Determination Of Rosin Residue In Duck Skin Tissue And Its Influencing Factors

China is one of the major producers of poultry, and the production of duck and goose has been ranking first in the world for many years. Because of oily skin and a lot of microvilli, it is difficult to get rid of duck feather just by a defeathering machine. Defeathering agent is usually employed in duck processing. However, small poultry processing enterprises are still using rosin in duck processing for its lower cost and better defeathering performance, although rosin was forbidden in hair/feather removal treatment of livestock and poultry products in China. Defeathering by rosin results in the residue of toxic substances in duck skin, and the rosin-defeathering duck poses a potential threat to consumer’s health. Therefore, determination of rosin residue in raw and cooked ducks and study on factors influencing the residue level are important for evaluation of the illegal use of rosin in duck processing, and for further study on the risk assessment. In this study, abietic acid (AA) and dehydrogenated abietic acid (DHAA), the major components of rosin, were used as the residue markers of rosin, and a method was established for simultaneous determination of AA and DHAA in duck skin. Both residues in raw and cooked duck samples in Nanjing agricultural product markets and cooked food stores respectively were measured, and the factors influencing residue level were studied. The main research contents are as follows:1. Establishment of an analytical method for simultaneous determination of AA and DHAA in duck meatsAA and DHAA were extracted with acetonitrile and cleaned by solid phase extraction, followed by chromatographic separation on C18 column with methanol/2 mM phosphoric acid (86/14, v/v) as mobile phase and detection by PAD and FLD, respectively. Limits of quantification for AA and DHAA were 0.050 μg/g and 0.015 μg/g, respectively. The method was applied to analysis of AA and DHAA residues in meats of rosin-defeathered ducks and commercial ducks. The results indicated that removal of duck feathers by means of rosin could lead to residues of AA and DHAA in duck skins. The proposed method could be used to identify those rosin-defeathered ducks and to monitor the illegal using of rosin in duck processing.2. Survey of AA and DHAA in raw and cooked duck samples in NanjingIn order to evaluate the illegal use of rosin in duck processing industry, raw duck samples produced by 15 duck processing enterprises were collected from agricultural products markets, while 20 cooked duck samples (salted duck-roasted and boiled ducks) were collected from different cooked food stores. AA and DHAA residues in raw and cooked duck skins were measured by the analytical method developed in this paper. The results indicated that 13 out of 15 raw duck samples were contaminated by AA and DHAA, with ranges of 0.22 to 4.42 μg/g and 0.36 to 5.75 μg/g, respectively; while 13 out of 20 cooked ducks were contaminated by AA and DHAA, with ranges of 0.65 to 3.83 μg/g and 0.42 to 2.46μg/g, respectively. The high positive rates of AA and DHAA in raw and cooked ducks,86.7% and 65.0%, respectively, show that rosin is still employed as a defeathering agent in the most of duck processing enterprises and cooking (boiling or roasting) can not remove the residues effectively.3. Factors influencing AA residue level in duck skinImpacts of various factors on AA residue level in the duck skin, including defeathering temperature, defeathering time, ratio of rosin in defeathering agent, and etc., were studied by simulating tests. The results show that all these factors influence AA level in duck skin to some degrees.