Comparison of mixed and layer by layer methods (whey protein isolate–tragacanthin) on the stability of 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 interaction. Therefore, in this study, the effect of these techniques on the stability of emulsions at different pH, and oil concentrations (1, 4, 8 and 16%) 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 mixed method, oil was added to the mixture of whey protein isolate–tragacanthin (0.4:1%) before being homogenized using ultrasound for 4 min. Then, the droplet size, zeta potential and rheological measurements were done 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 presence of polysaccharide in mixed method may decrease the efficiency of homogenization processing by using ultrasound. Based on rheological analyses, lower apparent viscosity of mixed emulsions in comparison with LBL one can be related to disruption of tragacanthin structure due to high intensity sonication of this polysaccharide for a longer time.

Keywords:

Tragacanthin , Protein–polysaccharide interaction , Rheological properties , Ultrasound , Zeta potential