Abstract
Hypothesis: Plant seeds store lipids in oleosomes, which are storage organelles with a triacylglycerol (TAG) core surrounded by a phospholipid monolayer and proteins. Due to their membrane components, oleosomes have an affinity for the air/oil–water interface. Therefore, it is expected that oleosomes can stabilise interfaces, and also compete with proteins for the air–water interface. Experiments: We mixed rapeseed oleosomes with whey protein isolate (WPI), and evaluated their air–water interfacial properties by interfacial rheology and microstructure imaging. To understand the contribution of the oleosome components to the interfacial properties, oleosome membrane components (phospholipids and membrane proteins) or rapeseed lecithin (phospholipids) were also mixed with WPI. Findings: Oleosomes were found to disrupt after adsorption, and formed TAG/phospholipid-rich regions with membrane fragments at the interface, forming a weak and mobile interfacial layer. Mixing oleosomes with WPI resulted in an interface with TAG/phospholipid-rich regions surrounded by whey protein clusters. Membrane components or lecithin mixed with proteins also resulted in an interface where WPI molecules aggregated into small WPI domains, surrounded by a continuous phase of membrane components or phospholipids. We also observed an increase in stiffness of the interfacial layer, due to the presence of oleosome membrane proteins at the interface.
Highlights
Plant oilseeds, such as soybeans, rapeseeds, and sunflower seeds, are cultivated worldwide for their oils
Comparable OS composition and droplet sizes were demonstrated by RomeroGuzmán et al for rapeseed oleosomes extracted at a pH value of 7.0 [26] using fluorescence microscopy and light scattering techniques, where the formation of large flocculates was attributed to the low surface charges and the presence of storage proteins [15]
As only light bands are shown in these molecular weight regions, we do not expect the storage proteins to play a major role in the interfacial composition and properties
Summary
Plant oilseeds, such as soybeans, rapeseeds, and sunflower seeds, are cultivated worldwide for their oils. Lipids are present in storage organelles, called oleosomes (OS, known as oil bodies or lipid droplets) [1]. OS are natural oil droplets with a triacylglycerol (TAG) core that is surrounded by a monomeric membrane layer, consisting of a phospholipid monolayer with anchored proteins [2,3,4] (Fig. 1). OS are disrupted with mechanical treatments and organic solvents to extract the TAG core for the production of plant oils for food purposes. The direct use of natural oil droplets, OS, would be much more environmentally friendly compared to pure phospholipids
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