Study On The Production Of Polycyclic Aromatic Hydrocarbons In "peking Roast Duck" With Air-jet Impingement Roasting Technique

As a traditional cate,"Peking roast duck"is favored by people home and abroad as the special flavor and culture. The traditional technology of roast duck is unique and dainty, roasted with wood fuels or charcoal combustion, depended on experienced masters to control the keypoint of process. The problem of dependence on human resource and the contamination problem brought by the roast technology are obvious after the Olympic Games. Fulfilling the autocontrol of roast duck industry and the clean process technology are significant for the international development of"Peking roast duck".The effect of new heating technology– Air Jet Impingement Roasting Technique to the production of Polycyclic Aromatic Hydrocarbons (PAHs) in roast duck skin was investigated in this research, to provide the information in products'safety to establish the best parameters of new roast process with other parameters. Firstly, the high performance liquid chromatography with fluorescence detection (HPLC–FL) method was optimized for the PAHs separation and detection; secondly, studied the sample pre-treatment and clean-up method for the PAHs in the roast duck skin, optimized the best extraction method for PAHs. Lastly, determineded and analyzed the PAHs contents in roast duck skin roasted with different temperatures by laboratorily designed equipment-air impingement roast duck oven, and combined with the analysis of commercially produced roast ducks, evaluated the effect of different roast process to the production of PAHs in duck skin. Main contents and conclusions are as follows:1. The best chromatograph condition of PAHs separation and detection was established: A Shim–pack VP–ODS (150×4.6mm, 5μm) analytical column at 30℃were used. A mobile phase of acetonitrile (CH3CN) and water (45/55, v/v) was linearly programmed to 80% CH3CN within 20min, and maintained for 10min, then back to initial condition with a stable flow rate of 1.0 ml/min. Fluorescence wavelengths were 290 nm (excitation wavelength) and 410 nm (emission wavelength). The injection volume was 20μl. Peaks were identified by comparing the retention time with that of standards and by co–chromatography. The detection limits are: B(a)P0.18ng/ml, 7,12–DMB(a)A 0.58 ng/ml, DB(a, h)A 0.63 ng/ml. The external standard plot method was used for quantification, the linearness of Regression equations for three PAHs are more than 0.99, the RSD % within–day are less than 2%, RSD% between–days are less than 3%. The repeatability and stability of the method is good.2. Studied the effect of the sample pre–treatment procedures to the PAHs recoveries like the alkaline saponification liquid–liquid partition and solid phase extraction and the best adapted method were: 95℃, 6 hours were chosen in alkaline saponification and the PAHs lose rate were less than 5%; Isooctane and DMF were chosen as liquid–liquid extraction and re–extraction organic solvents as the high recoveries; and SPE– florisil cartridge was chosen for the clean-up procedure, the cartridge(500mg/6ml)was pre–washed with 20ml CH2Cl2 / isooctane (1/1, v/v) before the concentrated isooctane extract was applied to it. A further 2ml isooctane was used to rinse the glassware and was applied to the cartridge too. 10ml isooctane was used to wash the column and PAHs were then diluted with 10ml benzene. The PAHs recoveries were between 92.92%～95.25%. The chromatography of PAHs in sample was good and the impurities were less, and didn't have much interference with the quality and quantity analysis. 3. The precision and recovery experiment showed that the whole method was good for the tract substance analysis. The recoveries in black spiked experiment were between 80.92%～85.56%, the RSD% were between 3.25%～4.66%. The PAHs contents detector in the roast duck skin were 0.13μg/kg～4.32μg/kg with the RSD% 7.33%～8.58%. The recoveries of spiked sample were 73.85%～80.31% with the RSD% 5.19%～9.54%.4. Analyzed the contents of PAHs in roast duck skin roasted with three different temperatures by laboratorily designed equipment-air impingement roast duck oven. The results showed that of sample analysis reveal that laboratory roast ducks are somewhat contaminated by three PAHs. The contents of PAHs generally increase as the roast temperature rises. The B(a)P contents were between 0.13～0.56μg/kg, and the highest content is far lower than maximum limit of 5μg/kg. 7,12-DMB(a)A contents were1.28～3.19μg/kg, DB(a, h)A 0.48～2.04μg/kg. PAH pollution is probably produced by the fat pyrolysis during the roast process. Analysis of commercial roast ducks shows that the content of B(a)P increases while 7,12–DMB(a)A decreases compared to the 210℃laboratory group, revealed the fuels combustion and fat pyrolysis may both influence the levels of these contaminants in the final product. The formation of PAHs in roast duck skin was varied as the different of roast process.