Changes Of Quality And Microflora Of Instant Octopus Products At Different Storage Temperatures

As an indispensable part of cephalopods, octopus plays a more and more important role in marine fishery resources. It’s well documented that octopus is a kind of nutrient-rich seafood with higher protein, lower fat and lower calorie. Containing rich natural taurine and trace elements, it is also highly effective in the prevention and treatment of cardiovascular diseases and cancers. Octopus is regarded as a high grade aquatic product and popular in the Mediterranean countries and Asia, particularly in Japan and Korea. Instant octopus products not only keep the abundant nutrition of octopus in maximum, but also have an attractive appearance and a distinctive taste. However, after death, cephalopods undergo very rapid protein degradation due to endogenous and bacterial enzymes. In addition, the bacterial composition is more complex in such kind of food without heating. The issue of quality and safety has become the bottleneck problem of octopus products development and market circulation. Given this, researching changes of quality and microflora of instant octopus products during storage is of great significance.In this study, the nutritional components of the mantle and tentacles of Octopus variabilis were comprehensively analyzed; total viable counts(TVC), total volatile basic nitrogen(TVB-N), pH value, trimethylamine(TMA) and sensory evaluation were used as main quality indicators, and the quality changes of instant octopus products at different storage temperatures were characterized; the changes of bacterial composition and amount were analyzed qualitatively and quantitatively by Metagenomics as well. The main results were as followed:1. The nutritional components of the mantle and tentacles of Octopus variabilis were comprehensively analyzed. The crude protein and crude fat contents of the mantle were respectively 14.47%and 0.55%, and were 13.58% and 0.34% in tentacles; the ratio of EAA/NEAA of two samples accorded with the amino acids mode recommended by FAO/WHO, and Val was the first limited amino acid, the essential amino acids index (EAAI) of the mantle and tentacles were 82.18 and 82.60, respectively; Octopus variabilis was rich in poly-unsaturated fatty acids, and the content of EPA and DHA in the mantle and tentacles were 36.00% and 41.33%, respectively; it contained abundant macro and micro elements, particularly zinc, and in which certain hazardous substances were lower than the standard. An overall look into data obtained showed that Octopus variabilis was a kind of nutrient-rich seafood with higher protein and lower fat and was worthy to popularization.2. Quality changes of instant octopus products at different storage temperatures were analyzed through biochemical and modern instruments analysis techniques. The TVC of instant octopus products at 25,15 and 5℃ exceeded the limit of consumption (6 lg cfu/g) on 4,11 and 80 days, respectively. At the beginning of storage, the TVB-N value was about 13.21 mg/100g flesh, and the TVB-N values at 25,15 and 5℃ exceeded the proposed acceptability limit of 30 mg N/100 g on 5,15 and 81 days, respectively. According to the results of sensory analysis, the shelf lives(SL) at 25,15 and 5℃, respectively, were 5,15 and 80 days. Contrary to the TMA value, the pH value of all groups showed an overall decline during the storage, and the higher the storage temperature was, the more apparent the trend was. However, the TVC and TVB-N value at-5 ℃ remained lower than the limits up to 90 days of storage and the SL was far longer than 90 days. Therefore, lower storage temperature had a significant effect on maintaining quality and extending shelf life of instant octopus products.3. The changes of bacterial composition and amount at different storage temperatures were analyzed qualitatively and quantitatively by Metagenomics. The results showed that the bacterial flora became more and more uniform during the storage. The bacteria exhibited a greater diversity on initial storage than other microorganisms. The predominant bacterial flora was composed of Enterobacter, Pseudomonas and Leuconostoc. Besides, a certain proportion of Weissella, Flavobacterium and Staphylococcus were also detected. During the storage at 25,15 and 5 ℃, a trend of increasing gram-positive bacteria was apparent, especially Staphylococcus and Weissella. Eventually, the predominant bacteria at 25, 15 and 5 ℃ were Weissella(73.58%), Staphylococcus(S1.22%) and Staphylococcus(33.24%), respectively. However, no significant changes of the bacterial flora were observed during the storage at-5℃ except a slight decrease of Pseudomonas, and the predominant bacteria was Enterobacter (31.37%). In conclusion, storing at-5℃ was conductive to maintaining initial microflora of instant octopus products and inhibiting the reproduction of spoilage bacteria.