The Methods For Measuring Nitrate And Nitrite In Food By Chemiluminescence

Northern traditional fermented food——sauerkraut and dried sausages fermented as raw materials, nitrat and nitrit was extracted from sauerkraut and dried sausages fermented by microwave and ultrasonic. The best extraction was determined; Nitrate was reducted by the zinc cadmium reduction method,achieved good results; Study on nitrite from auerkraut and dried sausages fermented by chemiluminescence detection,its luminescence mechanism was also discussed.First,the best extraction was determined. Nitrate and nitrite were extracted from sauerkraut and dried sausages fermented by ultra-sonic, and the effects of ratio of sample to liquid, extraction power, extraction time, extraction temperature were studied. Extraction of sauerkraut nitrate, nitrite experimental results show that:In the solid-liquid ratio of 1:50, extraction power of 40%, extraction time of 20min, extraction temperature 40℃under the conditions of extraction, measured nitrite content 3.80mg/kg. Extraction of dried sausages fermented, nitrate, nitrite experimental results show that:In the solid-liquid ratio of 1:50, extraction temperature 60℃, extraction power of 60%, extraction time of 20min under the conditions of extraction, measured nitrite content 12.72mg/kg.Nitrate and nitrite were extracted from sauerkraut and dried sausages fermented by microwave, and the effects of ratio of sample to liquid, extraction time, extraction temperature were studied. Extraction of sauerkraut nitrate, nitrite experimental results show that:in the solid-liquid ratio of 1:10, the temperature is 80℃under the conditions of microwave extraction 5min, measured nitrite content 3.95mg/kg. Extraction of dried sausages fermented nitrate, nitrite experiment showed that:In the solid-liquid ratio is 1:5, the temperature is 60℃under the conditions of microwave extraction 3min, measured nitrite content 13.51mg/kg.Compare ultra-sonic with microwave extraction effect, the experimental resultes show that the microwave can obtain good extraction results.Second, further study was made based on the nitrate method. We used zinc cadmium oscillating water bath method to reduce nitrate and compared with national standard method. We also studied the influence of nitrate-reducing effect by solid-liquid ratio, temperature, time, oscillation frequency, cadmium chloride concentration. Orthogonal was carried according to the results of single-factor experiments. The influence order of factors which obtained by Orthogonal was solid-liquid ratio >oscillation frequency= cadmium chloride concentration> temperature. The solid-liquid ratio has the greatest impact on the reducing effect, followed by oscillation frequency and cadmium chloride solution concentration. Temperature and time have the least impact on the reducing effect. The optimum reducing conditions were solid-liquid ratio 1:2, temperature 50℃, time of 40min, oscillation frequency of 180 turn/min, cadmium chloride solution concentration of 1.5%.The test results and operation diffcult level of this method were compared with standard cadmium column:this method has a better accuracy and practicality and is better than standard cadmium column in testing diffcult level and economic.Finally, to detect nitrite in sauerkraut and dried sausages fermented, based on nitrite can significantly enhance the chemiluminescence intensity of Lumino-KBrO3 chemiluminescence system. The effect of the concentration of reaction substances, acidity, interfering ions etc. on the analytical results was studied. The optimal reaction conditions of chemiluminescence were determined and the results were that:concentration of H2SO4 was 0.05mol/L, concentration of KBrO3 was 0.06mol/L, concentration of lumino was 1.50×10-4mol/L, concentration of NaOH was 0.25mol/L, the linear range was 0.001～10mg/L, the detection limite of NO2- was 8×10-5mg/L(3σ). The determination results of samples(n=11)were showed:dectect nitrite in sauerkraut is 2.84mg/kg, the relative standard deviation was 2.90%, the recovery was 101.00%; dectect nitrite in dried sausages fermented is 10.94mg/kg, the relative standard deviation was 3.55%, the recovery was 99.70%. It is clear that the method is sensitive and selective, comparing with traditionary method, which were rapid, simple, convenient.