Characterization of the charged components and their topology on the surface of plant seed oil bodies

The role of oleosins and phosphatidylcholines on the membrane mechanics of oleosomes

HYPOTHESIS

Oilseeds use triacylglycerides as main energy source, and pack them into highly stable droplets (oleosomes) to facilitate the triacylglycerides' long-term storage in the aqueous cytosol. To prevent the coalescence of oleosomes, they are stabilized by a phospholipid monolayer and unique surfactant-shaped proteins, called oleosins. In this study, we use state-of-the-art interfacial techniques to reveal the function of each component at the oleosome interface.

EXPERIMENTS

We created model oil-water interfaces with pure oleosins, phosphatidylcholines, or mixtures of both components (ratios of 3:1, 1:1, 1:3), and applied large oscillatory dilatational deformations (LAOD). The obtained rheological response was analyzed with general stress decomposition (GSD) to get insights into the role of phospholipids and oleosins on the mechanics of the interface.

FINDINGS

Oleosins formed viscoelastic solid interfacial films due to network formation via in-plane interactions. Between adsorbed phosphatidylcholines, weak interactions were observed, suggesting the surface stress response upon dilatational deformations was dominated by density changes. In mixtures with 3:1 and 1:1 oleosin-to-phosphatidylcholine ratios, oleosins dominated the interfacial mechanics and formed a network, while phosphatidylcholines contributed to interfacial tension reduction. At higher phosphatidylcholine concentrations (1:3 oleosin-to-phosphatidylcholine), phosphatidylcholine dominated the interface, and no network formation occurred. Our findings improve the understanding of both components' role for oleosomes.

Quercetin on the properties of rice bran oil body: Focused surface charge, oxidative stability and digestive properties

To further enhance the stability of rice bran oil body (RBOB) emulsions, this study examined the impact of various concentrations of quercetin (QU) on the microstructure, rheological properties, oxidative stability, and digestive properties of RBOB emulsions. The results indicated that by incorporating QU concentration, the particle size of RBOB emulsions could be significantly reduced to 300 nm; QU could improve the surface hydrophobicity, the emulsifying activity index and emulsification stability index of RBOB emulsions of 550, 0.078 m2/g and 50.78 min, respectively; the storage stability of RBOB emulsions was further improved; the higher concentration of QU could delay the oxidation of RBOB emulsions, among which, the 500 μmol/L concentration inhibited the strongest effect of oil oxidation. It also improved the thermal stability of RBOB emulsions. After gastrointestinal digestion, the free fatty acids release rate of RBOB emulsions with QU addition decreased to 14.68%, and RBOB emulsions were slowly hydrolyzed. Therefore, adding QU to RBOB helps to improve its stability and delay digestion.

Functionalizing Yeast Lipid Droplets as Versatile Biomaterials

Lipid droplets (LD) are dynamic cellular organelles of ≈1 µm diameter in yeast where a neutral lipid core is surrounded by a phospholipid monolayer and attendant proteins. Beyond the storage of lipids, opportunities for LD engineering remain underdeveloped but they show excellent potential as new biomaterials. In this research, LD from yeast Saccharomyces cerevisiae is engineered to display mCherry fluorescent protein, Halotag ligand binding protein, plasma membrane binding v-SNARE protein, and carbonic anhydrase enzyme via linkage to oleosin, an LD anchoring protein. Each protein-oleosin fusion is coded via a single gene construct. The expressed fusion proteins are specifically displayed on LD and their functions can be assessed within cells by fluorescence confocal microscopy, TEM, and as isolated materials via AFM, flow cytometry, spectrophotometry, and by enzyme activity assay. LD isolated from the cell are shown to be robust and stabilize proteins anchored into them. These engineered LD function as reporters, bind specific ligands, guide LD and their attendant proteins into union with the plasma membrane, and catalyze reactions. Here, engineered LD functions are extended well beyond traditional lipid storage toward new material applications aided by a versatile oleosin platform anchored into LD and displaying linked proteins.

The expression of genes encoding novel Sesame oleosin variants facilitates enhanced triacylglycerol accumulation in Arabidopsis leaves and seeds

Triacylglycerols (TAG), accumulate within lipid droplets (LD), predominantly surrounded by OLEOSINs (OLE), that protect TAG from hydrolysis. We tested the hypothesis that identifying and removing degradation signals from OLE would promote its abundance, preventing TAG degradation and enhancing TAG accumulation. We tested whether mutating potential ubiquitin-conjugation sites in a previously reported improved Sesamum indicum OLE (SiO) variant, o3-3 Cys-OLE (SiCO herein), would stabilize it and increase its lipogenic potential. SiCOv1 was created by replacing all five lysines in SiCO with arginines. Separately, six cysteine residues within SiCO were deleted to create SiCOv2. SiCOv1 and SiCOv2 mutations were combined to create SiCOv3. Transient expression of SiCOv3 in Nicotiana benthamiana increased TAG by two-fold relative to SiCO. Constitutive expression of SiCOv3 or SiCOv5, containing the five predominant TAG-increasing mutations from SiCOv3, in Arabidopsis along with mouse DGAT2 (mD) increased TAG accumulation by 54% in leaves and 13% in seeds compared with control lines coexpressing SiCO and mD. Lipid synthesis rates increased, consistent with an increase in lipid sink strength that sequesters newly synthesized TAG, thereby relieving the constitutive BADC-dependent inhibition of ACCase reported for WT Arabidopsis. These OLE variants represent novel factors for potentially increasing TAG accumulation in a variety of oil crops.

