In the previous papers, the authors observed the amount of copper adduct to casein increased with the storage days in the systems of aqueous solution and oil. Also it was found that the copper seriously affected on the rancidity of oil, but in the case of casein or copper-casein complex, the peroxide value remained low.
In this paper, the relation between the binding ability of various inorganic metal (copper, iron, zinc, magnesium) -casein complexes and the activity of metal-catalyzed autoxidation was investigated. Thus various inorganic metals (copper sulfate, ferrous chloride, ferric chloride, zinc nitrate, magnesium chloride) were mixed with casein in water, or, casein, various inorganic metals and soybean oil were mixed and heated for 1 hour at 180°C and the amount of adduct formed with these materials was measured. On the other hand various inorganic metal salts and various inorganic metal-casein complexes were admixed with soybean oil, and the peroxide values were measured during the autoxidation period at 60°C.
The results obtained were as follows :
For casein, the amount of adduct with copper or iron was most and that with zinc was found in the followed order, but, no adduct formation was observed with magnesium in the both cases of aqueous solution and oil.
The order of activity was Cu > Fe > Zn > Mg. Copper and iron were only metals which will have practical catalytic activities, and zinc and magnesium had little catalytic effect. But in the case of various inorganic metal-casein complexes, the peroxide value remained low.
A correlation exists between the binding ability of various inorganic metal-casein and the activity of metal-catalyzed autoxidation.
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