Simple extraction method of non-allergenic intact soybean oil bodies that are thermally stable in an aqueous medium

Soybean P34 Probable Thiol Protease Probably Has Proteolytic Activity on Oleosins

P34 probable thiol protease (P34) and Gly m Bd 30K (30K) show high relationship with the protease of 24 kDa oleosin of soybean oil bodies. In this study, 9 day germinated soybean was used to separate bioprocessed P34 (P32) from bioprocessed 30K (28K). Interestingly, P32 existed as dimer, whereas 28K existed as monomer; a P32-rich sample had proteolytic activity and high cleavage site specificity (Lys-Thr of 24 kDa oleosin), whereas a 28K-rich sample showed low proteolytic activity; the P32-rich sample contained one thiol protease. After mixing with purified oil bodies, all P32 dimers were dissociated and bound to 24 kDa oleosins to form P32-24 kDa oleosin complexes. By incubation, 24 kDa oleosin was preferentially hydrolyzed, and two hydrolyzed products (HPs; 17 and 7 kDa) were confirmed. After most of 24 kDa oleosin was hydrolyzed, some P32 existed as dimer, and the other as P32-17 kDa HP. It was suggested that P32 was the protease.

Solubility of soy lipophilic proteins: comparison with other soy protein fractions

Solubility of soy lipophilic proteins (LP) was studied as compared with that of other soy protein fractions. LP, β-conglycinin, glycinin, and soy protein isolate (N-SPI) were prepared under the condition to avoid heat denaturation. Solubility of LP was lower than that of other soy protein fractions under all the tested conditions varying in pH values and ionic strength. The solubility of LP was increased constantly by elevating temperature until 90 °C, whereas that of β-conglycinin and glycinin dropped at high temperature. Temperature-dependent change in solubility of N-SPI might reflect the balance among that of glycinin, β-conglycinin and LP. Based on the results of SDS-PAGE, determination of phospholipid content and Fourier Transform Infrared spectroscopy, we discussed the solubilization behavior of LP relating to its origin and composition.

Coagulation and rheological behaviors of soy milk colloidal dispersions

Coagulation and rheological behaviors of soy milk are reviewed from the viewpoint of colloidal dispersion system. From the results of relative viscosity in the range of small oil body volume fractions, oil bodies containing oleosin behave as rigid spheres. The Krieger-Dougherty equation was found to describe relative viscosities well under high oil body volume fraction. These results indicate that oil bodies in soy milk behave as though suspended matter. Cross-linking between colloid particles occurs when the coagulant is added, and bulky clusters are formed. The viscosity rises due to the hydrodynamic effects of these bulky clusters. A new viscosity equation that combines the Krieger-Dougherty equation and the effective volume fraction could describe the viscos behavior well for wide range of solid contents. Tofu is made by adding a coagulant to soy milk. For lipid concentrations of less than 2%, rupture stress increases depending on the lipid concentration, whereas at concentrations of more than 3%, rupture stress tends to decline. Kinugoshi tofu samples have a maximum value for rupture stress depending on lipid concentration. Digestion of oleosin in high-fat soy milk using papain treatment results in the centrifugal separation of soy milk cream easily. This result indicates that oleosin let oil bodies in soy milk stable. Therefore, it is important to control the state of soy milk colloidal dispersions.

Label-free in situ imaging of oil body dynamics and chemistry in germination

Plant oleosomes are uniquely emulsified lipid reservoirs that serve as the primary energy source during seed germination. These oil bodies undergo significant changes regarding their size, composition and structure during normal seedling development; however, a detailed characterization of these oil body dynamics, which critically affect oil body extractability and nutritional value, has remained challenging because of a limited ability to monitor oil body location and composition during germination in situ Here, we demonstrate via in situ, label-free imaging that oil bodies are highly dynamic intracellular organelles that are morphologically and biochemically remodelled extensively during germination. Label-free, coherent Raman microscopy (CRM) combined with bulk biochemical measurements revealed the temporal and spatial regulation of oil bodies in native soya bean cotyledons during the first eight days of germination. Oil bodies undergo a cycle of growth and shrinkage that is paralleled by lipid and protein compositional changes. Specifically, the total protein concentration associated with oil bodies increases in the first phase of germination and subsequently decreases. Lipids contained within the oil bodies change in saturation and chain length during germination. Our results show that CRM is a well-suited platform to monitor in situ lipid dynamics and local chemistry and that oil bodies are actively remodelled during germination. This underscores the dynamic role of lipid reservoirs in plant development.

