QUALITY OF MILK

Hokitika Guardian, 27 August 1929, Page 2

QUALITY OF MILK

THE MINERAL CONTENT,

SOLUBLE AND INSOLUBLE ASH

The British Journal of Agriculture says: Although the mineral portion of milk amounts to less than 1 per cent of the whole, it is very important and complex constituent. In milk itselr there are present (a) inorganic salts (b) inorganic bases combined with citric acid, and (c) calcium phosphorus and sulphur, combined in the aminoacid groups df the caseinogen molecule.

When the solids of milk are burnt to an. ash the citrates. are decomposed leaving the bases to some extent in the form of carbonates. The calcium of the caseinogen molecule remains, hut part of the phosphorus in this ports).*: of the milk solids with practically ail the sulphur, is lost during ashing. Milk- ash therefore does not wholly represent the mineral constituents of milk.

In the course of this investigation, determinations of the total ash water soluble and insoluble ash, total calcium and totril phosphorus were made and the results obtained throw some interesting light on the variations in the composition of the mineral portion cL the milk. .

The ash content of milk appears to have a seasonal variation. The ash percentage reaches a minimum in the summer (the grass months) and a minimum in the winter. It'is significant that the ash content should reach its highest point when the solids-not-fa.. percentage is low. The soluble portion of milk nsh con sietfl chiefly ‘of sodium chloride, while caloium phosphate is the main constituent of the insoluble ash. It is found that the percentages of soluble and insoluble ash and the ratio of the two are highly correlated with the percentages of solids not fat’.

DEFICIENCY IN SOLIDS. It is apparent that milk low in solids not ifat is rich in soluble ash and poor in insoluble ash. This point may have considerable physiological importance. Porcher states that sodium chloride (fciie principal salt in the' soluble ash) is one of the most variable constituents of milk, and the amount present in mnk is influenced by reason of its function in maintaining osmotic equilibrium in milk-secretion. Quoting analytical data supplied by Boggiid, Porcher finds tnat a high chloride content in milk is associated with a low percentage of lactose, and vice versa. This statement, when considered in conjunction with the solids-not-fat and soluble ash correlation, leads one to infer that deficiency in solids not fat is due in some measure to low lactose content. Soluble ash shows considerable variation with months of year. The percentage of soluble ash is _ considerably higher in the summer than in the winter. This is the reverse of the solids-not-ifat monthly variation. Assuming Porcher’s conclusions regarding the relation of lactose to sodium chloride to be correct, high soluble ash in milk indicates low lactose content, and therefore low percentages of solids -not fat in the. summer months are due to a deficiency in lactose. The insoluble ash percentage falls with the solids not fat, but the rate o r fall is not of the same magnitude as the rate of rise in the case of the soluble ash.

SEASONAL VARIATION. With regard to seasonal variation, phosphoric acid appears to be influenced but little, with the exception df a slight rise in May and June and a fall in July. Lime, on the other hand, shows a steady fall in the late spring and summer, reaching a low percentage in August, following which a sharp rise occurs.

It therefore appears that in the summer period, when the solids-not-fat percentage is low, the lime percentage is also low. This is not due to protein deficiency, since the ratio solids not fat is low at that period, and any deficiency in solids not fat in the summer months must therefore be due in the main to lactose. It is suggested that this low linie content in the summer months is due to a deficiency of calcium compounds other than the combined calcium in the caseinogen, but this can only be determined with any degree of certainty by more detailed analyses than were possible in this investigation. An interesting physiological point is thereby raised. Does the balance of the mineral constituents Of milk alter during the year, and, if ,so, is this change due to the great difference in the nature of winter compared with summer feeding? Jn ot'-e----words, does grass influence the composition of the mineral constituents of milk ?