Polysaccharides film formation

The objectives of this chapter are to (a) review research on polysaccharide film-formation and characteristics, (b) analyze mechanical and barrier properties (water vapour permeability, gas permeabilities and volatile permeability) of polysaccharide-based films, (c) summarize applications of polysaccharide films in food products, and (d) make conclusions as to the status of polysaccharide films and their future developmental direction. 

Polysaccharide film formation and film characteristics depend of the type of polysaccharides used. Table I.l summarize structure, formula and polysaccharide properties and Film characteristics... 

Starch is an abundant, inexpensive polysaccharide that is readily available from staple crops such as com or maize and is thus is mostly important as food. Industrially, starch is also widely used in papermaking, the production of adhesives or as additives in plastics. For a number of these applications, it is desirable to chemically modify the starch to increase its hydrophobicity. Starch modification can thus prevent retrodegradation improve gel texture, clarity and sheen improve film formation and stabilize emulsions [108], This may, for example, be achieved by partial acetylation, alkyl siliconation or esterification however, these methods typically require environmentally unfriendly stoichiometric reagents and produce waste. Catalytic modification, such as the palladium-catalyzed telomerization (Scheme 18), of starch may provide a green atom-efficient way for creating chemically modified starches. The physicochemical properties of thus modified starches are discussed by Bouquillon et al. [22]. 

It should also be noted that capability of gelation of the plant gum (polysaccharides)seems to take part significant role in the enzymatic film formation process. ... 

In a typical experiment the isocyanate (0.006 moles) was reacted with 1.5 g of the polysaccharide in 150 ml of a 5% LiCl/ N,N-dimethylacetamide solution at 90°C under nitrogen for two hours. The appearance of a strong infrared absorbance at 1705 cm l was an indication of carbamate formation. The derivatized polymer was isolated as a white powder by precipitation of the reaction solution into a nonsolvent such as methanol. Alternatively thin films were cast directly from solution the lithium salt could be removed by rinsing with acetone. Figure 1 illustrates the reaction of cellulose with phenyl isocyanate. 

Figure 8.12 illustrates the effect of complex formation between protein and polysaccharide on the time-dependent surface shear viscosity at the oil-water interface for the system BSA + dextran sulfate (DS) at pH = 7 and ionic strength = 50 mM. The film adsorbed from the 10 wt % solution of pure protein has a surface viscosity of t]s > 200 mPa s after 24 h. As the polysaccharide is not itself surface-active, it exhibited no measurable surface viscosity (t]s < 1 niPa s). But, when 10 wt% DS was introduced into the aqueous phase below the 24-hour-old BSA film, the surface viscosity showed an increase (after a further 24 h) to a value around twice that for the original protein film. Hence, in this case, the new protein-polysaccharide interactions induced at the oil-water interface were sufficiently strong to influence considerably the viscoelastic properties of the adsorbed biopolymer layer. 

In an effort to gain a better understanding of the initial fouling step leading to bacterial attachment and biofilm formation, we have investigated the adsorption of protein and polysaccharides onto thin metallic films and uncoated internal reflection elements from flowing solutions using attenuated total reflectance spectroscopy. The preliminary results will be described in this paper. 

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. 

The nitrocellulose polymer substrate was a fully nitrated derivative of cellulose, in which the free hydroxyl groups are substituted by nitro groups, and is thus hydrophobic in nature. Researchers have shown that the immobilization of proteins on nitrocellulose surfaces rehes on hydrophobic interactions. However, polysaccharides, being rich in hydroxyl groups, are hydrophilic in nature (42,61). The molecular forces for the carbohydrate-nitrocellulose interaction remain to be characterized, but it has been suggested that the three-dimensional (3D) microporous configuration of the nitrocellulose on the slides and the macropolymer characteristics of polysaccharides play important roles for the stable immobilization of many polysaccharides on the nitrocellulose surface. The polysaccharide molecules immobilized onto the nitrocellulose film are in a nonsite-specific format (Fig. 3). 

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