Sheikh KA, Saringat B, Bukhari NI
Semisolid formulations of palm–olein were prepared using design of experiment (DoE) methodology. The influence of formulation aids (emulsifier) and the processing variables (mixing and cooling) were investigated on the physicochemical properties of the formulated systems. The stable semisolid appearance was the response variable. The systems were characterised by microscopy, DSC, Rheology, and XRD. The factorial design generated a matrix of 22 experiments to investigate physicochemical properties of the systems. The systems formed stable semisolids (no syneresis), unstable semisolids showing syneresis or structured fluids, depending on the concentration of stearic acid and the preparation technique. The stable semisolids contained a−crystalline lamellar structure, not present in the unstable structured fluids. In addition, syneretic semisolids showed plate−like crystals, implying pressure sensitivity, associated with polymorphism in the stearic acid. The stable semisolids showed mixture of amorphous and crystalline stearic acid. In contrast, pure amorphous or crystalline stearic acid was present in the unstable semisolids and the structured fluids respectively (confirmed by XRD). Mode of mixing and the concentration of stearic acid appeared to be critical factors (p<0.01). DoE predicted a combination of factors to achieve stable semisolid systems. Confirmatory experiments yielded results within 1% of the predicted responses, demonstrating the reliability of the software.