Milk proteins and lactose
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. Individuals with milk protein allergy must avoid all milk products including cheese. Individuals with lactose intolerance tolerate cheese and small amounts of milk products.
Allergy to milk proteins
Milk protein allergy is a serious condition. The symptoms of an allergic reaction can vary from mild to severe, from eczema, vomiting and stomach pain, to asthma and systemic anaphylactic shock. Under special circumstances, death has occurred to milk. Even tiny amounts of milk/milk proteins can elicit severe allergic reactions in sensitized individuals.
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 micro flora in the colon.
Symptoms of lactase deficiency are stomach/intestinal distension accompanied with pain, flatulence and diarrhea. The individual sensitivity to lactose varies but most individuals tolerate small amounts of lactose, corresponding to approximately 100 ml of milk per day.
Milk - a very common ingredient
Milk is a common ingredient in several different kinds of food like ready to eat dishes including sausages and meatballs, cakes, cookies, bread etc. Dark chocolate is often contaminated with milk and the concentrations can be very high. Concentrations above 1000 mg casein/kg chocolate were found in the Nordic control project – Undeclared allergens.
Labelling
The presence of milk and products thereof including lactose in food products must always be declared, see further in the Food Information Regulation (EC) no 1169/2011.
Examples of methods of analysis
Cow's milk contains a number of different proteins. Caseins and the whey proteins lactoglobulin and lactalbumin are present in highest concentrations. Allergic individuals may react to one or several of these milk proteins. In addition, other proteins in cow's milk have been associated with allergic reactions. 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 or 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.
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.
Accredited methods should be used in official control. The Swedish Food Agency is accredited for analysis of casein in food.
Allergic reactions / Doses
The lowest dose of milk proteins/caseins that elicits an allergic reaction is not known. However, individual oral food challenge data can be compiled in order to estimate the proportion of the allergic population that would be likely to react to a certain dose of an allergen. The Swedish Food Agency has used such published data and developed a guide on how to calculate the risk of allergic reactions to certain concentrations of e.g. milk. The guide is in English and can be reached below (L 2022 nr 13).
The Swedish Food Agency has analysed concentrations of milk protein in food that have caused unexpected allergic reactions. The food and the descriptions of the allergic reactions have been sent to the Swedish Food Agency by the health care or by control authorities. A proportion of these reactions is presented in the table below. The presented examples are chosen in order to show that unexpected allergic reactions to milk protein can occur to different doses of milk, be caused by different food categories and cause different symptoms. The amount of food that has been consumed is estimated in most cases and the dose is thus partly estimated. Caseins constitute about 80 % of the total milk proteins.
| Food | Consumed amount | Casein conc. mg/kg | Estimated dose | Symptoms | Age (years) |
|---|---|---|---|---|---|
| Cinnamon bun | 15 g | 4 | 0.06 mg | Stomach pain | 3 |
| Pasta with tomato sauce |
200 g | 0.8 | 0.16 mg | Anaphylactic shock* | 3 |
| Bun | 60 g | 4.5 | 0.27 mg | Nausea, itching | 7 |
| Noodles | 30 g | 12 | 0.36 mg | Stomach pain, itching of the oral mucosa | 14 |
| Lasagna | 50 g | 7.5 | 0.38 mg | Anaphylactic shock* (asthma, itching) | 14 |
| Candies | 30 g | 30 | 0.9 mg | Anaphylactic reaction* | 6 |
| Chips | 15 g | 8 | 1.3 mg | Itching of the oral mucosa, swelling of the lips |
14 |
| Soy-based yoghurt | 20 ml | 107 | 2.1 mg | Anaphylactic shock* | 8 |
| Chocolate cake | 10 g | 250 | 2.5 mg | Anaphylactic shock*, (asthma, stomach pain, itching) | 10 |
| ”Icecream” (non-milk based) |
15 g | 18 | 2.7 mg | Stomach pain, swelling of the lips and throat |
14 |
| Biscuit | 25 g | 300 | 7.5 mg | Vomiting, asthma |
10 |
| Chocolate cake | 5 g | 1200 | 6.6 mg | Anaphylactic shock* | 9 |
| Soy-based formula | 250 ml | 40 | 10 mg | Asthma, vomiting |
5 |
| Soy-based ”cheese” | 20 g | 580 | 12 mg | Anaphylactic shock* | 20 |
| Chocolate | 10 g | 1300 | 13 mg | Itching | 1 |
| Meat balls | 20 g | 890 | 17 mg | Stomach pain, itching and swelling of the lips and throat |
- |
| Chocolate | 22 | 1000 | 22 mg | Anaphylactic shock* | 62 |
| Chips | 40 g | 830 | 36 mg | Fatal anaphylaxis** |
10 |
| Gravy | 4 g | 8900 | 36 mg | Urticaria, swelling of the lips |
20 |
| Fish soup | 50 g | 1000 | 50 mg | Anaphylactic shock* | 4 |
| Sausage | 100 g | 600 | 60 mg | Fatal anaphylaxis** |
15 |
| Coleslaw | 40 g | 2240 | 90 mg | Anaphylactic shock* | - |
| Pancake | 50 g | 4300 | 215 mg | Itchy throat |
- |
| Meal replace-ment | 35 g | 8900 | 310 mg | Anaphylactic shock* |
44 |
* Anaphylactic shock means that the allergic individual suffers from a severe allergic reaction that induces symptoms from several organs. At least one of the symptoms has to come from the airways, the circulation or the general condition needs to be severely affected in order for the reaction to be classified as an anaphylactic shock (The Swedish Association for Allergology).
** Fatal anaphylaxis means that the shock proceeds to unconsciousness and death
