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Tissue Digestion - The Tissue Digestion Process

> Chemistry of the WR2 Process
> Composition of Animal Tissues
> Effects of Alkaline Hydrolysis
> Results of the WR2 Process
> Applications of the WR2 Process
> Aldehyde-Containing Fixatives and Embalming Fluids
> Infectious Waste
> Biological Warfare Agents
> Chemotherapeutic Agents
> Control and Safety Systems

Effects of Alkaline Hydrolysis on:

Proteins
Alkaline hydrolysis ultimately leads to the breaking of all peptide bonds in proteins, the major solid constituent of all animal cells and tissues.  Sodium or potassium salts of free amino acids are generated by the hydrolysis; oligopeptides (small chains of amino acids) are generated as intermediates in the reaction. Some amino acids, such as arginine, asparagine, glutamine, and serine, are destroyed while others are racemized; i.e., the molecule is structurally modified from a left-handed configuration to a mixture of left-handed and right-handed molecules. In addition, the carbohydrate (sugar) side chains are released from glycoproteins. The protein coats of viruses are destroyed and the peptide bonds of prions are broken under the extreme conditions of temperature and alkali concentration used in the BioSAFE/WR2 Process.

Lipids
Simple fats consist of three fatty acid chains bound through ester bonds to a molecule of glycerol. During the Alkaline Hydrolysis Process, all of these ester bonds, as well as the sterol esters and phospholipids of cell secretions and cell membranes hydrolyze with consumption of the alkali, producing the sodium and potassium salts of fatty acids, namely, soaps.  Again, KOH may be the preferred alkali as potassium soaps remain liquid as the hydrolysate cools toward room temperature. Amide groups in glycolipids, another cell membrane constituent are also hydrolyzed, with consumption of the alkali. Polyunsaturated fatty acids and carotenoids (pigments) undergo molecular rearrangements and are, thus, destroyed.

Carbohydrates
As a group of polymers, carbohydrates are the constituents of cells and tissues that are the most slowly affected by alkaline hydrolysis. Both glycogen, the most common large polymer of glucose in animals, and starch, the most common large polymer of glucose in plants, are immediately solubilized.  However, the breakdown of these polymers requires much longer treatment than is required for large intracellular and extracellular polymers. Some large carbohydrate molecules, the b(1-4)-linked glycans, such as cellulose, are quite resistant to treatment. On the other hand, cellulosic materials usually occur only in the digestive tracts of grazing animals where, as a rule, they have been macerated and partially digested. Consequently, further degradation, even if slow, usually does not pose a problem. The Process also removes critical groups from the molecules of glycoproteins, glycosaminoglycans, and glycolipids, the principal carbohydrates of connective tissue, as well as from the chitinous exoskeletons of insects and other invertebrates (e.g., the carapace of crabs or lobsters); (1-3)-linked glycans, such as chondroitin sulfates, are slowly degraded. All monosaccharides, (simple sugars) such as glucose, galactose, and mannose, are rapidly destroyed by the hot aqueous alkaline solution.

Nucleic Acids
Nucleic acids are large, unbranched linear polymers, held together by phosphodiester bonds; which are similar to the simpler ester bonds of fats but include a phosphate group as part of the bond structure. These ester bonds are also hydrolyzed with consumption of the alkali, rapidly destroying ribonucleic acid (RNA) and more slowly destroying deoxyribonucleic acid (DNA).

Indigestible Materials
Paper, string, undigested plant fibers, and wood shavings (bedding) are among the cellulose-based items that may be associated with animal carcasses but are not digestible by alkaline hydrolysis. Rubber, most plastics, ceramics and stainless steel (catheters, needles, clips, and staples) also cannot be digested by alkaline hydrolysis, although silk and collagen sutures, which are protein in nature are rapidly digested.

mouseThe indigestible materials are completely sterilized by the BioSAFE/WR2 Process. They can be removed from the basket of the Digestor and disposed of as ordinary waste at a sanitary landfill, with appropriate treatment of any sharps. The undigested residue after alkaline hydrolysis of animal tissues and carcasses, specifically the inorganic component of bones and teeth (calcium phosphate), constitutes approximately 2% of the original weight of the tissue (less than 2% of the volume) and remains in the basket as bone “shadows”. It is completely sterile and is easily crushed to a powder (Figure II-2) that may be used as a soil additive.