Allergy to milk proteins
Allergy to milk is a reaction to the proteins in contrast to lactose intolerance, where the milk sugar, i.e. lactose is causing the problems.
Cow’s milk contains a number of different proteins. Caseins and the whey proteins lactoglobulin and lactalbumin are present in highest concentrations. Allergic individual may react to one or several of these milk proteins. Even other proteins in cow’s milk have been associated with allergic reactions. Milk protein allergy is a serious condition. Even tiny amounts of milk/milk proteins can elicit severe allergic reactions in sensitized individuals.
Milk is a common ingredient in the following food: sweet buns, cakes, cookies, meringues, potato gratins, pâtés, meatballs, hamburger, sausages, powder for gravy, legume salads, mayonnaise, pancakes, waffles, omelet’s, sweets, toffees and dark chocolate.
Milk might also be an ingredient in bread, mashed potatoes, vegetable soups, stews, fruit/berry desserts, curd, vanilla cream, ready to eat dishes with meat, fish and egg as well as mayonnaise.
Milk in small amounts is present in butter and margarine. Bread can be brushed with milk or milk protein (casein).
Lactose intolerance
Lactose (milk sugar) is a natural component in all kinds of milk. Lactose intolerant individuals have reduced levels of an enzyme, lactase, needed to hydrolyze lactose in the small intestine. Lactase deficiency allows the lactose to reach the large intestine where it is fermented by the colon micro flora. Symptoms of lactase deficiency are stomach/intestinal distension accompanied with pain, flatulence and in severe cases, diarrhea. The individual sensitivity to lactose varies but most individuals tolerate small amounts of lactose, corresponding to 100 ml of milk per day.
Labeling
The presence of milk and products thereof including lactose in food products must always be declared, see further in LIVSFS 2004:27 Livsmedelsverkets föreskrifter om märkning och presentation av livsmedel [in Swedish] (see link to the right).
Examples of methods of analysis
The caseins are the dominating proteins in milk and constitute about 80 percent of the proteins. The caseins are heat stable and thus suitable for the analysis of milk/milk proteins in food.
The whey proteins are the residual proteins in milk after removal of the caseins, i.e. about 20 percent of the proteins in milk. Lactoglobulin is one of the proteins in the whey fraction. Lactoglobulin is not as heat stable as the caseins but can be used as a complement for the analysis of milk in food products. The caseins are a better indicator for the presence of milk/milk proteins in compound food products unless only the whey fraction was included in the product to be analyzed.
Sensitive commercial ELISA test kits are available for the analysis of casein and lactoglobulin. The limit of quantification varies somewhat between different test kits and depends also upon the matrix. The limit of quantification for casein is as low as 0.5 mg/kg in certain matrixes. Test kits for lactoglobulin have even lower quantification limits however, with the exception for dark chocolate and other complex final food products. For such products the test kit is not suitable.
Casein can be detected in food samples using rapid methods, based on test strips, which are soaked in an extract of the food. Such tests are only qualitative, i.e. the result is given either as casein is present (positive) or casein is not present (not detected) in the food extract. Positive results need sometimes to be confirmed with quantitative methods. It is very important that qualitative test kits don’t give false negative results.
Lactose can be quantified with an enzymatic method (Lactose/galactose). The limit of quantification is just below 100 mg/kg. The enzymatic method is not suitable for the analysis of products where lactase has been added for the hydrolysis of lactose. Such products can be analyzed with chromatographic methods like HPLC or GC.
Providers of test kit often have a validation protocol to be submitted with the test kit upon request. Laboratories using commercial test kits must establish in house control of limit of detection and limit of quantification in actual matrices even if the test has been validated by the provider.
Allergic reactions / Doses
The concentration of casein detected in food product causing allergic reactions. These figures as well as the estimated doses can be a basis for those measures that can /should be taken. Caseins constitute 80 percent of the milk proteins. See link to the right.