Thesis (M.Sc.)--Chulalongkorn University, 1998

The objective of this investigation was to study the effect of inorganic phosphorus (Pi) on stability and physicochemical properties of milk whether its effect occurred intracellular or extracellular of mammary gland of crossbred Holstei Friesians. The 20 animals were divided into 2 groups depend on their milk quality test with 75% EtOH. Ten animals were assigned to positive EtOH test group. Other ten animals were assigned to negative EtOH test group. Experiments in each group were carried out both in vivo and in vitro. In in vivo study, animals received Pi 28.5 mg/min throughly 120 minutes of experimental period. Before the end of experimental period, blood sample was collected for mammary A-V difference, mammary extraction ratio and blood electrolyte concentration. The end of experimental period, milk was collected for milk stability test by ethanol (EtOH), milk composition, milk precipitation and the soluble salt balance (SSB) of milk. In in vitro study, an addition of Pi were performed at 3 levels of Pi 0.1, 0.5 and 0.9 mg/ml milk. After Pi addition, milk sample was carried out for stability test to compared with that of milk before Pi addition. During Pi solution infusion, animals in both groups showed significantly higher of plasma Pi concentration (P<0.01). Animals with the positive EtOH test showed a higher mammary A-V difference and mammary extraction ratio of Pi. Plasma electrolyte concentrations for Ca, Na, K, Cl and Mg were not affected by Pi solution infusion. The precipitation value of normal milk showed no differences of the optical density between before and after Pi infusion in each group. During testing the stability of milk with EtOH the occurrence of precipitation in the positive EtOH test was more than that of the negative EtOH test (P<0.01). A shift to higher stability from 68% to 75% or 80% were apparent after Pi infusion in positive EtOH test. During Pi infusion, the Pi concentration in milk markedly increased in both group. After Pi infusion, milk compositions of the positive EtOH test were in normal range as in the negative EtOH test exception for the milk Na concentration. Pi solution infusion did not affect to the fraction of casein concentration. The negative EtOH test had significant higher of K-casein concentration in milk than the positive EtOH test. The SSB were not affected by Pi infusion in both groups. The SSB of the negative EtOH test showed significant lower (P<0.01) when compared to the positive group. The addition of Pi in milk at 0.1, 0.5 and 0.9 mg Pi/ml milk would affect the stability of milk to EtOH test (P<0.01) in the positive EtOH testing group. From these results, it may conclude that Pi affected the stability and physicochemical properties of milk in dairy crossbred Holstein. Pi support the structure of casein micelle either in intracellular or extracelllar of mammary tissue. However, the physicochemical properties of milk and micelle forming are dependent on the property of each casein formation of individual animal.