Temperature uniformity mapping in a high pressure high temperature reactor using a temperature sensitive indicator

Recently, the first prototype ovomucoid-based pressure–temperature–time indicator (pTTI) for high pressure high temperature (HPHT) processing was described. However, for temperature uniformity mapping of high pressure (HP) vessels under HPHT sterilization conditions, this prototype needs to be optimized. To this end, this work aimed at the development of an ovomucoid-based indicator with combined pressure temperature dependent inactivation kinetics and a sufficient pressure temperature stability relevant for commercial HPHT sterilization. After varying buffer type and the pH at ambient pressure and temperature (pHi), an indicator based on 1 g/L ovomucoid in 0.1 M MES-NaOH buffer pHi 6.2 was selected. The inactivation behavior of this indicator system is characterized by pressure temperature dependent (combined Arrhenius–Eyring) first-order kinetics in the processing domain relevant for HPHT sterilization. This indicator showed good integrating properties under isobaric–isothermal and dynamic pressure temperature conditions. In a temperature uniformity study of a vertically oriented, pilot-scale HPHT vessel, pTTI readouts at different coordinates illustrated low and high temperature zones. As the inactivation of spores under HPHT is clearly positively temperature dependent, the food safety objective has to be verified in the former sampling zone