The authors observed that in the case of frying, especially whale meat, the frying-oil was colored and deteriorated by substances cozed out from the whale meat, for instance, by nitrogen compounds (protein, pyrrole substance) and metals (iron and copper, etc.) due to the decomposition of blood, etc. and whale oil. Also, the copper and iron in these frying oil were very often observed to be decreased during the storage.
In this paper, for making clear the reason of decrease of copper and iron in frying oil, a model test on the reaction between protein and copper in the system of aqueous solution and oil was carried out. Thus the copper of different stages in the concentration was mixed with casein in water, or, mixture of casein, copper (copper sulfate) and soybean oil was heated for 1 hour at 180°C, and the amount of aduct formed with these materials was measured.
The results obtained were as follows :
It was confirmed that the amount of copper adduct to casein increased with the storage days in both system of aqueous solution and oil, namely, it became clear the easy formation of copper-protein complex.
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