29B-22 |
Influence of environmental conditions on stability of O/W emulsions containing droplets stabilized by lecithin-chitosan membranes |
S. OGAWA1, E. A. Decker2, and D. J. McClements2. (1) Dept. of Food Science, Tokyo Univ. of Fisheries, 4-5-7 Konan, Minato, Tokyo, 108-8477, Japan, (2) Dept. of Food Science, Univ. of Massachusetts, Amherst, 236 Chenoweth Lab., Box 31410, Amherst, MA 01003-1410 Many food emulsions are subjected to environmental conditions that promote instability, such as elevated temperatures, freeze-thaw cycling, high mineral contents and mechanical agitation. There is currently a lack of natural emulsifiers available for creating food emulsions that can withstand many of these harsh conditions. Our objective was to create oil-in-water emulsions with improved stability to environmental stresses by combining the beneficial attributes of different kinds of emulsifiers to form multi-layered membranes around the oil droplets. We then intended to examine the stability of these emulsions to thermal processing, freeze-thaw cycling, high mineral contents and lipid oxidation. A primary emulsion containing small anionic droplets coated with a lecithin membrane was prepared by homogenizing 5 wt% corn oil with 95 wt% aqueous solution (1 wt% lecithin, 100 mM acetic acid, pH 3.0) using a high pressure valve homogenizer. A secondary emulsion (1 wt% corn oil, 0.2 wt% lecithin, 0.036 wt% chitosan, 100 mM acetic acid, pH 3.0) containing small cationic droplets coated with a lecithin-chitosan membrane was prepared by mixing the primary emulsion with an aqueous chitosan solution. The particle size distribution and particle charge of the primary and secondary emulsions were measured to examine their stability to thermal processing (30 to 90 C for 30 minutes), freeze-thaw cycling (-10C for 22 hours, 30C for 2 hours), high multivalent mineral contents (0 to 1000 mM CaCl2) and lipid oxidation (at 30 C). Secondary emulsions had better stability to droplet aggregation induced by environmental stresses after heating from 30 to 90 C, after four freeze-thaw cycles, and after adding up to 500 mM CaCl2 than primary emulsions. Differences between emulsions were attributed to the influence of chitosan on interfacial membrane properties and droplet-droplet interactions. Secondary emulsions also had better stability to lipid oxidation than primary emulsions, probably because of electrostatic repulsion between the positively charged droplets and iron ions. The ability to form emulsions containing droplets stabilized by multiple interfacial layers, rather than a single interfacial layer, may lead to the development of food products with improved stability to environmental stresses.
Session 29B, Food Chemistry: Lipids, antioxidants and emulsifiers
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