Physical behaviour and composition of low- and high-melting fractions of sediment in canola oil

The effects of haze composition variation on sedimentation phenomenon in canola oil were studied. Comparisons were made of the physical properties between an oil sediment (S5) and the high- and low-melting fractions obtained by step crystallisation at 32 and 5 °C (F32 and F5). The phase transition behaviour and crystalline characteristics of the sediments were examined by differential scanning calorimetry (DSC), hot-stage microscopy, spectrophotometry, and X-ray diffraction (XRD). The compositions of the sediments were determined by GC-MS. The melting behaviour of S5 resembled that of F5, whereas S5 behaved more like F32 in crystallisation. Oils containing F32 clouded much faster than oils containing F5. The interfacial surface free energies and the XRD patterns were similar for the two fractions, suggesting identical crystalline structures. The molecular origin of the varied phase transition behaviour of the sediments was attributed to the composition variation in waxes, particularly the acid component in the materials.