Physical properties of lipase-catalyzed transesterified blends of palm stearin and anhydrous milk fat

Palm stearin (PS) and anhydrous milk fat (AMF) blends, formulated by mixing 40 to 80% PS in increments of 10% (w/w), were subjected to transesterification catalyzed by lipases from Pseudomonas sp. and Rhizomucor miehei (Lipozyme IM60). The physical properties of the transesterified products were evaluated by slip melting point (SMP), differential scanning calorimetry (DSC), solid fat content (SFC) and X-ray diffraction (XRD) analyses. SMP results indicated that the Pseudomonas sp. lipase caused a bigger drop in SMP (15.6%) for a PS:AMF (40:60) blend compared to 12.5% reduction when R. miehei lipase was used. The same blend, when reacted with either of the lipases, had a residual SFC of 7.1% at 40°C. Generally, for all other ratios of PS:AMF blends, the % of reduction in SMP was higher in the Pseudomonas lipase-catalysed blends compared to the R. miehei lipase-catalysed blends. Pseudomonas lipase also successfully changed the polymorphic form of unreacted PS:AMF blends from a mixture of β and β′ crystals to a predominantly β′ mixture following transesterification. On the other hand, transesterification with R. miehei lipase resulted in a product that is β′ dominating