Stability food colloids

Socaciu, C. et al.. Carotenoid-rich fractions in sea buckthorn berry oleosomes separation, characterisation and stability in colloid supramolecular structures, in Proceedings of 4th International Congress on Pigments in Food, Hohenheim, Germany, Carle, R. et al., Eds., Shaker Verlag, Aachen, 2006, 203. 

The stability of colloid suspensions is an important criteria in the manufacture of a large number of industrial products where these are the basic building blocks (food colloids, pollution control, emulsions, wastewater treatment). 

Dickinson, E. (2007). Food colloids... Editorial overview. How do interactions of ingredients control structure, stability and rheology Current Opinion in Colloid and Interface Science, 12, 155-157. 

Dickinson, E. (2009). Hydrocolloids as emulsifiers and emulsion stabilizers. Food Hydro-colloids, 23, 1473-1482. 

Dickinson, E. (1993). Protein-polysaccharide interactions. In Dickinson, E., Walstra, P. (Eds). Food Colloids and Polymers Stability and Mechanical Properties, Cambridge, UK Royal Society of Chemistry, pp. 77-93. 

On the strength of all the examples presented in this chapter, the reader should be convinced that variations in self-assembly of food biopolymers in aqueous media can have an enormous influence on food colloid stability, rheology and microstructure. It therefore seems reasonable to infer that further study and understanding of the molecular mechanisms of self-assembly and interactions of biopolymers in aqueous solution should provide increased opportunities for the creation of new classes of structured soft materials with potential application for incorporation in a wide range of new food and pharmaceutical products. 

Nowadays it is well established that the interactions between different macromolecular ingredients (i.e., protein + protein, polysaccharide + polysaccharide, and protein + polysaccharide) are of great importance in determining the texture and shelf-life of multicomponent food colloids. These interactions affect the structure-forming properties of biopolymers in the bulk and at interfaces thermodynamic activity, self-assembly, sin-face loading, thermodynamic compatibility/incompatibility, phase separation, complexation and rheological behaviour. Therefore, one may infer that a knowledge of the key physico-chemical features of such biopolymer-biopolymer interactions, and their impact on stability properties of food colloids, is essential in order to be able to understand and predict the functional properties of mixed biopolymers in product formulations. 

In considering the impact of thermodynamically favourable interactions between biopolymers on the formation and stabilization of food colloids, a number of regular trends can be identified. One of the most important aspects is the effect of complexation on interfacial properties, including rates of adsorption and surface rheological behaviour. 

Adsorbed layers of mixed biopolymers are potentially non-equilibrium systems in terms of their structure and composition. Therefore one has to be aware that the impact of thermodynamical favourable interactions between biopolymers on the formation and stabilization of food colloids is dependent, not only on the total system composition, but also on the experimental procedure whereby the two interacting biopolymers are brought to the interface (McClements, 2004 Jourdain et aL 2008, 2009 Dickinson, 2008a). 

The biochemical stability of food colloids is now attracting considerable research interest because of its obvious relevance to the delivery and bioavailability of nutrients and nutraceuticals in vivo. In particular, the processes of enzymatic hydrolysis occurring at the triglyceride-water interface appear important because most dietary lipids are present in the human stomach at some stage in the form of emulsified droplets (size 20-40 pm) (Armand et al., 1994 McClements et al., 2008 Dickinson, 2008 Singh et cil, 2009 McClements and Decker, 2009). 

Dickinson, E. (1997b). Enzymic crosslinking as a tool for food colloid rheology control and interfacial stabilization. Trends in Food Science and Technology, 8, 334-339. 

The term food colloids can be applied to all edible multi-phase systems such as foams, gels, dispersions and emulsions. Therefore, most manufactured foodstuffs can be classified as food colloids, and some natural ones also (notably milk). One of the key features of such systems is that they require the addition of a combination of surface-active molecules and thickeners for control of their texture and shelf-life. To achieve the requirements of consumers and food technologists, various combinations of proteins and polysaccharides are routinely used. The structures formed by these biopolymers in the bulk aqueous phase and at the surface of droplets and bubbles determine the long-term stability and rheological properties of food colloids. These structures are determined by the nature of the various kinds of biopolymer-biopolymer interactions, as well as by the interactions of the biopolymers with other food ingredients such as low-molecular-weight surfactants (emulsifiers). 

Electrostatic and electrical double-layer forces play a very important role in a number of contexts in science and engineering. As we see in Chapter 13, the stability of a wide variety of colloids, ranging from food colloids, pharmaceutical dispersions, and paints, to colloidal contaminants in wastewater, is affected by surface charges on the particles. The filtration efficiency of submicron particles can be diminished considerably by electrical double-layer forces. As we point out in Chapter 13, coagulants are added to neutralize the electrostatic effects, to promote aggregation, and to enhance the ease of separation. 

Colloid stability enters our daily life in many different ways. A visit to the kitchen provides numerous examples of food colloids with microstructure and stability that are, in no small measure, an important aspect of their appeal to the palate For example, mayonnaise —a mixture of vegetable oil, egg yolk, and vinegar or lemon juice —is an emulsion of oil in water and is stable because the lecithin molecules in the egg yolk provide the needed stability. Milk is another example. We have seen others in the vignettes in Chapters 1 and 4. 

The widespread importance and ubiquitous nature of food products, together with scientific interest in their formation, stability and properties, have precipitated a substantial body of published literature on the subject. There are many books on food colloids [33,36,492,804—811] and several monograph series, including Food... 

Many food colloids are stabilized from proteins from milk or eggs [817]. Milk and cream, for example, are stabilized by milk proteins, such as casein micelles, which form a membrane around the oil (fat) droplets [817]. Mayonnaise, hollandaise, and bearnaise, for example, are O/W emulsions mainly stabilized by egg-yolk protein, which is a mixture of lipids (including lecithin), proteins, and lipoproteins [811,817]. The protein-covered oil (fat) droplets are stabilized by a combination of electrostatic and steric stabilization [817]. Alcohols may also be added, such as glycerol, propylene glycol, sorbitol, or sucrose sometimes these are modified by esterification or by... 

The principles of colloid stability, including DLVO theory, disjoining pressure, the Marangoni effect, surface viscosity, and steric stabilization, can be usefully applied to many food systems [291,293], Walstra [291] provides some examples of DLVO calculations, steric stabilization and bridging flocculation for food colloid systems. 

Steric stabilization appears to be the dominant stabilizing force in most food colloids [78,824], Casein-coated emulsion droplets provide an example. The presence of protein in an adsorption layer can also contribute viscoelasticity and provide a barrier to coalescence. 

Dalgleish, D.G. Aspects of Stability in Milk and Milk Products in Food Colloids, Bee, R.D. Richmond, P. Mingins, J. (Eds.), Royal Society of Chemistry, Cambridge, 1990, pp. 295-305. 

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