Viscoelastic properties of table margarine prepared from lipase-catalyzed transesterified mixtures of palm stearin and palm kernel olein

Abstract

A controlled-stress rheometer was used to evaluate dynamic viscoelastic (VE) performance of an experimental table margarine prepared from a transesterified palm stearin (PS):palm kernel olein (PKO) mixture (40:60 ratio) using Rhizomucor miehei lipase as the biocatalyst. Comparison was made using a commercial table margarine made of palm oil and palm kernel oil. The experiments were carried out over a period of three months with the margarines kept at 20 and 30C. Elastic parameters such as elastic moduli (G′), viscous moduli (G″), complex viscosities (η*) and tan δ were determined as functions of frequency and storage period. The experimental table margarine exhibited larger linear viscoelastic (LVE) regions than the commercial margarine, indicating a more elastic and firmer structure than the commercial product. Similarly, the frequency dependencies of the storage moduli and tan δ also revealed that the experimental table margarine samples exhibited a higher elasticity than its commercial counterpart. For both samples, the values of G′ were higher than G″ at any given frequency. The ratio of the absolute complex viscosities (|η*|) compared to the steady viscosity (η) shows that the commercial samples showed the lowest destruction due to steady shear compared to the experimental samples. Trans fatty acid (FA) content was found to be higher in the commercial (1.6%) than the experimental margarine (0.2%).