Research on Irradiation-induced Degradation Products and Mechanism of Chloramphenicol in Animal Derived Food
Veterinary drugs residuals in animal derived food bring about potential risks on the food safety issues. Food irradiation is a key technology for food safety. Food safety is focused on in the state”11th five years plan”. Several high-techs are welcomed to optimize the industrial structure, improve product quality and to ensure food safety. Food irradiation is the key one among them.The work chooses chloramphenicol as the object, honey and shrimp as the target food. The aim of the work is to answer several questions which are necessary to determine the irradiation is an appropriate technology to elimination the veterinary drugs residuals in animal derived food. These questions are: Can veterinary drugs degrade under irradiation? What are the radiolysis products, whether they are toxic? How does the degradation work?The degradation effect of chloramphenicol under irradiation was firstly studied by using aqueous solution. The results showed that under the absorbed doses of 9 kGy, the concentration of chloramphenicol decreased from 150 mg/L initially to 1%, the degradation rate was 99%. The higher the absorbed dose was, the better the removal effect of chloramphenicol was. The lower the initial concentration was, the more the drug was removed. The relationship between degradation effect, absorbed doses and initial concentration can be expressed by the equation: C/C0=A·e-BD, in which D meant absorbed dose, and constants A, B were rely on the initial concentration C0.Actually, since the chloramphenicol residual in food is too low to detect, the aqueous solution was also chosen to study the radiolysis products and mechanism. 8 main radiolysis products were determined by liquid chromatography tandem mass spectrometry （LC/MS/MS） analysis method, 3 of them were also the radiolysis products of solid chloramphenicol, others were reported at the first time. The toxicities of them were evaluated by retrieving information from the toxicological databases. Among these products, 2, 2-dichloroacetamide and 4-nitrobenzoic acid were of toxic effects, while the others had no toxicological records yet. However, the structures of these products without records were similar to chloamphenicol, so the toxicities were also similar. On the trace level, all the toxicities of the products can be ignored.By setting different atmosphere （nitrogen, nitric oxide） and additives （hydrogen peroxide, isopropanol, tert-butyl alcohol）, different radical （hydroxyl radical, hydrogen radicals, hydrated electronic） dominants in the irradiation process and different degradation effects and products formation effect would be studied. By LC/MS/MS qualitative-analysis and radiation chemical yield（G） quantitative-analysis, the result showed that OH·played the major role for degradation of chlorampheniocl in the radiation system of aqueous solution, followed by H·, eaq- can hardly initiate the degradation. The radicals also played the similar roles in the formation of radiolysis products. Ultimately, the degradation mechanism was proposed: In the chloramphenicol aqueous solution, the radiolysis of water yields reactive species such as OH·and H·which will cause H-abstraction reaction firstly, and then fragmentation and/or rearrangement of radicals caused degradation of chloramphenicol and information of main radiolysis products. In addition, OH·had another important role by causing OH-addition reaction.The degradation effect of low chloramphenicol residuals in food and quality of food after irradiation were studied. The gas chromatography-electron capture detector was explored for quantitative analysis of trace chloramphenicol. The indicators and their analysis methods of food quality study were under the national standard GB/T 18796-2005 and GB 2733-2005. The results showed that: When the initial concentration was 100μg/kg in honey and shrimp, the degradation rates reached more than 99% by irradiation of 9.3 kGy. The radiolysis products were too low to detect, so there would be no hazard. There were no significance changes of major nutrients in honey and shrimp after irradiation. Some indicators such as HMF in honey and volatile base of nitrogen in shrimp even got significantly better than before-irradiation.