Effect of Formaldehyde on the Heat Stability of Concentrated Milk and the Formation of Soluble Casein

Abstract

In order to clarify further the relationship between the heat stability ofcasein micelles and the formation of soluble casein upon heating concentrated milk, the effect of formaldehyde was examined. The addition of formaldehyde up to 20 mM markedly increased the heat stability of both concentrated skim milk and concentrated whey protein-free (WPF) milk. The stabilizing effect of formaldehyde was greater for concentrated skim milk than for concentrated WPF milk. The addition of formaldehyde depressed the formation of soluble casein upon heating concentrated milk. No soluble casein was formed on the addition of 20mM formaldehyde. It was confirmed by Sephadex G-200 gel filtration in the presence of 6.6m urea that cross-links among the casein components were formed in heated concentrated WPF milk containing formaldehyde. These facts suggest that formaldehyde may introduce cross-links among the casein components and prevent the formation of soluble casein accompanying the release of K>casein from micelles, thus stabilizing the casein micelles.