The influence of emulsifiers on the crystallisation behaviour of a palm oil-based blend

In margarine manufacture, blends containing palm oil show a slow rate of crystallisation and, occasionally, a tendency to recrystallise. This phenomenon is caused by the segregation of the triacylglycerol 1,3-dipalmitoyl 2-oleoyl glycerol that undergoes the polymorphic transition from the beta' to the beta form. Emulsifiers can be used to control fat crystallisation properties. Although some studies have been performed on crystallisation properties of emulsifiers, there are no conclusive results. The purpose of the present work was to investigate the effects of some selected emulsifiers on a fat blend containing palm oil. A fixed amount (2%) of sucrose esters or sorbitan esters was added. After melting, the samples were crystallised in bulk and submitted to temperature cycling. At regular intervals during crystallisation and after cycling, the hardness and the solid fat content of the samples were evaluated and the crystal morphology investigated with a polarised-light microscope. In addition, samples at the end of storage time were evaluated with X-ray diffraction in order to investigate the polymorphic behaviour. The addition of the emulsifiers showed an effect on the crystal morphology as well as the textural properties of the samples. The differences observed in the micro- and macrostructure are explained in terms of the acyl-acyl interactions between the fatty acid residues of the emulsifiers and the triacylglycerols.