ABSTRACT
This study was conducted to examine the physical and chemical characteristics of interesterified and non-interesterified blends of palm kernel oil and palm olein and to determine if there were significant differences in the physico-chemical properties between interesterified and non-interesterified blends in different product formulations.
Palm kernel oil and palm olein were mixed in different ratios (0%, 10%, 20%, 3%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% palm kernel oil in palm olein). They were then chemically interesterified using sodium methoxide as catalyst. The interesterified and non-interesterified blends were characterized for the following parameters: fatty acid profile, fatty acids in position-2, iodine value, refractive index, slip melting point, solid fat content by NMR, oxidative stability index, polymorphism by x-ray diffraction, and crystal aggregates by polarized light microscopy. The free fatty acid profile of the blends showed pools containing lauric, myristic, palmitic, oleic and linoleic acids which are nutritionally important because of the ease of absorption of the medium chain triacylglycerol, the high energy content of the long chain triacylglycerol and presence of unsaturated fatty acids that can be converted to essential fatty acids through elongation and desaturation. Expectedly, the iodine value increased with the proportion of palm olein in the blends and no significant difference (P≥0.05) was observed between the iodine value of 30% palm kernel oil and 0% palm kernel oil in palm olein. The iodine value and refractive indices of the blends were highly correlated (r2=0.9579). The slip melting point was inversely proportional to the proportion of palm olein in the blends.
The slip melting point proportionally decreased from 100% palm kernel oil to 40% palm kernel oil following which the trend became non-linear leading to eutectic phenomenon at 50%, 60%, 70% and 80% palm kernel oil in the blends. Similar observations were made in chemically interesterified and non-interesterified blends. The solid fat content profile was similar to the slip melting point. The rate of solid fat content evolution was dependent on both temperature and proportion of each fat in the blends. The drop in solid fat content was non-linear across the blends and temperatures in both chemically interesterified and non-interesterified blends. The oxidative stability index was temperature dependent but independent of the proportion of palm olein in the blend.
Higher oxidative stability of 90%, 80%, 70% and 60% palm kernel oil in palm olein were also observed. Although all the blends were β’ stable before and after chemical interesterification, the crystal network patterns in polarized light microscopy showed that chemical interesterificatoin further reduced the sizes of crystals and created a smoother network of crystals unlike the non-interetserified blends where there were liquid spaces in between crystal aggregates. There were no significant differences (P≥0.05) in the physical and chemical characteristics of interesterified and non-interesterified blends in some properties such as solid fat content, slip melting point, polymorphic forms and fatty acid in position-2, nevertheless, subtle differences were observed in polarized light microscopic studies. This study has shown that the application of palm kernel oil and palm olein can be significantly enhanced by blending and chemical interesterification. In certain applications such as in frying and shortening formulations, non-interesterified blends would perform as well as interesterified blends.
