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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.
2
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 (3,4) -
"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" (3).
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 (5,6) although some workers have noted higher losses of
vitamin C. Greater losses of vitamins occur with more severe heat treatment
(5,7).
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 (9).
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 (5,10), 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 (8).
3
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