Illustrating temperature uniformity in high pressure high temperature reactors using temperature sensitive indicators

摘要

In this work, the development of two protein-based indicator systems as well as their application to map the temperature uniformity of a high pressure (HP) vessel under high pressure high temperature (HPHT) processing conditions is discussed. The indicator systems were developed through a five-step approach with solvent engineering (purposely changing solvent conditions to obtain the desired indicator characteristics) as corrective feedback action. Ovomucoid, a proteinaceous trypsin inhibitor, was selected as candidate indicator, since it is commercially available and food-grade. In addition, the read-out upon treatment, residual trypsin-inhibitor activity, can be evaluated spectrophotometrically (step 1). Changing buffer type and pH resulted in the development of two ovomucoid-based indicator systems with specific inactivation windows (range of pressure temperature time conditions for inactivation) and specific temperature and/or pressure dependent kinetics (step 2). The inactivation behavior of 1 g/L ovomucoid in 0.1 M phosphate buffer pH 8.0 (OM-PhB8.0) was characterized by temperature dependent first-order kinetics in a milder HPHT processing range (400-700 MPa; T_(process) 95-110 °C; 0-20 min). The inactivation behavior of 1 g/L ovomucoid in 0.1 M MES buffer pH 6.2 (OM-MB6.2) was characterized by combined temperature and pressure dependent firstorder kinetics in a more intense HPHT processing range relevant for commercial sterilization (500-700 MPa; T_(process) 107-120 °C; 0-20 min). These indicators showed good integrating properties under static (step 3) and dynamic pressure temperature conditions (step 4). Given their temperature sensitivity under HP, their potential use for illustrating temperature uniformity was estimated high. In a final step, this potential was experimentally verified: by positioning OM-MB6.2 at different coordinates in a vertically oriented, pilotscale HPHT vessel, the temperature uniformity of the vessel was mapped. Read-out evaluation of OMMB6.2 indicated low and high temperature zones. These temperature zones are important for process impact evaluation on safety and quality attributes, respectively.