Effects Of Immersion Chilling And Freezing With Different Velocity And Subsequent Frozen Storage On Characteristics Of Grass Carp Cubes

Freezing processing is one of the most common and fundamental processing techniquesin the fish processing industry, but there is a decrease in water holding capacity and texturecharacteristics of the fish protein after freezing and thawing. Immersion freezing and chillingis a new low temperature processing technology. The paper investigated the quality changesof grass carp cubes under different freezing ways and explained from the ice crystals andprotein denaturation, studied the quality changes（physicochemical characteristics and textureproperties） of grass carp cubes and refrigerant impregnation into grass carp block duringimmersion chilling and freezing with forced convection at-20℃,-30℃under differentvelocity of refrigerant, the effect of ice crystals and the protein denaturation on water holdingcapacity and texture characteristics of grass carp cubes with different ICF conditions duringfrozen storage. The major studies were as following:1. The quality changes of grass carp cubes were investigated under various freezingprocessing of immersion and chilling freezing and traditional air-blast freezing. Resultsindicated that the freezing rate of ICF with ternary refrigerant exhibited1.54-fold higher thanthat of air-blasting freezing, and1.28-fold higher than that of ICF with alcoholic solutionworked as the refrigerant. Compared with the other two freezing processing, grass carp cubesfrozen in ternary refrigerant had higher content of salt-soluble protein, less reduced Ca²⁺-ATPase activity, drip loss and cooking loss, DHpeakΙ, П, Ш, formed smaller ice crystals andequivalent diameter during the freezing process. The results of physicochemical and texturalcharacteristics indicated that Immersion and chilling freezing assisted to reduce thedenaturation of fish protein, and the results of frozen grass carp cubes by ICF in ternaryrefrigerant exhibited this processing was the optimum to remain the inherent characteristics offoodstuff.2. The quality changes （physicochemical characteristics and texture properties） andrefrigerant impregnation into grass carp block during immersion chilling and freezing （ICF）with forced convection at-20℃,-30℃under different velocity of refrigerant were studied.Results indicated that, when velocity of refrigerant in ICF reached14.9L/min at-20℃and 11.2L/min at-30℃, the decrease of refrigerant impregnation, drop loss rate and Ca²⁺-ATPaseactivity were not remarkable, and no significant change was observed in hardness, gumminess,springiness, respectively, and maintained the optimum quality of grass carp cubes. From thedecrease rate of DHpeak Ι, DHpeak П and DHpeak Ш, the denaturation degree of myosinprotein was larger than sarcoplasmic protein and actin in the freezing process. DSC analysisresults showed that DHpeak Ι had a apparent positive correlation with Ca²⁺-ATPase activity,the higher Ca²⁺-ATPase activity was, the higher value of DHpeak Ι was.To some extent, the increased velocity reduced the impregnation of solute into the grasscarp cubes.3. The laws for quality changes of grass carp cubes were studies during frozen storage at-18℃. With the increasing of the frozen storage time, hardness, chewiness, resilience of grasscarp cubes declined, salt-soluble protein content and Ca²⁺-ATPase activity decreased. Thedenature degree of actin was lower than myosin and sarcoplasmic protein. There was asignificant increase in the area and equivalent diameter of ice crystal （P<0.05）, but roundnessof ice crystal did not change significantly （P>0.05）. Grass carp cubes with9.9L/min at-30℃had lower TBA value, L*and b*value, maintained better texture which further illustrated thechanges of characteristics related to hold water and protein denaturation. The rate of DHpeakΙ, П, Ш decrease was slower, the denature degree of protein was lower. The area of ice crystalwas2450μm²and equivalent diameter was42μm when frozen to12weeks. The large numberof small crystals can prevent tissue deformation and damage yielding a good quality of theproduct.