Emulsifying properties of a novel polysaccharide extracted from basil seed (Ocimum bacilicum L.): Effect of polysaccharide and protein content

Abstract

Emulsifying properties of basil seed gum (BSG) were evaluated in terms of emulsion droplet size distribution, rheological properties, visual phase separation, and adsorption properties. Soya oil-in-water emulsions (30% wt/wt) were formulated and stabilised by different concentrations of BSG (0.03–1% wt/wt). The effects of BSG concentration as well as purification (removal of proteins from BSG) on 0.3% (wt/wt) BSG-stabilised oil-in-water emulsions were tested. Emulsions with monomodal droplet distributions and with oil droplet size below 1.0 μm (d32) were formed with as little as 0.3% (wt/wt) BSG using a two-stage high pressure homogenizer at 35/8 MPa. The rheological properties of BSG emulsions appeared to be dependent on gum concentration and purification. Surface/interfacial tension measurements confirmed the adsorption of BSG at the oil-water interfaces. All gum preparations (crude, purified and protein-depleted) exhibited an ability to lower the interfacial tension. Microstructures confirmed that the purification of the gum reduces the adsorption properties, resulting in a higher degree of droplet aggregation/coalescence. Nevertheless, the BSG emulsions remained stable against phase separation for at least one month. BSG demonstrated excellent emulsifying and stabilising properties when compared to other polysaccharides. Protein-depleted BSG produced larger droplets than crude and purified BSG, but still it produced stable emulsions, comparable to other gums, such as sugar beet pectin. This suggests that the emulsifying and stabilising mechanism of the gum may not be only ascribed to the surface-active protein moiety, but could also be attributed to the hydrophobic character of the polysaccharide itself. Overall, BSG is a promising gum, which can be considered as a novel hydrocolloid emulsifier.