Can qualitatively similar temperature-histories be obtained in different pilot HP units?

An experimental protocol to harmonize the pressure and temperature-histories of model samples treated in different individual high pressure pilot units was developed. This protocol was based on the endpoint strategy. Step zero of this protocol consisted of an exploratory measurement of the pressure, temperature-history of the pressure transmitting medium in the different chambers without the use of a container. In steps one and two of the protocol, the temperature of a sample was measured, which was placed in a container. Two types of samples were considered, a pure water sample allowing free convection (step 1) and a viscous water-based system (using a water soluble thickener) preventing free convection in the sample container (step 2).The high pressure units differed primarily in pressure build-up and pressure release times. The suggested endpoint strategy enabled the minimization of differences in temperature-histories during the pressure holding phase. Pressure, temperature-histories measured in the different high pressure units and information on the inactivation kinetics of α-amylase based systems were used to compare the process impact of different pressure, temperature-histories on the enzyme inactivation. The differences in temperature-histories significantly influenced the degree of enzyme inactivation; in particular the temperature-histories during the pressure build-up phase substantially contributed to differences in residual enzyme activity.Industrial relevanceBoth in laboratory scale studies (e.g. microorganism and enzyme inactivation) as well as in the industrial implementation, different high pressure units are being used. Different layouts (e.g. vessel volume, sensor locations etc.) are observed leading to a.o. differences in pressure build-up and release and consequently in dynamic temperature pressure time conditions in different vessels and at different locations of one single vessel. Specific attention should be given to this issue, both in conducting kinetic studies as well as in scale-up from lab-scale processes to industrial scale processes. This manuscript shows that if the same process is implemented in different units, differences in pressure temperature time conditions are observed resulting in differences in impact (shown by enzyme inactivation). These differences can be minimized using an end point strategy, i.e. when implementing protocols based on a specified endpoint condition at the start of the holding phase.

Research Highlights
► The isothermal-endpoint pressure treatment procedure (IEPTP) can lead to similar temperature-histories of samples placed in different high pressure laboratory or pilot units.
► Reaching the same time temperature-histories increases comparability of data describing the effect of the process (e.g. microbial inactivation, enzyme inactivation and nutrient changes).
► Differences in chamber design and control system can be overcome by this strategy but it is evidenced that careful temperature measurement is necessary because also small differences in temperature (at higher temperature levels) can cause substantial differences in impact.
► The endpoint strategy presented in this paper can be used for creating isothermal and isobaric conditions. These conditions enable studies of kinetics under broad range of pressure temperature conditions.