Engineering the oil binding capacity and crystallinity of self-assembled fibrillar networks of 12-hydroxystearic acid in edible oils

The crystallinity and oil binding capacity of 12-hydroxystearic acid (12HSA)-vegetable oil organogels was modified by changing the post-crystallization annealing temperature from 5 degrees C to 30 degrees C for 24 h. The gels stored at 5 degrees C had a highly branched crystalline structure with small uniform pores, as determined by cryo-scanning electron microscopy. Large T-2 proton relaxation peaks at 50 to 70 ms determined by pulse nuclear magnetic resonance (pNMR) suggested the presence of highly immobilized oil at 5 degrees C. When the gels were stored at 30 degrees C, longer fibers and a less branched network were observed. At 30 degrees C, the 12HSA network's crystallinity was enhanced with fewer inclusions of liquid oil as determined by pNMR. When the gels were stored at 30 degrees C, a significantly shorter T-2 relaxation peak was observed. The increased crystallinity, at 30 degrees C, was attributed to a reduction in bulk supersaturation, resulting in a very high crystallographic mismatch nucleation barrier (Delta G*) which favored one-dimensional fiber growth. However, at a lower crystallization temperature of 5 degrees C, there is an increase in the supersaturation and hence the crystallographic mismatch barrier is significantly lower, increasing fiber tip branching. The nucleation-growth-branching-growth model for self-assembled fibrillar networks explains the differences in crystallinity, pore size and oil syneresis observed for the 12HSA-vegetable oil organogels. It was found that the gels stored at 30 degrees C syneresised 1.35 times faster than the gels stored at 5 degrees C. Furthermore, the change in the T-2 relaxations and the ratio of the complex viscosity/pore radius were 1.35 and 1.30 respectively.