Chitosan hydrogel formation using laccase activated phenolics as cross-linkers.

Chitosan hydrogels are gaining increasing interest for biomedical applications due to attractive properties such as biocompatibility. In order to replace toxic chemical cross-linkers for hydrogel formation, we investigated the cross-linking potential of laccase oxidized phenolics. HPLC-TOF-MS and ATR-FTIR demonstrated that phenolics were bond to glucosamine as chitosan model substrate. Phenolics concentrations required for hydrogel formation varied from 500µM for catechol to 5000µM for sinapic acid. The hydrogels showed different swelling and release properties assessed using methylene blue release as a model. Laccase oxidized caffeic acid and pyrogallol-chitosan hydrogels showed excellent behavior in up-taking water with a swelling of 208.7% for caffeic acid. Biocompatibility results did not show any significant inhibition of growth of HEK293 cell line when phenolics like catechol or eugenol were used. Therefore, this study demonstrates that laccase oxidized phenolics are potential cross-linking agents of chitosan as a novel green approach to synthesizing chitosan hydrogels.

Influence of gum tragacanth on the physicochemical and rheological properties of kashk.

In this study, the physicochemical properties of a low-fat dried yogurt paste (kashk) were determined, and the effects of different concentrations (0, 0·1, 0·3 and 0·5% w/w) of gum tragacanth exudates from Astragalus gossypinus on the stability and texture of the samples were investigated by measuring amount of syneresis, turbidity, particle size distribution (PSD), flow behaviour and viscoelastic properties. The flow behaviour index was not very sensitive to the concentration of gum, while a remarkable concentration dependency of the power-law consistency coefficient and Herschel-Bulkley yield stress was observed. The initial increase in the gum concentration at 0·1 and 0·3% levels led to a higher degree of syneresis, which was related to the depletion flocculation mechanism. However, the reduced amount of syneresis in samples containing 0·5% gum tragacanth was attributed to the significant increase in viscosity of the continuous phase, which is also accompanied by trapping of the aggregated casein particles. The presence of 3% salt in the samples may have led to the neutralization of charges on the surface of gum tragacanth; consequently, the non-adsorbing behaviour of high-ionic-strength polysaccharides inhibited the formation of electrostatic protein-polysaccharide complexes. Furthermore, maximum values of polydispersity, syneresis and tan δ at high frequencies were found in samples containing 0·1% gum tragacanth.