Koemelk : effecten van bewerkingen op gezondheid

A small percentage of the milk consumed in the Netherlands is raw, unprocessed milk. All milk distributed through shops and supermarkets are at least standardized and heat treated (e.g. pasteurized), and most of the consumption milk is homogenized. Yet, some consumers prefer to drink unprocessed, raw milk, because of its taste or expected positive health effect. In this report, the results of a literature research are presented. The changes in the milk as a result of processing and the potential effect of these changes on the health of humans are investigated. Although numerous references and claims have been made in the “grey literature”, there is only little scientifically sound research into this subject. The processing of milk has a clear influence on the composition and the physical structure of the milk. Because of food safety reasons, all consumption milk in the Netherlands must undergo a heat treatment. Through heating the number of bacteria present in the milk (both beneficial and harmful bacteria) will be reduced. Further, heat treatment causes denaturalization of proteins, growth hormones, enzymes and immunoglobulines. A second form of processing, performed in all but biodynamic consumption milk, is homogenization. Through homogenization large fat globules (circa 3-5 μm) in the milk are distributed into a large number of small fat particles (circa 1 μm), thus preventing the fat to form a creamy layer on top of the milk. Both processing steps have, next to the wanted effects, also some unwanted effects, which potentially lead to health effects in the consumer. First it is clear that the consumption of raw milk always implies a certain risk. Raw milk contains harmful bacteria, which will largely be killed during heating of the milk. The food safety risks of raw milk can, especially when used incidentally and in sensible persons, never be neglected, as this also can’t be totally neglected in pasteurized milk. As for all raw food products, this requires special care and good hygiene when working and storing raw milk. For an increased risk of Crohn’s diseases, commonly mentioned in association with the consumption of raw milk, the literature gave no clear answer. Clear is though, that as a result of homogenization, changes in the structure of the milk arise. The surface between the fatty and the watery part of the milk increases 4 to 10 times and different (protein)complexes are attached to the surface of the fat globules, next to the original Milk Fat Globule Membrane. As a result, homogenization leads to a better digestibility. This seems to be beneficial for persons with intestinal problems, though it might be unfavorable for persons with allergic complaints. Milk intolerance and milk allergy are disorders which have been most frequently investigated in relation to milk. On the basis of the change in composition/structure of processed milk, an effect on allergies could be expected. This effect is confirmed in animal studies. However, human clinical trials of short duration showed that these effects were difficult to demonstrate. In blinded interventions study persons, who themselves said to be allergic for homogenized milk, were not able to notice a difference in effect after consumption of homogenized and non-homogenized milk. These results take the edge of the suggestion that raw milk is always easier to tolerate or induces less allergic reactions than processed milk. Further, no prove was found that the drinking of milk in general increases the risk of heart problems or diabetes. Whether processing has an influence is not easy to say, as ample research exists, however, for type 2 diabetes there is a hypothesis on which an effect of homogenization on an increased risk can be based. In several large population based studies, a clear relation has been found between the drinking of raw milk and the reduced risk of having eczema, asthma or other allergic complaints.