The role of membrane components on the oleosome lubrication properties

HYPOTHESIS

Oleosomes are natural oil droplets with a unique phospholipid/protein membrane, abundant in plant seeds, from which they can be extracted and used in emulsion-based materials, such as foods, cosmetics and pharmaceutics. The lubrication properties of such materials are essential, on one hand, due to the importance of the in-mouth creaminess for the consumed products or the importance of spreading the topical creams. Therefore, here, we will evaluate the lubrication properties of oleosomes, and how these properties are affected by the components at the oleosome membrane.

EXPERIMENT

Oleosomes were extracted, and their oral lubricating properties were evaluated using tribology. To understand the influence of the oil droplet membrane composition, reconstituted oleosomes were also studied, with membranes that differed in protein/lecithin ratio. Additionally, whey protein- and lecithin-stabilised emulsions were used as reference samples. Confocal laser scattering microscopy was used to study the samples visually before and after tribological analysis.

FINDINGS

Oleosomes followed a ball-bearing mechanism, which was probably related to their high physical stability due to the presence of membrane proteins. When the membrane protein concentration at the surface was reduced, the droplet stability weakened, leading to plating-out lubrication. Following our results, we elucidated the oleosome lubrication mechanism and showed their possible control by changing the membrane composition.

Insights into the emulsification mechanism of the surfactant-like protein oleosin

Oleosins are proteins with a unique central hydrophobic hairpin designed to stabilize lipid droplets (oleosomes) in plant seeds. For efficient droplet stabilization, the hydrophobic hairpin with a strong affinity for the apolar droplet core is flanked by hydrophilic arms on each side. This gives oleosins a unique surfactant-like shape making them a very interesting protein. In this study, we tested if isolated oleosins retain their ability to stabilize oil-in-water emulsions, and investigated the underlying stabilization mechanism. Due to their surfactant-like shape, oleosins when dispersed in aqueous buffers associated to micelle-like nanoparticles with a size of ∼33 nm. These micelles, in turn, clustered into larger aggregates of up to 20 µm. Micelle aggregation was more extensive when oleosins lacked charge. During emulsification, oleosin micelles and micelle aggregates dissociated and mostly individual oleosins adsorbed on the oil droplet interface. Oleosins prevented the coalescence of the oil droplets and if sufficiently charged, droplet flocculation as well.

Degeneration of oil bodies by rough endoplasmic reticulum -associated protein during seed germination in Cannabis sativa

Oil bodies serve as a vital energy source of embryos during germination and contribute to sustaining the initial growth of seedlings until photosynthesis initiation. Despite high stability in chemical properties, how oil bodies break down and go into the degradation process during germination is still unknown. This study provides a morphological understanding of the mobilization of stored compounds in the seed germination of Cannabis. The achenes of fibrous hemp cultivar (Cannabis sativa cv. 'Chungsam') were examined in this study using light microscopy, scanning electron microscopy and transmission electron microscopy. Oil bodies in Cannabis seeds appeared spherical and sporadically distributed in the cotyledonary cells. Protein bodies contained electron-dense globoid and heterogeneous protein matrices. During seed germination, rough endoplasmic reticulum (rER) and high electron-dense substances were present adjacent to the oil bodies. The border of the oil bodies became a dense cluster region and appeared as a sinuous outline. Later, irregular hyaline areas were distributed throughout oil bodies, showing the destabilized emulsification of oil bodies. Finally, the oil bodies lost their morphology and fused with each other. The storage proteins were concentrated in the centre of the protein body as a dense homogenous circular mass surrounded by a light heterogeneous area. Some storage proteins are considered emulsifying agents on the surface region of oil bodies, enabling them to remain stable and distinct within and outside cotyledon cells. At the early germination stage, rER appeared and dense substances aggregated adjacent to the oil bodies. Certain proteins were synthesized within the rER and then translocated into the oil bodies by crossing the half membrane of oil bodies. Our data suggest that rER-associated proteins function as enzymes to lyse the emulsifying proteins, thereby weakening the emulsifying agent on the surface of the oil bodies. This process plays a key role in the degeneration of oil bodies and induces coalescence during seed germination.

Walnut (Juglans regia L.) kernel oil bodies recovered by aqueous extraction for utilization as ingredient in food emulsions: Exploration of their microstructure, composition and the effects of homogenization, pH, and salt ions on their physical stability

Natural oil-in-water emulsions containing plant oil bodies (OBs), also called oleosomes, rich in health-promoting omega-3 polyunsaturated fatty acids (ω3 PUFA) are of increasing interest for food applications. In this study, we focused on walnut kernel OBs (WK-OBs) and explored their microstructure, composition and physical stability in ionic environments as well as the impact of homogenization. A green process involving aqueous extraction by grinding of WK allowed the co-extraction of OBs and proteins, and centrifugation was used to recover the WK-OBs. Confocal laser scanning microscopy images showed the spherical shape of WK-OBs with an oil core envelopped by a layer of phospholipids (0.16 % of lipids) and embedded proteins. Their mean diameter was 5.1 ± 0.3 µm. The WK-OBs contained 70.1 % PUFA with 57.8 % ω6 linoleic acid and 12.3 % ω3 α-linolenic acid representing 68 % and 11.6 % of the total fatty acids in the sn-2 position of the triacylglycerols (TAG), respectively. Trilinolein was the main TAG (23.1 %). The WK-OBs also contained sterols (1223 ± 33 mg/kg lipids; 86 % β-sitosterol), carotenoids (0.62 ± 0.01 mg/kg lipids; 49.2 % β-carotene), and tocopherols (322.7 ± 7.7 mg/kg lipids; 89 % γ-tocopherol), confirming their interest as health-promoting ingredients. The decrease in the size of WK-OBs under high-pressure homogenization avoided phase separation upon storage. The anionic WK-OB surface at neutral pH was affected by stressful ionic environments (pH, NaCl, CaCl2), that induced aggregation of WK-OBs and decreased the physical stability of the emulsions. Emulsions containing WK-OBs are promising to diversify the market of the ω3-rich plant-based food products and beverages.

