PHYSICAL CHEMISTRY OF FOOD
Learning outcomes of the course unit
The aim of the module is knowledge and understanding of the principles underlying physical processes and chemical reactions, by means of models, peculiarity of the Physical Chemistry. At the end of the module, the students would show the ability of applying the acquired knowledge and understanding to the study of the structure and physical properties of foods and to the main production and preservation processes.
At the end of the module, the student will show rigorous knowledge about:
- Classical thermodynamics, applied to the chemical reactions, to the foods and to the biological systems for understanding the main machinery related to food preservation and production and the basics of the main techniques for studying the structure and physical properties of foods;
- transport processes, explained by means of non-equilibrium thermodynamics models, and their importance in food processes;
- stability of the colloidal systems and their involvement in the food field.
No preliminary examinations are requested.
Course contents summary
The first part of the module is devoted to the equilibrium thermodynamics with special reference to food science (water activity, food phase diagrams, etc.).
The second part deals with non-equilibrium thermodynamics and transport processes, particularly those involved in food processing and preservation ( viscosity, diffusion, sedimentation).
The third part is connected with the colloidal systems and with their stability, particularly as far as the food systems are concerned.
1. Equilibrium thermodynamics applied to chemical, biological and food systems with a statistical thermodynamics outline. Variables and state functions. The laws of thermodynamics. The temperature and pressure dependence of thermodynamic quantities. Thermochemistry. Calorimetry. Outline of statistical Thermodynamics. Exercises.
2. Changes of state: physical transformations of pure substances. Phase diagrams. Clapeyron and Clausius-Clapeyron equations. Gibbs phase rule
3. Changes of state: physical transformations of simple mixtures. Open systems and partial molar quantities. Ideal and real solutions. Raoult and Henry laws. Fugacity and activity. The water activity in foods and food preservation. Regular solutions. Ideal mixing and excess functions. Phase equilibria in binary systems. Fractional distillation. Azeotropes, eutectic, partially miscible liquids, binary mixtures compounds forming. Phase transition in food materials. The glassy state and the glass transition.
4. Solutions of macromolecules. Solvent chemical potential. Colligative properties. Osmotic pressure. Molecular weight measurements. Membrane equilibria. Dialysis equilibrium. Donnan equilibrium.
5. Equilibria of chemical reactions. Thermodynamics of chemical equilibrium. Gibbs free energy and equilibrium constant. Activity and ionic strength. Exergonic and endergonic reactions. Coupled reactions.
6. Non-equilibrium thermodynamics and transport processes. Order out of caos. Force and flow. Phenomenological equations. Theorems. Onsager law. Dissipation function. Steady state concept. Mobility of the ions in solution. Electrophoresis. Diffusion. Sedimentation. Viscosity.
7. Colloidal Systems. Dispersed systems. Size and shape of colloidal particles. Ostwald classification. Surface tension and surface free energy. Van de Waals forces. Lennard-Jones potential. Intermolecular forces in colloidal systems. DLVO theory. Hydrophobic interactions, hydrophobic hydration and Hydrophobic effect : model for the interpretation. Structure and classification of surfactants. Micelle formation. Casein Micelles. Emulsifiers and stabilizers in foods. Cohesion and adhesion work, spreading coefficient, wettability. Ostwald ripening. Gibbs isotherm. Laplace pressure. The most common food colloids: Emulsions, foams, dispersions and suspensions, gels. Methods of preparation. Examples: beer, whipped cream, ice-cream, meringue, butter, mayonnaise. Marangoni effect. Physico-chemical properties of a food colloid. Micro-emulsions. Lyotropic and thermotropic liquid crystals.
- Pieter Walstra, Physical Chemistry of Foods, Marcel Dekker, Inc, New York (2003)
- Eric Dickinson, An Introduction to Food Colloids, Oxford Science Publications (1992)
During lectures, done by means of computer ppt presentations, available to the students before classes in the web site of the class, general topics related to the use of chemico-physical models for studying food and biological systems will be discussed. Lectures will be implemented by means of problem solving and “question time” like activities in order to maximize the understanding level of the students.
Assessment methods and criteria
There is a written examination on the whole syllabus during scheduled examination sections. If necessary, an oral examination will be added, to discuss written answers.
The final written examination consist of open questions and problem solving in such a way that the students can prove knowledge and understanding of the module subjects.
In case of a positive result of the written tests, the obtained marks will contribute to the final result for the exam of the class of “Food Structure and Physical Properties”, being the final mark the average between the marks obtained in the two modules constituting the class.