Sugar-sugar interactions in oil suspensions containing surfactants and effects on macroscopic phenomena

Abstract

Surfactants are used in confectionery production to control the viscosity and yield value of molten chocolate. To develop a deeper understanding of the structure-function relationship of surfactants in food-related particle suspensions, the apparent viscosity, yield value, sedimentation, and particle interactions of 10 wt% confectioner's sugar-in-canola oil suspensions were investigated in the presence of up to 1 wt% commercial soy lecithin, polyglycerol polyricinoleate (PGPR), citric acid esters of monoacylglycerols (CITREM) or ammonium phosphatides (AMP). Atomic force microscopy (AFM) was used to measure attractive forces at the nano-Newton scale between a sugar substrate and a sugar crystal-functionalized AFM cantilever in an oil environment. For all but PGPR, addition of surfactant reduced the adhesion force between sugar surfaces up to a critical concentration above which the force increased, implying the presence of additional interactions. This critical concentration was assumed to be when monolayer coverage of the sugar surfaces by surfactant occurred (0.05 wt% for lecithin, 0.10 wt% for CITREM and AMP). No critical concentration was found for PGPR, with its greatest effect for each analysis occurring at the highest concentrations tested (0.60 and 1.00 wt%). The significance of these interactions on macroscopic phenomena such as apparent viscosity and sedimentation was also assessed. Like with the AFM data, there was an optimal concentration of added surfactant above which viscosity increased. Sedimentation rate greatly decreased with addition of PGPR while being only slightly affected by addition of lecithin, CITREM and AMP. An argument regarding their efficacy was made based on the relative sizes of the polar headgroup and nonpolar tail groups of the molecules, which contributed to how they adsorbed to the sugar surface. Overall, these results suggested that surfactant properties such as molecular weight and head group properties played an important role in modifying the interactions between sugar crystals in an oil-continuous environment.

Keywords: Chocolate; Particle interactions; Sugar crystals; Surfactant; Viscosity.