Application of the ‘Determiner L P-AMY G2’ for forensic identification of saliva

Like blood and semen, saliva is considered an important evidence in criminal investigations. Saliva identification has been performed by detecting α-amylase activity using the Blue Starch method or by detecting salivary α-amylase with the RSIDTM-Saliva. However, the Blue Starch method has low specificity, whereas the RSIDTM-Saliva test is costly. Therefore, there is a need for a new saliva identification method that solves these problems. Currently, an α-amylase isozyme kit “Determiner L P-AMY G2” is widely used as a diagnostic reagent and it can specifically detect non-salivary-type α-amylase activity. Since α-amylase activity in saliva is derived from salivary-type α-amylase, it was hypothesized that saliva could be identified by calculating the ratio of salivary-type α-amylase activity to total α-amylase activity (RS value). As a result, saliva and other body fluids (semen, vaginal fluid, urine, and blood) could be distinguished using an RS value of 0.950 as a reference. This method was able to detect saliva even when diluted 10,000-fold and could identify saliva in mixtures with seminal fluid or vaginal fluid. Therefore, this method detects salivary α-amylase with higher sensitivity than existing methods and is considered to be a potential novel saliva identification technique with practical applications.