279. The estimation of lactose in milk

Abstract

THE estimation of lactose in milk by copper reduction methods gives results which are usually somewhat lower than those obtained by the polarimetric method. An adequate explanation of this discrepancy is still lacking. Recent work(i,2,3) has shown that a second sugar, probably glucose, is present in milk, but the proportion is very small and would not account for the differences in the lactose percentages obtained by the two methods. The present paper reports an examination of several of the methods of lactose estimation. METHODS (a) Volumetric copper reduction methodsThe direct volumetric copper reduction method of Lane & Eynon(4) may be applied to milk, as they suggest, by adding the milk, diluted 1:10, from a burette to the boiling alkaline copper solution. Carried out in this way the method is rapid and gives concordant results. It may be still further simplified, however, so that dilution of the milk and filling of the burette with each diluted sample is eliminated. The milk under examination (3 or 3-5 ml.) and also 30 ml. of water are added to the measured quantity of alkaline copper solution and the titration is completed by the addition of 0-5 % lactose solution from a burette. For the final accurate titration the 0-5 % lactose solution is run in to within 0-5 ml. of the end-point before boiling is commenced.Comparison of results for lactose content obtained by direct titration with results obtained after deproteinization. Clarification of milk with dialysed iron (5) gives a filtrate of the same pS. as the milk and free from the deproteinizing agent, but the dialysed iron does not remove calcium. As it has been shown that calcium salts cause a decrease in the amount of copper reduced(6,7,8) a further treatment of the dialysed iron filtrate with potassium oxalate becomes necessary. Table 1 gives results showing the effect of clarification with dialysed iron and of subsequent decalcification on the lactose estimation by the volumetric copper reduction method. It will be seen that treatment with dialysed iron results in a lower value for .lactose content and that this effect is largely eliminated by the decalcification with oxalate.Farmer(9) modified Lane & Eynon's method to include a clarification of the milk with lead acetate and sodium fluoride which remove both the protein and the calcium. The effect of clarification of milk samples by Farmer's method is shown in Table 2. There was no appreciable difference in the results except

The composition of sow's milk during lactation with particular reference to the relationship between protein and lactose

“…After being filtered through linen to extract any foreign particles each milk sample was stored at 1° C. for not more than 1 week before analysis. Protein was determined by the macro-Kjeldahl method (N x 6-38), fat by the Gerber method, lactose by McDowell's adaptation (17) of Lane & Eynon's method and dry matter and ash by the methods described by Ling (18).…”

The effects of a low-protein food supplement on the yield and composition of milk from grazing dairy cows and on the composition of their diet

“…Each cow's samples were bulked separately in two 5-day lots which were termed ' Bulk 1' (the first ten milkings of the measurement period) and 'Bulk 2' (the last ten milkings). The bulked samples from each cow were analysed for the following constituents: butterfat by the Gerber method (British Standards Institution, 1936); total solids by evaporation at 100° C.; solids-not-fat by calculation; lactose by McDowell's (1941) modification of the Lane-Eynon method; total nitrogen by micro-Kjeldahl procedure; non-casein nitrogen by the same method after precipitation of casein by Ling's (1948) modification of Moir's acetic acid and sodium acetate method; casein by calculation. In the autumn periods the Bulk 2 milks of eight of the cows, one from each of the subgroups selected at random, were analysed for non-protein nitrogen; protein was precipitated with 15 % (w/v) trichloroacetic acid and micro-Kjeldahl analysis was carried out on the supernatant fluid.…”

Bone development in suckled pigs

“…Chemical analysis. T h e total solids in the milk samples were determined by drying at 100' (Ling, 1948), crude protein by the macro-Kjeldahl method, lactose by McDowell's (1941) adaptation of Lane and Eynon's method, fat by the Gerber method, ash by the method described by Ling (1948), Ca by a modification of the standard oxalate method which prevented co-precipitation of Mg (Holth, 1949), and P by the method of Rickey & Avens (1955).…”