EFFECTS OF HEAT ON MILK ii 



Certain recent experiences, however, tend to show that it may 

 not be wise wholly to ignore the theory put forward some years 

 ago by Barlow that children fed exclusively on boiled milk are 

 inclined to develop a scorbutic tendency, and it is possible that 

 further examination of the physiological changes which milk 

 undergoes in process of heating might tend to throw some light 

 upon this. These may be briefly summarised as follows : — 



Up to 70° C. there is no apparent change, but about this tem- 

 perature a change takes place in the albumin : it is not precipitated, 

 but it is converted into a form which is easy of precipitation by 

 acids, magnesium sulphate, and other precipitants of casein. The 

 view most generally held that casein and albumin exist in milk 

 in combination with bases explains the behaviour of albumin in 

 heated milk. The mucoid proteid of Storch loses water at, and 

 probably below, yo^ C. 



At or a little below 80° C. the milk begins, as we have seen, to 

 alter in flavour, and certain organised principles (enzymes), the 

 nature of which is not fully known, undergo a change. The 

 presence of these principles in normal milk, and in milk which 

 has been heated up to a point not exceeding 80° C, and the fact 

 that they undergo a change when this temperature has been passed 

 may be shown by the following simple experiment : — If a small 

 quantity of a i per cent solution of Hydroquinone is added to 

 milk at varj'ing temperature up to 80', and hydrogen peroxide is 

 then dropped into the solution, a distinct rose coloration, turning 

 later to a crushed strawberry tint, will take place on the milk being 

 allowed to stand a few moments, a reaction which is absent if the 

 milk has been raised to a temperature above that point 



At about 100° C. calcium citrate may be deposited in a slight 

 degree, and if the milk be kept for some time at this temperature 

 slight oxidation sets in, with production of traces of formic acid, 

 and a deposition of salts takes place on the fat globules, causing 

 them to rise but slowly to the surface when the milk is subse- 

 quently cooled. The alteration in taste is more marked, and fusion 

 of the fat globules occurs. 



It should be mentioned also that milk which has been raised 

 to the boiling point is resistant to the action of rennet. 



The secretion of milk and influences bearing- upon it — The 

 mammary gland forms milk from the materials derived through 

 the lymph from the blood, and cannot be regarded simply as filter- 

 ing apparatus. It is well known that the gland cells are function- 

 ally active only for a certain period after parturition. The whole 



