The effects of blending palm oil (PO) with soybean oil (SBO) and lard with canola oil, and subsequent chemical interesterification (CIE), on their melting and crystallization behavior were investigated. Lard underwent larger CIE-induced changes in triacylglycerol (TAG) composition than palm oil. Within 30 min to 1 h of CIE, changes in TAG profile appeared complete for both lard and PO. PO had a solid fat content (SFC) of ~68% at 0°C, which diminished by ~30% between 10 and 20˚C. Dilution with SBO gradually lowered the initial SFC. CIE linearized the melting profile of all palm oil-soybean oil (POSBO) blends between 5 and 40°C. Lard SFC followed an entirely different trend. The melting behavior of lard and lard-canola oil (LCO) blends in the 0-40°C range was linear. CIE led to more abrupt melting for all LCO blends. Both systems displayed monotectic behavior. CIE increased the DP of POSBO blends with ≥80% PO in the blend and lowered that of blends with ≤70% PO. All CIE LCO blends had a slightly lower DP vis-à-vis their noninteresterified counterparts.Our present understanding of the nature of fat crystal networks is limited. Solid fat crystals and crystal agglomerates in spreads interact to form a continuous three-dimensional solid-fat network, which is ultimately responsible for the rheological properties of the plastic fat system. However, little is known about this three-dimensional network.Factors that influence the network properties of plastic fats include (i) crystal habit, which includes crystal polymorphism, size, number, shape, and aggregation behavior; (ii) chemical composition; (iii) solid/liquid ratios; (iv) triacylglycerol (TAG)-TAG intersolubility; (v) crystallization procedure including cooling rate, degree of supercooling, mechanical working, and tempering; and (vi) the presence of non-TAG components, such as phospholipids and sterols (1-3). Linear and nonlinear interactions among some or all of these factors are also possible.There is a growing trend in the spreadable fats industry to incorporate as much monounsaturated liquid oil as possible into spreads for nutritional reasons. However, this has led to technical difficulties with respect to spread stability and textural properties. Another trend is the increased use of interesterification, which is a method of choice in the fat industry to manipulate spread properties (4). Reviews on interesterification have been presented elsewhere (5-7). As shown in the past with complex systems (e.g., lard, milk fat), interesterification can substantially alter the physical properties of fats.Within this framework, the purpose of this study was to evaluate the physical, crystal, and rheological properties of Palm oil-soybean oil (POSBO) and lard-canola oil (LCO) systems after blending and chemical interesterification. Quantification of microstructure was performed by a fractal geometry approach. In the first of three parts, we examine the melting and crystallization behavior of these two systems.
EXPERIMENTAL PROCEDURESNeutralized, bleached, and deodorized p...
