Engineering interfacial properties by anionic surfactant-chitosan complexes to improve stability of oil-in-water emulsions.

摘要

Oil-in-water emulsions (10% w/w n-tetradecane) were prepared at pH = 5.7 by using, as surface active agents, electrostatically formed complexes of sodium stearoyl lactylate (SSL) at 0.4% (w/w) and chitosan (CH) in a concn. range between 0 and 0.48% w/w. Use of complexes in emulsions with a low concn. of CH (<0.24% w/w) resulted in highly flocculated systems; instead, with increased level of CH, emulsions had a smaller average droplet size and exhibited greater stability during storage. Emulsions stabilized by SSL/CH complexes showed non-Newtonian flow behaviour with pronounced shear thinning. Among all formulations studied none showed a gel-like behaviour since in all cases the G' (storage modulus) was lower that G'' (loss modulus). Adsorption kinetics of pure SSL and SSL/CH complexes to the oil/water interfaces were evaluated using an automated drop tensiometer (ADT). Even though complexation of SSL with CH resulted in a delay of the adsorption of the surface active species at the oil/water interface, the inclusion of the polysaccharide resulted in substantially improved interfacial properties as indicated by a significant increase of the dilatational modulus. Also, the enhanced interfacial properties of emulsion droplets resulted in improved stability against freeze-thaw cycling. Results may facilitate the development of frozen foods such as desserts with an ameliorated stability and favourable sensorial characteristics. [This paper was presented at the Delivery of Functionality in Complex Food Systems Symposium held in Guelph, Canada, August 2011.]