Fractal dimension in palm oil crystal networks during storage by image analysis and rheological measurements

- The study indicated palm oil recrystallised without polymorphic transformation.
- Recrystallisation due to secondary nucleation change the viscoelasticity of PO.
- Fractal dimension of the crystal networks increased during storage.

The aims of this study are to determine the physicochemical properties and to quantify the fractal dimension of refined, bleached and deodourised palm oil (RBDPO) crystal network using image analysis and rheological methods during four weeks of storage at 15, 20 and 25 °C. There was no progressive increase in solid fat content (SFC) after one week of storage. X-ray diffraction indicated RBDPO stabilised in the β′ polymorphic form without transformation to β polymorph upon storage. However, photomicrographs of the crystal networks showed new small crystals formation in between the crystal clusters and on the surface of the existing crystals. The fractal dimensions of RBDPO crystal networks by image analysis (Db) and rheological measurements (Df) increased from day 1 to week 4 of storage. The results also showed good agreement between (Db) and (Df) in quantifying the hardness, storage modulus (G′) and mass distribution of RBDPO crystal networks during storage.