The Quality Change And Control Of Skipjack Tuna During Frozen Storage

Currently,skipjack tuna fishing industry at the Western and Central Pacific is highly competitive.Since China joined the purse-seine fishing,we had a rapid development,while compared to Europe,Japan and other countries,there was still much room for improvement.Preservation techniques played an important role in the whole chain of skipjack industry.This paper studied the quality changes of the purse seine skipjack during frozen storage,compared the effects of different temperatures on its quality,different composition of ice glazing on the quality control and the differences of after cooking quality under different frozen temperatures.The main contents and results are as follows:(1)The effects of different temperature(-18 ?,-25 ?,-33 ?)for skipjack freshness quality changes during frozen storage was researched,the increases of total plate count,total volatile basic nitrogen(TVBN)and hiatamine were slower under lower temperature,the change of pH was not obvious.TVBN and histamine had significantly differences between ordinary and dark muscle.(2)Depending on quality changes of skipjack and using dynamics and Arrhenius equation,the shelf life prediction model was established.The reaction activation energy of TVBN,histamine were 3625.5 J/mol,2867.5 J/mol,respectively.(3)The changes of proteins,fats and color during frozen storage were studied.The quality of proteins in ordinary muscle was higher than dark muscle,including higher water-holding capacity(WHC),myofibril extractability,shear force and lower myofibril fragmentation index(MFI),myoglobin oxidation rate.Temperature on lipid oxidation had significant differences(p<0.05).The myoglobin oxidation rate was lower in-33 ? compared with the other two temperature,the changes of WHC and myofibril extractability were not significant,MFI and shear force trends showed a negative correlation.The whiteness of ordinary and dark muscle both increased.(4)The ice glazing with d-sodium erythorbate and alginate had a favorable effect on quality control,which played an optimal effect on freshness quality,fat and myoglobin oxidation,structural properties of myofibrillar proteins(p<0.05).Adding alginate alone had a certain effect on the quality control,particularly in the control of fat oxidation,was superior to complex salt.(5)The effect of frozen temperature on protein denaturation of cooked skipjack was significant.On analysis of volatile flavor compounds and characteristic odor of cooked skipjack,it found that aldehydes,alcohols and other fishy flavor substances were reduced after cooking.The relative contents and smell substances of the sample-33 ? was minimum,however the relative content of hydrocarbon substances were more then-25 ?,-18 ?.Texture analysis showed that the lower temperature of the cooked skipjack,the greater hardness,gumminess,chewiness and shear force,while there was not significant change in springiness,cohesiveness and resilience.Color analysis found that the difference of cooked fish muscle from different frozen temperatures is remarkable,it assumed low frozen temperature then low whiteness but high redness.