Characterization of Insect Frass Properties

Before the heat treatment, uninoculated frass was subjected to measurement of pH, water activity (a_w) and moisture content. To measure the pH, a digital pH meter (Portamess 911, Knick, Berlin, Germany, with SI analytics electrode, Mainz, Germany) was used at room temperature, after addition of 17 mL of demineralized water to 10 g of frass according to the method of [22 (link)]. A water activity meter (LabMaster a_w, Novasina, Lachen, Switzerland) was used to determine the water activity (i.e., the amount of water available for microbial growth), after water activity and temperature (25 °C) were stable for 5 min. Moisture content (i.e., the total amount of water present) was determined by calculating the difference in weight of 5 g frass before and after overnight oven drying at 105 °C. All measurements of pH, a_w and moisture content were performed in triplicate.