DETERMINATION OF PHYSICAL PROPERTIES AND CRYSTALLIZATION KINETICS OF OIL FROM ALLANBLACKIA SEEDS AND SHEA NUTS UNDER DIFFERENT THERMAL CONDITIONS

Abstract

In this study, the fatty acid content, melting and cooling profiles, crystallization properties at different cooling rates and kinetics of crystallization of Allanblackia seed oil (ASO) and shea nut oil (SNO) were investigated. The fatty acid content was determined using gas chromatography coupled with mass spectrometry (GC/MS). The melting and cooling profiles, crystallization and crystallization kinetics were investigated using differential scanning calorimetry (DSC) and the fat morphology was investigated using polarized light microscopy. The GC/MS results showed that ASO contains a high amount of saturated fats as compared with SNO. The DSC analysis revealed that ASO has a high melting temperature of 35.3±2.1 °C and crystallizes earlier (16.8±0.3 °C) in the constant rate cooling experiments. The crystallization patterns of both oils were observed to be dependent on the cooling rate. Under isothermal conditions, it was observed that both ASO and SNO showed high and low melting peaks with the low melting peak disappearing as the crystallization progressed. The Avrami model was used to estimate the crystallization kinetics of the oils under the isothermal conditions and it was inferred that ASO has a faster nucleation and subsequent crystal growth as compared with SNO. At room temperature SNO formed overlapping fat crystal particles while ASO gave distinct crystallized fat fractions during the crystallization at room temperature, as shown by the polarized light microscopy.

Practical applications: The high melting temperature, the rate and the nature of crystallization of Allanblackia seed oil gives it good material functionality and desired plasticity, properties associated with possible industrial application. Additionally, the presence of high stearic acid content makes the Allanblackia seed oil a healthy choice for food, hence it can be used as a substitute for cocoa butter in the food industry.

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