T. Haentjens

Quantitative evaluation of thermal processes using time-temperature integrators

Abstract The further development of new heating technologies, process assessment and process optimization in the thermal processing of foods is limited by the applicability of currently used process evaluation methodologies. Therefore, considerable effort has been and will continue to be put into the development of specific sensors — time-temperature integrators (TTIs) — which can allow faster, easy and correct determination of the impact of a process on a product attribute without the need for detailed knowledge of the actual time-temperature history of the product. This article presents the current state of the art regarding TTI development to monitor thermal processes, as well as a discussion of the possible applications and limitations of several types of TTI systems.

I. The development of an enzymic time temperature integrator to assess thermal efficacy of sterilization of low‐acid canned foods

Abstract Heat inactivation kinetics of Bacillus subtilis α‐amylase at reduced moisture content was studied under steady state and under non‐steady state conditions by monitoring the decrease in enthalpy associated with the heat deterioration of the enzyme. The high thermostability of the enzymic systems, obtained due to a reduction of the moisture content, allowed the systems to be applied in sterilization processes. Moreover, because Bacillus subtilis α‐amylase equilibrated above a saturated salt solution of an equilibrium relative humidity of 76 at 4°C yielded a z‐value of 9.7°C, this system can be used to monitor the thermal destruction of spores of proteolytic strains of Clostridium botulinum, characterized by a z‐value of 10°C, and hence, allows the measurement of the lethal efficacy of a sterilization process of low acid canned foods.

Potential Bacillus subtilis alpha-amylase-based time-temperature integrators to evaluate pasteurization processes.

Thermal inactivation kinetics of Bacillus subtilis alpha-amylase (BSA) in different environmental conditions was studied by performing isothermal experiments. As a response property, residual enzymic activity and residual heat of enzyme deterioration were chosen. A comparison of processing values determined from the read-out of a system with actual integrated processing values revealed the potentials of these systems as time-temperature integrators to be used in the pasteurization domain (temperatures of 70 to 100 degrees C) for target attributes with z-values ranging from 6 to 12 degrees C.

II. The use of an enzymic time temperature integrator to monitor lethal efficacy of sterilization of low‐acid canned foods

Abstract Based on a theoretical simulation study, the feasibility of a Bacillus subtilis α‐amylase based TTI for evaluation of safety of sterilization of low‐acid canned foods with an allowed tolerance of 10% was analyzed and its practical usefulness delineated. The enzymic TTI was successfully applied to (i) determine the influence of the end‐over‐end rotational speed and of the viscosity of the brine on the spatial distribution of process‐lethalities in a particulated food model system, thermally treated in a water cascading retort, and to (ii) evaluate the lethality distribution and hence determine the coldest zone in a water cascading retort.

Recent advances in process assessment and optimisation.

After stating the general principle of food preservation, this paper focuses on currently available methods to evaluate quantitatively the integrated time temperature impact during and/or after a thermal preservation process. In this context, both the physical-mathematical approach and the use of time temperature integrators are briefly reviewed and recent evolutions are indicated. Also new trends with regard to thermal process optimisation are highlighted.