Research On Quality Changes Of Euphausia Superba Under Different Storage Conditions

Euphausia superba has caught increasing attention from scientists all over the world due to its abundant reserves and high nutritive value. Previous studies focused mainly on oil and active enzyme while the quality changes of Euphausia superba under different storage conditions were rarely reported. Therefore, investigation on this subject is of great guiding significance on its processing, business operation and consuming process. Meanwhile, investigation on the mechanism of its quality change can also provide scientific basis for the development of novel preservative agent.By measuring the changes of main nutrient ingredients and adopting methods of sensory evaluation and histological slide observation, this research conducted a comprehensive evaluation on the quality change of Euphausia superba under different storage conditions. The investigation is divided into three parts as follows.Part Ⅰ:Physico-chemical analysis of protein ingredients under different storage conditions.In this part, soluble protein content, amino acid content, enzyme activity of crude protease and its pH value were respectively measured in Euphausia superba extract processed at different temperature and time duration. Changes of protein ingredients under different storage conditions were evaluated by analyzing the rate of autolytic activity.Part Ⅱ:Physico-chemical analysis of lipids ingredients under different storage conditionsOil of the whole krill processed at different temperature and time duration was extracted using chloroform methanol method. After determining the total lipid content and the proportion of phospholipid and astaxanthin in it, we obtained the overall changes of lipid ingredients in Euphausia superba under different processing conditions and then made an analysis of the lipid changes under different storage conditions. Part III:Sensory evaluation and histological slide observation of Euphausia superba under different storage conditionsEach Euphausia superba processed at different temperature and time duration was given a mark according to the sensory evaluation standard. Meanwhile, HE stain was applied to help analyze the quality changes of Euphausia superba under different processing conditions in a macroscopic view.Conclusion:(1) The changes of protein ingredients:The result indicates that, with the time prolonged, the content of soluble protein in Euphausia superba decreases while amino acid content increases. Temperature, on the other hand, mainly affects the degrees of these changes. Meanwhile, the activity of enzyme increases to a peak and decreases thereafter. Temperature, determining when it reaches its peak and whether the activity is strong or weak, is inversely proportional to the two factors. The pH value of Euphausia superba is proportional to time until it remains constant at about8.4.(2)The changes of oil:The total content of lipid first decreases and then begins to increase at12h due to the free fatty acid. And the speed of lipolysis increases with the rise of temperature. The content of phospholipid is comparatively constant (keeping1:2with the total content). The content of astaxanthin, however, increases with the drop of temperature, which indicates that the rise of temperature can accelerate the oxidation of astaxanthin.(3) The analysis of sensory evaluation indicates that, during the krill-related food processing, time and temperature are key factors to guarantee good quality. Krill should be processed within3h when it is0-4℃, and within1h if it is above10℃. Through histologic slide observation, it is found that with time prolonged, the closely-arranged muscles of Euphausia superba gradually evolves some interspaces and eventually break into small fractures. Moreover, his trend increases with temperature rising or time prolonging.