Enhancement of physicochemical characteristics of palm olein and winged bean (Psophocarpus tetragonolobus) seed oil blends

Incorporation of oils from non-conventional sources into palm olein through the blending process generates a sustainable source of novel oleins with improved physicochemical and functional properties. The objective of this study was to evaluate the effects of blending winged bean (Psophocarpus tetragonolobus) seed oil (WBSO) and palm olein (POo) on the physicochemical properties of the blends. Blends of WBSO (25, 50 and 75% w/w) with POo were prepared and changes in fatty acid (FA) and triacylglycerol (TAG) compositions, iodine value (IV), cloud point and thermal behaviour were studied. Reductions in palmitic (C16:0) and oleic (C18:1) acids with concomitant increases in linoleic (C18:2) and behenic (C22:0) acids were observed as the amount of WBSO increased in the blends. Blending WBSO and POo at 75:25 increased the unsaturated FA content from 56% in palm olein to 64% in the blend, producing the highest IV of 70.5 g I2/100g. At higher WBSO ratios, triunsaturated and diunsaturated TAG species within the blends increased while disaturated TAG species decreased. The lowest cloud point (8.8 °C) was obtained in the oil blend containing 50% WBSO, while the cloud point further increased with increasing amount of WBSO in the blends. This was possibly attributed to increased trisaturated TAG with very long-chained saturated FA (C20 to C24) inherently present in WBSO within the blends. Thermal behaviour analysis by differential scanning calorimetry of the oil blends showed higher onset temperatures for crystallisation with increasing proportions of WBSO in POo, with melting thermograms correspondingly showing decreasing onset melting temperatures. These findings showed that blending WBSO with POo enhanced the physicochemical characteristics of the final oil blends, resulting in higher unsaturation levels and improved cloudiness resistance.