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How precisely does the five common ways of cooking an egg - boil, fry, raw, scramble, omelette - and the issue of low/high heat less/more cooking time, affect the resulting protein molecules?

Please note that this question has nothing to do with salmonella, thanks. This question has nothing to do with the fats or oils used for cooking. This question has nothing to do with health or nutrition outcomes.

I want to know factually the outcome for the protein molecules due to the different cooking methods.

I ask because "what form you put protein molecules in to" drastically affects ongoing cooking, cuisine, recipes.

I observe that "egg protein science" seems to have varied drastically, even controversially, the last 40-50 years. Hence the question here, as this is a place you can get FACTS, I have found.

(As an aside, I noticed there is a huge amount of confused, contradictory, controversial, or even almost political information about eggs. It's one of those issues that is difficult to google, the first 999,999 results are IF YOU EAT EGGS YOU WILL DIE OF SALMONELLA don't mention Japan Hence the "food science" tag which may help :O )

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    I noticed there is a huge amount of confused, contradictory, controversial, or even almost political information about eggs Well, I'd say it's somewhat on the level of almost most food/health topics. And "political" is the right word because obviously there is not only the question of health aspects, but also the question about animal issues. Also, undoubtedly, the issue is that even if you read the most recent pubmed meta review (2020) that I could easily find, which comes to the result that eggs are not an issue, they obviously have to list all the issues with their respective...
    – AnoE
    Commented Jun 24 at 14:28
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    ... probabilities, and to the reader not trained in medical statistics, it looks like there are dozens of egg-related health issues. Even if their conclusion then say that "up to 1 egg per day is fine" (they do not say that more than 1 egg is a problem!), the untrained reader will of course assume that it is. Especially if they have an agenda. Fascinating topic!
    – AnoE
    Commented Jun 24 at 14:29
  • (In terms of "government health advice", sure, "egg advice" from governments (in the West) has always been a dumpster fire amongst dumpster fires.)
    – Fattie
    Commented Jun 24 at 14:52
  • You list 'raw' as a cooking method. Do you mean 'raw pasteurized' or actually 'raw'?
    – JimmyJames
    Commented Jun 24 at 16:05
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    @AndrewMorton what a remarkable internet tip, thanks!
    – Fattie
    Commented Jun 25 at 11:42

1 Answer 1

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Little to no difference, at least in ways that are measurable outside of the laboratory. The only difference is the rate at which heat is applied and how it is applied, which changes how fast the egg sets.

This is assuming you are talking about the egg albumen (egg white), which is about 90% water and 10 % albumen proteins. Ovalbumin makes up about 55% of the protein in the albumen, and the rest are pretty similar biochemically; mostly being phosphoglycoproteins. Because there is so much water present in the albumen, the method of heating makes little difference to the outcome - the water content won't mix with fat/oil.

What happens in the yolk is more complex because it is a mixture of proteins, salts and fats along with water, but follows the same general trend.

What happens when you heat egg white is that at a certain point when heating, the ovalbumin (and other proteins) change from an ordered 3-D structure into a disordered beta-sheet conformation, exposing hydrophobic amino-acid residues, which then cause the sheets to tangle together to produce insoluble aggregates. This process follows first-order reaction kinetics and is irreversible1 (you can't unboil an egg...).

However, from ref 1 above, it would seem that a faster heating results in smaller aggregations of protein. This might mean alterations in the texture of the denatured proteins (would need experimental validation to prove), with smoother textures being produced with short cooking times, but it would be very hard to control in the kitchen and most people wouldn't notice the difference and very few are going to wait the 5000 minutes (about 3.5 days) used in the paper to see if an egg is grainy textured.

The addition of salt results in larger aggregates while heating2, and many people salt their eggs while cooking (certainly for scrambled and fried), but no-one complains of grainy eggs from that.

On the other hand, you can induce gel formation in heat denatured egg proteins3 by the addition of salts and glucose (actually glucono-delta-lactone, which might be an interesting alternative if you are really into molecular gastronomy.

As mentioned in a comment from @GentlePurpleRain, the reason you can get a perfectly cooked egg is that the denaturation points of the yolk and the white differ, with the yolk's being higher (and less defined because of the complex mix in it). This means you can get a solid white before the yolk fully sets.

Refs:

  1. Weijers M, Barneveld PA, Cohen Stuart MA, Visschers RW. Heat-induced denaturation and aggregation of ovalbumin at neutral pH described by irreversible first-order kinetics. Protein Sci. 2003 Dec;12(12):2693-703. doi: 10.1110/ps.03242803. PMID: 14627731; PMCID: PMC2366979.

  2. Choi SJ, Moon TW. Influence of sodium chloride and glucose on the aggregation behavior of heat-denatured ovalbumin investigated with a multiangle laser light scattering technique. J Food Sci. 2008 Mar;73(2):C41-9. doi: 10.1111/j.1750-3841.2007.00615.x. PMID: 18298715.

  3. Choi SJ, Lee SE, Moon TW. Influence of sodium chloride and glucose on acid-induced gelation of heat-denatured ovalbumin. J Food Sci. 2008 Jun;73(5):C313-22. doi: 10.1111/j.1750-3841.2008.00770.x. PMID: 18576975.

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    I would add that the reason that it is possible to cook a perfect soft-boiled egg is because the two main proteins in the yolk will denature at different temperatures. If you can heat the egg to just the right temperature to affect one protein but not the other, you end up with a nice, thick, but still liquid yolk. Commented Jun 24 at 17:44
  • @GentlePurpleRain Good point, I'll edit that in.
    – bob1
    Commented Jun 24 at 20:15
  • Thanks. What you added is true, but is not what I said. I was talking specifically about the yolk. It contains two different main proteins (as well as many others in much smaller quantities). If the egg is raw, you have a liquid, runny yolk. If you cook the egg enough to denature one of the proteins, you get a thick, gooey yolk like in a soft-boiled egg. If you heat the egg more, so the second protein is also denatured, you get a solid, crumbly yolk like in a hard-boiled egg. That is why sous-vide is perfect for soft-boiled eggs. Commented Jun 26 at 15:33

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