Design of an indicator system to validate that foods have undergone high hydrostatic pressure processing

High Hydrostatic Pressure (HHP) processing has been successfully commercialized by several companies around the world on foods such as hams, fruit juice, jams, guacamole and oysters to reduce the risk of microbial contamination and extend shelf life. Isostatic compression transfers pressure instantly and uniformly throughout the pressure medium providing a non-thermal process alternative for the pasteurization of temperature-sensitive foods. Foods suspended in the pressure medium are assumed to follow the isostatic principle.; The unique design of the HHP equipment restricts access to the interior of the pressure vessel during operation thereby preventing direct measurement of the pressure using standard pressure gauges. No methods have been reported for measuring the pressure within the HHP vessel or within a food product during the HHP process.; An indicator device was successfully developed by uniaxially compressing powdered copper into a pre-formed tablet and measuring the density before and after HHP processing. The increase in density of the tablet was found to correlate with the HHP compression force between 400–600 mega-pascals (MPa) and with the length of time of the HHP process between 1 and 10 minutes.; The density of indicators located within two types of hams were less than the density of indicators measured in the water of the HHP processing vessel compressed at the same pressure. No significant difference was observed between the two types of hams suggesting that the moisture content of the hams did not affect the compression of the indicator. The difference in density of the indicators equates to approximately 9 MPa less pressure within the hams.; This discovery suggests that the isostatic principle does not apply to hams when HHP processed between 400–600 MPa. Consideration for the effect of the product must be accounted for when developing processes for pasteurization or sterilization of foods using HHP technology.