The Preparation And Hypolipidemic Activity Of Chitosan Stearate

Chitosan (CS), a cationic mucopolysaccharide, has exhibited a certain hypolipidemicactivity, which has received considerable interest. In particular, the food grade CS with highmolecular weight （Mw） and high degree of deacetylation (DD) has studied widely onreducing weight and its hypolipidemic effect. To improve the hypolipidemic effect of CS withhigh Mwand high DD, chitosan stearate complexes (CSCs) were prepared by the interactionbetween the high-molecular-weight and high-DD CS and stearic acid which ownedhydrophobic alkyl chain.CSCs were synthesized by the electrostatic interaction between the amino group of CSand the carboxyl group of stearic acid in the liquid phase. Anhydrous diethyl ether was usedto wash the precipitate to remove the stearic acid. The formation and characteristics werestudied by FT-IR spectroscopy, X-ray diffraction (XRD), Thermogravimetric analysis (TGA)and Scanning electron microscopy (SEM). The content of nitrogen was measured by Kjeldahmethod, and the ratio of combined stearic acid was also calculated. The results showed thatmaximal CS was adsorbed to stearic acid when the ratio of n(COO-)/n(NH3+) was about0.6,whereas least CS was adsorbed via electrostatic interaction (R=0.11). Alternative dryingmethods that firstly freeze the product frozen and then defrosted with hot water and lastlyvacuum drying was used to retain the porous characteristics of the product. The results fromFT-IR spectra revealed that the complexes were CSCs, rather than the mixture of CS andstearic acid. The X-ray diffraction spectra exhibited that the crystal structure of CS wasdestroyed and the crystallinity of complexes decreased with the increasing content of stearicacid adsorbed by CS through electrostatic interaction. The TGA curves revealed CSCs wereprone to less thermally stable in case that amine groups bound more stearic acid viaelectrostatic attraction, which temperature Tmaxwere240-305oC. A rough, discontinuousmicrostructure with many gaps was observed for CSC powder surface from SEMmicrographs.The swelling behaviors of CSCs were studied. Solubility of CSCs was investigated bypreparing different solutions. The swelling degree and viscosity were measured in simulatedcondition and the structure stability of CSCs was investigated by compared FT-IR spectra ofCSCs swelling before and after. The results showed that CSCs didn’t dissolve in the distilledwater and alkaline solution and showed the partial loss of solubility in acidic aqueous media.Swelling behavior of CSCs and CS occurred in acidic solutions and showed that the swellingdegree of CSCs (1320%-1925%) was lower than that of CS (3180%) but much larger thanthat of cellulose (470%). The viscosity of the swelling body became greater as the R of CSCincreased. Moreover, the chemical structure of CSC didn’t change after the swelling.The lipids-binding capacity of CSC was investigated in the conditions simulated humandigestive tract. The in vitro assays show that the fat-binding capacity of CSC(R=0.11) washigher than that of CS, reaching17.2g/g, while CSC with higher R had lower fat-bindingcapacity. The bile salt-binding capacities of CS and CSC were affected by pH significantly. AtpH6, CSC adsorbed98.6%of deoxycholic acid salt, which much higher than that of CS. The complexes of CS adsorbed more deoxycholic acid salt than CS per se at the same pH.Moreover, CSC which was more hydrophobic bound bile salt more effectively.The hypolipidemic activitives of chitosan stearate were evaluated in rats fed high-fatdiets. By measuring changes in body weight, organ index and blood lipid levels in rats andobservating the differeces of livers, the hypolipidemic effect of chitosan stearate wasexamined. Compared with HF group, CSC group showed decreased body weight gain, serumtotal cholesterol (TC), as well as decreased triglyceride (TG). Moreover, serum TC, TG,LDL-C of rats in CSC group was lower than those of CS group. The obtained resultssuggested that chitosan stearate own a certain lipid-lowering effect.