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Tissue Digestion - Technical Information

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The Effect on Plant and Animal Tissues

The Effects of Heating with Aqueous Sodium Hydroxide on the Biochemical Constituents of Plant and Animal Tissues

Proteins
This is a major constituent of animal cells and tissues. The effects of alkaline treatment include the breaking of all amide (peptide) bonds and generation of the sodium salts of free amino acids, with oligopeptides as intermediates in the reaction. Heating with alkali also destroys arginine, asparagine, glutamine, serine, threonine, cysteine, and cystine with racemization of the L-amino acids to D,L mixtures. In addition, carbohydrate (sugar) side chains are released from glycoproteins. Protein coats of viruses are also destroyed and the peptide bonds of prions should be broken under the extreme conditions of temperature and alkali concentration used in the process.

Nucleic Acids
There is rapid depolymerization of ribonucleic acid (RNA) and slower destruction of deoxyribonucleic acid (DNA). This is most important in its implications for potentially infectious materials. Both RNA and DNA viruses are completely destroyed by the hot, pressurized alkali solution.

Lipids
All carboxylic ester bonds of the triglycerides of common fat and the sterol esters and phospholipids of cell secretions and cell membranes hydrolyze with consumption of the NaOH, producing sodium salts of fatty acids (i.e., soaps). Amide bonds in glycolipids (fatty acylamides and N-acetyl groups bound to the aminosugars) are slowly hydrolyzed, with consumption of the NaOH. Polyunsaturated fatty acids and carotenoids (pigments) undergo double bond rearrangements and are destroyed.

Carbohydrates
As a group of biopolymers, carbohydrates are the least rapidly affected constituents. Starch and glycogen, large polymers of glucose, are immediately solubilized but require much longer treatment than other chemical constituents for breakdown of the polymers. Other large (1-4)-linked glycans, such as cellulose, are quite resistant to treatment. Glycoprotein and glycolipid carbohydrate side chains, glycosaminoglycans, and insect chitins are deacetylated at their N-acetyl hexosamine constituents and, in the case of (1-3)-linked glycans, are slowly degraded. All monosaccharides, such as glucose, galactose, and mannose, are rapidly destroyed by the hot aqueous alkaline solution.

Refractive Materials
Some materials are unaffected by the alkaline hydrolysis, although they are sterilized by the elevated temperature. These include many materials with which animal carcasses are often associated, such as cellulose (paper, undigested plant fibers, wood shavings, string), rubber, most plastics, ceramics, and stainless steel (catheters, needles, clips, and staples), all of which are retained in the processing basket and may be easily removed. Silk and collagen sutures, however, being proteins, are rapidly digested. Bone and tooth fragments, also retained in the basket, are easily crushed and may be used as bone meal on institutional landscaping projects.