Mechanism of N-Nitrosothiazolidine Formation at the Stage of Fish Meal Preparation

Abstract

Both cysteamine (CysA) and thiazolidine (THZ) are considered to be the precursors of N-nitrosothiazolidine (NTHZ). Regarding the occurrence of these compounds in foods, how-ever, almost no data has been available so far. Present study has revealed the existence of about 200μg/kg of CysA in fresh sardine meat, while the CysA content in the meat de-creased below 30% of the initial level after being boiled, and only 5% of CysA was retained in the meal samples after freeze-drying of the boiled meat. On the contrary, very small quantity of THZ were detected in the fresh sardine meat, however, the contents remarkably increased upon boling to reach 128μg/kg, and the levels did not change even after lyophiliza-tion. Fish meal samples made from whole bodies of fresh sardines were found to contain larger amounts of THZ than those of CysA, in contrast; the THZ levels in the samples made from decomposed fish were appearently lower than those made from fresh materials. It was confirmed that nitrosothiazolidine-4-carboxilic acid (NTZC) was formed in the sardine meal samples after treatment with NO₂ gas, and the yield of NTZC reduced by lowering the fresh-ness of raw fish materials. Based on the afbrementioned results, it may be proposed that the following two pathways exist in the formation of NTHZ in fish meal during manufacturing process, viz., (1) formation of NTHZ by nitrosation of THZ, and (2) formation of NTHZ by decarboxylation of NTZC.