Colin Berry on his blog now added an interesting comment quoting an old paper by Lea and Hannan. I have this paper (not only the abstract). This paper is on the "effect of activity of water, of pH and of temperature on the primary reaction between casein and glucose". Not exactly the same that expected on the Shroud. However, it is a good example of the changes in color in a simple "Maillard system".
What does one read in this paper ? The changes in color were studied only at 37°C with different values of pH and Relative Humidity (RH). The color was expressed in Lovibond units. Look at Wikipedia to see what Lovibond (old) scale is. Let’s say that bellow 2 no color is truly seen. At 3 it is yellow, at 5 yellow-brown. What I read is that after 64 days at 37°C. and 70% RH a color between 2.6 (pH 6.3) and .4.4 (pH 10) can be seen.
More interesting is the subsequent paper here by the same authors : "A note of the relative rates of reaction of several reducing sugars and sugar derivatives with casein" Biochimica Acta et Bipohysica Acta 4 (1950), p.532-534 that is available for free (I can’t give the link. Just use "advanced search" in Google Scholars). Now, with the same methods, the authors studied the color development after 4, 8 and 16 days at 37°C (pH 6.3 and 70% RH). They used 8 different carbohydrates.The Lovibond color for glucose after 16 days of storage was 0.3 (nearly no color, like in the previous experiment). But the color of arabinose was 2.5 and that of xylose was 2.7 after 16 days only. It means, as expected, that the color depends also on the carbohydrate and glucose used in the first paper is one of the worst.
There are many other parameters to study. Particularly the last step of the Maillard reaction (polymerisation and production of true melanoidins).
At least, I hope now that nobody will claim that there is no Maillard reaction and no color at room temperature.
I happened to notice that Colin Berry is responding in his blog with a regular blog posting. That is fine. Editing an extant posting and providing a link-only is not fine. The best netiquette is to provide a meaningful comment, perhaps an extract, and a link. And I would be happy, always, to accept such a comment. I don’t really understand the problem or Colin’s anger. Anyway, Colin writes:
Hello again Thibault. To avoid any misunderstanding re your latest comment on The Other Site, let me tell you how I came to link the 1949 Lea and Hannan Biochim.Biophys.Acta paper with the claim that the rate of the casein-glucose reaction increases a massive 40,000-fold between 0 degrees C and 80 degrees C.
[ . . . ]
You say you have the entire paper, but you also appear to be suggesting ( I may be mistaken) that there is no mention in that paper of the 40,000 factor. Is that so? Have both my sources quoted the wrong paper?
As a courtesy, I would have alerted
youThibault to this posting by inserting a link on The Other Site [that is this blog], as I tried to earlier for anoxie and Jos, but Dan Porter is up on his high horse again, passing judgement on my “netiquette”, deleting my links, and engaging yet again in some highly personal remarks at my expense. I shall be avoiding that site and its despot of a blogmeister even more than I do already – at least for the forseeable future. I simply don’t have the time or patience to respond to the steady stream of low-level ad hom flak that emanates from that site.
No games. Here is the link.