The Mechanism Of Water Holding Capacity Mediated By Protein Oxidation In Dosidicus Gigas During Thawing

Frozen Dosidicus gigas mantle muscle was studied in this paper.The Dosidicus gigas was thawed by traditional thawing methods（water soak thawing,running water thawing,salt water thawing,air thawing and refrigeration）andnewthawingmethods（microwavethawingand ultrasound-assisted thawing）.The relationship between muscle water holding capacity（WHC）and protein oxidation of the Dosidicus gigas was analyzed during thawing.Used hydroxyl radical oxidation system（H₂O₂ concentration:1,5,10,50 mmol/L,respectively）to simulate Dosidicus gigas muscle in vitro,systematically studied the effects of oxidation system on water holding capacity,physicochemical properties of myofibrillar protein,protein structure and conformation,and muscle microstructure,revealed the causal relationship between protein oxidation and WHC,clarified the mechanism of protein oxidation mediated thawing loss.This paper can innovate and enrich the basic theory of aquatic raw materials,and provide valuable fundamental theoretical basis on controlling purge loss of frozen squid during thawing.The main conclusions are as follows:1.Dosidicus gigas was thawed by traditional thawing methods,the results showed that the thawing time of running water method was the shortest way,and then was the salt water thawing way.The thawing loss and cooking loss of the five different thawing ways were significantly different（p<0.01）.Water holding capacity of salt water thawing and refrigeration thawing methods were higher than water soak thawing and air thawing way,and the experimental results of low field nuclear magnetic resonance confirmed these results.carbonyl content,total sulfhydryl content and dityrosine content of the five different thawing way were significantly different（p<0.01）at the sample different temperature points.The results of correlation analysis showed that there was an internal relationship between protein oxidation and WHC during the thawing process of Dosidicus gigas.Comprehensive protein oxidation index,salt water thawing and refrigeration thawing methods were considered to be the most suitable way to thaw frozen Dosidicus gigas.2.Dosidicus gigas was thawed by two new thawing methods which were refrigeration thawing,500,700,900 W microwave thawing and 100,300,500 W ultrasound-assisted thawing.The results were as follow.The thawing time of microwave thawing is obviously less than that of refrigeration thawing,and the microwave power is negatively correlated with thawing time.There was no significant difference in elasticity and cohesiveness among the four thawing methods（p>0.05）,while the hardness,chewiness and resilience of samples by the refrigerator thawing were significantly higher than the microwave thawing methods.The muscle brightness and WHC of 500 W microwave thawing sample were the best.At the same time,There were significant differences in carbonyl,total sulfhydryl,surface hydrophobicity and dityrosine content in samples with different thawing methods（p<0.05）,while the 500 W microwave thawing exerted the lowest carbonyl content,surface hydrophobicity and dityrosine content,the highest total sulfhydryl.In conclusion,500 W microwave treatments are good for maintaining the water holding capacity and delaying protein oxidation during thawing process.The thawing time of ultrasound-assisted thawing is claerly less than 4℃refrigerated thawing,which is proportional to temperature and ultrasonic power.The WHC of U5-5 was the best,followed by U5-3.The L*and b*values of ultrasound-assisted thawing were significantly lower than refrigeration thawing（p<0.05）,and a*values were significantly higher than refrigeration thawing（p<0.05）.With the increase of ultrasound power,L*values gradually decreased and a*values gradually increased.There were significant differences between the effects of thawing methods in terms of hardness,cohesiveness,chewiness,resilience of jumbo squid mantle（p<0.05）,while no significant differences in springiness（p>0.05）.There were significant different in carbonyl content,total sulfhydryl content,surface hydrophobicity and dityrosine content under different thawing methods（p<0.05）.Among them,the carbonyl content of U5-3,U5-5 was the lowest and there was no significant difference（p<0.05）.U5-3 had the highest total sulphydryl content and the least surface hydrophobicity and dityrosine content.In summary,U5-3,U5-5 are good for maintaining the WHC and delaying protein oxidation during thawing process.From the correlation analysis results of protein oxidation and WHC index,there was a certain internal relationship between protein oxidation and WHC during the thawing process of Dosidicus gigas.3.Hydroxyl radical oxidation system（H₂O₂ concentration:1,5,10,50mmol/L,respectively）was used to simulate Dosidicus gigas muscle in vitro,the results showed that:with the increase of oxidation concentration,cooking loss rate,centrifugal loss rate and relative percentage of free water increased gradually,and water retention decreased.Compared with the control group,carbonyl content of Dosidicus gigas myofibrillar protein increased significantly,when the concentration of H₂O₂ reached 50 mmol/L,the carbonyl content increased by 53.59%（p<0.01）,total sulfhydryl content decreased significantly,surface hydrophobicity and dityrosine content increased significantly（p<0.01）.Some chromogenic amino acids decreased,resulting in a decrease in the absorption peak of the ultraviolet（UV）absorption spectrum of the protein,the fluorescence intensity of the source decreased,and the maximum absorption peak of endogenous fluorescence shifted red.From the sodium dodecyl sulfatepolyacrylamide gel elctrophoresis（SDS-PAGE）,it was found that not only the crosslinking but also the degradation occurred during the oxidation process.The Raman spectrum showed that the content ofα-helix decreased and the content ofβ-sheet,β-turn and unordered with the increase of H₂O₂concentration.The degree of damage to the muscle microstructure increased,resulting the muscle fiber spaces dilatation,loose structure.The fragmentation was gradually occurred,the myofibril fragmentation index（MFI）was increased,the index of 50 mmol/L was about 1.5 times than the control group（0 mmol/L）.