Food polymers

Tolstoguzov Consulting, 47 Route de Vevey, 1009 Fully, Switzerland, tolstoguzov.v bluewin.ch 

Food polymers and the behaviour of their mixtures are mainly responsible for the structure-properties relationship in both food and chyme. The two basic features of food are that its biopolymers, proteins and polysaccharides are its main construction materials and water is the main medium, solvent and plasticizer. In other words, three components— protein, polysaccharide and water—are the main elements of food structure that are principally responsible for quality of foods (see also Chapter 13). 

Foods are always a multicomponent physical system, so interactions between components are more significant than the chemical and physical properties of components. Food structures are mainly arranged by noncovalent, nonspecific interactions of proteins and polysaccharides in an aqueous medium. For instance, the most studied structural food macromolecules are soybean proteins, gluten, milk proteins, and starch. But despite detailed knowledge about individual components, the control of dough and milk system functionality remains empirical (but see Chapters 19 and 20). 

Finally, food processing implies the conversion of biological systems based on specific interactions of components into foods with nonspecific interactions between components. For this reason the thermodynamic approach is especially applicable for studying the role of food polymers and water in structure-property relations. The logical starting point is therefore to consider mixed aqueous solutions of biopolymers. 

2 Interactions of Food Biopolymers in Molecular and Colloidal Dispersions 

---

Liquid or solid films which reduce or prevent adhesion between surfaces solid-solid, solid-paste, solid-liquid. Waxes, metallic soaps, glycerides (particularly stearates), polyvinyl alcohol, polyethene, silicones, and fluorocarbons are all used as abherents in metal, rubber, food, polymer, paper and glass processing. 

The concept and use of food polymer science in describing the behavior of starch during and after thermal treatment has been developed (20,21). In... 

The plate dryer is limited in its scope of apphcations only in the consistency of the feed material (the products must be friable, free flowing, and not undergo phase changes) and diying temperatures up to 320°C. Applications include speci ty chemicals, pharmaceuticals, foods, polymers, pigments, etc. Initial moisture or volatile level can be as high as 65 percent and the unit is often used as a final dryer to take materials to a bone-dry state, if necessary. The plate dryer can also be used for heat treatment, removal of waters of hydration (bound moisture), solvent removal, and as a product cooler. 

A. R. Mackie, J. Mingins, and R. Dann, in Food Polymers, Gels and Colloids, (E. Dickinson, ed.), Royal Society of Chemistry, Cambridge, 1991, pp. 96-111. 

The continued use of aw in foods does not preclude the use of other concepts or measurement methods, such as the food polymer science approach proposed by Slade and Levine (1991) or rotational and translation mobility as measured by NMR. Rather, it may be most useful to combine these various approaches, recognizing the strengths, perspective (i.e., distance and time scales), and limitations of each. Then, each approach can be utilized where it is most applicable so as to build a multilevel understanding of the workings of specific food systems. 

Since its introduction, the food polymer science approach has been used to understand structure-function relationships in foods, the effect of... 

State diagrams are an integral part of the food polymer science approach and are further explored and expanded upon in Section III.D.5. For the interested reader, Javenkoski (2001) developed instructional visualization media (three QuickTime animations) for aqueous phase transitions in food systems and investigated their use for improving the comprehension of phase transitions by students enrolled in an introductory food science and human nutrition course. 

The introduction of Slade and Levine s food polymer science approach has mobilized (no pun intended ) a large number of researchers to pursue the question of how the glass transition concept applies to the processing and... 

As discussed earlier, the usefulness of the food polymer science approach to the study of water dynamics in foods has been widely demonstrated by numerous researchers studying both model and real food systems. Along with the success of the approach, there still exist a number of areas of concern that need to be mentioned. 

The food polymer science approach is being applied successfully in the food industry for understanding, improving, and developing food processes and products. However, to date, the glass transition generally remains more of a research and development tool than a routine quality assurance measure of food processability and stability. 

Ruan, R.R., Long, Z., Song, A., and Chen, P.L. 1998. Determination of the glass transition temperature of food polymers using low field NMR. Lebensm. Wiss. Technol 31, 516-521. 

Slade, L. and Levine, H. 2003. Food polymer science approach to studies on freshness and shelf life. In Freshness and Shelf Life of Foods (K.R. Cadwallader and H. Weenen, eds), pp. 214—222. ACS Symposium Series 836, American Chemical Society, Washington, DC. 

Dickinson, E., Euston, S.R. (1991). Stability of food emulsions containing both protein and polysaccharide. In Dickinson E. (Ed.). Food Polymers, Gels and Colloids, Cambridge, UK Royal Society of Chemistry, pp.132-146. 

The Karl Fischer titration,30 which measures traces of water in transformer oil, solvents, foods, polymers, and other substances, is performed half a million times each day.31 The titration is usually performed by delivering titrant from an automated buret or by coulometric generation of titrant. The volumetric procedure tends to be appropriate for larger amounts of water (but can go as low as 1 mg H20) and the coulometric procedure tends to be appropriate for smaller amounts of water. 

This work reports rheological measurements of food polymer suspensions and emulsions. These are typical of a large number of foods and their rheological behaviors. 

This unit describes a method for measuring the viscosity (r ) of Newtonian fluids. For a Newtonian fluid, viscosity is a constant at a given temperature and pressure, as defined in unit hi. i common liquids under ordinary circumstances behave in this way. Examples include pure fluids and solutions. Liquids which have suspended matter of sufficient size and concentration may deviate from Newtonian behavior. Examples of liquids exhibiting non-Newtonian behavior (unit hi. i) include polymer suspensions, emulsions, and fruit juices. Glass capillary viscometers are useful for the measurement of fluids, with the appropriate choice of capillary dimensions, for Newtonian fluids of viscosity up to 10 Pascals (Newtons m/sec 2) or 100 Poise (dynes cm/sec 2). Traditionally, these viscometers have been used in the oil industry. However, they have been adapted for use in the food industry and are commonly used for molecular weight prediction of food polymers in very dilute solutions (Daubert and Foegeding, 1998). There are three common types of capillary viscometers including Ubelohde, Ostwald, and Cannon-Fenske. These viscometers are often referred to as U-tube viscometers because they resemble the letter U (see Fig. HI.3.1). 

Sample preparation may require as little as 5 min (e.g., cutting a sample cube of cheese) or an hour or more (e.g., preparation of a food polymer solution and pouring in a mold). The time to run a test will depend on the deformati on rate and the degree of deformation chosen for the specimen of interest. Typically, uniaxial compression of a specimen can be performed in 5 to 20 min. 

Table 4 HPLC Methods for Quantitating C Vitamers in Foods (Polymer Columns Fluorescence Detection)... 

Dickinson, E. (Ed.) Food Polymers, Gels and Colloids, Royal Society Chemistry Cambridge, 1991. 

Cameron RE, Donald AM. In Dickinson E, ed. Food Polymer, Gels, and Colloids. London, UK The Royal Society of Chemistry 1991 301. 

Barker, G. C., and Grimson, M. J. (1991). Computer simulations of the flow of deformable particles. In Food Polymers, Cels and Colloids, Dickinson, E. (Ed.), pp. 262-271. Royal Chem. Soc., London. 

---