29B-23 |
Influence of molecular weight and concentration of chitosan on physicochemical stability of O/W emulsions |
S. CHI, S. Zivanovic, P. M. Davidson, C. Basurto, and J. Weiss. Dept. of Food Science & Technology, Univ. of Tennessee, Food Chemistry & Biophysics Labs., 2605 River Dr., Knoxville, TN 37996-4591 Chitosan is increasingly being used to improve microbiological stability of products such as food emulsions. However, addition of long-chain carbohydrates has been known to decrease emulsion stability thereby reducing the quality of products. Thus, use of chitosan may potentially destabilize o/w-emulsions. The purpose of this study was to evaluate the physicochemical stability of emulsions prepared with chitosan (150KDa) and chitosan oligosaccharide lactate. Emulsion premixes were prepared by blending 37.5%(w/w) corn oil with 3.6% aqueous Tween 20 solution. Premixes were high-pressure homogenized to reduce the particle size to 0.5-0.1µm. Chitosan solutions were prepared in 1%(v/v) acetic acid and mixed with emulsions to produce dispersions containing 0.1 to 0.7wt% chitosan at oil concentrations of 20wt%. The pH of emulsions was adjusted to 4.5 using 2M NaOH. Emulsions were stored at 24±1ºC and samples withdrawn in regular intervals to determine particle size distribution, creaming profile and viscosity (t=0.005-50Pa). Particle size distribution of chitosan oligosaccharide-stabilized emulsions remained approximately constant over the 10-day storage test regardless of oligosaccharide concentration. The mean diameter d32 of emulsions containing between 0.2 and 0.5wt% low molecular weight chitosan increased from 0.21 to 0.5µm while droplet size of emulsions containing <0.1wt% or >0.5wt% chitosan only increased from 0.21 to 0.32µm. Results correlated with creaming stability experiments that showed no creaming for oligosaccharide-stabilized emulsion while showing extensive creaming for emulsion stabilized with low molecular weight chitosan at concentrations between 0.2 and 0.5wt%. Viscosity measurements indicated an increase in viscosity from oligosaccharide to low-molecular weight chitosan-stabilized emulsions. Extent of shear thinning increased with increasing chitosan concentration suggesting more pronounced flocculation. Results were explained in terms of depletion flocculation caused by the presence of low molecular weight chitosan. Results have important implications for food manufacturers. While emulsions may be microbiologically more stable using higher molecular weight chitosans, their physicochemical stability may be decreased.
Session 29B, Food Chemistry: Lipids, antioxidants and emulsifiers
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