226. The effect of commercial drying and evaporation on the nutritive properties of milk

Abstract

With 1 Figure) THE experiments to be described here form a continuation of our work(1,2) on the effect of various commercial heat treatments on the nutritive value of milk. In the present series of experiments we have turned our attention to dried and evaporated milks. Thanks to the kindness of Messrs Aplin and Barrett, Ltd. we have been able to obtain from their Frome factory two types of dried milk and one of evaporated, all prepared simultaneously from one bulk of raw milk. THE PREPARATION OF THE MILKSThe processing was carried out on 1 October 1937 and was as follows: 1500 gal. of mixed milk from Somerset herds of predominantly Shorthorn type were placed immediately after receipt at the dairy in a large storage tank. After thorough mixing a sample was withdrawn for analysis. Batches were then drawn off and submitted to the following processes:(1) Raw milk. 17 gal. were withdrawn and of this 10 pints were put immediately into sterile thermos flasks and brought to the Institute at Reading the same evening. The remainder was cooled to 35° F., 50 pints were put into sterile thermos flasks and the rest into a churn. This milk was dispatched to Reading by rail and was received in the laboratory at 10 a.m. the following morning. There was some clotting in both batches, especially in the uncooled one.(2) Spray-dried milk. 500 gal. of raw milk were passed over an open tinned copper forewarmer and then flash-heated in an internal tubular heater to 160° F. and held at this temperature for 1-4 min. Some of the tin was missing from the forewarmer and the milk was probably exposed in it to naked copper for about 20 sec. during which time the temperature was raised from 45 to 110° F. The milk was then concentrated at 110° F. in a Kestner climbing film evaporator. This process was completed in 10 min. when the milk reached a concentration of 45% total solids. Within 30 min. of concentration the milk was fed into a Kestner spray-drier with an inlet temperature of 320-329° F. and an outlet temperature of 203° F. For the bulk of the milk the time of passage through the drier was about 30 sec, variations were from about 5 sec. to about 15 min. (this latter figure applies to mill? which unavoidably adhered to the sides of the drier). The milk powder was then put into 1 and 3f lb. tins and sealed at once in an atmosphere of 75% N 2 and 25% C0 2 .(3) Roller-dried milk. 50 gal. of raw milk were flash-heated to 160° F. as in the case of the spray-dried mill?-The milk was then fed at this temperature on to Hatmaker rollers running at 45 lb. steam pressure and 13 rev./min. After milling it was put into tins and sealed as already described.

The utilization of non-protein nitrogen in the bovine rumen. 5. The isolation and nutritive value of a preparation of dried rumen bacteria

“…In thepresent work the biological value was found to be 88'2,which is high and compares favourablywith that of dried-milk protein when determined by the same technique by Henry, Houston, Kon & Osborne (1939) and Henry, Kon, Lea & White (1948). It also lies between the values of 85'5 for yeast and 93 4 for milk found by Mitchell (1923-4b) using his balancesheet method and feeding the proteins at a level of 5 % in the diet.…”

Observations on the use of 2,4-dinitrophenylhydrazine and of 2,6-dichlorophenolindophenol for the determination of vitamin C in raw and in heat-treated milk

“…However, in evaporated milk, although the results for AA agreed by both methods, DHA was over-estimated when hydrogen sulphide was used. Henry, Houston, Kon & Osborne (1939) and Doan & Josephson (1943) both found DHA in evaporated milk, an unexpected result since DHA is destroyed even by the mild heat treatment used for pasteurization (Hartman & Dryden, 1965). Table 4 shows that when E. coli reduction was used little DHA was detected in evaporated milk, a finding in agreement with that of Doan & Josephson (1943) when they used the bacterial reduction method of Gunsalus & Hand (1941).…”

Creep feed rations for suckling pigs : with additional studies relating to the vitamin content of swine milk and blood plasma /

“…The method used by Braude et al (194&* 1947) for assaying the riboflavin content of sows' milk was that of Henry et al (1939) which had been proven acceptable for In an attempt to resolve the obvious conflicts in results, collaboration between Davis et al and Braude et al was undertaken.…”

“…)-The method of extraction of riboflavin from cows' milk reported byHenry et al» (1939) and applied by Braude et al to sows' milk was basically a methanol extraction. The sample of milk along with 95% methyl alcohol and glacial acetic acid was boiled under reflux In an atmosphere of nitrogen and then centrifuged.…”