changes in milk protein with heat

[kisnow]

Here's a question for any food chemists out there. Background: My son, who has been allergic to milk for all of his 13 years, has just recently discovered (under medical supervision) that he can tolerate and enjoy milk that has been cooked. He has eaten cheese that has been melted on top of chicken parm under the broiler, ice cream that has been made custard-style with milk that has simmered at 206 degrees, and lots of baked goods including butter cookies. But, he had a mild reaction in his throat to a biscotti that had a white chocolate icing. I've tried to find info on the temperature that changes the milk proteins casein and whey, but all I have found so far tends to relate to the pasteurization process.

Question: Does anyone know the specific temperature that changes the milk proteins--I think the term is "denaturing"? Based on our experience, I would think it would have to be above 100 degrees (to account for the white chocolate reaction). But what is the minimum temperature that it would need to be held at. Obviously, I'd rather investigate this issue from the comfort of my computer than from the inside of an ER-- don't really want to turn the boy into a guinea pig in my kitchen. As we adjust to our new dining possibilities, I'm just trying to figure out how "cooked" is "cooked"?

[Little Colleen]

I work in the medical field & was reading about this recently...I can't give you the answer but I can tell you who can. Dr. Hugh Sampson (allergist) at Toronto's Mount Sinai Hospital is presently doing research on this topic and is working on developing a blood test that he hopes can be used commercially to determine who can safely tolerate heated milk (since not all milk-allergic kids can)....also allergist Dr. Rbt Wood and research nurse Kim Mudd at Baltimore Johns Hopkins are also working with this problem, and have even been able to increase exposure such that some kids have eventually even been able to tolerate milk that hasn't been heated. I am sure if you were to contact these people they would be glad to give you some info; most researchers are more interested in being helpful than secretive.

Interesting ... they think it has to do with the way the proteins change shape as the milk is heated such that the immune systems do not recognize them as an allergen. If you do find out what temp/time combination is essential I too would be interested in hearing....!

[ChickenStu]

Probably more likely that the problem is with the whey proteins, as casein proteins are primarily just nutritive.

The most numerous whey protein coagulates around 172 F, but thats about all the info I can find/remember...just re read the milk section in on food and cooking last week. Thanks Harold McGee!

[dougal]

There are lots of areas of cooking where "scalded" milk is called for.

At an empirical level, I've taken this to mean heating to almost but not quite boiling, but sufficiently hot that on cooling, a skin forms.

I believe the skin is a protein product ...

Wikipedia suggests that the temperature for this is 82C - but that seems to be a conversion of the round number of 180F - so don't take it as being precise!

However, I'd suspect that what is happening is enzymic, rather than pure thermal destruction of one or more specific proteins - that's called 'burnt milk'!

And the thing about enzymic reactions is that they don't happen instantly - they take a variable amount of time at different temperatures.

So, just as with pasteurisation, you'd have to specify a time at whatever temperature ...

I suspect that any taste/mouthfeel changes may be associated with the transformations that are desired - and hence unavoidable.

Any experimentation at lower temperatures is going to involve longer, possibly much longer, holding times. And here I'm thinking of sous vide methodologies ...

But, hey, if you have a milk-treatment protocol (heat pan to boiling point and then cool naturally) that works for you, then exploit it!

[kisnow]

Thanks-- I have read about some of Dr. Wood's research via the Food Allergy & Anaphalaxis Network. I've never contacted a doc out of the blue with a research question, but perhaps I'll give it a try.

And I also think the structure of the protein changes via heat to something that isn't recognized as an invader. It's also interesting that some cheeses, especially hard cheeses seem to be less problematic for my son. We had been humming right along on a dairy-free diet for him for years until last summer when we discovered that he had actually eaten some sundried tomato pesto that had parmesan in it, and he didn't have a reaction. That got us wondering if had outgrown his allergy over the years. We had him tested-- both skin-prick and blood tests-- which indicated he was still wildly allergic. I pressed the issue with our allergist and she finally allowed us to do an oral challenge in her office (as opposed to the ER with an IV all set up.) And lo, and behold, he was able to eat two muffins made with milk.

I know cheese making involves heating the milk to various temperatures, but I'm also wondering if the aging process of hard cheeses also helps to break the protein down. I wish there was some specific answer to these qustions, but I have a feeling that it will all depend on the milk and what it's mixed with as well as whatever is happening in my son's body at the time.

As an aside, he had his first slice of cheese pizza tonight and had no ill effects-- which led to another slice, and then another, and then another! For a 13 year old boy, the ability to go out to pizza with his friends is worthy of doing a huge happy dance in our family!

[scott123]

http://www.globalgourmet.com/food/special/2004/onfood/milk.html

Do a search on the page for 'Whey Proteins.' It's that section where he talks about lactoglobulin, the most abundant whey protein, which happens to be denatured by heat at 172 deg. f. He also talks about acid coagulation and whey drainoff processing for a 'true' ricotta.

White chocolate is made with whole milk powder. Whole milk powder, as far as I know, is made using a spray process and probably isn't exposed to lactoglobulin denaturing temps.

You might want to pick up some powdered casein (bodybuilding site) and some powdered whey protein isolate and, under your doctor's supervision, test him for both. Again, like milk powder I believe they're a spray dried process. That might allow you to narrow it down to the whey.

[ChickenStu]

The process of making cheese breaks it down into curds and whey through coagulation. Thus eliminating a lot of the whey proteins.