Palm stearin, the cheaper and more solid fraction of palm oil, is a useful hard
fat in the manufacture of edible fat such as margarine. However, with slip melting
points ranging between 46 to 56°C, only 10% of palm stearin can be added to a
standard table margarine. This study was conducted to investigate the performance of
lipase-catalysed transesterified fat blends containing high levels of palm stearin
(minimum 40%) when processed into table margarine.
In the first part of the work, the effect of several reaction conditions on
lipase-aided transesterification of palm stearin was studied. Results on the effect of
lyophilisation of enzyme on transesterification indicated increases in % triglyceride
(TG) when drying time was increased. The maximum yield was at 4 or 6 hours of drying. Studies on the effect of reaction time indicated that 8h of reaction produced
the highest % TG remaining and Rhizomucor miehei and A lcaligenes lipases both
showed maximum rates at 6h reaction time. The transesterification process also
decreased the slip melting point (SMP) of palm stearin slightly after 24h reaction
with R. miehei lipase registering the largest decrease (5.5°C) compared to the initial
unreacted mixture. The catalytic stability of R. miehei and Pseudomonas lipases,
after being subjected to ten runs of repeated usage indicated that the lipases can be
reused to produce fairly constant products on a large scale.
The rates of transesterification were found to vary with different lipase
sources. Bacterial lipase of Pseudomonas was found to have the fastest rate of
reaction (50.0h⁻¹) followed by R. miehei lipase (27.1h⁻¹). Generally, both the above
lipases also produced the highest degree of transesterification and % FFA.
Pseudomonas lipase-catalysed mixtures caused the biggest drop in SMP and solid fat
content (SFC) in all the three mixtures studied
