Chapter 15: Identification of Saliva

15.1: Biological Characteristics of Saliva

• The human salivary glands produce 1.0–1.5 L of saliva daily.

• About 70% of saliva is produced from the submandibular salivary glands, 25% from the parotids, and 5% from the sublingual salivary glands.

• Saliva is largely water containing small quantities of electrolytes, proteins, antibodies, and enzymes.

  

Amylases

• Amylases: Are enzymes that cleave polysaccharides such as starches, which are composed of D-glucose units connected by α1→4 linkages.

• Starches contain two types of glucose polymers:

  • Amylose consists of long, linear chains of glucose residues connected by α1→4 linkages.
  • Amylopectin is highly branched and consists of linear chains of glucose residues connected by α1→4 linkages with the branch points connected by α1→6 linkages.

• Two types of amylases are characterized:

  • β-Amylases found in plant and bacterial sources cleave only at the terminal-reducing end of a polysaccharide chain.
  • Human α-amylases cleave at α1→4 linkages randomly along the polysaccharide chain.

• Human salivary α-amylase (HSA): Encoded by the Amy1 locus, synthesized at the salivary glands and secreted into the oral cavity.

• Human pancreatic α-amylase (HPA): Encoded by the Amy2 locus, is synthesized by the pancreas and secreted into the duodenum through the pancreatic duct.

  

  

15.2: Analytical Techniques for Identification of Saliva

Presumptive Assays

• Visual Examination

  • The lighting techniques used to search for semen stains can be utilized in searching for saliva stains.
  • Microscopic examination with proper histological staining can also be performed to identify the buccal epithelial cells, indicating the presence of a saliva stain.

• Determination of Amylase Activity

  • Starch–Iodine Assay

  • Iodine is used to test for the presence of starch.

  • The amylose in starch reacts strongly with iodine to form a dark blue complex, while amylopectin develops a reddish-purple color.

  • Colorimetric Assays

  • Dye-labeled amylase substrates such as dye-conjugated amylose or amylopectin are utilized.

  • These substrates are not soluble in water.

    

    

Confirmatory Assays

• Identification of Human Salivary α-Amylase

  • Immunochromatographic Assays: RSID®-Saliva kit.
  • Enzyme-Linked Immunosorbent Assay (ELISA): Antibody—Antigen—Antibody Sandwich

• RNA-Based Assay: These assays utilize reverse transcriptase polymerase chain reaction methods to detect gene expression levels of mRNAs for saliva identification.

  

  

Application of RT-PCR Assay for Saliva Identification