"The Detrimental Effects of Heat Treatment"

Many years ago when pasteurisation was a relatively new phenomenon, dire warnings were made of its harmful effects on the health-giving properties of untreated milk. Pottenger completed his famous cat experiments (1) and concluded that unpasteurised milk was better for health than pasteurised. Studies on rats over several generations showed that haemoglobin counts were higher in the untreated milk-fed rats compared to the pasteurised fed group; hair loss occurred in the pasteurised milk group and after four generations those on pasteurised milk failed to lactate and could be bred no further (2). Even sanatoria made a point of obtaining specially tuberculin-tested untreated milk for their patients.

These early experiments were too unsophisticated to withstand modern statistical analysis but this does not deny their historical value. Reference can, however, be made to more recent and precise experiments which have compared untreated with heat-treated milk.

"The Effect on Flavour"

This effect is obvious to the consumer and has been noted by researchers - "Fresh milk has a delicate flavour contributed by compounds of low molecular weight in trace amounts. Heat treatment affects the flavour of milk and produces detectable off-flavours".

"The Effect on Nutritional Value"

The components thought to be most affected here are the water soluble vitamins and the proteins. There is approximately a 10% loss of vitamins BI, B6, B12 and folate and a 25% loss of vitamin C although some workers have noted higher losses of vitamin C. Greater losses of vitamins occur with more severe heat treatment .

The proteins in milk are of two kinds - casein and whey. Caseins are remarkably heat stable but the whey proteins, which are of much higher nutritional value, are denatured by heat treatment (5,8). The degree of denaturation varies depending on the temperature and time of heat exposure - 10% during pasteurisation, 70% during ultra heat treatment. Homogenisation has a further destabilising effect.

Several experiments have reported adverse effects of heat treated whey proteins on baby pigs and calves. Although no such effects have been reported for humans and it is generally assumed that such denaturation is of no practical significance, some workers argue that the effects of the cross-linking of whey proteins caused by heating may be detrimental to the consumer, possibly via an effect on nutritional value and also perhaps by the increased potential to trigger some form of allergic reaction.

Vitamins and minerals can be bound to proteins and this binding can facilitate their absorption from the digestive system. Pasteurisation destroys the ability of certain proteins in milk to bind the important vitamin folate and hence help its absorption. Heat treatment might also cause a similar inactivation of other protein carriers, for example those for zinc and vitamin B12.

"The Effect on Allergic Reactions"

Milk allergy has a relatively low incidence in this country (approx. 1% of the adult population (13)). Although it is widely believed that heat treatment will reduce milk's ability to provoke an allergic reaction in sensitive individuals, this may not be so in all cases.

Milk allergy can be divided into two types:
Anaphylactic Allergy
Atopic Allergy

In the first instance, heat treatment does diminish, but does not completely destroy, the allergenic properties of milk (9, 16). In the second type of allergy, atopic, it was found by one researcher that heat processing may render milk more harmful to atopic individuals. The B-lactoglobulin from fresh raw cow's milk had a lower allergy-causing reactivity than that from pasteurised or otherwise heat-processed milk.

One doctor has even gone so far as to suggest that the response of the body to heat-denatured milk protein may contribute to the development of atherosclerosis. He has produced evidence linking the introduction of the Holder pasteurisation technique and its geographical distribution to the incidence of heart disease. Such results, though interesting, should be treated cautiously, since they are statistical associations and not evidence of cause and effect. Whilst others have not found supporting evidence for this theory, it is clear that more critical research is necessary before heat treatment is universally enforced.

"The Effects of Heat Treatment on Disease Bacteria"

The major advantage of pasteurisation, if not the only one, is its ability to destroy pathogenic bacteria. There are, however, two fundamental questions to be asked: Does all pasteurised milk offer absolute protection from infection? Does the consumption of all untreated milk post a significant health risk?