Sugar Starvation Disrupts Lipid Breakdown by Inducing Autophagy in Embryonic Axes of Lupin (Lupinus spp.) Germinating Seeds

Under nutrient deficiency or starvation conditions, the mobilization of storage compounds during seed germination is enhanced to primarily supply respiratory substrates and hence increase the potential of cell survival. Nevertheless, we found that, under sugar starvation conditions in isolated embryonic axes of white lupin (Lupinus albus L.) and Andean lupin (Lupinus mutabilis Sweet) cultured in vitro for 96 h, the disruption of lipid breakdown occurs, as was reflected in the higher lipid content in the sugar-starved (-S) than in the sucrose-fed (+S) axes. We postulate that pexophagy (autophagic degradation of the peroxisome-a key organelle in lipid catabolism) is one of the reasons for the disruption in lipid breakdown under starvation conditions. Evidence of pexophagy can be: (i) the higher transcript level of genes encoding proteins of pexophagy machinery, and (ii) the lower content of the peroxisome marker Pex14p and its increase caused by an autophagy inhibitor (concanamycin A) in -S axes in comparison to the +S axes. Additionally, based on ultrastructure observation, we documented that, under sugar starvation conditions lipophagy (autophagic degradation of whole lipid droplets) may also occur but this type of selective autophagy seems to be restricted under starvation conditions. Our results also show that autophagy occurs at the very early stages of plant growth and development, including the cells of embryonic seed organs, and allows cell survival under starvation conditions.

Effects of Concentration and Type of Lipids on the Droplet Size, Encapsulation, Colour and Viscosity in the Oil-in-Water Emulsions Stabilised by Rapeseed Protein

The objective of this study was to extract the rapeseed protein from by-products and further examine the effect of lab-made rapeseed protein on the droplet size, microstructure, colour, encapsulation and apparent viscosity of emulsions. Rapeseed protein-stabilised emulsions with an increasing gradient of milk fat or rapeseed oil (10, 20, 30, 40 and 50%, v/v) were fabricated using a high shear rate homogenisation. All emulsions showed 100% oil encapsulation for 30 days of storage, irrespective of lipid type and the concentration used. Rapeseed oil emulsions were stable against coalescence, whereas the milk fat emulsion showed a partial micro-coalescence. The apparent viscosity of emulsions raised with increased lipid concentrations. Each of the emulsions showed a shear thinning behaviour, a typical behaviour of non-Newtonian fluids. The average droplet size was raised in milk fat and rapeseed oil emulsions when the concentration of lipids increased. A simple approach to manufacturing stable emulsions offers a feasible hint to convert protein-rich by-products into a valuable carrier of saturated or unsaturated lipids for the design of foods with a targeted lipid profile.

Improve stability and application of rice oil bodies via surface modification with ferulic acid, (-)-epicatechin, and phytic acid

Rice bran oil bodies (RBOBs) are one of the most exploited functional components from rice bran by-products and are predominantly based on oleosin stabilization. In this study, we explored the effects of different concentrations of added (-)-epicatechin, ferulic acid, and phytic acid on the RBOBs stability. The results revealed that the incorporation of all three natural phytoconstituents could reduce the RBOBs particle size and increase emulsifying properties, demonstrating increasing surface hydrophobicity (p < 0.05), and a good antioxidant effect, which was especially obvious with (-)-epicatechin incorporation. Fourier transform infrared (FT-IR) spectroscopy data demonstrated that these three small molecule substance classes can modify with oleosin on RBOBs surface by covalent and noncovalent effects. Raman spectroscopic analysis illustrated that the vibrational modes of disulphide bonds in oleosin were modified by these three plant natural ingredients. The interactions between the three phytoconstituents and the model protein were investigated by molecular docking experiments.

Formation, digestion properties, and physicochemical stability of the rice bran oil body carrier system

Rice bran is a major by-product of rice processing with abundant nutrient content. Oil bodies (OBs), which are fat particles with unique physicochemical stability, are specialized organelles for the storage of oils and fats in plant tissues. In this study, we extracted OBs from rice bran, to evaluate the function of hydrophobic nutrients efficiently delivered by OBs. The carrier system was prepared by sonicating curcumin with medium chain triglycerides (MCT) into rice bran oil bodies (RBOBs). Emulsions comprising different RBOB mass fractions were characterized. The results showed that the highest encapsulation efficiency (EE, 87.67%), optimal particle size (190 nm), and best storage stability were achieved with the 1.5 wt% RBOBs. Based on activity evaluation data, the carrier system can achieve sustained oil release in the intestine and shows high bioaccessibility (61.04%; IC50 in Caco-2 cells was 77.21 μg/mL), which is important for promoting grain by-product utilization.

