Oxidation of Milk Fat Globule Membrane Material. I. Thiobarbituric Acid Reaction as a Measure of Oxidized Flavor in Milk and Model Systems

The thiobarbiturie acid (TBA) reaction was used for investigating oxidized flavor in model systems containing fat globule membrane material and ascorbie acid.Triehloroaeetic acid was used to flocculate the proteins and the TBA reaction was carried out and determined in the filtrate.The method is highly satisfactm:¢ in reproducing and measuring rapid oxidation rates in the model system.When applied to milk, lactose was found to contribute considerable interference in the TBA reaction.This was shown by chromatographic separation and spectrophotometric analyses of TBA pigments.A satisfactory application for milk uses trichloroacetic acid to remove fat and protein and ethanolic-TBA to increase the rate of color formation at 60 C, a temperature at which lactose degradation is minimized.Results are presented showing quantitative reeovmT of oxidized inilk from mixtures of oxidized and nonoxidized milk.Effect of exposing homogenized nfilk to direct sunlight for 20-rain intervals is readily detected by the method.Relation between organoleptic and TBA analyses is indicated.Detection of lipid oxidation in foods organoleptically is considered the most sensitive and reliable method, though it does not lend itself well to quantitative measurements.The natural complexity of milk and the relatively small amounts of material or changes therein responsible for oxidized flavor have limited most studies to organoleptic evaluations.The use of a model system will overcome some of the inherent problems associated with the complexity of milk, but may introduce others such as the comparison of organoleptic sensations between milk and simpler systems.Olson and Brown (4) reported that small quantities of aseorbie acid added to copper-contaminated washed eream resulted in intense oxidized flavor.Fat globule lnembrane material obtained by churning washed cream reacts in a similar manner, even without the addition of eopper (3).The reaction proceeds very rapidly and the intense flavors are difficult to evaluate organoleptieally.The 2-thiobarbiturie acid (TBA) reaction has been widely applied J~eceive~i for