Effect Of Different Pre-frozen Methods On The Quality Of Small Yellow Croaker

Physicochemical properties, such as pH value, TVBN value, activity of Ca2+-ATPase, TBA value, sensory attributes, total sulfydryl, salt solubility protein, texture characteristics, drip loss, electric conductivity and microstructure, were investigated for the small yellow croaker (Larimichthys polyacti) stored at-4.3℃and-18℃(pre-frozen to-18℃by-80℃cryogenic refrigerator, pre-frozen to-60℃by-80℃cryogenic refrigerator and pre-frozen to-60℃by liquid nitrogen, respectively) in order to evaluate the effect of different pretreatments on the quality of small yellow croaker from Zhoushan and provide theoretical basis for extending the shelf life of small yellow croaker. The main results of this study were as follows.(1) The small yellow croaker showed to be water of77.13±2.35%, fat of3.08±1.21%, protein of17.54±2.13%, ash of1.04±0.65% and others of1.21±0.58%according to the determination of basic contents.(2) The freezing point of small yellow croaker was investigated to be-2.3℃, and the partial freezing temperature was set to be-4.3±0.5℃.(3) According to the analysis of physicochemical propertie, such as pH value, TVBN value, activity of Ca2+-ATPase, TBA value, total sulfydryl, salt solubility protein, texture characteristics, drip loss and electric conductivity, with the prolong of storage time, the pH value decreased first, then increased, TVBN value, TBA value, drip loss and electric conductivity increased gradually with the values of the sample treated by liquid nitrogen increasing at the slowest rate. The activity of Ca2+-ATPase, total sulfydryl, salt solubility protein, hardness, springiness, chewiness and resilience decreased gradually with the extension of storage time and the values of the sample treated by liquid nitrogen decreasing at the slowest rate. The above results suggested that the quality of small yellow croaker were deteriorated during storage time and the treatment of liquid nitrogen kept the freshness and prolonged the shelf life of small yellow croaker.(4) The sensory attributes, such as colour, flavour and taste of the steamed small yellow croaker frozen by different methods were also investigated. The results demonstrated that the sensory assessment of small yellow croaker decreased with the extension of storage time, and the samples treated by liquid nitrogen still at high level after seven month.(5) According to the analysis of the microstructure of small yellow croaker pre-frozen by different ways, the results demonstrated that the structure of fresh small yellow croaker shown to be close, there was no obvious gap at the muscle fibers. The gap at the muscle fibers became more and more obvious with the extension of storage time, and the gap became flake at last, while the structure of samples treated by liquid nitrogen still shown to be close and no obvious gap after seven month.(6) According to comparison of the quality of small yellow croaker pre-frozen by different methods, the results shown that the quality of small yellow croaker by partial freezing had no obvious difference with the groups by freezing storage in nine days. The quality of samples treated by liquid nitrogen was better than other groups among the freezing samples after seven month, ssuggesting that the treatment of liquid nitrogen had obvious advantages in keeping the quality of small yellow croaker.