The influence of chemical interesterification on the physicochemical properties of complex fat systems. 2. Morphology and polymorphism

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Abstract
Palm oil‐soybean oil (POSBO) blends and lard‐canola oil (LCO) blends were chemically interesterified with sodium methoxide. Changes in crystal morphology using polarized light microscopy and crystal polymorphic behavior using X‐ray diffraction spectroscopy (XRD) were studied. Spherulitic crystalline particles, measuring 10–20 µm, were detected in palm oil (PO). These spherulitic particles were characterized by a dense core surrounded by a lower‐density halo region. PO fat‐crystal morphology was not greatly altered on addition of soybean oil (SBO), except for a gradual reduction in spherulite size as the amount of SBO in the blends was increased. Chemical interesterification (IE) did not alter PO or POSBO blend fat‐crystal morphology significantly. Irregular particles and spherulites of different sizes and shapes were observed in lard, from small crystals to irregular, angular crystal aggregates. Changes in lard fat‐crystal morphology due to the addition of canola oil (CO) were concentration‐dependent. In general, spherulite diameter decreased with increasing CO addition. IE dramatically altered lard fat‐crystal morphology—IE induced the formation of more symmetrical spherulitic crystalline particles, and the halo‐to‐core ratio was increased significantly. XRD spectroscopic analysis of POSBO blends revealed small changes in the long spacings of PO fat crystals with either blending or IE; all values were close to 45 Å. Short spacings of fat crystals in noninteresterified (NIE) POSBO blends suggested the predominance of β′ polymorphs. IE led to an increase in the proportion of the β polymorph in PO and POSBO blends. Long spacings of NIE lard fat crystals suggested the presence of a bilayer structure in their unit cells (45 Å). Dilution with ≥10% canola oil led to the appearance of a second reflection at 35 Å. β′ polymorphs were predominantly detected in NIE lard and NIE LCO blends. The β polymorph became more evident with increasing addition of CO. Fat crystals in IE lard and IE LCO blends displayed a single long‐spacing reflection at 40 Å. IE of lard and LCO blends induced the formation of β polymorphs.