Department of Food and Microbial Technology; Laboratory of Food Technology; Katholieke Universiteit Leuven; Kardinaal Mercierlaan 92; B-3001 Leuven; Belgium

Phone: 00-32-16-32.15.85, Fax: 00-32-16-32.19.60

e-mail: marc.hendrickc@agr.kuleuven.ac.be

http://www.agr.kuleuven.ac.be/lmt/vdt/general/foodtech.htm

High pressure is an emerging technology with high potentials as a new unit operation in food processing and preservation. The most likely applications will be in combination processes, especially with moderate temperature elevation. However, there are a number of scientific, technological and industrial difficulties to be overcome in order to successfully apply HP/T processes on foods, both from a legislative point of view and from optimal quality and consumer acceptance requirements. These technological/industrial difficulties require a scientific kinetic basis, requiring kinetic models and parameters for all safety and quality aspects.

The general objective of the project is therefore to develop a scientific food engineering basis for design, evaluation and optimization of combined HP/T processes which will enable a justified industrial application of this novel preservation technology. The critical issues (i) safety (legislative), (ii) optimal quality and consumer acceptability and (iii) performant technology are the specific project focuses. The deliverables of the project are kinetic-based methodologies to help in solving these issues. The objective is reached through implementation of 8 research tasks. The project will start with a detailed kinetic study on different safety and quality aspects including inactivation of food quality related enzymes (task 1), inactivation of microorganisms (task 2), changes in food structure (task 3) and changes in nutritional and sensorial quality aspects (task 4). In each task an increasing order of complexity in the composition of the medium (from simple model systems over complex model systems to real foods) is considered. Based on the kinetic information gathered, concepts for quantitative process impact evaluation (task 5) will be formulated. Hence, these will be the basis for evaluation of process impact uniformity and repeatability (task 6), shelf life studies (task 7) and process optimization (task 8).

In this presentation, merely the inactivation of food quality related enzymes will be focused. Several food quality related enzymes including PPO, LIP, PME, MYR, CSL and PG have been kinetically studied and pressure-temperature domains in which inactivation occurs, were demarcated. For avocado PPO and soybean LIP a pressure-temperature kinetic diagram was constructed. In such a two-dimensional diagram the lines represent combinations of constant pressure and temperature characterized by the same inactivation rate constant. Antagonistic effects of pressure and temperature were observed at high temperature and low pressure for PPO and at low temperature and high pressure for LOX. For both enzyme systems, mathematical equations quantifying the combined effect of pressure and temperature on inactivation were finalized. Also for orange PME, thermal inactivation (75°C) was counteracted by pressure. As it is well established that enzyme inactivation kinetics largely depend on intrinsic factors, case studies have been performed with respect to the influence of some food relevant intrinsic factors such as pH and addition of anti-browning agents for PPO, pH and enzyme concentration for LOX and pH and addition of Ca²⁺ ions for PME.