Research On Freshness And Rheological Properties Of Paralichthys Olivaceus During Storage

In this paper, physico-chemical and textural changes of Olive flounder (Paral-iIchthys olivaceus) in different storage conditions (controlled freezing point, biologicalpreservatives and controlled freezing point combined preservatives) were investigated.The modern means of Matter test were applied for estimating the fresh timeliness andshelf life of Flounder. And the paper provided experimental data and theoretical basisfor the application of such fish preservation technology.Firstly, changes on the freshness indicators as pH, K value, TVB-N, total number ofbacteria, sensory scores, as well as indicators of textual characteristics as tissuestructure, rheological properties and texture profile analysis of Flounder were servedunder controlled freezing point storage, which were compared with the samples underrefrigerated condition. The results suggested that color of flounder fish graduallybecame gray, the surface gradually became viscous, and the muscle became loose; inthe meantime, its springiness and sensory scores decreased. K value and TVB-N rosewhile pH and total viable counts decreased first then increased with the time of storage;the space of the myofibril increased, the tissue structure showed a tendency to rupture,while the changes of elastic modulus and stress-relaxation time are not obvious. But theelastic modulus and viscosity of the samples in freezing point storage was higher thanfresh samples, as the stress-relaxation time and rupture strength was less than freshsamples while the declining trend of rupture strength was obvious. TPA results showedthat hardness, elasticity and chewiness were to a downward trend, but the changing ofthe cohesiveness were not regular. Compared with chilled samples, the indicators of thesamples during freezing point storage were better. The shelf life of freezing pointstorage samples was found to be16d more than chilled samples, which suggested thatthe condition of freezing point could effectively inhibit microbial growth and activityof the enzyme in the meat of Flounder samples, lower the respiratory activity of cells so as to achieve better preservation effect.Secondly, the quality and texture changes of Paralichthys Olivaceus meat duringbiological preservatives at4±0.5℃. Sensory scores, freshness indicators of Flounder,with emphasis on the tissue structure, rheological properties and texture profile analysiswere investigated. The results showed that the changing trend in sensory scored, pH, Kvalue, TVB-N, TVC, rheological properties and tissue structure were similar with thetrend of chilled samples, but the corrupting rate is slower. The change of springinesswhich increased in the early days and decreased soon after was different from thechilled samples’ TPA results, which might be caused by the preservation mechanism ofthe preservatives. It is obviously that the shelf life was prolonged9days by thebiological preservatives compared to4days without biological preservatives.Biological preservatives can significantly keep the natural quality through itsantibacterial, antioxidant and inhibition of enzyme activity.Finally, Changes of freshness indicators (pH value, K value, TVB-N, and totalnumber of bacteria), tissue structure, rheological properties and texture profile analysisof Flounder were determined with super-chilling combined with preservatives. Theresults showed that it is dramatically that the condition of controlled freezing pointcombined with preservatives could decrease the rising velocity of pH value, K value,TVB-N, and total number of bacteria. Variation of the elastic modulus for the samplesin the entire storage process is not obvious, but smaller than the controlled freezingpoint samples in the early0-16d; Variation of the stress-relaxation time and viscosity ofthe samples is not obvious either which could be related with complex internal structureof the Flounder fish; The rupture strength deceased with time of storage while it leveledoff late. Compared with the single storage condition as controlled freezing point orbiological preservatives chilled conditions, Shelf life extension under controlledfreezing point combined with preservatives was17days and10days. That is to say, theshelf life was30days which showed that the condition of controlled freezing pointcombined with preservatives has the best preservation effect.