QUALITY OF MILK

Timaru Herald, Volume CXXV, Issue 18352, 24 August 1929, Page 10

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 a very important and complex constituent. In the milk itself there are present (a) inorganic salts, (b) inorganic bases combined with citric acid, and (c) calcium, phosphorus, and sulphur, combined in the amino-acid groups of 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, but part of the phosphorus in this portion of the milk solids, with practically all the sulphur, is lose during ashing. Milk-ash therefore does not wholly represent the mineral constituents cf milk. In the course of this investigation determinations of the total ash. water soluble and insoluble ash, toal calcium, and total phosphorous were made and the results obtained throw some interesting light on the variations m the composition of the mineral portion of milk. The ash content of milk appears to have a season variation. The ash percentage reaches a maximum 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-fat percentage is low. The soluble portion of milk-ash conconsists chiefly of sodium chloride, while calcium phosphate is the main constituent of the 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 percentage of solids-not-fat. It is apparent that milk low in solids not fat is rich in soluble ash and poor in soluble ash. This point may have considerable physiological importance. Porcher states that sodium chloride (the principal salt in the soluble ash) is one of the most variable constituents of milk, and the amount present in milk is influenced by reason of its function in maintaining osmotic equilibrium in milk-secretion. Quoting analytical data supplied by Boggild, Pocher finds that 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 colids-not-fat and soluble ash correlation, leads one to infer that deficiency in solids not. fat is due in some measure to Jo*" lactose content.

Soluble ash shows considerame variation with months or yea*, ih® percentage of soluble asn is considerably higher in the summer tnan in tne winter. This is the reverse ot one solids-not-fat monthly variation, Assuming Porcher’s conclusions regarding the relation of lactose to sodium chloride to be correct, nigh soluDie 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 nercentage falls with the solids-not-fat but the rate of fall is not of the same magnitude as the rate of rise in the case of the soluble ash.

With regard to seasonal variation, phosphoric acid appears to be influenced but little, with exception of 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.

j 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 lime 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? In other words, does grass influence the composition of the mineral constituents of milk?