Development of a pressure indicator for high hydrostatic pressure processing of foods

A tablet comprised of uniaxially compressed powdered copper was developed to measure the pressure within a High hydrostatic pressure (HHP) processing system. The density of the tablet increased proportionately as HHP increased between 400 and 600 MPa (P<0.001). Tablet density increased as time-at-pressure increased between 1, 5 and 10 min (P<0.012) when held at constant HHPs between 400 and 600 MPa. No significant increase in tablet density was found when tablets were HHP processed at 7, 15 or 24 °C between 400 and 600 MPa (P>0.29). The change in density of the tablet placed in the geometric center of a large food product, such as a ham, indicated that the ham received approximately 9 MPa less pressure than the HHP system delivered ( P <0.017), challenging the assumption that all foods follow the isostatic rule. This finding may have implications when determining the microbial lethality for large food items pasteurized or sterilized using a HHP process. The indicator may also serve as a HACCP verification tool for HHP-processed foods.