Effect of Polar Hydrocarbon Contents on Oil-Water Interfacial Tension and Implications for Recent Observations in Smart Water Flooding Oil Recovery Schemes

For decades now, low salinity water flooding (LSWF) oil recovery has emerged as an environmentally benign and cost-effective method for improved oil recovery, where research findings have reported pH and interfacial tension effects. Considering the effect of oil chemistry on interfacial tension and the potential of this chemistry to have a direct relationship with LSWF, we measured the interfacial tension of four crude oils with composition varying from those of conventional to unconventional ones. We also characterized the crude oil samples using infrared spectroscopy and a wet chemistry method based on asphaltene precipitation. Our research approach has enabled us to relate the composition of crude oil to the interfacial tension trend at pH encountered in improved oil recovery schemes. Our research methodology, based on an integrated approach to using infrared spectroscopy and interfacial tensiometry, has also enabled us to propose a more robust theoretical explanation for current observations in LSWF related to pH and interfacial tension. In this regard, oil-water interfacial tension depends on the concentration of polar components, such that the higher the concentration of polar groups in crude oil, the higher the interfacial tension at a given pH of aqueous solution. We have also shown that the acid-base behavior of polar groups at the oil-water interface provides a theoretical interpretation of the explicit relationship between oil-water interfacial tension and the electrostatic components of interfacial tension as given by the energy additivity theory.

Extraction of structurally intact and well-stabilized rice bran oil bodies as natural pre-emulsified O/W emulsions and investigation of their rheological properties and components interaction

The isolated plant oil bodies (OBs) have shown promising applications as natural pre-emulsified O/W emulsions. Rice bran OBs can be used as a new type plant-based resource with superior fatty acids composition and abundant γ-oryzanol. This paper investigated the method of extracting structurally intact and stable rice bran OBs. Due to the adequate steric hindrance and electrostatic repulsion effects, rice bran OBs extracted by NaHCO₃ medium had smaller particle size, better physical stability, and natural structure. The protein profile of NaHCO₃-extracted rice bran OBs showed oleosin-L and oleosin-H, while exogenous proteins in PBS and enzyme-assisted- extracted rice bran OBs could interact with interfacial proteins through hydrophobic forces to aggregate adjacent OBs, further remodeling the OBs interface. It was also found that the small-sized rice bran OBs could adsorb on the interface of the larger-sized rice bran OBs like Pickering stabilizers. Rice bran OBs exhibited pseudoplastic fluids characteristic, but underwent a transition from solid-like to liquid-like behavior depending on the extraction method. The disorder of NaHCO₃-extracted rice bran OBs protein molecules increased their surface hydrophobicity. The random coil structure favored more proteins adsorption at the interface of rice bran OBs extracted by PBS. Enzyme-assisted extraction of rice bran OBs had the highest content of β-sheet structure, which facilitated the stretching and aggregation of protein spatial structure. It was also confirmed the hydrogen bonding and hydrophobic interaction between the triacylglycerol or phospholipid and proteins molecules, and the membrane compositions of rice bran OBs differed between extraction methods.

Oil Bodies from Chia (Salvia hispanica L.) and Camelina (Camelina sativa L.) Seeds for Innovative Food Applications: Microstructure, Composition and Physical Stability

Exploring and deciphering the biodiversity of oil bodies (OBs) recovered from oilseeds are of growing interest in the preparation of sustainable, natural and healthy plant-based food products. This study focused on chia (Salvia hispanica L.) and camelina (Camelina sativa L.) seed OBs. A green refinery process including ultrasound to remove mucilage, aqueous extraction by grinding and centrifugation to recover OBs from the seeds was used. The microstructure, composition and physical stability of the OBs were examined. Confocal laser scanning microscopy images showed that chia and camelina seed OBs are spherical assemblies coated by a layer of phospholipids and proteins, which have been identified by gel electrophoresis. The mean diameters determined by laser light scattering measurements were 2.3 and 1.6 µm for chia and camelina seed OBs, respectively. The chia and camelina seed OBs were rich in lipids and other bioactive components with, respectively, 64% and 30% α-linolenic acid representing 70% and 53% of the total fatty acids in the sn-2 position of the triacylglycerols, 0.23% and 0.26% phospholipids, 3069 and 2674 mg/kg oil of β-sitosterol, and lipophilic antioxidants: 400 and 670 mg/kg oil of γ-tocopherol. Phenolic compounds were recovered from the aqueous extracts, such as rutin from camelina and caffeic acid from chia. Zeta-potential measurements showed changes from about -40 mV (pH 9) to values that were positive below the isoelectric points of pH 5.1 and 3.6 for chia and camelina seed OBs, respectively. Below pH 6.5, physical instability of the natural oil-in-water emulsions with aggregation and phase separation was found. This study will contribute to the development of innovative and sustainable food products based on natural oil-in-water emulsions containing chia and camelina seed OBs for their nutritional and health benefits.

An alternative angiosperm DGAT1 topology and potential motifs in the N-terminus

The highly variable cytoplasmic N-terminus of the plant diacylglycerol acyltransferase 1 (DGAT1) has been shown to have roles in oligomerization as well as allostery; however, the biological significance of the variation within this region is not understood. Comparing the coding sequences over the variable N-termini revealed the Poaceae DGAT1s contain relatively high GC compositional gradients as well as numerous direct and inverted repeats in this region. Using a variety of reciprocal chimeric DGAT1s from angiosperms we show that related N-termini had similar effects (positive or negative) on the accumulation of the recombinant protein in Saccharomyces cerevisiae. When expressed in Camelina sativa seeds the recombinant proteins of specific chimeras elevated total lipid content of the seeds as well as increased seed size. In addition, we combine N- and C-terminal as well as internal tags with high pH membrane reformation, protease protection and differential permeabilization. This led us to conclude the C-terminus is in the ER lumen; this contradicts earlier reports of the cytoplasmic location of plant DGAT1 C-termini.

