Soy milk oleosome behaviour at the air-water interface

The emulsifying ability of oleosomes and their interfacial molecules

Oleosomes are natural oil droplets, present in all organisms and abundant in oilseeds. After their aqueous extraction from oilseeds, they can be directly utilized as oil droplets in food, cosmetics and all types of oil-in-water emulsion systems. However, to expand the potential uses of oleosomes as green ingredients and to valorize oilseeds as efficient as possible, we explored their emulsifying ability. Oleosomes were extracted from rapeseeds, and 10.0 wt% oil-in-water emulsions were created after homogenization with 0.5-6.0 wt% oleosomes, and the droplet size of the emulsions and their structure was measured by laser diffraction and confocal laser scanning microscopy (CLSM), respectively. The emulsion with an oleosome concentration lower than 1.0 wt% gave unstable emulsions with visible free oil. At oleosome concentrations at 1.5 wt% or higher, we obtained stable emulsions with droplet sizes between 2.0 and 12.0 µm. To investigate the role of the oleosome interfacial molecules in stabilizing emulsions we also studied their emulsifying and interfacial properties (using drop tensiometry) after isolating them from the oleosome structure. Both oleosomes and their isolated interfacial molecules exhibited a similar behavior on the oil-water interfaces, forming predominantly elastic interfacial films, and also showed a similar emulsifying ability. Our results show that oleosomes are not stabilizing the oil-in-water emulsions as intact particles, but they provide their interfacial molecules, which are enough to stabilize an oil-water surface up to about 2 times bigger than the initial oleosome surface. The understanding of the behavior of oleosomes as emulsifiers, opens many possibilities to use oleosomes as alternative to synthetic emulsifiers in food and pharma applications.

Stability Issues, Probable Approaches for Stabilization and Associated Patents in the Pharmaceutical Field for Oleosome, A Novel Carrier for Drug Delivery

Oleosomes are oil-containing micro-carriers of natural origin that are comprised of special oleosin proteins embedded with a monolayer of phospholipids having a triacylglycerol core. Due to their unique structure and non-toxicity in the biological system, these oil carriers are becoming very eye-catching for formulation development in the field of pharmacy. Consequently, oleosome offers emoliency, occlusivity, self-emulsification, anti-oxidant, and film-forming properties, which leads to controlled and sustained release of encapsulated bio-actives. It is also feasible to load oil-soluble ingredients, such as fragrance, vitamins (retinol), and lipophilic drug moieties inside the core. Being a natural carrier, it shows some stability issues (leakage of oil from the core, oxidation of the loaded oil, aggregation of oil droplets), which are controllable. In this review, we have focused on the various stability issues, the techniques (coating, surface modification, solvents) and how to overcome those problems, and how to load any lipophilic drug into the oil core, and we have also linked patent research works in the field of formulation development.

Proton Low Field NMR Relaxation Time Domain Sensor for Monitoring of Oxidation Stability of PUFA-Rich Oils and Emulsion Products

The nutritional characteristics of fatty acid (FA) containing foods are strongly dependent on the FA’s chemical/morphological arrangements. Paradoxically the nutritional, health enhancing FA polyunsaturated fatty acids (PUFAs) are highly susceptible to oxidation into harmful toxic side products during food preparation and storage. Current analytical technologies are not effective in the facile characterization of both the morphological and chemical structures of PUFA domains within materials for monitoring the parameters affecting their oxidation and antioxidant efficacy. The present paper is a review of our work on the development and application of a proton low field NMR relaxation sensor (¹H LF NMR) and signal to time domain (TD) spectra reconstruction for chemical and morphological characterization of PUFA-rich oils and their oil in water emulsions, for assessing their degree and susceptibility to oxidation and the efficacy of antioxidants. The NMR signals are energy relaxation signals generated by spin–lattice interactions (T₁) and spin–spin interactions (T₂). These signals are reconstructed into 1D (T₁ or T₂) and 2D graphics (T₁ vs. T₂) by an optimal primal-dual interior method using a convex objectives (PDCO) solver. This is a direct measurement on non-modified samples where the individual graph peaks correlate to structural domains within the bulk oil or its emulsions. The emulsions of this review include relatively complex PUFA-rich oleosome-oil bodies based on the aqueous extraction from linseed seeds with and without encapsulation of externally added oils such as fish oil. Potential applications are shown in identifying optimal health enhancing PUFA-rich food formulations with maximal stability against oxidation and the potential for on-line quality control during preparation and storage.

