Biopolymer-stabilized conjugated linoleic acid (CLA) oil-in-water emulsions: Impact of electrostatic interactions on formation and stability of pectin-caseinate-coated lipid droplets

Abstract

Conjugated linoleic acid (CLA) may be used as a nutraceutical, supplement or pharmaceutical due to its potential health benefits. In this study, CLA oil-in-water emulsions were fabricated using biopolymers as stabilizers: sodium caseinate as an emulsifier and pectin as a coating material. The effect of electrostatic interactions on the formation of these mixed biopolymer coatings, as well as on the stability of the resulting emulsions, was determined by systematically varying pH and ionic strength. Caseinate-coated CLA droplets were stable from pH 7 to 5 due to the strong electrostatic repulsion between them, but aggregated from pH 5 to 3 due to weakening of the electrostatic repulsion near the protein’s isoelectric point. Pectin addition greatly improved emulsion aggregation stability, particularly at levels sufficient to saturate the caseinate-coated oil droplet surfaces. Indeed, emulsions with pectin-to-caseinate ratios>1:1 were stable under acidic solution conditions (pH 5 to 3). Ionic strength had a pronounced impact on droplet aggregation, which was pH dependent. At pectin-to-caseinate ratios of 2:1, emulsions were stable against NaCl addition (0 to 200mM) at pH 3.5 and 4.0 due to strong electrostatic attraction between protein and polysaccharide molecules in the interfacial complexes, but they were unstable to NaCl addition at pH 3.0, 4.5, and 5.0 due to a weaker electrostatic attraction between the biopolymers. Mixed biopolymer-coated emulsions were stable against thermal processing (90°C, 20min). These results have important implications for the development of natural CLA delivery systems for utilization in foods and other products.