By using an electrostatic technique to adsorb sodium alginate onto the surface of the dairy protein-corn oil droplets, the researchers suggest that the stability of dairy proteins, known to be highly sensitive to environmental conditions such a pH, could be improved.
"This relatively simple electrostatic deposition method could be used by the food industry to extend the range of conditions where dairy proteins can be used as emulsifiers," wrote the authors, led by D. Julian McClements, in the Journal of Food Science.
Recent figures from Frost & Sullivan reveal emulsifiers, along with fat replacers, are leading growth in the food additive industry: since 2001 the market value of emulsifiers rose by some 5.6 per cent. Emulsifiers are used by food makers to reduce the surface tension between two immiscible phases at their interface - such as two liquids, a liquid and a gas, or a liquid and a solid - allowing them to mix.
The researchers prepared the emulsions by mixing droplets sodium caseinate-coated corn oil droplets with anionic (negatively charged) sodium alginate under neutral conditions (pH7). By reducing the pH of the solution to 3.5 (acidic conditions) the negatively charged alginate adsorbed to the cationic (positively charged) caseinate-coated droplets.
"We have selected sodium caseinate as the emulsifier and sodium alginate as the polysaccharide because these substances are both natural and are already widely used in the food industry," explained the researchers.
The researchers report that relatively small particle sizes could be obtained over a range of alginate concentrations (0.1 to 0.4 weight per cent). The stability to pH and salt concentrations of the protein-coated droplets was increased due to a relatively thick layer of alginate forming around the droplets.
"Further studies are required to better understand the relationship between the molecular characteristics of adsorbing polysaccharides, the properties of the adsorbed polysaccharide layers, and the bulk physicochemical properties of emulsions (for example, stability, rheology, and mouthfeel)," concluded the researchers.
The researchers note that this is in-line with their previous studies using pectin to coat beta-lactoglobulin (whey protein)-corn oil droplets. They also extended this to produce "colloidosomes", novel oil-on-oil particles in an aqueous emulsion, said to have important implications for the food industry by reducing an emulsion's susceptibility to gravitational separation, to develop novel controlled or triggered release systems, or to compartmentalize active agents.
Calcium alginate is already used in the food industry as a thickening agent, and sales of sodium alginate are reported to exceed $100m annually.
Source: Journal of Food Science
Published on-line ahead of print, 17 October 2007, doi: 10.1111/j.1750-3841.2007.00534.x
"Improvement of Stability of Oil-in-Water Emulsions Containing Caseinate-Coated Droplets by Addition of Sodium Alginate"
Authors: S. Pallandre, E.A. Decker, and D.J. McClements