Enzymatic interesterification to produce rapeseed oil-based zero-trans and dialkylketones-free fats

Abstract: The development of lipids with improved nutritional properties is of increasing interest. In this context, this study aims at evaluating the potential of interesterification (IE) to produce new fats, entirely based on rapeseed oil (RO), with a specific focus on process-induced contaminants: the dialkylketones (DAKs). For that, 3 blends made of RO and fully hydrogenated RO (FHRO) with different ratio (%) (60/40, 70/30 and 80/20) were both enzymatically (EIE, TLIM) and chemically interesterified (CIE, sodium methoxide). The triacylglycerol (TAG) composition (by RP-HPLC-RI), the solid fat content melting profiles (by p-NMR), the melting curves (by DSC), the polymorphism (by powder X-ray diffraction) and the hardness (by cone penetrometry) were examined and compared before and after IE. The DAK content was assessed using SPE and GC-FID after microwave-assisted saponification. The DSC melting curves and the TAG compositions were analyzed as a function of the batch-enzymatic reaction time; they were used to highlight the modifications in melting properties and to quantify their kinetics. Our results indicate that IE improved both functional and textural characteristics. The EIE fats had similar TAG profile and physicochemical properties as the CIE ones, however with better preservation of the tocopherol content and were DAKs-free. DAKs were formed during CIE, C18:1-C18:1 and C18:1-C18 chain-lengths being the major ones; interestingly, it was shown that the type and amount depend on the initial composition and on the unsaturation degree.

This study provides valuable information for the edible oil industry. It shows that using FHRO as hard fat and RO as soft oil is a suitable solution to produce by interesterification new healthy zero-trans products suitable for margarine applications. EIE is preferred over CIE for two reasons: better preservation of the tocopherol content: higher vitamin supply and better oxidative stability, and absence of unwanted DAKs contaminants.