Study On The Freeze Feature And Effects Of Pickled And Ice-coating Process In Frozen-storage On The Quality Of Catfish

Catfish was the research object, The samples were put in two groups under two different frozen conditions in- 25 ℃ and 50 ℃, Determine the freezing curve respectively, dry consumption rate and drip loss rate were measured after freeze completely thawed, in order to study the properties of catfish fillets freeze at two freezing conditions to be a reference for catfish processing technology. In the freezing process of catfish fillets, the freezing curve was in line with the characteristics of aquatic freeze, the catfish freezing point was-0.7 ± 0.1 ℃, it was within the freezing point range of freshwater fish. Catfish fillets were freezing at two conditions in-25 ℃ and-50 ℃ had different freezing curve,-25 ℃ was slow freeze while-50 ℃ was fast freeze. In the quick freezing in-50 ℃, the catfish fillets through the maximum ice crystals generated area by 10 min, while the time in slow freezing at-25℃ was 31 min, the dry consumption rate and drip loss rate in fast freeze samples were 2.1% and 1.8%,in contrast the two indexes in slow freeze samples were 2.9% and 3.3%. Therefore, in the freezing process of catfish, took quick freeze could make the freeze fish through its maximum ice crystals generated area quickly, reduced freeze damage to the muscle cells and let down the dry consumption rate and drip loss rate of catfish fillets. Q uick freeze had better effects to maintain the quality of frozen catfish.In the study of effects of ice-coating process to the quality of frozen catfish, the catfish samples were divided into the ice-coating group and co ntrol group, each group was frozen in two temperatures at-25 ℃-18 ℃, determined the assessment standards in p H,water holding capacity, volatile basic nitrogen(TVB-N), texture profile analysis(TPA) of each group every 15 days, The results showed that in 90 days frozen storage the p H, water holding capacity, hardness and springiness of each catfish samples reduced in different degrees with the increase of frozen storage time, while TVB-N value went upward trend,; the indexes of samples frozen at-25 ℃ changed slower than the samples frozen at-18 ℃in the same condition; the parameters of control group had a larger change than ice-coating group under the same freezing temperature. The quality of catfish decreased gradually with the extension of frozen time, but the rate of decline was different in different catfish samples groups, the quality of the control group declined fastest in-18 ℃ while ice-coating group in-25 ℃ declined slowest. Freezing temperature had a significant impact on the catfish quality, reduce the frozen temperature could delay the rate of decline in the quality of frozen catfish effectively to maintain the freshness of samples. Compared with the control group by directly frozen, ice-coating could delay the spoilage of catfish better.In the study of effects of pickled process to the quality of frozen catfish, The part of the catfish fillets was made to pickled process, the other part was control group, two groups were frozen in the temperatures at-18 ℃, determined the assessment standards in sensory evaluation,water holding capacity,volatile basic nitrogen(TVB-N), hardness springiness, gumminess, chewiness of each group every 15 days. The results showed that in 90 days frozen storage the sensory evaluation, hardness, springiness, gumminess and chewiness of each catfish samples declined in different degrees with the increase of frozen storage time, while TVB-N value increased gradually; the water holding capacity dropped after the first rise in pickled group samples while it continued to decline in control group samples, that might because of effects of the dehydration on catfish by pickled to make the water in samples reduced in early time and thus the water holding capacity increased gradually, then the water holding capacity went down gradually with the samples began decaying in late storage time; Frozen time is one of the factors that influenced the quality of catfish frozen storage, the assessment standards of pickled group had a smaller change than control group under the same frozen storage time. Based on the above results, pickled process could delay the decaying due to the extension in frozen storage time, Compared with the control group by directly frozen that untreated, Pickled process could keep the fresh degree of the products better and it was a good method to extend storage time of the catfish.