RESUMO
Double (w1/o/w2) emulsions are potential fat replacers in foods. Fats are known for their lubricating properties, which contribute to texture perception. It is therefore of interest to understand how the composition of double emulsions influences lubrication properties. This study focuses on the understanding of the influence of the fraction of inner dispersed aqueous phase w1 and the gelation of the w1 droplets on the lubrication properties of double emulsions. The addition of an inner water phase w1 to the oil droplets decreased friction at low entrainment speeds due to adsorption of the lipophilic emulsifier polyglycerol polyricinoleate (PGPR) at the hydrophobic tribo-surface. At higher entrainment speeds, double emulsions with w1 fractions of up to 6% (corresponding to fat reduction of 20%) displayed comparable tribological behavior as full-fat single (o/w2) emulsions. For double emulsions with gelled w1 droplets at higher w1 fractions of up to 15% (corresponding to fat reduction of 50%), an increase in friction was observed compared to full-fat single (o/w2) emulsions. The increase in friction is probably related to the presence of gelled droplets expelled from the inner w1 into the outer w2 phase, and to the deformability of (w1/o) droplets. Lubrication decreased when gelled particles were expelled from the inner w1 phase to the outer w2 phase. Lubrication also decreased when the deformability of (w1/o) droplets decreased, since less deformable (w1/o) droplets spread less easily on the tribo-pair surface. Knowledge about lubrication properties of double emulsions can be used in future studies to relate composition to sensory perception and develop double emulsions further as fat replacers.
