Effects Of Ozone Induced Myofibrillar Protein Oxidation On The Water-Holding Capacity In Grass Carp Surimi Gel

The water-holding capacity in surimi gel is one of the most important factors that influence the quality and economic value of surimi-based products,so how to improve the water-holding capacity of surimi gel has always been a research focus in aquatic products processing both at home and abroad.Deodorizing by ozone is one of the key progress in the production of fresh water surimi,however,the effects of ozone on surimi protein oxidation have received little attention,and the effects of ozone on surimi gel properties and water-holding capacity are still unclear.This study investigated systematically the effect of different concentrations of ozone water rinsing on the color,aroma characteristics and myofibrillar protein oxidation of grass carp and further discussed the mechanism of ozone-mediated protein oxidation on water retention of surimi gel,which aimed to understand the protein oxidation caused by ozone and its influence on the quality of grass carp surimi gel.It provides a theoretical basis for the application of ozone in surimi industry and the quality improvement of surimi products.Conclusions of this study were as following:1.The ozone water of 0,1,3,5,7 and 10 mg/L was used for rinsing samples during the preparation of grass carp surimi,respectively.The results showed that surimi treated with 3,5,7 and 10 mg/L of ozone water had higher L^*and whiteness values than that of the control and 1 mg/L ozone water group.There were clear differences in the aroma of surimi treated with different concentrations of ozone treatments.An evident loss of fishy smell in the surimi after rinsing compared to the control samples.Thirty-two kinds of volatile compounds were identified from the different surimi samples including 8aldehydes,3 alcohols,1 ketone,1 alkene,16 alkanes,2 aromatic compounds,and 1 other compound.The relatively abundant compounds were aldehydes,alcohols,and alkanes among the volatile compounds.The main volatile compounds that contribute to a fishy smell are hexanal,heptanal,and1-octen-3-ol,and these significantly declined after rinsing with ozone water.In conclusion,the whiteness and flavor of grass carp surimi could be improved by ozone water rinsing.2.Ozone water rinsing could lead to the oxidation of myofibrillar protein in surimi to a certain extent.Incubation of surimi with increased concentrations of ozone water resulted in a gradual generation of MP carbonyl derivatives?P<0.05?.The carbonyl content of the 10 mg/L ozone water group was 1.9 times that of the control group.Additionally,the total sulphydryl content in 1,3,5,7and 10 mg/L of ozone water group decreased by 8.41%,15.02%,11.91%,26.83%and 33.83%,respectively,comparing with the 0 mg/L group.The secondary structure of the protein has changed,part ofa-helix was converted into?-sheet,during this process.The surface hydrophobicity of the MP increased,accompanied by a loss in tryptophan residues fluorescence,indicating ozone-induced protein oxidation caused a conformational transition in the MP of the surimi.Further,the Sodium dodecyl sulfates-Polyacrylamide gel electrophoresis?SDS-PAGE?found that ozone water rinsing caused cross-linking and aggregation of MPs,which could be contributed to the generation of disulfide bonds.3.Effect of ozone water rinsing on the surimi gel quality was analyzed,which prepared through two-step heating method?40?/30min,90?/30min?.The results showed that the L^*and whiteness of surimi gel increased gradually with the increase of ozone water concentration.The ozone water treatment?1⁷mg/L?could raise the gel strength,hardness,gumminess,water-holding property and the proportion of immobilized water in the surimi gel,which was proportional to the ozone water concentration.However,high concentration of the ozone water?10 mg/L?treatment reduced the gel strength,the water-holding property and increased the proportion of free water in the surimi gel.The magnetic resonance image?MRI?also directly proven that more immobilized water was trapped within the structure of gel with the increase of ozone water concentration?1⁷ mg/L?,this was in accordance with the result of WHC and T₂ relaxation distribution.In addition,the gels treated with ozone water?1⁷ mg/L?had more continuous,smooth and denser network structures than that of control group according to scanning electron microscope.At the same time,it was found that with the increase of ozone water concentration?0⁷ mg/L?,the content of hydrophobic interaction maintaining gel structure decreased,while the content of disulfide bond increased significantly.And the decrease ofa-helix content and the increase of?-sheet content in protein gels also were detected by Raman spectra,which all contributed to the formation of an ordered gel structure.4.Combining the "capillary theory" and the Young-Laplace equation quantitatively studied the correlation between the water holding capacity and the pore diameter,surface hydrophilicity,capillary pressure of surimi gels treated with different concentrations of ozone water.The results showed that with the increase of ozone water concentration?1⁷ mg/L?and oxidation degree,the gel pore diameter gradually drcreased,the surface hydrophilicity and the capillary force?water holding capacity?of the gel structure gradually increased.The small gel pore diameter and the high hydrophilic gel surface were beneficial to increase the gel water holding capacity and reduce the cooking loss of gels.It was worth noting that the gel pore diameter fulfilled a key role in the water retention of gel.In addition,the intensity of the O-H stretch band gradually reduced,accompanied by an increase in the intensity of the O-D peak centered around 2500 cm^-1 during the deuteration process.After 3 hours of deuteration,the O-D peak areas of gel samples treated with 0¹0 mg/L ozone water were2.94×10⁶,2.78×10⁶,3.11×10⁶,2.04×10⁶,2.22×10⁶,2.45×10⁶,respectively,indicating high concentration of ozone water treatment could promote the interaction between protein and water in surimi gel.5.In summary,grass carp MP oxidation caused by a moderate concentration of ozone water could improve the gel strength and water retention of surimi gel,the mechanism of which was that ozone-mediated MP oxidation produced the uniform and dense gel structure with small pore diameter by increasing the intermolecular interaction?disulfide bond?of the surimi gel.And it also boosted surface hydrophilicity and capillary force?water holding capacity?of gel structure and enhanced the interactions of protein with water molecules in the gel,which in turn could increase the proportion of immobile water and capillary water in the surimi gel,favoring more water to remain in the gel network structure.