Distribution of radioactive 32 P in buffaloes' skimmed milk as affected by processing

The distribution of phosphorus between the soluble and colloidal phases in buffaloes' skimmed milk, and the effects of five heat treatments on it, was determined by the rennet coagulation technique. The original P in milk and radioactive 32 P incorporated into milk, both in vitro and in vivo , were estimated for total and soluble phases by chemical and radioassay methods. The heat treatments consisted of pasteurisation (15 s at 71.8°C), pre‐warming (5 min at 96°C), sterilisation (15 min at 121.5°C), and cooling for 24 h at 4–6 and 0°C. When 32 P was added in vitro about 60% remained in the soluble phase; if incorporated in vivo , about 39% was in the soluble phase, while the level of the original P was about 38%. Pasteurisation, pre‐warming and sterilisation progressively decreased the soluble in‐vitro incorporated 32 P to about 58, 48 and 34%, respectively. Cooling at 4–6 and 0°C altered the soluble in‐vitro incorporated 32 P to approximately 53 and 57%, respectively, from about 64% in the raw milk. On the other hand, changes in partitioning of either in‐vivo incorporated 32 P or original P due to any of the five processing treatments were small, non‐uniform and not statistically significant.