Plant oil bodies and their membrane components: new natural materials for food applications

Plants store triacylglycerols in the form of oil bodies (OBs) as an energy source for germination and subsequent seedling growth. The interfacial biomaterials from these OBs are called OB membrane materials (OBMMs) and have several applications in foods, e.g., as emulsifiers. OBMMs are preferred, compared with their synthetic counterparts, in food applications as emulsifiers because they are natural, i.e., suitable for clean label, and may stabilize bioactive components during storage. This review focuses mainly on the extraction technologies for plant OBMMs, the functionality of these materials, and the interaction of OB membranes with other food components. Different sources of OBs are evaluated and the challenges during the extraction and use of these OBMMs for food applications are addressed.

Oil Bodies Cream from Olive Paste: Extraction of a Functional Ingredient for Developing a Stable Food Emulsion

Oil bodies (OBs) dispersed in an aqueous medium form a natural emulsion with high physical and microbiological stability. This work was focused on the development of a new protocol for extracting OBs from olive paste, through the extraction of an olive oil body cream (OOBC) with a yield of about 43% (wt/wt) in approximately 2 h. The proximate analysis revealed the presence of moisture, lipids and proteins as well as the contents of polyphenols and flavonoids, and the antioxidant powers were determined. The rheological and tribological performances of the OOBC were evaluated. Moreover, we measured a size distribution in the range of 0.7–1.7 m, by using a standard optical microscope. The results have demonstrated clearly that the OOBC extracted from the olive paste can be used as a functional and vegan ingredient in food emulsions.

Characterization of lipid droplets from a Taxus media cell suspension and their potential involvement in trafficking and secretion of paclitaxel

Our paper describes the potential roles of lipid droplets of Taxus media cell suspension in the biosynthesis and secretion of paclitaxel and, therefore, highlights their involvement in improving its production. Paclitaxel (PTX) is a highly potent anticancer drug that is mainly produced using Taxus sp. cell suspension cultures. The main purpose of the current study is to characterize cellular LDs from T. media cell suspension with a particular focus on the biological connection of their associated proteins, the caleosins (CLOs), with the biosynthesis and secretion of PTX. A pure LD fraction obtained from T. media cells and characterized in terms of their proteome. Interestingly, the cellular LD in T. media sequester the PTX. This was confirmed in vitro, where about 96% of PTX (C⁰_PTX,_aq [mg L^-1]) in the aqueous solution was partitioned into the isolated LDs. Furthermore, silencing of CLO-encoding genes in the T. media cells led to a net decrease in the number and size of LDs. This coincided with a significant reduction in expression levels of TXS, DBAT and DBTNBT, key genes in the PTX biosynthesis pathway. Subsequently, the biosynthesis of PTX was declined in cell culture. In contrast, treatment of cells with 13-hydroperoxide C18:3, a substrate of the peroxygenase activity, induced the expression of CLOs, and, therefore, the accumulation of cellular LDs in the T. media cells cultures, thus increasing the PTX secretion. The accumulation of stable LDs is critically important for effective secretion of PTX. This is modulated by the expression of caleosins, a class of LD-associated proteins with a dual role conferring the structural stability of LDs as well as regulating lipidic bioactive metabolites via their enzymatic activity, thus enhancing the biosynthesis of PTX.

Economic purification of recombinant uricase by artificial oil bodies

Rasburicase is an expensive treatment used to control hyperuricemia caused by tumour lysis syndrome (TLS). In this study, a non-chromatographic method was designed based on nano-oil bodies for convenient and economical purification of the recombinant uricase. For this purpose, two chimaeras were synthesized with a different arrangement of the uricase, caleosin and intein fragments. After confirming the protein expression by measuring the uricase activity at 293 nm, purification was conducted through oil-body construction. The results were resolved on the 12% SDS-PAGE gel. Finally, the stability of the oil bodies was examined against different salts, surfactants, temperatures, and pH values. According to our results, the overexpression of uricase-caleosin chimaera under the T7 promoter in Escherichia coli led to the production of soluble protein, which was successfully purified by artificial oil bodies. The active uricase was subsequently released through the self-splicing of intein. Further investigations highlighted the importance of the free C-terminus of caleosin in constructing artificial oil bodies. Moreover, surfactants and low temperature, in contrast to salts, improved the stability of oil bodies. In conclusion, caleosins are an efficient purification tag reducing the cost of purification compared to conventional chromatography methods.

Abscisic acid activation of oleosin gene HvOle3 expression prevents the coalescence of protein storage vacuoles in barley aleurone cells

Protein storage vacuoles (PSVs) in aleurone cells coalesce during germination, and this process is highly coupled with mobilization of PSV reserves, allowing de novo synthesis of various hydrolases in aleurone cells for endosperm degradation. Here we show that in barley (Hordeum vulgare L.) oleosins, the major integral proteins of oleosomes are encoded by four genes (HvOle1 to 4), and the expression of HvOle1 and HvOle3 is strongly up-regulated by abscisic acid (ABA), which shows antagonism to gibberellic acid. In aleurone cells, all HvOLEs were subcellularly targeted to the tonoplast of PSVs. Gain-of-function analyses revealed that HvOLE3 effectively delayed PSV coalescence, whereas HvOLE1 only had a moderate effect, with no notable effect of HvOLE2 and 4. With regard to longevity, HvOLE3 chiefly outperformed other HvOLEs, followed by HvOLE1. Experiments swapping the N- and C-terminal domain between HvOLE3 and other HvOLEs showed that the N-terminal region of HvOLE3 is mainly responsible, with some positive effect by the C-terminal region, for mediating the specific preventive effect of HvOLE3 on PSV coalescence. Three ACGT-core elements and the RY-motif were responsible for ABA induction of HvOle3 promoter activity. Transient expression assays using aleurone protoplasts demonstrated that transcriptional activation of the HvOle3 promoter was mediated by transcription factors HvABI3 and HvABI5, which acted downstream of protein kinase HvPKABA1.

