Forensic Science - Saliva

What is saliva rich in?

• Amylase.

• Mucin.

• Proteins.

• Salts.

• Cells containing DNA.

How is saliva detected on clothing?

It fluoresces under UV light.

Name 3 saliva tests.

• Phadebas test.

• Starch-iodine.

• Radial diffusion.

What does a positive Phadebas test look like?

A blue colour indicating amylase (possible saliva).

What role does mucus play in saliva?

It binds food particles and lubricates food as it moves down the oesophagus.

What is the function of lysozyme in saliva?

It acts as an antibacterial enzyme that lyses bacteria, preventing microbial overgrowth in the mouth.

Besides the salivary gland, where else can amylase be found?

• Pancreatic glands.

• Urine.

• Blood.

• Semen.

What is the principle behind the Phadebas forensic saliva test?

Amylase digests starch microspheres containing cross-linked blue dye, releasing the dye into solution and producing a blue colour.

What does a blue colour indicate in a Phadebas test?

A positive amylase test, suggesting that saliva is present.

What is the main difference in data type between the Phadebas press test and tube test?

• Press test → Qualitative.

• Tube test → Semi-quantitative.

Which Phadebas test requires an already identified stain or swab?

The Phadebas tube test.

What is the incubation time and temperature for the Phadebas press test?

40 minutes at room temperature.

What is the incubation time and temperature for the Phadebas tube test?

30 minutes at 37 degrees celcius.

What reagent stops the amylase reaction in the tube test?

Sodium Hydroxide.

What wavelength is used to measure absorbance in the Phadebas tube test?

620nm.

Why is centrifugation used after adding NaOH in the tube test?

To pellet undigested material and allow clear observation of the blue supernatant.

What control acts as a positive control in the Phadebas tube test?

A saliva sample (e.g. buccal swab).

What control acts as a negative control in the tube test?

Sterile distilled water.

What is the purpose of the blank control in the tube test?

To calibrate the spectrophotometer and set baseline absorbance.

How id amylase activity quantified in the tube test?

By measuring absorbance and converting values using a standard curve.