Air-water interfacial behaviour of whey protein and rapeseed oleosome mixtures

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.

Structure and functions of oleosomes (oil bodies)

Oleosomes are natural oil droplets, abundant in plants and more specifically in seeds, composing 20-50 wt% of their mass. The structure of oleosomes is the mechanism that seeds developed to safely store energy in the form of triacylglycerols and use it during germination. For this, the phospholipid/protein membrane that covers and protects the triacylglycerols has been wisely developed during evolution to grant them extreme stability against physical and chemical stresses. The remarkable property-performance relationships of oleosomes have generated a lot of interest to incorporate them in oil-in-water emulsions and take advantage of their sophisticated membrane. However, the structure-function relationship of the molecular components in the oleosome membrane is still not well understood and requires more attention in order to take complete advantage of their potential functions. The aim of this review is to give insights into the architecture of the oleosomes and to discuss the exploitation of their properties in advanced and broad applications, from carrying and protecting sensitive molecules to bio-catalysis.

The behaviour of sunflower oleosomes at the interfaces

Oleosomes are particles equipped with a sophisticated membrane, comprising a continuous monolayer of phospholipids and hydrophobic proteins, which covers the triglyceride core and grants them extreme physical and chemical stability. The noteworthy qualities of oleosomes have attracted strong interest for their incorporation in emulsion formulations; however, little is known about their emulsifying properties and their behaviour on interfaces. For these reasons, oleosomes were isolated from sunflower seeds (96.2 wt% oil, 3.1 wt% protein) and used as an emulsifier for the stabilization of O/W and W/O interfaces. In both cases, oleosomes showed high interfacial and emulsifying activity. Individual oleosome particles had a broad size distribution from 0.4 to 10.0 μm and it was observed that the membrane of the larger oleosomes (>1-5 μm) was disrupted and its fractions participated in the newly formed interface. Oleosomes with a smaller diameter (<1 μm) seemed to have survived the applied mild emulsification step as a great number of them could be observed both in the bulk of the emulsions and on the interface of the emulsion droplets. This phenomenon was more pronounced for the W/O interface where oleosomes were absorbed intact in a manner similar to a Pickering mechanism. However, when the triglycerides were removed from the core of oleosomes in order to focus more on the effect of the membrane, the remaining material formed sub-micron spherical particles, which clearly acted as Pickering stabilisers. These findings showcase the intriguing behaviour of oleosomes upon emulsification, especially the crucial role of their membrane. The study demonstrates relevance for applications where immiscible liquid phases are present.

Magnetic Oleosome as a Functional Lipophilic Drug Carrier for Cancer Therapy

In the present study, we fabricated magnetic oleosomes functionalized with recombinant proteins as a new carrier for oil-based lipophilic drugs for cancer treatment. The bioengineered oleosome is composed of neutral lipids surrounded by a phospholipid monolayer with embedded oleosin fusion proteins. The oleosin was genetically fused to a nanobody of a green fluorescent protein (GFP). A recombinant protein consisting of immunoglobulin-binding protein LG fused to GFP was used to couple the oleosome to an antibody for targeted delivery to breast cancer cells. The lipid core of the oleosome was loaded with magnetic nanoparticles and carmustine as the lipophilic drug. The magnetic oleosome was characterized using transmission electron microscopy and dynamic light scattering. Moreover, the specific delivery of oleosome into the target cancer cell was investigated via confocal microscopy. To examine the cell viability of the delivered oleosome, a conventional 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was carried out. Furthermore, an animal study was conducted to confirm the effect resulting from the delivery of the anticancer drug-loaded oleosomes. Taken together, the fabricated lipophilic drug-loaded magnetic oleosome can be a powerful tool for oil-based drug delivery agent for cancer therapy.