Aqueous Integrated Process for the Recovery of Oil Bodies or Fatty Acid Emulsions from Sunflower Seeds

An aqueous integrated process was developed to obtain several valuable products from sunflower seeds. With a high-shear rate crusher, high-pressure homogenization and centrifugation, it is possible to process 600× g of seeds in 1400× g of water to obtain a concentrated cream phase with a dry matter (dm) content of 46%, consisting of 74 (w/w dm) lipids in the form of an oil-body dispersion (droplet size d(0.5): 2.0 µm) rich in proteins (13% w/w dm, with membranous and extraneous proteins). The inclusion of an enzymatic step mediated by a lipase made possible the total hydrolysis of trigylcerides into fatty acids. The resulting cream had a slightly higher lipid concentration, a ratio lipid/water closer to 1, with a dry matter content of 57% consisting of 69% (w/w) lipids, a more complex structure, as observed on Cryo-SEM, with a droplet size slightly greater (d(0.5): 2.5 µm) than that of native oil bodies and a conserved protein concentration (12% w/w dm) but an almost vanished phospholipid content (17.1 ± 4.4 mg/g lipids compared to 144.6 ± 6 mg/g lipids in the oil-body dispersion and 1811.2 ± 122.2 mg/g lipids in the seed). The aqueous phases and pellets were also characterized, and their mineral, lipid and protein contents provide new possibilities for valorization in food or technical applications.

How plants solubilise seed fats: revisiting oleosin structure and function to inform commercial applications

Plants store triacylglycerides in organelles called oil bodies, which are important fuel sources for germination. Oil bodies consist of a lipid core surrounded by an interfacial single layer membrane of phospholipids and proteins. Oleosins are highly conserved plant proteins that are important for oil body formation, solubilising the triacylglycerides, stabilising oil bodies, and playing a role in mobilising the fuel during the germination process. The domain structure of oleosins is well established, with N- and C-terminal domains that are hydrophilic flanking a long hydrophobic domain that is proposed to protrude into the triacylglyceride core of the oil body. However, beyond this general understanding, little molecular level detail on the structure is available and what is known is disputed. This lack of knowledge limits our understanding of oleosin function and concomitantly our ability to engineer them. Here, we review the state of play in the literature regarding oleosin structure and function, and provide some examples of how oleosins can be used in commercial settings.

Deciphering the properties of hemp seed oil bodies for food applications: Lipid composition, microstructure, surface properties and physical stability

Hemp seed oil bodies (HSOBs) are of growing interest in response to the demand of consumers for healthy and natural plant-based food formulations. In this study, we used minimal processing including aqueous extraction by grinding and centrifugation to obtain HSOBs. We determined the lipid composition of HSBOs, their microstructure, and the impact of the homogenization pressure, pH and minerals on their surface properties and the physical stability of the emulsions. HSOBs contain high levels of well-balanced PUFA with LA/ALA = 2.9, γ-tocopherol, lutein and phytosterols. The mean diameter of HSOBs was 2.3 ± 0.1 μm with an isoelectric point in the range of pH 4.4 to 4.6. Homogenization of hemp seed extracts induced a decrease in the size of HSOBs but did not eliminate the sedimentation of the protein bodies composed of the globulin edestin. By changing the surface properties of HSOBs, pH values below 6 and NaCl induced the aggregation of HSOBs, while CaCl₂ induced both aggregation and membrane-fusion mediated coalescence of HSOBs by involving probably the anionic phospholipids together with membrane proteins. This study will contribute to extend the range of novel food products and designed emulsions containing hemp seed proteins and oil bodies.

In silico proteolysis and analysis of bioactive peptides from sequences of fatty acid desaturase 3 (FAD3) of flaxseed protein

Flaxseed (Linum usitatissimum), commonly known as linseed is an oilseed crop, emerging as an important and functional ingredient of food and has been paid more attention due to its nutritional value as well as beneficial effects. It is mainly rich in is α-linolenic acid (ALA, omega-3 fatty acid), fibres and lignans that have potential health benefits in reducing cardiovascular diseases, diabetes, osteoporosis, atherosclerosis, cancer, arthritis, neurological and autoimmune disorders. Due to its richness in omega-3 fatty acid, a group of enzymes known as fatty acid desaturases (FADs) mainly introduce double bonds into fatty acids’ (FAs) hydrocarbon chains that produce unsaturated fatty acids. Fatty acid desaturase 3 (FAD3), the commonest microsomal enzyme of omega-3 fatty acid, synthesizes linolenic acid (C18:3) from linoleic acid located in endoplasmic reticulum (ER) facing towards the cytosol. The emerging field of bioinformatics and large number of databases of bioactive peptides, helps in providing time-saving and efficient method for identification of potential bioactivities of any protein. In this study, 10 unique sequences of FAD3 from flaxseed protein have been used for in silico proteolysis and releasing of various bioactive peptides using three plant proteases, namely ficin, papain and stem bromelain, that are evaluated with the help of BIOPEP database. Overall, 20 biological activities were identified from these proteins. The results showed that FAD3 protein is a potential source of peptides with angiotensin-I-converting enzyme (ACE) inhibitory and dipeptidyl peptidase-IV (DPP-IV) activities, and also various parameters such as ∑A, ∑B, A_E, W, B_E, V and DHt were also calculated. Furthermore, PeptideRanker have been used for screening of novel promising bioactive peptides. Various bioinformatics tools also used to study protein’s physicochemical properties, peptide’s score, toxicity, allergenicity aggregation, water solubility, and drug likeliness. The present work suggests that flaxseed protein can be a good source of bioactive peptides for the synthesis of good quality and quantity of oil, and in silico method helps in investigating and production of functional peptides.

