Polysaccharides emulsions

Different polysaccharides change the perception of flavour, thus xanthan is superior to gum guar in the perception of sweetness. Mixtures of xanthan and locust bean gum have improved flavour release and texture when used in pies and pat s compared to starch. Many foods are emulsions, examples being soups, sauces and spreads. Exopolysaccharides are used to stabilise these emulsions and prevent the phases from... 

A strain of Acinetobacter calcoaceticus produces an unusual polysaccharide called emulsan. It is a complex polymer comprising about 15% fatty acyl esters and 20% protein. This structure enables it to act as an emulsifying agent, stabilising hydrocarbon/water emulsions at very low concentrations (0.1-1.0%). This property,... 

GA is mainly used for fat microencapsulation because it produces stable emulsions in the case of most oils in a wide pH range, and it has the ability to form films (Kenyon, 1995). Barbosa et al., 2005 studied the photostability of the microencapsulated carotenoid bixin in different edible polysaccharide. They found out that microencapsulated bixin in GA was three to four times more stable than the one microencapsulated with maltodextrin, and about ten-fold than in homogeneous solvents. 

In a recycling system, the aqueous discharge effluent from both centrifiiges is returned to the extractors for additional oil recovery, the water being reused. During this extraction process the viscosity of the emulsions increases because peel polysaccharides, mainly pectins, are transported with the emulsion. Enzymatic breakdown of the internal links of the pectin, catalysed by endopolygalacturonase activity, produces an important decrease in the viscosity of the emulsion [16]. In addition, enzymatic treatment removes pectins from the emulsion and contributes to it destabilization [17]. 

E. ten Grotenhuis, M. Paques, G. A. van Aken 2000, (The application of diffus-ing-wave spectroscopy to monitor the phase behavior of emulsion-polysaccharide systems),/. Colloid Interface Sci. 227, 495. 

Gum acacia is a unique polysaccharide, with some peptides as part of the structure and has a range of different uses. It was originally the gum in gum sweets although some gum sweets do contain modified starch as a substitute. The replacement of gum is not because the substitute performs better but because there have been supply problems with gum acacia. Gum acacia is likely to be encountered in bakeries in small quantities when it has been used to make emulsions of citrus oils as a bakery flavour. It is possible to use gum acacia in making dry flavours from oils such as citrus by making an emulsion and then spray drying it. 

Another example of a food emulsion is the ice cream, in which the colloidal dispersion of ice particles is achieved together with tiny entrapped air bubbles in an emulsion consisting of fats, sugar, and thickening agents (polysaccharides). 

Microspheres are particles ranging between 1 and 100 pm. They are typically formed from degradable polymeric materials such as albumin, polysaccharides, or poly(a-hydroxy acids) by precipitation or phase-separation emulsion techniques [6, 332]. The relatively large diameters of microspheres make their extravasation into the tumor mass difficult and the uptake of microspheres by the RES is very rapid. 

McClements, 2006 Anal et al., 2008). Different combinations of proteins and polysaccharides (e.g., P-lactoglobulin + pectin, carrageenan or alginate casein + pectin) have been investigated within the context of multilayer emulsion stabilization (Guzey and McClements, 2006). It seems that the main technical challenge associated with the utilization such complex formation for layer-by-layer emulsion stabilization is the avoidance of bridging flocculation (McClements, 2005, 2006). 

Benichou, A., Aserin, A., Garti, N. (2002). Protein-polysaccharide interactions for stabilization of food emulsions. Journal of Dispersion Science and Technology, 23, 93-123. 

Dickinson, E. (2008). Interfacial structure and stability of food emulsions as affected by protein-polysaccharide interactions. Soft Matter, 4, 932-942. 

Electrostatic and non-electrostatic biopolymer complexes can also be used as effective steric stabilizers of double (multiple) emulsions. In this type of emulsion, the droplets of one liquid are dispersed within larger droplets of a second immiscible liquid (the dispersion medium for the smaller droplets of the first liquid). In practice, it is found that the so-called direct water-in-oil-in-water (W/O/W) double emulsions are more common than inverse oil-in-water-in-oil (O/W/O) emulsions (Grigoriev and Miller, 2009). In a specific example, some W/O/W double emulsions with polyglycerol polyricinoleate (PGPR) as the primary emulsifier and WPI-polysaccharide complexes as the secondary emulsifying agent were found to be efficient storage carriers for sustained release of entrapped vitamin Bi (Benichou et al., 2002). 

