Factors affecting the ethanol stability of bovine milk

Summary Changes in the ethanol (EtOH) stability/pH profile of skim-milk induced by forewarming have been investigated as a function of temperature and duration of forewarming and of milk pH prior to heating. Forewarming increased the EtOH stability of a milk in the mid-pH range, shifting the profile laterally to more acid pH values, with little effect being observed on the maximum and minimum EtOH stabilities. No significant changes in forewarming effects were obtained on adding the sulphydryl-blocking agent, N-ethylmaleimide, indicating the lack of involvement of serum protein interactions in the stabilizing effects of forewarming. It is suggested that the observed effects of forewarming are due to a heat-induced precipitation of colloidal calcium phosphate. This suggestion is supported by measurements of Ca2+ levels in forewarmed and untreated skim-milk as a function of pH and is in agreement with the previously suggested mechanism for the EtOH-induced coagulation of skim-milk. The effects of permitted additives (citrate, phosphate and Ca) on the EtOH stability of forewarmed milk paralleled their effect on untreated milk. A comparison is made of the effects of forewarming on the heat and EtOH stabilities of skim-milk.