Drying properties and DNA content of saliva samples taken before, during and after chewing gum

Drying properties of forensically relevant biological materials including saliva are lacking research despite being known to affect casework-relevant phenomena, including DNA transfer. We previously observed that saliva collected from someone chewing gum and deposited on various surfaces did not dry, raising questions about the effects of chewing gum on the drying properties of saliva. The DNA content of saliva samples under differing conditions is also not well known. This study investigated the drying properties and DNA content of saliva deposited on glass from samples collected before, during and after chewing gum. Samples taken before chewing gum dried the fastest and an inverse relationship between the time since chewing gum began and saliva drying time was found; as the time between the chewing and sample collection decreased, the drying time increased. All samples except those taken at the two minutes mark of chewing dried within the 96 h–27 days observation period. DNA yield initially decreased as chewing begun, then recovered during and after chewing, sometimes to be greater than the control sample. These observations contribute to our limited knowledge regarding variables affecting saliva samples. However, further research to facilitate activity level assessments regarding saliva samples is desirable.