Studies on Minerals of Milk and Milk Products

II. Calcium, Magnesium, and Phosphorus Contents and P/Ca Ratio in Milk Ash

Abstract

The contents of Ca, Mg, and P of the same samples as dseribed in the previous report were estimated by the chelate titration method and the molybdenum blue method, and P/Ca ratios calculated. The Ca contents of individual raw milk, composite raw milk, market milk, skim-milk powder, and whole-milk powder were 148.04(n=71), 149.89(n=83), 156.43(n=107), 152.72(n=15), and 146.01(n=7) mg per g of ash, respectively. The Mg contents of the same milk and milk products were 13.83, 15.69, 15.83, 14.29, and 13.41mg and the P contents of them were 126.68, 123.64, 124.26, 118.87, and 119.01mg per g of ash, respectively. Accordingly, the sum total of K, Na, Ca, and Mg contents occupied about 46% of milk ash.
Of the 3 elements, Ca showed the most remarkable difference in content between seasons and between regions, and was almost constant in content. The mean value of P/Ca ratio of raw milk was about 0.81. This value was the lowest in mid-summer and the highest in winter and early spring during the year. A remarkable increase in Ca and a slightly decrease in P contents were observed in the late period of lactation. Therefore, the P/Ca ratio was lower in late-lactation-period milk than in normal milk. Since milk yields increase from winter to early spring, the seasonal change of P/Ca ratio as stated above cannot be explained from the increase of late-lactation-period milk.
The correlation coefficient between P/Ca ratio and P content was positive (P<0.001), but that between P/Ca ratio and Ca contents was insignificant (P>0.5). Accordingly, the seasonal changes in P/Ca ratio was not due to the presence of abnormal milk in which the salt balance had been lost by excess of Ca or Mg ions.
The Mg content increased gradually with advance in lactation stage. The most remarkable change in individual cows was shown in the content of Ca of the 3 elements.