Study On Control Of Lipid Oxidation And Mechanisms Of 2-dodecylcyclobutanone In Irradiated Chilled Meat

Food safety concerns everyone's health and has attracted more attention around the world. Meat safety accidents take place frequently because of being polluted easily with pathogenic bacteria such as E. coli O157: H7, Salmonella, Bacillus Clostridium botulinum and so on. In addition, because the quality of meat is usually under the hygiene standards, there is a great obstacle on the domestic consumption and international trade. Irradiation technology as one of physical means can kill the pathogenic microorganisms, saprogenic bacteria and parasites thoroughly in meat. Then it can improve the hygiene quality, enhance the safety of meat and protect people's health. At the same time, however, irradiating meat will increase the speed of free radicals formation, and start the chain reaction of free radicals to speed up lipid oxidation. Because of the disadvantage of lipid oxidation, the advantages of irradiation sterilization and security safeguard function can not be brought into full play in lipid-containing food, such as chilled meat and so on. It has become the technologic bottleneck in food irradiation industry.Concerning of the application of irradiation technology and the requirement of international trade and inspecting market, detection method and standard for irradiated lipid-containing food are eagerly needed. But it has not established the detection method for irradiated food containing lipid in our country. And the related research is also lack. 2-Alkylcyclobutanones (2-ACBs) mentioned in this paper, are the specific products of the irradiated lipid-containing food. The research results showed that the 2-ACBs come from the fatty acids or triglyceride ester in food by irradiating. The concentration of 2-ACBs is increasing linearly with the absorbed doses rising. Up to now, the 2-ACBs only have been found in the irradiated food containing lipid, however, they have never been found in any non-irradiated food. So it can be used to as indicators to detect lipid-containing food irradiated or not, or to evaluate the absorbed dose. 2-Dodecylcyclobutanone (2-DCB) is one kind of 2-ACBs, which is the radiolysis product of palmitic acid and palm triglyceride in food. The alkyl chain of 2-DCB is short and saturated, and 2-DCB are more stable compared with other kinds of 2-ACBs. In most food, the palmitic acid content is higher than most of other fatty acids, it is more practical to use its radiolytic product, 2-DCB, as the main specific marker detecting irradiated food.Analysis of control of lipid oxidation and characteristics of 2-DCB in irradiated chilled meat are the main objects of this paper. The primary factors have been studied which influence lipid oxidation in the irradiated chilled meat, the quantitative analysis method, and the generation mechanism and the changing rules of 2-DCB. The main projects and research results are as follows:1. It determined the optimal and synthesized processing techniques to control lipid oxidation in irradiated chilled meat. By detecting the microbial indicators (including the total number of bacteria, E. coli, and Salmonella, etc.), the sensory evaluation (color, flavor, flavor, etc.), the lipid oxidation indicators (peroxide value, thiobarbituric acid value, etc.) and protein corruption indicators (volatile nitrogen base value), it was decided that the optimal absorbed dose of irradiated chilled meat was 2-3 (kGy). Under this dose condition, the antioxidation of tea polyphenols (TP), rosemary, tocopherol (VE), tert-butyl hydroquinone (TBHQ), butylhydroxytoluene (BHT) was investigated individually. The research results showed that tea polyphenols has unique advantage on controlling lipid oxidation in irradiated chilled meat. The orthogonal experiment of four orthogonal factors and three levels was adopted to study the best combination of antioxidants to control lipid oxidation. The effects of different oxygen concentration in package on lipid oxidation in irradiated chilled meat were also analyzed. On the basis of early experiments, by an orthogonal experiment of three factors through three levels, it was found that chilled meat irradiated at 2 kGy with vacuum package and 50 mg TP addition can has low extent of lipid oxidation with long shelf life and excellent quality.2. The detection method of irradiated food containing lipid–Gas chromatographic / Mass spectrometric analysis of 2-Alkylcyclobutanones was determined. By optimizing the type and concentration of eluting solvent, and the extent of deactivated silica on the extraction efficiency, the extraction condition of 2-DCB was established as aether/hexane (1:99) and 4% extent of deactivated silica were. It showed that the silica gel column separation method had lower cost, larger quantity of analytic sample, and lower detection limit as compared with the EN 1785 method.3. A convenient and rapid method for quantitative analysis of 2-DCB was developed which was extracted by supercritical fluid extraction and analyzed by gas chromatography/mass spectrometry. The main affecting factors of pressure, temperature, time, and CO2 flow on SFE were investigated and optimized with respect to extraction yield of 2-DCB. The optimized extracting condition can be described as 20 MPa, 70℃, 30 min and 1 ml/min respectively. With the same sample, the correlative parameters of the consuming time, the consuming organic solvent , operating cost and extraction yield were compared with European standard method EN 1785. The results showed that SFE-CO2 method have the similar extraction yield with European standard method EN 1785, the operation time and the consuming organic solvent reduce 35% and 60% respectively according to European standard method EN 1785, and this method had lower operating cost。4. According to different irradiated doses, storage time and temperatures, package styles and adding free radical scavenger in irradiated food, The changing rules of 2-DCB were investigated for the fist time. The results showed that there was a significant linear relationship between irradiated doses in the range of 0.5-10.0 kGy and the concentration of 2-DCB, and the linear relationship still existed during storage. The amount of 2-DCB reduced regularly during storage under the same temperature. The effects of different packaging atmosphere (O2, N2 and vacuum) on both the generation and the stability of 2-DCB were similar during storage. So it indicate that under controlled condition, 2-DCB could be used as specific indicator to detect lipid-containing food irradiated or not and to evaluate the possible absorbed doses. The changing rules of 2-DCB in irradiated beef indicate that applyed lower absorbed doses, packaged avoiding light, stored under lower temperature, and adding free radical scavenger can decrease the concentration of 2-DCB in irradiated food containing lipid.5. For the first time, the effects of target free radicals on the generation of 2-DCB were analyzed by adding different free radical scavenger into irradiated sample system. According to the changing rules of 2-DCB which obtained in early experiments, the process of 2-DCB generation concerning with free radicals was described. The dominant free radical that leads 2-DCB to generate was eaq- which comes from H2O radiolysis except for alkyl free radical which comes from lipid molecule radiolysis directly.