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 characterization of soybean oil body integral oleosin isoforms and the effects of alkaline pH on them

Oil body, an organelle in seed cell (naturally pre-emulsified oil), has great potentials to be used in food, cosmetics, pharmaceutical and other applications requiring stable oil-in-water emulsions. Researchers have tried to extract oil body by alkaline buffers, which are beneficial for removing contaminated proteins. But it is not clear whether alkaline buffers could remove oil body integral proteins (mainly oleosins), which could keep oil body integrity and stability. In this study, seven oleosin isoforms were identified for soybean oil body (three isoforms, 24 kDa; three isoforms, 18 kDa; one isoform, 16kDa). Oleosins were not glycoproteins and 24 kDa oleosin isoforms possessed less thiol groups than 18 kDa ones. It was found that alkaline pH not only removed contaminated proteins but also oleosins, and more and more oleosins were removed with increasing alkaline pH.

Development of a novel strategy to isolate lipophilic allergens (oleosins) from peanuts

Background

Peanut allergy is one of the most severe class I food allergies with increasing prevalence. Especially lipophilic allergens, such as oleosins, were found to be associated with severe symptoms, but are usually underrepresented in diagnostic extracts. Therefore, this study focused on isolation, molecular characterization and assessment of the allergenicity of peanut oleosins.

Methods and Results

A comprehensive method adapted for the isolation of peanut oil bodies of high purity was developed comprising a stepwise removal of seed storage proteins from oil bodies. Further separation of the oil body constituents, including the allergens Ara h 10, Ara h 11, the presumed allergen oleosin 3 and additional oleosin variants was achieved by a single run on a preparative electrophoresis cell. Protein identification realized by N-terminal sequencing, peptide mass fingerprinting and homology search revealed the presence of oleosins, steroleosins and a caleosin. Immunoblot analysis with sera of peanut-allergic individuals illustrated the IgE-binding capacity of peanut-derived oleosins.

Conclusion

Our method is a novel way to isolate all known immunologically distinct peanut oleosins simultaneously. Moreover, we were able to provide evidence for the allergenicity of oleosins and thus identified peanut oleosins as probable candidates for component-resolved allergy diagnosis.

Oleosins (24 and 18 kDa) are hydrolyzed not only in extracted soybean oil bodies but also in soybean germination

After oil bodies (OBs) were extracted from ungerminated soybean by pH 6.8 extraction, it was found that 24 and 18 kDa oleosins were hydrolyzed in the extracted OBs, which contained many OB extrinsic proteins (i.e., lipoxygenase, β-conglycinin, γ-conglycinin, β-amylase, glycinin, Gly m Bd 30K (Bd 30K), and P34 probable thiol protease (P34)) as well as OB intrinsic proteins. In this study, some properties (specificity, optimal pH and temperature) of the proteases of 24 and 18 kDa oleosins and the oleosin hydrolysis in soybean germination were examined, and the high relationship between Bd 30K/P34 and the proteases was also discussed. The results showed (1) the proteases were OB extrinsic proteins, which had high specificity to hydrolyze 24 and 18 kDa oleosins, and cleaved the specific peptide bonds to form limited hydrolyzed products; (2) 24 and 18 kDa oleosins were not hydrolyzed in the absence of Bd 30K and P34 (or some Tricine-SDS-PAGE undetectable proteins); (3) the protease of 24 kDa oleosin had strong resistance to alkaline pH while that of 18 kDa oleosin had weak resistance to alkaline pH, and Bd 30K and P34, resolved into two spots on two-dimensional electrophoresis gel, also showed the same trend; (4) 16 kDa oleosin as well as 24 and 18 kDa oleosins were hydrolyzed in soybean germination, and Bd 30K and P34 were always contained in the extracted OBs from germinated soybean even when all oleosins were hydrolyzed; (5) the optimal temperature and pH of the proteases were respectively determined as in the ranges of 35-50 °C and pH 6.0-6.5, while 60 °C or pH 11.0 could denature them.

Composition, properties and potential food applications of natural emulsions and cream materials based on oil bodies

Oil bodies are micron- or submicron-sized organelles found mainly in parts of plants such as seeds, nuts or some fruits and their main role is to function as energy stores.

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.

