The results of principal component analysis in electronic nose and electronic tongue showed that the volatile odor of grass carp treated by above 300 MPa were changed, and the taste profiles of the grass carp treated by 200, 400 and 500 MPa were different slightly from the control group. The amount of volatile compounds detected in the sample of six groups was 32, 31, 35, 41, 44 and 40, respectively, and aldehydes, ketones and alcohols were found as the main substances. After the process of UHP, the relative content of alcohols was reduced prominently, but aldehydes and ketones was improved significantly, as well as the kinds of aldehydes and ketones was increased when pressure exceeded 200 MPa.The effects of pressure, time and content of potato starch on the gel properties of grass carp surimi were studied. Gel strength of grass carp surimi were reduced significantly by UHP treatment. It was maximal in the group of 300 MPa, and showed a trend of decrease when pressure exceeded 300 MPa. Hardness and chewiness were improved observably, however the change of springiness and cohesiveness were not obvious when pressure beyond 300 MPa. Whiteness and water-holding ability of surimi increased with the pressure enhancing. The change on gel properties of grass carp surimi were not apparent when the time above 10 min at 300 MPa. In terms of content of potato starch, gel strength of surimi could be improved by starch, and it was greatest in the group that starch content was 8%. Textural properties of surimi samples had improved significantly with the content of starch exceeded 4%. The rangeability of whiteness was smaller, and difference of water-holding ability was not significant when content beyond 6%. Then, on the basis of single factor experiment, UHP technology of surimi had been optimized by response surface method. The result showed that the best UHP technology were: 340 MPa, 12 min, starch content 8%, and in this condition the gel strength was 421.07±19.13 g×cm.The change on sulfhydryl content, solubility of gel, SDS-PAGE, microstructure and secondary protein structure of grass carp surimi treated by different UHP conditions were analyzed. The sulfhydryl content was reduced when pressure exceeded 200 MPa, and the difference of sulfhydryl content was not obvious when time beyond 10 min at 300 MPa. At the same time, solubility of gel was increased with pressure exceeded 200 MPa, as the extension of time it showed a trend of increase slowly. Compared to control group, the intensity of myosin heavy chain had weakened slightly by enhance of pressure and extension of time. The microstructure of grass carp surimi that treated by pressure surpassed 200 MPa had becomed smooth, compact and balance compared with the surimi of control group. The results of infrared spectroscopic analysis showed that β-sheet was the main secondary structure in the grass carp surimi. After UHP process, secondary protein structure occurred rearrangement, and content of random coil were significantly increased. Comprehensive Analysis, the surimi gel properties could be improved when the pressure exceeded 200 MPa through destroyed of hydrogen bond, increased of disulfide bond and other reasons.