Dickinson, E., Galazka, V.B. (1991). Emulsion stabilization by ionic and covalent complexes of p-lactoglobulin with polysaccharides. Food Hydrocolloids, 5, 281-296. 

Figure 3.4 Effect of polysaccharide on protein-stabilized emulsions. The diameter ratio, j43nuxtlire / J43protem is plotted against the molar ratio R (moles polysaccharide / moles protein). Here J43nuxtlire is average droplet diameter in fresh emulsion prepared with protein + polysaccharide, and d43pTOtQm is average diameter in emulsion stabilized by protein alone. Key , , legumin + dextmn (48 kDa) or legumin + dextran (500 kDa), respectively (0.5 w/v % protein, 10 vol% oil, pH = 8.0, /= 0.1 M) (Dickinson and Semenova, 1992) O, , asi-casein + pectinate and p-casein + pectinate at pH = 7.0, / = 0.01 M (2.0 w/v % protein, 40 vol% oil), respectively , p-casein + pectinate at pH = 5.5, / = 0.01 M (2.0 w/v % protein, 40 vol% oil) (Semenova et al, 1999). Reproduced from Semenova (2007) with permission.

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. 

Tuinier, R., de Kruif, C.G. (1999). Phase separation, creaming, and network formation of oil-in-water emulsions induced by an exocellular polysaccharide. Journal of Colloid and Interface Science, 218, 201-210. 

Let us consider now the case of a specific ionic polysaccharide. The unique properties of complexes of the cationic chitosan with non-ionic sorbitan esters provides an interesting example. Grant and co-workers (2006) have established that mixtures of chitosan and surfactant form emulsion-like solutions and/or creams, where the surfactant component is present as droplets or micelle-like particles and the chitosan solution acts as the system s continuous phase. It was established that the length and the degree of saturation of the surfactant hydrocarbon chain have a significant impact on the development of the chitosan-surfactant complexes. Moreover, an optimal distance between the chitosan s protonated amine groups is required for effective interactions to occur between the polysaccharide and the sorbitan esters. 

In an OAV emulsion system containing a mixture of surfactant + polysaccharide, the stability behaviour will generally depend on two sets of factors (i) the nature of the surfactant-polysaccharide interactions at the surface of the emulsion droplets, and (ii) the surfactant-polysaccharide interactions in the aqueous medium between the droplets (Dickinson et ah, 1993 Dickinson, 2003 Aoki el al., 2005 Klinkesom et ah, 2004 Chuah et ah, 2009). 

Dickinson, E., Goller, M.I., Wedlock, D.J. (1993). Creaming and rheology of emulsions containing polysaccharide and non-ionic or anionic surfactants. Colloids and Surfaces A Physicochemical and Engineering Aspects, 75, 195-201. 

Table 7.1 shows that rather similar results were also found by Makri et al. (2005) for samples of coarse emulsions containing thermodynamically incompatible mixtures of legume seed protein + xanthan gum. The protein surface load was found to be enhanced in the presence of xanthan gum, especially at elevated ionic strengths. That is, there was observed to be an increase in the adsorption of legume seed proteins at the surface of the emulsion droplets which could be attributed to an increase in the thermodynamic activity of the proteins in the system in the presence of the incompatible polysaccharide (see Table 7.1). Associated with the greater extent of protein adsorption, the authors reported an enhancement in the emulsion stability.

The presence of a thermodynamically incompatible polysaccharide in the aqueous phase can enhance the effective protein emulsifying capacity. The greater surface activity of the protein in the mixed biopolymer system facilitates the creation of smaller emulsion droplets, i.e., an increase in total surface area of the freshly prepared emulsion stabilized by the mixture of thermodynamically incompatible biopolymers (see Figure 3.4) (Dickinson and Semenova, 1992 Semenova el al., 1999a Tsapkina et al., 1992 Makri et al., 2005). It should be noted, however, that some hydrocolloids do cause a reduction in the protein emulsifying capacity by reducing the protein adsorption efficiency as a result of viscosity effects. 

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