Studies of the composition of milk

Abstract

May, measured quantities of water, showed that this method of sampling withdrew proportional parts of the contents of the can.All samples were taken and kept in two-quart glass fruit jars fitted with glass lids and rubber rings, and were preserved with for- maldehyde added previous to the beginning of sampling in the pro- portions recommended by Palmer. 8* After delivery to the laboratory all samples were kept under refrigeration until the analyses had been completed.Determinations.Direct determinations of specific gravity and of percentage of fat, total protein, ash, and total solids were made on all samples.The specific gravity was determined by the use of a chainomatic specific-gravity balance.The percentage of fat was determined by the Roese-Gottlieb method, using about 5 grams of the sample.Total nitrogen was found by the Official Kjeldahl method, using metallic mercury.The per- centage of nitrogen multiplied by 6.38 is tabulated as the percentage of protein.The percentage of ash was determined on a 10-gram sample to which 3 centimeters of strong nitric acid had been added.Except for the smaller quantities of sample and of nitric acid, the procedure of the Official method was followed.The ignition was made in an electric muffle furnace.The percentage of total solids was determined from a 2-gram sample weighed into a tared tin-foil dish.The water was evaporated on a boiling water bath and the final drying done in an electrically heated oven adjusted to give a temperature of approxi- mately 100 degrees Centigrade.All weighings of samples were made by difference, using Mojonnier weighing crosses and weighing pipettes delivering approximately 2 grams for the total solids, 5 grams for the fat and total nitrogen, and 10 grams for the ash determinations.The percentages of lactose a and of solids-not-fat were found by difference: percentage of lactose = percentage of total solids (percentage of fat + percentage of total protein + percentage of ash) percentage of solids-not-fat = percentage of total solids percentage of fat THE EXPERIMENTAL DATA Tables 1 to 5 inclusive give the complete analytical data for each sample studied, arranged in the order of ascending fat percentage.The percentages of water, altho used in the statistical study, are not included in these tables.Table 1 includes the data for all samples 'Percentages of lactose were also determined with the use of the polariscope by the Official method of the Association of Official Agricultural Chemists.However, as the percentages so determined have been found to be subject to inaccuracies they were not used in the present study.BULLETIN No. 325 [Mai different cows, the authors believe that the results, especially as to the relations existing between the various components, fairly repre- sent the milk of each breed of cows studied, and that the results of all the analyses taken together are similarly representative of the mixedm ilk of large numbers of cows of all breeds.It should be pointed out that the protein content of milk as de- termined from these investigations is higher 3 in relation to the fat content than is usually reported in the literature, and that the lactose does not regularly increase with increasing fat up to a certain fat content and then regularly decrease but that it is nearly constant in percentage to about 5.0 percent of fat and then tends to decrease with further increases in fat.* I " TlN CO " U3 O5 >-i in >-< ri I ^-K