Abstract
Collagen powder hydrolysates were reacted with a solution of commercial mimosa bark tannin extract. The mixture was prepared at ambient temperature and prepared at 80°C to determine what reactions, if any, did occur between the collagen protein through its amino acids and the polyphenolic condensed tannin. The reaction products obtained were analyzed by matrix assisted laser desorption ionization time-of-flight (MALDI ToF) mass spectrometry. Reactions between the two materials did appear to occur, with the formation of a relatively small proportion of covalent and ionic linkages at ambient temperature but a considerable proportion of covalent linkages tannin-protein amino acids and the disappearance of ionic bonds. The linkages between the two materials appeared to be by amination of the phenolic –OHs of the tannin by the amino groups of the non-skeletal side chains of arginine, and by esterification by the –COOH groups of glutamic and aspartic acid of the aliphatic alcohol-OH on the C3 site of the flavonoid units heterocycle of the tannin. The proportion of covalent linkages increases markedly and predominate with increasing temperatures. This tightening of the tannin-protein covalent network formed may be an additional contributing factor both to leather wear resistance and performance as well to leather shrinking when this is subjected to excessive temperatures.
Highlights
Vegetable tannins, both hydrolysable and condensed ones, are polyphenolic materials that have been used for a long time for the manufacture of heavy-duty leather
The interaction between any of the two types of vegetable tannins and the collagen of hides to prepare leather has always been known to depend on the strong complexation of the tannin with the collagen protein by the innumerable secondary forces acting between them
The experiment conducted were to examine by matrix assisted laser desorption ionization time of flight (MALDI ToF) mass spectrometry the products obtained by reaction of a condensed tannin with collagen at ambient temperature and at 80°C to determine if covalently co-reacted structures occur, in which cases and to what extent in the two cases
Summary
Both hydrolysable and condensed ones, are polyphenolic materials that have been used for a long time for the manufacture of heavy-duty leather. The interaction between any of the two types of vegetable tannins and the collagen of hides to prepare leather has always been known to depend on the strong complexation of the tannin with the collagen protein by the innumerable secondary forces acting between them While this is age-old acquired and recognized knowledge, the effect of temperature on both vegetable tanning and on excessive temperatureinduced shrinking of tanned leather has been ascribed to many existing effects, such as moisture loss and leather drying and others [10,11,12,13,14,15]. The presence in leather of the combination of tannin with collagen, this being a proteic material, renders probable that in this case covalent and ionic bonds between the two substances do occur at ambient and higher temperature These might play a role in leather stability as well as in its shrinking under excessive temperature conditions. The work presented here it is only aimed at, and limited to determine if covalently bonded structures occurs between collagen and tannin in view to render possible to understand in future their contribution to leather shrinking and stability as a function of the temperature
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