Studies on the refractive index of milk

Summary

A number of routine natural and artificial factors that are likely to affect the values of the refractive index and refractive constant of cow and buffalo milk have been investigated.

Colostrum exhibits a high R.I. and K, both of which reach normal levels in 3 to 5 days after parturition.

Differences in the two constants of milk occur from milking to milking, from day to day and between milks from different quarters of the udder. But the order of variation is unpredictable in every case. The different portions of a milking, however, exhibit a more or less uniform R.I. and a steady rise in the value of K from fore milk to strippings. But in all instances, pooling of the total yield from the animal restores the values to normal limits.

The rainy season, when lush pasture is available for cattle, appears to Cause a marked rise in the limits of R.I. of milk, while the limits of K remain the same all through the year.

Rigorous boiling of milk causes a steady rise in the values of both R.I. and K.

All the data point to the fact that factors which cause a rise in the fat-free solids of milk also increase the measure of the R.I. The refractive constant, on the other hand, remains within normal limits owing to a corresponding change in the density of milk under natural conditions of variation.