The integral and extrinsic bioactive proteins in the aqueous extracted soybean oil bodies

Soybean oil bodies (OBs), naturally pre-emulsified soybean oil, have been examined by many researchers owing to their great potential utilizations in food, cosmetics, pharmaceutical, and other applications requiring stable oil-in-water emulsions. This study was the first time to confirm that lectin, Gly m Bd 28K (Bd 28K, one soybean allergenic protein), Kunitz trypsin inhibitor (KTI), and Bowman-Birk inhibitor (BBI) were not contained in the extracted soybean OBs even by neutral pH aqueous extraction. It was clarified that the well-known Gly m Bd 30K (Bd 30K), another soybean allergenic protein, was strongly bound to soybean OBs through a disulfide bond with 24 kDa oleosin. One steroleosin isoform (41 kDa) and two caleosin isoforms (27 kDa, 29 kDa), the integral bioactive proteins, were confirmed for the first time in soybean OBs, and a considerable amount of calcium, necessary for the biological activities of caleosin, was strongly bound to OBs. Unexpectedly, it was found that 24 kDa and 18 kDa oleosins could be hydrolyzed by an unknown soybean endoprotease in the extracted soybean OBs, which might give some hints for improving the enzyme-assisted aqueous extraction processing of soybean free oil.

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.

In vitro assessment of the bioaccessibility of fatty acids and tocopherol from soybean oil body emulsions stabilized with ι-carrageenan

The present investigation aimed to expand the knowledge of the in vitro bioaccessibility of fatty acids and tocopherol from natural soybean oil body emulsions stabilized with different concentrations of ι-carrageenan. Several physicochemical parameters including proteolysis of the interfacial layer, interfacial composition, and microstructure were evaluated with regard to their impact on the bioaccessibility of fatty acids and tocopherol. Results from simulated human digestion in vitro indicated that the bioaccessibility of total fatty acids and tocopherol decreased (62.7-8.3 and 59.7-19.4%, respectively) with the increasing concentration of ι-carrageenan. During the in vitro digestion procedure, ι-carrageenan affected physicochemical properties of the emulsions, thereby controlling the release of fatty acids and tocopherol. These results suggested that soybean oil body emulsions stabilized with ι-carrageenan could provide natural emulsions in foods that were digested at a relatively slow rate, the important physiological consequence of which might be increasing satiety.

Soy milk oleosome behaviour at the air-water interface

Soy milk is a highly stable emulsion mainly due to the presence of oleosomes, which are oil bodies and function as lipid storage organelles in plants, e.g., in seeds. Oleosomes are micelle-like structures with an outer phospholipid monolayer, an interior filled with triacylglycerides (TAGs), and oleosins anchored hairpin-like into the structure with their hydrophilic parts remaining outside the oleosomes, completely covering their surface (K. Hsieh and A. H. C. Huang, Plant Physiol., 2004, 136, 3427-3434). Oleosins are alkaline proteins of 15-26 kDa (K. Hsieh and A. H. C. Huang, Plant Physiol., 2004, 136, 3427-3434) which are expressed during seed development and maturation and play a major role in the stability of oil bodies. Additionally, the oil bodies of seeds seem to have the highest impact on coalescence, probably due to the required protection against environmental stress during dormancy and germination compared to, e.g., vertebrates' lipoproteins. Surface pressure investigations and Brewster angle microscopy of oleosomes purified from raw soy milk were executed to reveal their diffusion to the air-water interface, rupture, adsorption and structural modification over time at different subphase conditions. Destroying the surface portions of the oleosins by tryptic digestion induced coalescence of oleosomes (J. Tzen and A. Huang, J. Cell. Biol., 1992, 117, 327-335) and revealed severe changes in their adsorption kinetics. Such investigations will help to determine the effects behind oleosome stability and are necessary for a better understanding of the principal function of oleosins and their interactions with phospholipids.

Process improvement for semipurified oleosomes on a pilot-plant scale

Semipurified oleosomes were isolated on a pilot-plant scale using improved-process extraction conditions. The improved process consisted of continuous centrifugation in a three-phase decanter with recirculation of slurry until most of the oleosomes were recovered. Oleosome fractionation, oleosin identification, and isoflavone and saponin mass distributions and recoveries were investigated. The improved pilot-plant oleosome extraction process was achieved in 8 h. A total of 91%± 1% of soybean oil was recovered as intact oleosomes. The oil content of the aqueous supernatant and the residue fractions were low at 2% and 3%, respectively. The aqueous supernatant fraction contained 40% total soybean protein. About 76% of the proteins present in the oleosome fraction were soybean storage proteins. Washing the semipurified oleosomes with a 0.1 M Tris-HCl, pH 8.6 containing 0.4 M sucrose, and 0.5 M NaCl resulted in the recovery of the associated storage proteins. The recovery of these proteins in addition to the protein in aqueous supernatant accounted for 79% of the total soybean storage proteins fractionated by this process. Oleosins were detected at 17 and 18 kDa. Isoflavones and saponins partitioned into the oleosome, aqueous supernatant, and residue fractions at different ratios with the majority, about 82 and 63 mole%, respectively, in oleosome and aqueous supernatant fractions, making these fractions an attractive source for phytochemicals.