Enhancement of quality of food and related systems by control of molecular mobility

• Unité de recherche: PCRD EU
• Numéro de projet: 95.0872
• Titre du projet anglais: Enhancement of quality of food and related systems by control of molecular mobility

Mots-clé (Anglais)

Molecular mobility; viscoelasticity; phase diagrammes; glass transition temperature; glucose; maltose; maltotriose; pullulan

Autre Numéro de projet (Anglais)

EU project number: FAIR-CT96-1085

Programme de recherche (Anglais)

EU-programme: 4. Frame Research Programme - 4.3 Biomedical/Health research

Description succincte (Anglais)

See abstract

Partenaires et organisations internationales (Anglais)

Dr. Yrjö Roos, University of Helsinki FI; Dr. Costas Biliaderis, Aristotle University of Thessaloniki, GR; Dr. Steve Ring, Institute of Food Research, Norwich UK; Prof. John Blanshard, University of Nottingham, UK: Dr. Wim Agterof & Prof. Jim Leslie, Unliever Research Laboratory, NL; Dr. Marcus Hemminga, Wageningen University, NL; Dr. Martine Le Meste, ENSBANA, F; Mr. Hervé Bizot, INRA, F

Résumé des résultats (Abstract) (Anglais)

We have continued our research these last 12 months on measuring the temperature dependence of the mechanical properties (viscosity) of mainly of aqueous solutions of glucose, using the 'disc bending' Dynamic Mechanical Thermal Analysis (DMTA), as well as the ARES and SR5 plate plate rheometers. A description of these instruments and methodology was given in Annex 2 of the 1st Year Individual Progress Report. These measurements have been complemented by DSC determinations of the glass transition onset Tg value as a function of scanning rate. The aim of the new measurements was to extend the domain of measurement over which the temperature dependence of the 'avenge' molecular relaxation time could be modeled using the WLF equation. This was done for glucose solutions with 40,80 and 100% solids and an 82.4% glucose syrup. The effect of the higher molecular weight could be remarked. The temperature dependence of the relaxation time is described by the WLF equation with concentration dependent constants.
We have completed the modeling of the transition lines in the 4 state diagrams and have given equations for the melting point line, the Tg glass transition line and the weakly concentration dependent Tg' line. The 'onset of meltin' or freeze-drying collapse' transition line also has a weak concentration dependence, contrary to most previous findings for phase diagrams. We have been able to give a plausible explanation for the finding that the shear loss modulus G' peak temperatures occur at higher temperatures than the disc-bending DMTA E' loss modulus peak T, in terms of a temperature dependent complex Poisson's ratio v*(T) that relates the shear modulus G*(T) to the bending-tensile modulus E*(T).
Finally for the applications of Task 5 we have presented our in situ, real time DMTA heat shock studies on ice creams, cycled between -90C and -600C for 3 or more days. We have shown that the DMTA measurements of the temperature dependence of the bending viscoelastic modulus E*(T) during freezing and can easily distinguish different ice creams. We have found that the magnitude of the modulus at each temperature during slow cooling or heating (0.2oC/min) is only proportional to the volume of ice, and not its distribution in different crystal sizes. This then makes this laborious DMTA technique less interesting for studying the sensitivity of different ice creams to heat shock effects.

Références bases de données (Anglais)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 95.0872