The Study Of The Blue Scad Fillet Fat Oxidation During Storage

Oxidative rancidity of fat in food is one of the main reasons for food spoilage. While fish products are rich in polyunsaturated fatty acid, so they are prone to become oxidative rancidity influenced by the factors of air and temperature, which will destroy sensory properties of food and decrease their commodity value. Meanwhile harmful peroxides and free radicals will come out in rancidity process and they can damage people's health even cause carcinogenic effects. In order to establish and control the quality during shelf life of blue scad fillet, systematic study were conducted on the characters of fat oxidation changes during shelf life and the main factors influencing fat oxidation and degradation in blue scad fillet. The research results were as follows:1. Influence of temperature on blue scad fillet AV, POV, COV and TBARS of blue scad fillet were on the upward trend basically at different temperatures during storage. Indicators of fats oxidation in fillet stored at 20℃were evident lowerthan those stored at 25℃(P<0.01, which indicated temperature was a significant factor influencing fat oxidation. The higher the temperature was, the faster the oxidative rancidity of fats was. So it was necessary to provide a temperature as low as possible to store blue scad fillet. As instant snack food, however, blue scad fillet is usually stored at the normal temperature.2. Determination indicators of fats oxidation and correlation analysis of sensory evaluation The quality of blue scad fillet was declining during storage. During shelf life, with increasing storage day brightness of fillet fell, while redness rose and yellowness remained stable. According to the sensory evaluation(sensory scoring, L,a) on blue scad fillet during shelf life and Pearson correlation coefficient of measured value of fat oxidation indicators(AV, POV, COV, TBARS), there were both very significant correlations between AV or TBARS and sensory measured value(︱P︱>0.9), which indicated that each of AV and TBARS can be used as quality indicator for attribute change of blue scad fillet. 3. Influence of content of oxygen on fat oxidation of blue sacd fillet Oxidation indicators of fat(AV and TBARS ) in blue scad fillet stored in the air with 10% oxygen were obvious lower than those stored in the air with 21% oxygen content(CK group) (P<0.05). Fat oxidized on the premise of oxygen existence and concentration of oxygen had a close relation with fat oxidation. If concentration of oxygen in package can be lowered, fat oxidation can be reduced obviously.4. Study on the antioxidant effect of antioxidant on blue scad fillet Fillets were treated with various antioxidants(VE,TP and extract from rosemary) solely at the amount of 0.02% and with combinations of two antioxidants(VE+TP,VE+ extract from rosemary, TP+ extract from rosemary) at equal amount, then synergies were analyzed simply. Study showed that antioxidant effects of every antioxidant group on blue scad fillet were obvious. And antioxidant effect of natural compound antioxidants (TP+ extract from rosemary) was best, which showed that there was positive synergy between TP and extract from rosemary. While AVs treated with compound antioxidants (VE+ extract from rosemary, TP+VE) were larger than those treated with single antioxidant (TP, extract from rosemary), which showed there was negative synergy between two ingredients of compound antioxidants (VE+ extract from rosemary, TP+VE). After studying on the synergistic antioxidant effect of compound antioxidants (TP+ extract from rosemary) on blue scad fillet, such conclusion was reached that antioxidant effect on fillet was optimal when the addition proportion between TP and extract from rosemary was 3:1.5. Study on inhibition of fat oxidation during shelf life of blue scad fillet Through quadratic general rotation experiment design, effect of corporate action on fat oxidation of amount of natural compound antioxidant (X1), content of oxygen (X2) and storage temperature (X3) during shelf life of blue scad fillet can be expressed with equation below: Y2=3.779-0.3779X1+0.3196X2+1.089X3+0.0347X12+0.1089X32-0.1075X1X3+0.09500X2X3Thereamong sequence of factors influencing fat oxidation was storage temperature (X3) > amount of natural compound antioxidant (X1) > content of oxygen (X2). Storage temperature had the maximum impact on fat oxidation, then amount of spraying natural compound antioxidant had medium impact and content of oxygen had minimum impact. There were greatly significant differences for all the three factors. Optimum technology for storage of blue scad fillet was got via experiment: the lower the temperature was, the better the effect on inhibiting fat oxidation of blue scad fillet was. As instant snack food, however, blue scad fillet is usually stored at the ambient temperature. The concentration of natural compound antioxidant (proportion of TP and extract of rosemary was 3:1) added in fillet was 0.2g/kg, and meantime the lower content of oxygen the better the antioxidant effect was. Vacuum packaging, sealing desoxidizer in package and modified atmosphere packaging (MAP) were all effective on declining fat oxidation during shelf life of blue scad fillet.6. Forecasts of shelf lives for blue scad fillet with various packaging forms Calculating from dynamical equation, shelf life of blue scad fillet was 296 days that sprayed with natural compound antioxidant at concentration of 0.02%, packaged at normal pressure and stored at 20℃.And when temperature was 25℃shelf life would be 239 days around, when temperature 30℃life 165 days. Shelf life for fillet was 373 days when desoxidizer was sealed in package and stored at 20℃,when temperature 25℃life 287 days and at 30℃life 190 days. Shelf life was about 369 days when fillet was vacuum packaged and stored at 20℃,when at 25℃shelf life 278 days and at 30℃life 178 days. While shelf life was 409 days or so when fillet was gas packaged (ratio of CO2 and N2 was 3:7) and stored at 20℃, when at 25℃life about 322 days and at 30℃life 216 days around. From the data above, it can be concluded that shelf life of fillet which was sealed with desoxidizer, vacuum packaged and gas packaged (ratio of CO2 and N2 was 3:7) can be lengthened by 26.0%,24.6% and 38.1% respectively than that was packaged at normal pressure.