Soft matter food physics--the physics of food and cooking

This review discusses the (soft matter) physics of food. Although food is generally not considered as a typical model system for fundamental (soft matter) physics, a number of basic principles can be found in the interplay between the basic components of foods, water, oil/fat, proteins and carbohydrates. The review starts with the introduction and behavior of food-relevant molecules and discusses food-relevant properties and applications from their fundamental (multiscale) behavior. Typical food aspects from 'hard matter systems', such as chocolates or crystalline fats, to 'soft matter' in emulsions, dough, pasta and meat are covered and can be explained on a molecular basis. An important conclusion is the point that the macroscopic properties and the perception are defined by the molecular interplay on all length and time scales.

The role of intact oleosin for stabilization and function of oleosomes

Lipid storage in plants is achieved among all plant species by formation of oleosomes, enclosing oil (triacylglycerides) in small subcellular droplets. Seeds are rich in this pre-emulsified oil to provide a sufficient energy reservoir for growing. The triacylglyceride core of the oleosomes is surrounded by a phospholipid monolayer containing densely packed proteins called oleosins. They are anchored in the triacylglycerides core with a hydrophobic domain, while the hydrophilic termini remain on the surface. These specialized proteins are expressed during seed development and maturation. Particularly, they play a major role in the stabilization and function of oleosomes. To better understand the importance of oleosins for oleosome stabilization, enzymatic digestion of oleosins was performed. This made it possible to compare and correlate changes in the molecular structure of oleosins and changing macroscopic properties of oleosomes. Tryptic digestion cleaves the hydrophilic part of the oleosins, which is accompanied by a loss of secondary structures as evidenced by Fourier-transform infrared and sum frequency generation spectra. After digestion, the ability of oleosins to stabilize oil-water or air-water interfaces was lost. The surface charge and the associated aggregation behavior of oleosomes are governed by interactions typical of proteins before digestion and by interactions typical of phospholipids after digestion.

Formation of complex interface and stability of oil-in-water (O/W) emulsion prepared by soy lipophilic protein nanoparticles

A lipophilic protein nanoparticle (LPP) was fabricated by ultrasonication of the soy lipophilic protein (LP), which contains hydrophobic proteins and phospholipids. This LPP (Rh = 136 ± 0.8 nm, ζ-potential = -20 mV, pH 7.0) had an improved dispersibility and acted as an emulsifier. The oil/water (O/W) emulsion stabilized by this LPP exhibited superior physical stability over long-term storage (8 weeks), during a stress storage test (200 mM NaCl addition and heating at 90 °C), and in the presence of Tween 20 (1.0-4.0 wt %), in contrast to those emulsions stabilized by β-conglycinin and glycinin. Langmuir-Blodgett method and interface pressure determination revealed that LPP formed rigid and rough granular film at air/water interface. The excellent stability of emulsions stabilized by LPP highlights the synergic effect between hydrophobic proteins and phospholipids. These findings suggest that the complexes of hydrophobic protein aggregates and biosurfactant could form a stable interface which could be developed into a novel strategy to fabricate a stable food emulsion.

Soybean oleosomes behavior at the air-water interface

Soy milk is a highly stable emulsion, the stability being mainly due to the presence of oleosomes or oil bodies, spherical structures filled with triacylglycerides (TAGs) and surrounded by a monolayer of phospholipids and proteins called oleosins. For oleosomes purified from raw soymilk, surface pressure investigations and Brewster angle microscopy have been performed to unveil their adsorption, rupture and structural changes over time at different subphase conditions (pH, ionic strength). Such investigations are important for (industrial) food applications of oleosomes, but are also useful for the understanding of the general behavior of proteins and phospholipids at interfaces. In addition a better comprehension of the highly stable oleosomes can lead to advancements in liposome manufacturing, e.g., for storage and transport applications. Although oleosomes have their origin in food systems, their unique stability and physical behavior show transferable characteristics which lead to a much better understanding of the description of any kind of emulsion. This study is one of the first steps toward the comparison of natural emulsification concepts based on different physical structures: e.g., the animals' low density lipoproteins, where apolipoproteins with phospholipids are located only at the interface and plant oleosomes with its oleosins, which are embedded in a phospholipid monolayer and reach deep inside the oil phase.