Structure protein-polysaccharide mixtures

The Dynamics of Formation and Structure of the Air-Water Interface in the Presence of Protein-Polysaccharide Mixtures... 

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). 

The preparation of pure nucleic acids is as yet an unsolved problem. It is quite easy to prepare nucleic acid fractions that are free of proteins, polysaccharides, etc., but invariably they are mixtures of many very similar nucleic acids whose further separation becomes extraordinarily difficult. Most investigations on the chemical structure of nucleic acids have been carried out on such nucleic acid fractions, just as in the beginning of protein research all structural principles were derived from heterogeneous protein mixtures. The validity of the results need not be doubted on this account, however. 

The diverse applications of complex polysaccharide/protein offer new tools to improve the quality of texture and stability of food products, cosmetics, and pharmaceuticals, plus the ability to generate new functional structures at the micro- and the nanoscale [4, 80]. More studies should be conducted on the factors that influence and affect the structures of protein-polysaccharide complexes to better understand the associative interactions of mixtures and achieve full potential as stabilizers, foaming, emulsifying, and haulers as matrices. 

Interactions between proteins and polysaccharides give rise to various textures in food. Protein-stabilized emulsions can be made more stable by the addition of a polysaccharide. A complex of whey protein isolate and carboxymethylcellulose was found to possess superior emulsifying properties compared to those of the protein alone (Girard et al., 2002). The structure of emulsion interfaces formed by complexes of proteins and carbohydrates can be manipulated by the conditions of the preparation. The sequence of the addition of the biopolymers can alter the interfacial composition of emulsions. The ability to alter interfacial structure of emulsions is a lever which can be used to tailor the delivery of food components and nutrients (Dickinson, 2008). Polysaccharides can be used to control protein adsorption at an air-water interface (Ganzevles et al., 2006). The interface of simultaneously adsorbed films (from mixtures of proteins and polysaccharides) and sequentially adsorbed films (where the protein layer is adsorbed prior to addition of the polysaccharide) are different. The presence of the polysaccharide at the start of the adsorption process hinders the formation of a dense primary interfacial layer (Ganzelves et al., 2008). These observations demonstrate how the order of addition of components can influence interfacial structure. This has implications for foaming and emulsifying applications. 

Glycosaminoglycans are solubilized from stromal or other tissues by extracting the source tissue with dilute acid or alkali. Hyaluronan is electrostatically bound to specific proteins called hyaladherins, which possess a structural domain of -100 amino acids termed a link module. Other glycosaminoglycans are O-linked to serine and threonine residues of polypeptides and these bonds hydrolyze before the rest of the polysaccharide. The protein moiety precipitates when trichloroacetic acid or ammonium sulfate is added to the cooled mixture. The composition of the GAGs (including hyaluronan) was identified by chromatographic separation of the purified polysaccharides, followed by their hydrolysis in boiling 1.0 M HC1 for 2 1 h and identification of the individual monosaccharide components. 

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