A comparison of lipid shortening functionality as a function of molecular ensemble and shear: Crystallization and melting

The crystallization and melting enthalpies of 24 shortening systems containing fully hydrogenated fats in dilutions of 10-25% (w/w) in soybean oil was studied, as was that of five commercially available shortenings. The mixtures of fully hydrogenated fats in soybean oil were processed using a constant cooling scheme designed to cool soybean oil at 10 degreesC/min. Each shortening system used was processed with and without shearing. The molecular diversity within each fat system was investigated using gas chromatography (GC). DSC was used to obtain the melting and crystallization enthalpies of the studied fats. It was found that the starting molecular ensemble and the presence or absence of shearing cause changes in the growth mode of the crystal as well as in the enthalpies of crystallization and melt. A positive relation was found between an increase in SSS in a sample and the onset temperature of crystallization for all sheared samples except those composed of cottonseed in soybean oil or lard in soybean oil. As well, samples containing high percentages (w/w) of PPS, PSS, PSP, and SSS exhibited higher melting points than the samples which had a higher percentage of SSS alone. The selected market shortenings exhibited similar enthalpies and trends in onset temperature of crystallization and melt as that of their composite partially and fully hydrogenated fats. The market shortenings with similar compositions exhibited similar enthalpy of melt and crystallization curves. Sheared canola systems had a higher onset of melt than the unsheared systems. The positions of the peak maxima of the melting enthalpy curves also change in the presence of under shear, with cottonseed having a lower peak maxima than lard for the sheared samples at all dilutions, and the soybean samples peak maxima being lower than the canola peak maxima for the sheared samples at all dilutions. This work therefore provides evidence that the control of melting behavior of shortening systems is highly dependent on the presence of shear (and therefore the extent of shear). Furthermore, this work highlights the importance of the phase behavior of PSP, PPS, PSS, and SSS to typical industrial shortening systems. It is further made clear that changes in melting and crystallization behavior of shortening systems can be significantly affected by manipulating the amounts of TAGs containing mixtures of palmitic and stearic acid, as opposed to just the addition of tristearin. (C) 2003 Elsevier Ltd. All rights reserved.