physicochemical and functional properties of crawfish chitosan as ...
physicochemical and functional properties of crawfish chitosan as ...
physicochemical and functional properties of crawfish chitosan as ...
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
- 0.5% <strong>chitosan</strong> solution only. Even though <strong>chitosan</strong> alone does not produce emulsion (Knorr,<br />
1982; in Cho et al.,1998), the emulsifying capacity <strong>of</strong> soy protein in the presence <strong>of</strong> <strong>chitosan</strong> w<strong>as</strong><br />
greatly enhanced (Figure 8).<br />
According to Belitz <strong>and</strong> Grosch (1999), emulsion is b<strong>as</strong>ically a disperse system <strong>of</strong> one or<br />
more immiscible liquids, <strong>and</strong> emulsifiers are compounds which form interface films <strong>and</strong> thus<br />
prevent the disperse ph<strong>as</strong>es from flowing together. Proteins are amphoteric, meaning they behave<br />
<strong>as</strong> dipolar ions carrying both positive <strong>and</strong> negative charges. Depending on pH, they can exist <strong>as</strong><br />
polyvalent cations, anions or zwitterions. They can possess the same number <strong>of</strong> positive <strong>and</strong><br />
negative charges resulting in the net charge <strong>of</strong> zero at the isoelectric point. If the pH value is<br />
higher than the isoelectric point (pI), the protein will have a negative charge, where<strong>as</strong> a positive<br />
charge if the pH value is lower than the pI.<br />
Soy protein h<strong>as</strong> a pronounced minimum solubility in the pH range <strong>of</strong> 3.0 to 6.0 (Belitz<br />
<strong>and</strong> Grosch, 1999). Its isoelectric point is variable depending on the ions present <strong>and</strong> their<br />
concentration. In our study, at approximately near pH 4.0 (Brooks <strong>and</strong> Morr, 1984), protein w<strong>as</strong><br />
at its isoelectric point, w<strong>as</strong> the le<strong>as</strong>t soluble, <strong>and</strong> precipitated ("isoelectric precipitation").<br />
Unlike other polysacchrides, <strong>chitosan</strong> possesses a positive ionic charge, <strong>and</strong> h<strong>as</strong> both<br />
reactive amino <strong>and</strong> hydroxyl groups, which give it the ability to chemically bond with negatively<br />
charged protein (Li et al., 1992). Chitosan is pH-dependent. When pH is less than 6.5, <strong>chitosan</strong> in<br />
solution carries a positive charge along its backbone, thus makes it possible for its use <strong>as</strong><br />
emulsifier in many application (Rout, 2001). Because <strong>of</strong> its polar groups, <strong>chitosan</strong> also provides<br />
additional stabilization due to hydration forces (Del Blanco et al., 1999). According to Filar <strong>and</strong><br />
Wirick (1978), <strong>chitosan</strong> functions only in acid systems to show possible utility <strong>as</strong> a thickener,<br />
stabilizer, suspending agent or film former.<br />
57
Change language