Revisiting the crystallization behavior of stearyl alcohol : stearic acid (SO : SA) mixtures in edible oil

Abstract

Mixtures of stearyl alcohol and stearic acid were some of the first identified oleogelators with potential for food applications. Previously, a synergistic enhancement in gel strength was identified at a stearyl alcohol : stearic acid (SO : SA) ratio of 7 : 3 and 8 : 2, which was attributed to their needle-like crystal morphology. In the present study, we have meticulously characterized this system with a variety of techniques at different gelator ratios. Accelerated oil loss tests showed the stability of the gels mirrors the mechanical strength with ∼1 wt% oil loss in the firm gels and >10 wt% in the weak formulations. X-ray diffraction and light microscopy suggest that the crystal networks which form the hardest gels (8 : 2, 7 : 3) and weakest gels (5 : 5, 4 : 6) are similar, and thus crystal morphology and crystal size cannot solely explain the observed enhancement in mechanical strength and stability. Scanning electron micrographs clarified that all oleogels crystalized in a platelet-like, rather than needle-like microstructure. Using the scaling theory of cellular solids, the enhancement in mechanical strength of the 8 : 2 SO : SA oleogel was shown to be mainly due to an increase in the scaling exponent of the hardness to the mass fraction of the crystalline material, and not the total amount of crystalline network solids, the size of the platelets or the interactions between them.