Relation of Composition of the Aqueous Phase to Oxidized Flavor Development by Dialyzed Globular Milk Fat

Abstract

Six per cent dialyzed milk fat and 4ppm copper were incorporated into: 1) salt solutions containing sodium citrate, phosphate buffer, NaCl, KCl, and CaCl2, and mixtures of those solutions; 2) salt solutions containing amounts of sodium caseinate ranging from 0.50 to 5.0%; 3) salt solutions containing 2 to 10% α-lactose; 4) the above model systems in presence of ascorbic acid.After 48 hr at 3-5C, oxidation rates and intensity were measured in terms of the optical density (OD) of the 2-thiobarbituric acid test.Both rates and intensity of oxidized flavor development varied significantly in the various salt solutions and their mixtures. Increasing lactose concentration increased the oxidation rates significantly in all systems, (OD increased from 0.32 to 0.50 in phosphate and 0.14 to 0.21 in citrate). The reverse of this trend was obtained in presence of an increased concentration of sodium caseinate (OD decreased from 0.25 to 0.05 in phosphate and 0.15 to 0.05 in citrate). Homogenized fat showed much lower oxidation rates in presence of casein than did nonhomogenized fat.In a salt-free system (water), ascorbic acid behaved as an antioxidant at concentrations from 0.50-2.0mg and a weak prooxidant at concentrations from 2-10mg per 100ml. This behavior was reversed in presence of salt solutions, with the oxidation intensity varying considerably depending on the composition of the model system.These results clearly demonstrate the importance of the aqueous phase in determining both rate and intensity of oxidized flavor development.