Heat stability of milk: the mechanism of stabilization by formaldehyde

Abstract

SUMMARYThe increase produced by formaldehyde (HCHO) in the heat stability of milk did not occur when milk was treated with HCHO at temperatures up to 60°C followed by dialysis at 5°C. However, the minimum in the heat coagulation time (HCT)–pH curve was irreversibly removed if the milk was preheated at 80–C for 10 min in the presence of 5 mM-HCHO. Although this treatment blocked the ε-amino groups of lysyl residues, the stabilizing mechanism is considered to be due to the cross linking action of HCHO which reduced the level of non-sedimentable, κ-casein-rich protein dissociated from the micelles on heating. The specific crosslinking agent, dimethyl suberimidate, modified the HCT-pH profile of milk in a manner similar to preheating at 80°C for 10 min with 5 mM-HCHO, supporting the crosslinking hypothesis. The results of this study appear to lend some support to the proposal of Kudo (1980) that the minimum in the HCT-pH curve of milk is due to the dissociation of κ-casein from the micelles on heating at high temperatures at pH values greater than 6η7.