Efficacy of whey protein–tragacanth on stabilization of oil-in-water emulsions: Comparison of mixed and layer by layer methods

• Layer by layer and mixed emulsions compared when ultrasound used for homogenization.
• Influence of different pH and oil concentrations on emulsion stability was studied.
• Sonication caused tragacanthin depolymerization leading to decreasing the viscosity.
• Tragacanthin led to increasing of viscosity and ζ-potential of stabilized emulsions.

Layer by layer (LBL) and mixed emulsions are two well known techniques in which charged proteins and polysaccharides are linked to each other via electrostatic interactions. Therefore, in this study, the effect of these techniques on the stability of emulsions at different pHs (3, 5 and 7), and oil concentrations (1, 4, 8 and 16% w/w) was studied. Regarding LBL method, tragacanthin (1% w/w) was added to whey protein isolate-coated emulsion, following by ultrasound treatment for 0.5 min. However, in the mixed method, oil was added to the soluble mixture of whey protein isolate–tragacanthin (0.4:1% w/w) before being homogenized using ultrasound for 4 min. Then, the droplet size, zeta potential and rheological measurements were performed to investigate the stability mechanisms. According to our findings, in contrast to mixed emulsions, LBL ones were stable at pH 5 in the presence of different oil contents. Furthermore, LBL emulsions had lower particle size than mixed emulsions which illustrates that the presence of polysaccharide in the mixed method may decrease the efficiency of homogenization processing by using ultrasound. Based on rheological analyses, lower apparent viscosity of the mixed emulsions in comparison with LBL can be related to bridging flocculation due to applying high power sonication for long time.

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