| Nitrite and nitrate are one category of food additives and they are widely used in curing process of fish and meat food as food color fixative. Although nitrite has the chromogenic、curing、bacteriostatic action, it has great harm. Nitrite can turn the normal hemoglobin to methemoglobin and make it lose the function of carrying oxygen. It still can combination the secondary amine or tertiary amine into strong carcinogen-nitrosamines, which can lead to cancer. In this paper, we established a method of detecting nitrite and nitrate in aquatic products, and did some initial research on the concentration of nitrite and nitrate in storage conditions. In addition, we not only used UHP to study it’s sterilization effect, but also study the effect of UHP on nitrite and nitrate in weever. Specific results are as follows: 1、An reagent-free ion chromatography method was established for detection of nitrite and nitrate in aquatic products, we used Dionex ICS-1500, IonPac AG11-HC(4x50mm) guard column, IonPacASll-HC (4×250mm) anion exchange column, ASRS ULTRAⅡ(4mm) suppressor, KOH isocratic elution and suppressed conductivity detector did qualitative and quantitative analysis. The method was linear for nitrite(0.02-5mg/L) and nitrate(0.2-50mg/L), all the correlation coefficients were over0.999, the detection limit of nitrite and nitrate is0.0186mg/L and0.0277mg/L, and the average recoveries were from60%to81%in weever. In addition, the method was applied for some seafood which came from different markets, we detected the content of nitrite and nitrate, and evaluated their safety.2、Nitrite and nitrate were stable in water at room temperature、4℃、-18℃,their concentration had no significant change within3days. The concentration of nitrite had a rising trend as time prolonging,and nitrate had a similar change trend as time prolonging in4℃and-18℃storage conditions:first rise gradually, then down. The concentration of nitrite had a similar change trend as time prolonging, when the weever was in4℃and-18℃sealed storage conditions:early in a rising trend, medium-term decline, in the later rise again. But nitrate didn’t have significant change. On the whole, the condition of nitrite at4℃was lower than-18℃, higher temperature is helpful to decrease nitrite.Nacl could improve the concentration of nitrite in weever, Vc could reduce it, but the concentration of nitrate had no obvious change and remained stable trend. In3%salt curing process, the concentration of nitrate increased in the first four days, then kept stable; the concentration of nitrite early in a rising trend, medium-term decline, in the later rise again. In3%salt and0.05%Vc curing process, the concentration of nitrate and nitrite increased then kept stable after the11th day. On the whole,0.05%Vc could effectively reduce nitrite in the storage process.3、The more pressure the better bacteriostatic effect, the longer pressure holding time the better bacteriostatic effect. The pressure processing10min, not only can effectively play a bacteriostatic effect, but also accelerate UHP speed and reduce energy consumption. The weever was at0-400MPa,10min, the total plate count increased as time prolonging. With the increase of pressure, the time of the total plate count exceeded106CFU/g prolonged, this showed that UHP can improve the quality of weever during cold storage. Nitrite and nitrate content, retention time and peak shape were almost no influence after UHP. The weever was at0-300MPa, along with the extension of storage time, nitrite dropped; with the decrease of the pressure, nitrite declined significantly. |
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