Partners and International Organizations
(English)
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Katholieke Universiteit Leuven (B), Unilever Research Laboratories, Vlaardingen (NL), Technical Research center of Finland (FIN), Bundesforschungsanstalt für Ernährung, Karlsruhe (D), Ruprecht Karl Universität, Heidelberg (D), Technische Universität, Berlin (D), National Technical University, Athens (EL), EPS International, Temse (B), ABB Pressure Systems ab, Vaestraas (S), Nestec Ldt, Lausanne (CH)
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Abstract
(English)
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PARTNER 10 A: KINETICS OF HP/T-INDUCED INACTIVATION OF FOOD-QUALITY RELATED ENZYMES
The measurement of tomato pectin methylesterase (PME) inactivation curves under various P/T combinations was completed at temperatures other than 75 °C. The counteracting effects of pressure and temperature were again observed. However at a given temperature, the pressure level required to make inactivation faster than at 0.1 MPa decreased with decreasing temperature. Arrhenius and Eyring equations were clearly not suited for the modelisation of the inactivation kinetics. Hence, empirical mathematical equations were used to describe the behaviour of k (the first order inactivation constant rate) over the investigated P/T range.
The data set for tomato polygalacturonase (PG) was completed as well. Completely unlike PME, it had been found heat resistant at 0.1 MPa, but surprisingly pressure-labile under hyperbaric conditions. In this case pressure and temperature acted synergestically, and an increase in either pressure or temperature inevitably led to a faster inactivation. This behaviour was more related to a 'classical' Arrhenius/Eyring type of behaviour, and a similar model was used to describe the response of the inactivation rate constant to the treatment conditions.
The precipitation problems encountered with the cysteine sulphoxide lyase (CSL)-containing Brussels sprouts extracts once solved (see second reporting period), it was possible to complete the inactivation data set for this enzyme over a suitable portion of the P/T plane. Although less spectacular than for PME, counteracting effects of pressure and temperature were again observed for this enzyme. Again, empirical mathematical equations had to be used to properly describe the behaviour of this enzyme.
PARTNER 10 B: KINETICS OF HP/T-INDUCED CHANGES IN FOOD STRUCTURE
A combination of high hydrostatic pressure, temperature and pressure holding time can be used to induce phase separation in miscible HM-pectin/WPI mixtures. By varying these parameters the degree of denaturation of the proteins can be influenced. Denaturation provokes phase separation in a ternary pectin-WPI-water system, leading to a concentration of the molecular species involved. Similar textures can be obtained either by HPT- or heat treatment as indicated by rheological measurements, even if the denaturation profiles are different. Significant changes in texture could only be achieved when the protein phase is gelled. To achieve this, all WPI species must have a denaturation degree above 60%.
An intelligent combination of viscosity enhancement by phase separation and provocation of gelation due to a sufficiently high denaturation and concentration by phase separation of the WPI upon a combined pressure/temperature or pure temperature treatment offers a potential to structure food systems in a controlled way, i.e. by provoking gelation.
In order to apply the concept of structure formation by protein denaturation and subsequent phase separation in an efficient way, the phase behaviour and kinetic data of denaturation must be established as a function of concentration and over the whole range of processing parameters (pressure, holding time, temperature). To establish and facilitate the creation and control of new food textures, the obtained data must be combined with a quantitative description of the resulting textures by rheology and micro-structural analysis of the structures formed.
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