Mapping temperature uniformity in industrial scale HP equipment using enzymatic pressure–temperature–time indicators

The potential of two previously developed pressure–temperature–time indicators (pTTIs) to detect temperature differences during high pressure (HP) processing was assessed. In a first theoretical approach, numerical integration of pressure, temperature-profiles and kinetic data of inactivation of the pTTIs, Bacillus amyloliquefaciens α-amylase and Bacillus subtilis α-amylase, was applied to translate hypothetical temperature profiles under pressure into indicator read-outs. This resulted in the definition of the application window with regard to initial temperature of the pressure medium (equal to the high pressure wall), the pressure level, build-up rate and holding time. Both indicators showed great potential for use in HP pasteurization processing. Secondly, in an experimental part, the temperature uniformity in a horizontally oriented, industrial scale HP equipment was mapped for the first time, using these indicators. Differences in indicator read-outs were obtained in the radial plane of the HP vessel, and based on the kinetic data of the pTTIs, attributed to temperature differences. Of course, this temperature non-uniformity will only result in process non-uniformity if the temperature dependency of the kinetics of the target attribute (safety, quality) is sufficiently temperature sensitive in the studied pressure, temperature-range.