Influence of interfacial properties/structure on oxygen diffusion in oil-in-water emulsions.

Oxygen diffusion played an important role in the lipid oxidation of food emulsions. In this study, a simple method was developed to quantitatively observe the oxygen diffusion in the oil-water biphasic system, and it was further applied to investigate the relationship between the oxygen diffusion and lipid oxidation in O/W emulsions. Various factors that related to the emulsion oxidation were considered, from their influence on the oxygen diffusion and lipid oxidation in the emulsions. Results showed that there was obvious correlation between the oxygen diffusion and lipid oxidation in O/W emulsions, which reveals the inhibition of oxygen diffusion could apparently slow down the lipid oxidation. Moreover, the changes of oil phase, water phase and interfacial layer of the emulsions, which were related to the oxygen diffusion, could improve the oxidative stability of the emulsions effectively. Our findings are helpful for deep understanding the mechanisms of the lipid oxidation in food emulsions.

Formation and application of edible oleogels prepared by dispersing soy fiber particles in oil phase.

Oleogels containing less saturated and trans-fats were considered as an ideal option to replace the solid fats in foods. In this research, oleogel was fabricated by dispersing soy fiber particles (SFP) in soy oil, and further it was used in bread preparation. Effect of the particle size, particle content and the second fluid content on the formation of oleogels were evaluated, based on the appearance and rheological properties. Results showed that the suspension of SFP in soy oil (24%, w/w) could be transformed into gel-like state, upon the addition of the second fluid. The SFP based networks were dominated by the capillary force which was originated from the second fluid. The rheological properties and yield stress of the oleogels could be modulated by particle size and particle content of SFP in oil phase, as well as the second fluid content in the system. When the oleogels were applicated in bread preparation, a layered structure could be formed in the bread, indicating the possibility of replacing the solid fats in bakery products by our oleogels. Our results offered a feasibility approach for oil structuring with natural raw materials, and developed a new approach to replace the solid fats in foods.

Fibrillization kinetics and rheological properties of panda bean (Vigna umbellata (Thunb.) Ohwi et Ohashi) protein isolate at pH 2.0.

Recently, research interests are growing regarding the formation and mechanisms of amyloid fibrils from plant proteins. This study investigated the fibrillization kinetics and rheological behaviors of panda bean protein isolate (PBPI) at pH 2.0 and 90 °C for various heating times (0-24 h). Results showed that PBPI formed two distinct classes of fibrils after heating for 10 h, including flexible fibril with a contour length of ∼751 nm, and rigid fibril with periodicity of ∼40 nm. The secondary structural changes during fibril formation were monitored by circular dichroism spectroscopy and indicated that ß-sheet content increased first (0-12 h) and then decreased (>12 h), which coincided with similar changes in thioflavin T fluorescence. The gel electrophoresis revealed that the polypeptides of PBPI were progressively hydrolyzed upon heating, and the resulting short fragments were involved in fibril formation rather than PBPI monomer. PBPI-derived fibrils showed extremely high viscosity and storage modulus. A plausible molecular mechanism for PBPI fibrillation process was hypothesized, including protein unfolding, hydrolysis, assembly into matured fibrils, and dissociation of the fibrils. The findings provide useful information to manipulate the formation of legume proteins-based fibrils and will benefit future research to explore their potential applications.

Advances in Bioactivity of MicroRNAs of Plant-Derived Exosome-Like Nanoparticles and Milk-Derived Extracellular Vesicles.

MicroRNA (miRNA) is a class of small noncoding RNA involved in physiological and pathological processes via the regulation of gene expression. Naked miRNAs are unstable and liable to degradation by RNases. Exosome-like nanoparticles (ELNs) secreted by plants and extracellular vesicles (EVs) found in milk are abundant in miRNAs, which can be carried by ELNs and EVs to target cells to exert their bioactivities. In this review, we describe the current understanding of miRNAs in plant ELNs and milk EVs, summarize their important roles in regulation of inflammation, intestinal barrier, tumors, and infantile immunological functions, and also discuss the adverse effect of EV miRNAs on human health. Additionally, we prospect recent challenges centered around ELN and EV miRNAs for interventional applications and provide insights of grain-derived ELNs and miRNAs interventional use in human health. Overall, plant ELNs and milk EVs can transfer miRNAs to mitigate the pathological status of recipient cells by mediating the expression of target genes but may also exert some side effects. More studies are required to elucidate the in-depth understanding of potential interventional effects of ELN and EV miRNAs on human health.

Evolution of physicochemical and antioxidant properties of whey protein isolate during fibrillization process.

