Linen is made from the fiber of the flax plant. The composition of linen is usually greater than 90% cellulose, a small amount of cross-linked hemi-cellulose, pectin, and less than 5% lignin as a structural component. Linen textiles and clothing are among the earliest fabrics known to man and date back many thousands of years. In ancient Egypt linen was worn as clothing as well as used for burial shrouds and mummification. The linen of the Shroud of Turin is of a 3:1 herringbone twill weave. The process of weaving it was more complex than producing the altogether more common plain weave. Examples are therefore very rare, but they are known from at least a millennium before Christ’s lifetime.
The basic chemistry of cellulose is that of many molecules of the sugar glucose linked together through a beta-1,4-bond. That is, the number 1 carbon of one glucose is linked to the number 4 carbon of another glucose through an acetal or glycosidic linkage. Linkages exist in three dimensions. In the case of cellulose, the glycosidic linkage is from above the plane of the glucose as shown in the following diagram. This is referred to as the beta linkage.
A related structure is amylose, a component of starch, which is also linked through glucose molecules, but in this case by alpha-1,4 bonds. The glycosidic linkage from one glucose to another is below the plane of the glucose molecule as shown in the following diagram.
The uniqueness of each structure is shown by specific protein enzymes that will attack and digest one structure but not the other. For example, cellulases, which are mainly associated with microorganisms found in the soil, will attack only the beta-1,4-glucose linked celluloses at the linkage site. While amylases found in the digestive tract, will attack and digest alpha-1,4-glucose linked amyloses but not celluloses. Another related structure is chitin, a major structural component of fungal cell walls. In this case, the beta-1,4-linked glucose molecules have an N-acetyl group at the second carbon of glucose as shown in the following diagram. Chitinases are enzymes that only digest the chitin structure at the linkage site.
The bacterial cell wall peptidoglycan is a beta-1,4-linked glucose polymer composed of alternating units of N-acetylglucosamine (as in chitin) and N-acetylmuramic acid. N-acetylmuramic acid is an N-acetylglucosamine (chitin) with a pyruvic acid (PA) group attached at the third carbon of the glucose molecule. Linked to the PA group is a short peptide (amino acids in a chain) which are in turn cross-linked by amino acids to another peptide. The bridge peptides are in turn attached to the peptide on another peptidoglycan strand forming a network. See the following structure.
Enzymes produced by bacteria and fungi can release the N-acetyl groups at C-2 and the entire cross-linking peptide bridge at C-3 leaving behind a structure that is basically cellulose, the major building block of linen. Undoubtedly the Shroud linen is riddled with various pieces of chitin and peptidoglycan in various phases of degradation. However, no scientific instrument or treatment would be able to distinguish the cellulose originating from the linen flax versus the cellulose originating from fungal chitin and bacterial peptidoglycan degradation. Thus any radiocarbon dating of the Shroud of Turin would be null and void.
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