The Effect of pH and Storage Temperature on the Stability of Emulsions Stabilized by Rapeseed Proteins

Rapeseed press cake (RPC), the by-product of rapeseed oil production, contains proteins with emulsifying properties, which can be used in food applications. Proteins from industrially produced RPC were extracted at pH 10.5 and precipitated at pH 3 (RPP3) and 6.5 (RPP6.5). Emulsions were formulated at three different pHs (pH 3, 4.5, and 6) with soy lecithin as control, and were stored for six months at either 4 °C or 30 °C. Zeta potential and droplet size distribution were analyzed prior to incubation, and emulsion stability was assessed over time by a Turbiscan instrument. Soy lecithin had significantly larger zeta potential (−49 mV to 66 mV) than rapeseed protein (−19 mV to 20 mV). Rapeseed protein stabilized emulsions with smaller droplets at pH close to neutral, whereas soy lecithin was more efficient at lower pHs. Emulsions stabilized by rapeseed protein had higher stability during storage compared to emulsions prepared by soy lecithin. Precipitation pH during the protein extraction process had a strong impact on the emulsion stability. RPP3 stabilized emulsions with higher stability in pHs close to neutral, whereas the opposite was found for RPP6.5, which stabilized more stable emulsions in acidic conditions. Rapeseed proteins recovered from cold-pressed RPC could be a suitable natural emulsifier and precipitation pH can be used to monitor the stability in emulsions with different pHs.

Comparison of the Oil Quality of Light and Dark Walnuts under Different Storage Conditions

The skin of the walnut kernels can get dark during the pre- and post-harvest stages of the production. Dark kernels are less palatable for most consumers but are still edible and maybe preferable, especially in the ground form, for industrial use. In this study, we investigated the differences between oil oxidation indexes, fatty acid and tocopherol compositions of the oils, total polyphenol contents and antioxidant capacities of the extracts of light and dark walnuts. In addition, we evaluated the effects of packaging under nitrogen and vacuum-packaging techniques and storage temperature on these characteristics of both light and dark walnuts during storage for 6 months. Peroxide values and free fatty acid contents of all samples were higher at the end of storage compared to initial values, being more noticeable at 20°C than at 4°C. Increases in the free fatty acid contents were quite higher in dark walnuts than the light ones (6.1 and 3.1 fold, respectively) and the highest values of conjugated diene and peroxide were determined in the samples packaged under air and stored at 20℃. Dark walnuts had lower total phenolic, α- and γ-tocopherol contents and antioxidant activities compared to the light ones. Total phenolic and tocopherol contents decreased over time. We conclude that due to the antioxidant compounds in the fruit, oxidation parameters of dark walnuts are still acceptable at the end of 6-month storage even in the packages with air and at non-refrigerated conditions.

In situ nanomechanical properties of natural oil bodies studied using atomic force microscopy

Natural oil bodies (OBs) from plant organs represent an important category of functional ingredients and materials in a variety of industrial sectors. Their applications are closely related to the membrane mechanical properties on a single droplet level, which remain difficult to determine. In this research, the mechanical properties of the membranes of OBs from soybean, sesame, and peanut were investigated in-situ by atomic force microscopy (AFM). Different regions of the force-deformation curves obtained during compression were analyzed to extract the stiffness Kb or Young's modulus of the OB membranes using Hooke's law, Reissner theory, and the elastic membrane theory. At higher strains (ε = 0.15-0.20), the elastic membrane theory breaks down. We propose an extension of the theory that includes a contribution to the force from interfacial tension based on the Gibbs energy, allowing effective determination of Young's modulus and interfacial tension of the OB membranes in the water environment simultaneously. The mechanical properties of the OBs of different sizes and species, as well as a comparison with other phospholipid membrane materials, are discussed and related to their membrane compositions and structures. It was found that the natural OBs are soft droplets but do not rupture and can fully recover following compressive strains as large as 0.3. The OBs with higher protein/oil ratio, have smaller size and stronger mechanical properties, and thus are more stable. The low interfacial tension due to the existence of phospholipid-protein membrane also contributes to the stability of the OBs. This is the first report measuring the mechanical properties of OB membranes in-situ directly.

The effect of monovalent (Na+, K+) and divalent (Ca2+, Mg2+) cations on rapeseed oleosome (oil body) extraction and stability at pH 7

Oleosomes are storage vehicles of TAGs in plant seeds. They are protected with a phospholipid-protein monolayer and extracted with alkaline aqueous media; however, pH adjustment intensifies the extraction process. Therefore, the aim of this work was to investigate the extraction mechanism of rapeseed oleosomes at pH 7 and at the presence of monovalent and divalent cations (Na⁺, K⁺, Mg²⁺_, and Ca⁺²). The oleosome yield at pH 9.5 was 64 wt%, while the yield at pH 7 with H₂O was just 43 wt.%. The presence of cations at pH 7, significantly enhanced the yield, with K⁺ giving the highest yield (64 wt.%). The cations affected the oleosome interface and their interactions. The presence of monovalent cations resulted in aggregation and minor coalescence, while divalent cations resulted in extensive coalescence. These results help to understand the interactions of oleosomes in their native matrix and design simple extraction processes at neutral conditions.

