Effect of Surface Protein Concentration on the Heat Stability of Systems Containing Homogenized Fat Globules from Recombined Milk

Recombined milk was treated by differential centrifugation to yield a number of discrete fractions of fat globules. The composition and heat stability of these fractions were determined. Heat stabilities were measured after adjustment of the fractions to comparable levels of protein and fat. As predicted, the amount of protein associated with the fat increased in parallel to the fat globule size. Heat stability decreased as the surface protein concentration increased. Therefore, surface protein concentration is a key determinant of heat stability. Both casein and serum protein were found on the fat globule surfaces and, although casein was always the predominant surface protein, the surface layer of the largest fat globules contained a higher proportion of serum protein. Depletion of serum protein before homogenization resulted in decreases in heat stability with increased adsorption of casein at the fat/serum interface.