Enzymatic incorporation of stearic acid into canola oil to produce trans-free structured lipids for possible margarine formulation
Lumor, Stephen Enyam
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Incorporation of stearic acid into canola oil to produce a trans-free structured lipid (SL) as a healthy alternative to partially hydrogenated fats for margarine formulation was investigated. This study showed that Lipozyme RM IM from Rhizomucor miehei was more suitable for the process than Candida rugosa lipase isoform 1 (LIP1). The activity of LIP1 was not enhanced after immobilization on Celite 545, Duolite A7, and Sephadex G-25. Regiospecific analysis 13using C NMR spectrometry showed that stearic acid was incorporated into canola oil, mainly at the sn-1,3 positions. However, most SL products did not have adequate solid fat content or ²’ crystal forms for tub margarine. Solid fat content (SFC) and crystal properties of the trans-free SLs were optimized by blending with palm mid-fraction (PMF). Addition of sucrose stearate (S-170), sorbitan tristearate (STS), and distilled monoglycerides (DMG) to one of the blends, SL40:PMF (70:30, w/w), did not improve crystal polymorphism, but had significant effects on crystal morphology. The emulsifiers significantly delayed crystal growth, resulting in smaller crystal sizes compared to the control. However, they were unable to inhibit the formation of granular crystals (30 to 140 µm), which are undesirable in margarine after 4 weeks of storage at 0ÚC. These crystals aggregates were not observed upon visual and physical examination, and may therefore not impart the sensory properties of the finished products negatively. Consequently, a trans-free margarine (MG-X) was formulated with a blend of a SL synthesized by reacting canola oil with 40% stearic acid (w/w), PMF, and cottonseed oil (CTO). Physical and sensory attributes of MG-X and two commercial margarines (MG-A and MG-B) were studied. MG-X was considerably harder than MG-A and MG-B, least cohesive, and its adhesiveness was intermediate between those of MG-A and MG-B. Stability of MG-X to syneresis was also intermediate between those of MG-A and MG-B. Sensory evaluation showed that MG-X was comparable to MG-A in terms of spreadability and texture only, but was significantly different from MG-B in all attributes. Also, more subjects were willing to accept MG-X in spite of its sensory properties if it carried a health claim.