Xylanase B from the hyperthermophile Thermotoga maritima as an indicator for temperature gradients in high pressure high temperature processing

Within the scope of high pressure food sterilization, an important issue that should be taken into account in refining process and equipment design is the time- and position-dependent temperature gradient that exists throughout the pressure vessel and the product load. Since enzymes from thermophilic microorganisms show good prospects for the development of indicators to map out the temperature non-uniformity in high pressure high temperature (HPHT) processing, in this work, the potential of xylanase B from Thermotoga maritima (XTMB) was investigated. Its inactivation at isothermal–isobaric conditions was best described by a first-order model. The pressure dependence of the D values was negligible at HPHT, the temperature dependence however was substantial. The Thermal Death Time (TDT) model, and its corresponding parameters, describing this large temperature dependence were successfully validated under dynamic processing conditions, relevant for industrial HPHT applications.Industrial relevanceDespite extensive research progress on high pressure high temperature (HPHT) processing as a new food sterilization technique, food industry should be aware of a possible non-uniform temperature distribution, occurring in the pressure vessel and its consequence for the quality and safety of treated products. Since direct measurement of the temperature distribution is not feasible with the measuring devices currently available and constructive computation of the temperature profile by numerical simulation is inadequate, the development of specific temperature-sensitive wireless sensors, or pressure–temperature–time indicators (pTTIs) can be put forward. In this work, xylanase B from Thermotoga maritima (XTMB) was evaluated as a potential enzymatic indicator for mapping the temperature non-uniformity in HPHT processing.

Research Highlights
► Sensor development for mapping temperature inhomogeneities in HP sterilization.
► XTMB-4M met the three sensor requirements.
► Large sensitivity for temperature differences.
► Inactivation at isothermal-isobaric conditions by a first-order model.
► Successful validation of the TDT model under dynamic processing conditions.