Study On Quality Change Of Mackerel Under Different Storage Methods

Mackerel (Pneumatophorus japonicus) is an important pelagic fish with high nutritional value, which is rich in protein, unsaturated fatty acid and mineral elements.The fish bone in mackerel is few and easy to be removed. So, mackerel is a suitable raw material for canned food. Because of the high content of histidine and unsaturated fatty acids, mackerel is easy to spoilage for the accumulation of excessive histamine and other harmful substances if appropriate actions are not taken after fishing. That seriously affects the subsequent processing of mackerel. In this paper, the nutritional components of back muscle from mackerel are analyzed, and then the freshness of mackerel stored in ice, refrigerated sea water (RSW) system and the frozen library are studied. On this basis, the preservation method that mackerel is precooled in RSW system and then instant frozen is researched. Microbial activity is the main factor for the spoilage of mackerel. So the microbial changes of mackerel stored in RSW system are studied and the dominant spoilage bacteria of mackerel are identified. The results are as follows:In the muscle of mackerel, the moisture content is 77%, followed by 20.56% of crude protein,7.63% of crude fat,0.87% of ash; the muscle of mackerel is rich in mineral elements. Among all the mineral elements, potassium counts for 2772.23mg/kg, which is the highest, followed by phosphorus whose content is 2112.81mg/kg. Besides content of mineral elements that are harmful to human do not exceed the limits.25 kinds of fatty acids are detected from muscles of mackerel, saturated fatty acids counts for 46.90% which is the highest, followed by polyunsaturated fatty acids whose content is 34.17% and monounsaturated fatty acids whose content is 18.93%. Content of DHA and EPA are up to 30.08%. There are 17 kinds of amino acids detected form muscles of mackerel. Among these amino acids, the content of glutamate is 4.31% which counts for the most. And the muscles are also rich in lysine (2.19%) which could make up for the lack of it. The content of essential amino acids is 9.53%. In summary, mackerel is one kind of nutritious and healthy food which is of great significance for regulating people’s diet structure.With the extension of storage time, TVB-N, K value, microorganisms and other indicators are rising, but the sensory quality continuously deteriorats. The relationships between TVB-N, K value and freshness are better than other indicators. The preservation performance of the methods that samples are precooled in RSW system and then instant frozen is better than other methods because it could make the central temperature drop rapidly, inhibiting the biological activity of endogenous and the accumulation of histamine, on the other hand, samples that are precooled could get through-1℃～-5℃ quickly, which is called zone of maximum ice crystal formation, inhibiting the growing of crystal.In this way, that treatment is favorable for the subsequent processing.The microbial composition of raw materials is complicated and the advantageous microorganisms are Pseudomonas sp. and Psychrobacter sp.; With the extension of storage time, the microbial composition of mackerel becomes simple gradually, the content of Psychrobacter sp. and Shew anella sp. increasing rapidly, from 16.67% to 50.00% and 3.33% to 35.71%, respectively. Particularly, the content of Shewanlla sp. increases more than 10-folds. At the end of shelf-life, the proportion of Shewanella sp. adds up to 41.67%, which is significantly higher than other microorganisms. Shewanella sp. is the dominant spoilage bacteria of mackerel under this storage as a result.In summary, mackerel is rich in nutritional materials, but easily to spoilage. Preservation method that combined RSW and instant frozen could make the central temperature of samples decrease quickly, which shortens the time that samples get throuth-1℃～-5℃ quickly, which is called zone of maximum ice crystal formation. So it has good preservation effect. In addition, through the isolation and identification of spoilage microorganisms, it is concluded that Shewanella sp. is the dominant spoilage bacteria of mackerel under storage. The aim of this research is to make reference to the marine preservation and the control of spoilage bacteria of mackerel.