Using a skim milk agarose gel plate assay to screen for stomach contents in forensics

Stomach contents, such as vomit, are sometimes found at crime scenes and are typically used in forensic examinations. Previously, a simple method for identifying stomach contents using fibrin blue as a substrate was widely used; however, the sale of fibrin blue has been discontinued. Therefore, in this study, we investigated a simple method for testing pepsin activity under acidic conditions using skim milk or hide-remazol brilliant blue R, which are available as alternative substrates. Body fluids (nasal secretions, saliva, urine, semen, sweat, and blood), stomach contents, and feces were examined by adding them to wells or placing them on prepared skim milk or hide-remazol brilliant blue R agarose gel plates. The plates were incubated at 37 °C and observed hourly for 6 h. Dissolution spots were observed around stomach contents and semen, whereas no dissolution spots were observed with other body fluids or feces. By combining a seminal fluid test (colorimetric acid phosphatase or prostate-specific antigen assay), it was possible to distinguish between stomach contents and semen. In addition, similar results were obtained with skim milk agarose gel plates in stained and actual forensic samples, suggesting that the combined use of agarose gel and seminal fluid tests would be useful for screening stomach contents in forensic practice.