Rheology of food emulsions

Effect of Food Surfactants on the Rheology of Food Emulsions... 

Surfactants play a major role in the rheology of food emulsions. Both interfacial and bulk rheologies have to be considered and these will be summarized below. 

These systems are widely used in many food products. A section will be devoted to the interfedal phenomena in food colloids, in particular their dynamic properties and the competitive adsorption of the various components at the interlace. The interaction between proteins eind polysaccharides in food colloids will be briefly described. This is followed by a section on the interaction between polysaccharides and surfactants. A short review will be given on surfactant association structures, microemulsions and emulsions in food [3]. Finally, the effect of food surfactants on the interfacial and bulk rheology of food emulsions will be briefly described. The formation of aggregation networks and the application of fractal concepts is then considered. This is followed by a section on applications of rheology in studying food texture and mouth feel. 

One of the important factors that affects the rheology of food emulsions is the presence of networks that are produced by the droplets or by the thickeners. These networks or gels control the consistency of the product euid hence its acceptability by the customer. This can be illustrated from the work of van den Tempel [25] and Papenhuizen [26] who studied gels consisting of 25% glyceryl stearate in peuaflBn oil (a model system for margarine). Creep experiments at various stress values showed... 

Most food emulsions are highly complex systems in terms of both composition and structure and also kinetically and thermodynamically speaking [69]. To control the formation, stability, and rheology of food emulsions requires an understanding of the interactions between the various elements present in the system [70]. Recently, progress has been made in understanding the interaction behavior at the 0/W interface between some of the components found in food emulsions, particularly between different proteins and surfactants and, to a lesser extent, between proteins and fat crystals. 

Quality attributes of food emulsions, such as appearance, stability, and rheology, are strongly influenced by the size of the droplets that they contain (Friberg and Larsson, 1997 McClements, 1999). For example, the creaming stability of an emulsion decreases as droplet size increases. Analytical techniques that provide quantitative information about droplet size are therefore required to aid in the development and production of high-quality emulsion-based food products. A variety of analytical techniques have been developed to measure droplet size, e.g., laser diffraction, electrical pulse counting, sedimentation techniques, and ultrasonic spectrometry (McClements, 1999). These techniques are used for fundamental research, product development, and quality assurance. This unit focuses on the two most commonly used techniques in the food industry, laser diffraction and electrical pulse counting. 

Dickinson, E. and Pawlowsky, K. 1996. Effect of high-pressure treatment of protein on the rheology of flocculated emulsions containing protein arxl polysaccharide. J. Agric. Food Chem. 44 2992-3000. 

Factors Influencing Emulsion Rheology A variety of factors determine the rheological properties of food emulsions. Some of the most important of these factors are highlighted below. 

The general framework of interfacial rheology has been dealt with systematically by several previous authors Joly (214), Goodrich (215), Lucassen (216), Edwards et al. (217), and Noskov and Logho (218). Reviews on interfacial rheology in general have been published by Warburton (219) and Miller and cowor-kers (27, 220). Several researchers have attempted to correlate emulsion stability with interfacial tension and interfacial rheology. The literature up to 1988 has been reviewed by Malhotra and Wasan (221). An introduction to the subject of food emulsions was published by Lucassen-Reynders (222) and more recently by Murray and Dickinson (223) and Murray (224). 

Phospholipids are amphiphilic compoimds with high surface activity. They can significantly influence the physical properties of emulsions and foams used in the food industry. Rodriguez Patino et al. (2007) investigated structural, morphological, and surface rheology of dipalmitoylpho-sphatidylcholine (DPPC) and dioleoyl phosphatidylcholine (DOPC) monolayers at air-water interface. DPPC monolayers showed structural polymorphisms at the air-water interface as a function of surface pressure and the pH of the aqueous phase (Fig. 6.18). DOPC monolayers showed a... 

Brummer, R. Rheology Essentials of Cosmetics and Food Emulsions ISBN 3-540-25553-2... 

A typical characteristic of many food products is that these are multi-phase products. The arrangement of the different phases leads to a microstructure that determines the properties of the product. Mayonnaise, for example, is an emulsion of about 80% oil in water, stabilized by egg yolk protein. The size of the oil droplets determines the rheology of the mayonnaise, and hence, the mouthfeel and the consumer liking. Ice cream is a product that consists of four phases. Figure 1 shows this structure schematically. Air bubbles are dispersed in a water matrix containing sugar molecules and ice crystals. The air bubbles are stabilized by partial coalesced fat droplets. The mouthfeel of ice cream is determined by a combination of the air bubble size, the fat droplet size and the ice crystal size. 

Dickinson, E., Pawlowsky, K. (1997) Effect of i-carrageenan on flocculation, creaming, and rheology of a protein-stabilized emulsion. Journal of Agricultural and Food Chemistry, 45, 3799-3806. 

Klinkesom, U., Sophanodora, P., Chinachoti, P., McClements, D.J. (2004). Stability and rheology of com oil-in-water emulsions containing maltodextrin. Food Research International, 37, 851-859. 

Chen, J., Dickinson, E. (1999a). Interfacial ageing effect on the rheology of heat-set protein emulsion gel. Food Hydrocolloids, 13, 363-369. 

Lucassen-Reynders, E.H., Benjamins, J. (1999). Dilational rheology of proteins adsorbed at fluid interfaces. In Dickinson, E., Rodriguez Patino, J.M. (Eds). Food Emulsions and Foams Interfaces, Interactions and Stability, Cambridge, UK Royal Society of Chemistry, pp. 195-206. 

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). 

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