预冷处理对冻罗非鱼片品质的影响

Effect of Pre-cooling Treatment on Quality of Frozen Tilapia Fillets

拟在现有冻罗非鱼片工艺中加入预冷工序。将新鲜罗非鱼片用冰水浸渍,放入不同温度(-4、-7、-18℃)条件下冻藏,定期测定pH值、色差、失水率、挥发性盐基氮(total volatile base nitrogen,TVB-N)值和质构等参数,分析预冷对冻藏品质的影响。结果显示,预冷对p H值影响最显著的温度为-7℃,10~20 d时-7℃预冷处理组罗非鱼片p H值仍在继续下降,而其对照组已开始回升。随着贮藏时间延长,罗非鱼片色差亮度L*值与红度值a*均呈现下降趋势,且贮藏温度越低,下降幅度越小,同时发现对照组L*值和a*值普遍低于预冷处理组。同时,贮藏温度越低,失水率越高,30 d罗非鱼片失水率达到最高值,-18、-7℃对照组此时失水率达7.47%、6.82%。-4℃及-7℃预冷处理对罗非鱼片TVB-N值影响较大,20 d后与对照渐趋一致;但30 d时-18℃罗非鱼片预冷处理组与对照组仍有较大差别,TVB-N值分别为8.04 mg/100 g和9.87 mg/100 g。20 d前随贮藏温度降低罗非鱼片预冷处理组与对照组的咀嚼性差异增大,之后则趋于一致。贮藏期间硬度无显著差异,弹性仅在-4℃内罗非鱼片处理组与对照组间有较明显差异,其余差异均不显著(P>0.05)。内聚性的变化因无明显规律不作为评判指标。综上,预冷处理对罗非鱼冻鱼片部分冻藏品质指标有较明显的改善作用,利于保持鱼片品质,可作为生产企业的借鉴。

This study was an attempt to examine the viability of pre-cooling before freezing of tilapia fillets.Fresh tilapiafillets were soaked in ice water prior to frozen storage at different temperatures,which served as a treatment group,and thosedirectly frozen were used as a control group.The pH,color,drip loss after thawing,total volatile base nitrogen(TVB-N)andtexture parameters of the fillets were measured at regular intervals during frozen storage to evaluate the effect of pre-coolingon the quality of frozen fish fillets.The results showed that the pH of fish fillets frozen at?7℃was more influenced bypre-cooking than at other freezing temperatures,and it decreased from day10to20of storage at?7℃but began to increaseagain at other freezing temperatures.Both color L*and a*values decreased continuously during the storage process,andthe decrease was smaller at lower storage temperature.These color parameters were increased by pre-cooling as comparedto control.In addition,post-thaw exudative moisture loss was higher at lower freezing temperature,reaching its maximumvalue on day30of storage,7.47%and6.82%at?18and?7℃,respectively.The TVB-N value of frozen fish fillets at?4and?7℃was more significantly affected by pre-cooling during the first20days of storage,but no significant differencewas observed later.There was a big difference between the TVB-N values with and without pre-cooling on day30of storage?18℃,which were8.04and9.87mg/100g,respectively.An increased difference in chewiness between the treatmentand control groups was observed during the first20days of frozen storage at lower temperature,which tended later to beconsistent.No significant difference in hardness was noted at the same temperatures but there was a significant difference inelasticity between the two groups at?4℃(P>0.05),but not at other temperatures(P<0.05).However,cohesiveness waschanged irregularly.In conclusion,pre-cooling treatment can improve some quality attributes of frozen talipia fillets,therebymaintaining their quality.