Compatibility, biopolymer

In addition to the necessary protection of the contents of the emulsion droplets, effective encapsulation technology requires that the release of the active matter be controlled at a specified rate. Benichou et aL (2004) have demonstrated that a mixture of whey protein isolate (WPI) and xanthan gum can be successfully used for the controlled release of vitamin Bi entrapped within the inner aqueous phase of a multiple emulsion. The release profile, as a function of the pH of the external aqueous phase, is plotted in Figure 7.25. We can observe that the external interface appears more effectively sealed against release of the entrapped vitamin at pH = 2 than at pH = 4 or 7. It was reported that an increase in the protein-to-potysaccharide ratio reduced the release rate at pH = 3.5 (Benichou et aL, 2004). More broadly, the authors suggest that compatible blends of biopolymers (hydrocolloids and proteins) should be considered excellent amphiphilic candidates to serve as release controllers and stability7 enhancers in future formulations of double emulsions. So perhaps mixed compatible biopolymers wall at last allow researchers to... 

The results of mechanical properties (presented later in this section) showed that up to 20 phr, the biofillers showed superior strength and elongation behavior than CB, cellulose being the best. After 30 phr the mechanical properties of biocomposites deteriorated because of the poor compatibility of hydrophilic biopolymers with hydrophobic natural rubber(results not shown). While increasing quantity of CB in composites leads to constant increase in the mechanical properties. Scanning electron micrographs revealed presence of polymer-filler adhesion in case of biocomposites at 20 phr. 

As shown in Fig. 25b, the systematic tuning of emission wavelength was achieved by the combinatorial introduction of substitutents at the two diversity points on the fluorescent core skeleton. In addition to the synthetic versatility and predictability on emission wavelengths, these novel fluorophores were compatible with the modification of biopolymers and successfully applied in the immunofluorescence (see Fig. 25c). 

In order to improve the mechanical properties of PHB or poly(3HB-co-3HV), many have reported on blending these biopolymers with other, both degradable as well as non-degradable, materials. However, due to the lack in compatibility between most polymers no substantial improvements in mechanical properties were reported upon, up to now [90]. 

However, this study is of great importance since Gill and Ballesteros demonstrated first by numerous examples [46,82,101] that the exchange of alcohol with polyols improves the compatibility of the sol-gel processing to biopolymers. This showed a method for modification of the silica precursors. 

Thus, the increasing application of the various intrinsic properties of biopolymers, coupled with the knowledge of how such properties can be improved to achieve compatibility with thermoplastics processing, manufacturing, and end-use requirements, and has fueled technological and commercial interest in biopolymers. 

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. 

These coefficients can be evaluated for any biopolymer by taking an arbitrary chain length and determining the allowed values of frequencies for any set of boundary conditions. In our calculations we have assumed that the ends of the chain are fixed and we determine the frequency of the modes that permit an odd number of half wavelengths to be present on the chain. The eigenvectors for these frequencies are determined from the dispersion curves for an infinite chain. To make these calculations more compatible with experiment we have determined the absorption cross section which can be related to the Einstein coefficient by the following expression... 

The above drawbacks of the linear polyfunctional macromolecular supports are to a greater extent overcome by the use of appropriate polyethers as soluble supports for biopolymer synthesis. Absence of any steric effect, equivalence of functional groups and compatibility with the biopolymers being synthesized can be expected from polyethyleneglycols, which are linear polyethers with two hydroxy groups at the chain ends (21). 

On mixing solutions of a protein and a polysaccharide, four kinds of mixed solutions can be obtained. Figure 3.1 shows that two single-phase systems (1 and 3) and two-types of biphase systems (2 and 4) can be produced. The two-phase liquid systems 2 and 4 differ in the distribution of biopolymers between the co-existing phases. The biopolymers are concentrated either in the concentrated phase of system 2 because of interbiopolymer complexing, or within separated phases of system 4 because of incompatibility of the biopolymers. The term biopolymer compatibility implies miscibility of different biopolymers on a molecular level. The terms incompatibility or limited thermodynamic compatibility cover both limited miscibility or limited cosolubility of biopolymers (i.e., system 2) and demixing or phase separation... 

Biopolymer incompatibility is a general phenomenon typical of aU polymers. Biopolymer incompatibility occurs even when their monomers would be miscible in all proportions. For instance, sucrose, glucose and other sugars are normally cosoluble in the common solvent, water, while different polysaccharides usually are not miscible. The transition from a mixed solution of monomers to polymers corresponds to the transition from good to limited miscibility. Normally, a slight difference in composition and/or structure is sufficient for incompatibility of macromolecules in common solvent (Tolstoguzov 1991, 2002). Compatibility or miscibility of unlike biopolymers in aqueous solutions has only been exhibited by a few biopolymer pairs (Tolstoguzov 1991). 

For instance, denaturation and partial hydrolysis of proteins oppositely influence their incompatibility with other biopolymers (Tolstoguzov 1991). Most biopolymers are polyelectrolytes. Factors such as pH and salt concentration affect their interactions with one another, with the solvent and their compatibility. For instance, when the pH is shifted to their isoelectric point (lEP), the thermodynamic incompatibility of proteins is usually enhanced by self-association of the protein molecules. Generally, protein-neutral polysaccharide mixtures separate into two phases when the salt concentration exceeds 0.15 M. 

Table 1 Comparison of synthetic and biopolymer solvent compatibilities and post-spinning crosslinkers investigated to date... 

When (S-lg adsorbs at the air-water interface in the presence of PS three phenomena can occur (i) the polysaccharide adsorbs at the interface on its own in competition with the protein for the interface (competitive adsorption) (ii) the polysaccharide complexates with the adsorbed protein mainly by electrostatic interactions or hydrogen bonding (Dickinson, 2003), and (iii) because of a limited thermodynamic compatibility between the protein and polysaccharide, the polysaccharide concentrates the adsorbed protein. In a previous work we have shown that the existence of competitive or cooperative adsorption between the (3-lg and the PS could be deduced from the comparison of rr-time curves for the single biopolymers and for the mixtures (Baeza et al., 2005b). 

To probe the structural changes of a composite film that subjected to a destructive force, we measured the AE event simultaneously with the tensile test. Figure 9 shows the correlation between the stress-strain curve and the AE hit pattern. For the PEO-free samples, AE activity detected only at the peak stress, when the samples were completely destructed. This confirms the homogeneity of the composite films. Since the two biopolymers are compatible, they are able to transfer stress evenly. For the samples containing with PEO, the phenomena are similar, the samples emitted sound at the peak stress however, signals were continually collected as the PEO fiber were pulled and broken, being consistent with the results shown in Figures 7 and 8. 

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