Chemical and enzymatic interesterification of tristearin/triolein‐rich blends: Microstructure and polymorphism

Abstract

AbstractMixtures of fully hydrogenated canola oil and high‐oleic sunflower oil were interesterified chemically and enzymatically with sodium methoxide and Candida antarctica lipase, respectively. Polymorphic behavior and crystal morphology of the10–100% blends before and after interesterification were studied using powder X‐ray diffraction spectroscopy and polarized light microscopy. X‐ray analysis revealed a predominance of the β' form in the IE‐blends (interesterified, both chemical and enzymatic) and the β form crystals in the NI‐blends (non‐interesterified). Dilution and crystallization at 20, 30, 40 and 50 °C did not change the polymorphism of the NI‐blends, but did in the IE‐blends. Small changes in the long spacings of the blends after interesterification were observed. Small‐angle reflections centered at 45 Å suggested the presence of a 2L lamellar crystalline structure. Needle‐like crystals were predominant in the IE‐blends while large symmetrical spherulites were observed in the NI‐blends crystallized at 30 °C for 24 h. Over 75% of the structural elements had areas between 1 and 20 µm2 in the NI‐ and IE‐blends, and the NI‐blends showed a higher percentage of crystals in this range compared to the IE‐samples. The box counting dimension (Db) increased as a function of crystalline area fraction in polarized light micrographs of the samples. Moreover, a higher Db in the chemically interesterified sample relative to the enzymatically interesterified sample at an equivalent area fraction, was attributed to the homogeneity in the distribution of crystalline mass.