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.

Improving the Stability of Oil Body Emulsions from Diverse Plant Seeds Using Sodium Alginate

In this study, peanut, sesame, and rapeseed oil bodies (OBs) were extracted by the aqueous medium method. The surface protein composition, microstructure, average particle size d 4 ,   3 , ζ-potential of the extracted OBs in aqueous emulsion were characterized. The stability of the OB emulsions was investigated. It was found that different OB emulsions contained different types and contents of endogenous and exogenous proteins. Aggregation at low pHs (<6) and creaming at high pHs (7 and 8) both occurred for all of three OB emulsions. Sodium alginate (ALG) was used to solve the instability of OB emulsions under different conditions-low concentration of ALG improved the stability of OB emulsions below and near the isoelectric point of the OBs, through electrostatic interaction. While a high concentration of ALG improved the OB emulsion stability through the viscosity effect at pH 7. The OB emulsions stabilized by ALG were salt-tolerant and freeze-thaw resistant.

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.

Effect of pH on physicochemical properties of oil bodies from different oil crops

The objective of this study was to determine the effects of pH on the physicochemical properties of soybean oil bodies (SBOBs), peanut oil bodies (PNOBs) and sunflower oil bodies (SFOBs). The mean particle diameter_[4,3] (D_[4,3]) of oil bodies (OBs) changed to a stationary trend with increased pH. The surface hydrophobicity (H₀) of SBOBs, PNOBs and SFOBs significantly decreased with increasing pH 2-12. The emulsifying activity index of SBOBs, PNOBs and SFOBs decreased with increased pH from 2 to 10. The viscosity modulus (G″) value of SBOBs at pH 4 was significantly higher than at pH 7 and pH 9. The initial elastic modulus (G') and G″ values of PNOBs at pH 9 were significantly higher than at pH 4 and pH 7. The G″ values of SFOBs at pH 4 and pH 9 were significantly lower than at pH 7. The steroleosin protein bands of SBOBs significantly decreased at pH 12. The protein bands of PNOBs were reduced at pH 2-4 and pH 10-12, and protein bands decreased most obviously at pH 2. The enthalpy of denaturation (ΔH) values of the oil body (OB) protein at pH 9 were significantly higher than at pH 4 and pH 7. The results showed that the ζ-potential, D_[4,3], emulsifying property and H₀ of SBOBs, PNOBs and SFOBs were similar to the change of pH value. The three types of OBs have better stability away from the isoelectric point.

Lauric Acid-Modified Nitraria Seed Meal Composite as Green Carrier Material for Pesticide Controlled Release

To alleviate the adverse effects of pesticide residues on the environment, development of a more safe, economical, and reliable usage approach of pesticides is critically urgent. In the present study, a novel pesticide carrier LA-NSM (lauric acid-modified Nitraria seed meal) with controlled release property was prepared through grafting esterification of lauric acid onto Nitraria seed meal substrates. The structure of the obtained samples was characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, and contact angle measurements. The results indicated that LA-NSM products had a well-defined hydrophobic surface and irregular holes for efficient loading of pesticide molecules. Deltamethrin (DEL), a representative insoluble pyrethroid insecticide in water, was deliberately selected as the index pesticide to evaluate the loading and releasing efficiency of LA-NSM. The loading capacity of LA-NSM for DEL can reach about 1068 mg/g. pH, humidity of soil, and temperature had a significant influence on controlled release performance of LA-NSM@DEL. Moreover, the releasing kinetics of LA-NSM@DEL composites could be fitted well with the Higuchi model. Overall, the highly hydrophobic property, excellent loading, and controlled release ability of LA-NSM made it a promising candidate in agricultural applications.

Genome sequence of Jatropha curcas L., a non-edible biodiesel plant, provides a resource to improve seed-related traits

Jatropha curcas (physic nut), a non-edible oilseed crop, represents one of the most promising alternative energy sources due to its high seed oil content, rapid growth and adaptability to various environments. We report ~339 Mbp draft whole genome sequence of J. curcas var. Chai Nat using both the PacBio and Illumina sequencing platforms. We identified and categorized differentially expressed genes related to biosynthesis of lipid and toxic compound among four stages of seed development. Triacylglycerol (TAG), the major component of seed storage oil, is mainly synthesized by phospholipid:diacylglycerol acyltransferase in Jatropha, and continuous high expression of homologs of oleosin over seed development contributes to accumulation of high level of oil in kernels by preventing the breakdown of TAG. A physical cluster of genes for diterpenoid biosynthetic enzymes, including casbene synthases highly responsible for a toxic compound, phorbol ester, in seed cake, was syntenically highly conserved between Jatropha and castor bean. Transcriptomic analysis of female and male flowers revealed the up-regulation of a dozen family of TFs in female flower. Additionally, we constructed a robust species tree enabling estimation of divergence times among nine Jatropha species and five commercial crops in Malpighiales order. Our results will help researchers and breeders increase energy efficiency of this important oil seed crop by improving yield and oil content, and eliminating toxic compound in seed cake for animal feed.