Abstract
The skim milk, demineralized at various demineralization rates as previously reported, was subjected to ultracentrifugation at 127, 000×g at 5°C for 45min. Analyses of the supernatant and of the colloidal phase were performed in connection with calcium, phosphorus, citric acid and protein fraction as the demineralization proceeded. 1) The calcium content of the whole skim milk was 104mg per 100ml and a 76% demineralization caused decrease in its content down to 50mg. In the soluble phase, decrease of calcium content by demineralization was not so much as in the whole skim milk. Namely, while calcium content in the soluble phase was 41mg per 100ml without demineralization, 32mg of it remained at the 76% demineralization. 2) On the other hand, the content of phosphorus in the soluble phase, 46mg per 100ml at initial, remarkably decreased to 23mg upon demineralization; citric acid, 185mg to 73mg. The ratio of calcium to phosphorus plus citric acid in the soluble phase, therefore, increased as the demineralization proceeded. 3) The residual protein in the soluble phase, originally 0.8%, significantly increased as much as 1.5% upon demineralization.