Whey protein isolate (WPI) fibrils have great potential for applications in future food manufacture due to their improved properties. However, the evolution of their properties during fibrillization is still not fully understood. Here, we investigate variational characteristics of WPI fibrils during formation process. WPI fibrils with a semiflexible and linear structure were formed and showed high aspect ratio after heat treatment. The conversion, fluorescence intensity and isoelectric point of WPI were increased with heating time. Moreover, the antioxidant activity of WPI was improved after fibrillization and was dependent on heating time. This could be attributed to the structure transformation of protein and the exposed amino acids with sulfur groups or aromatic side chains in the fibrillated system. Our findings move a step forward for a detailed understanding on the dynamical changes of WPI properties during fibrillization, which would provide a guidance for WPI fibril applications and future food technology development.

Prolamin-based complexes: Structure design and food-related applications.

Prolamins are a group of safe food additives that are biocompatible, biodegradable, and sustainable. Zein, gliadin, kafirin, and hordein are common prolamins that have been extensively studied, particularly as these form colloidal particles because of their amphiphilic properties. Prolamin-based binary/ternary complexes, which have stable physicochemical properties and superior functionality, are formed by combining prolamins with polysaccharides, polyphenols, water-soluble proteins, and surfactants. Although the combination of prolamins with other components has received attention, the relationship between the structural design of prolamin-based complexes and their functionalities remains uncertain. This review discusses the production methods of prolamin-based complexes, the factors influencing their structural characteristics, and their applications in the food industry. Further studies are needed to elucidate the structure-function relationships between prolamins and other biopolymers, as well as the toxicological effects of these complexes in food.

Interfacial behaviour of ß-lactoglobulin aggregates at the oil-water interface studied using particle tracking and dilatational rheology.

During processing, proteins are easily self-assembled into different aggregates, such as nanoparticles and fibrils. Protein aggregates exhibit a strong interfacial activity due to their morphologies and functional groups on the surface. Their interfacial structure and rheological properties at the oil-water interface have a significant effect on the stability and fat digestion of emulsions in food. In this study, ß-lactoglobulin (ß-lg) aggregates including ß-lg nanoparticles (ß-lg NP) and ß-lg fibrils (ß-lg F) were prepared in solution by controlling the heating temperature and pH, and their surface properties including the electric potential, hydrophobicity, and density of free thiol groups were characterized. The adsorption kinetics, interfacial rheology, and displacement by bile salts (BSs) of native ß-lg and its aggregates at the oil (decane)/water interfaces were studied using particle tracking microrheology and dilatational rheology. From the movement of tracer particles at the interface, ß-lg NP and ß-lg F were found to adsorb faster than native ß-lg, and they were found to form interfacial films with a marginally higher elasticity. During the process of protein adsorption, the films of ß-lg and its aggregates are not uniform. In the process of protein displacement, ß-lg NP has the strongest ability while native ß-lg has the weakest ability to resist BS substitution, which is consistent with the results from in vitro digestion experiments. The present study reveals the microrheological behaviour of protein aggregates at the oil-water interface and demonstrates that ß-lg thermal aggregates exhibit an excellent emulsification ability and can be used to control fat digestion. The study also illustrates the applicability of microrheological methods to the study of interfacial rheology and its complementarity with dilatational rheological methods.

Molar mass effect in food and health.

It is demanded to supply foods with good quality for all the humans. With the advent of aging society, palatable and healthy foods are required to improve the quality of life and reduce the burden of finance for medical expenditure. Food hydrocolloids can contribute to this demand by versatile functions such as thickening, gelling, stabilising, and emulsifying, controlling texture and flavour release in food processing. Molar mass effects on viscosity and diffusion in liquid foods, and on mechanical and other physical properties of solid and semi-solid foods and films are overviewed. In these functions, the molar mass is one of the key factors, and therefore, the effects of molar mass on various health problems related to noncommunicable diseases or symptoms such as cancer, hyperlipidemia, hyperglycemia, constipation, high blood pressure, knee pain, osteoporosis, cystic fibrosis and dysphagia are described. Understanding these problems only from the viewpoint of molar mass is limited since other structural characteristics, conformation, branching, blockiness in copolymers such as pectin and alginate, degree of substitution as well as the position of the substituents are sometimes the determining factor rather than the molar mass. Nevertheless, comparison of different behaviours and functions in different polymers from the viewpoint of molar mass is expected to be useful to find a common characteristics, which may be helpful to understand the mechanism in other problems.

Novel strategy for enhancing the color intensity of ß-Carotene: Enriching onto the oil-water interface.

A novel strategy to enhance the color intensity of ß-carotene (BC), namely, "interfacial enriching", was developed in this work. As the sole emulsifier in W/O emulsion, BC particles were enriched onto the droplet surface through emulsifying process. By increasing the concentration of BC in oil phase from 1 mg/g to 5 mg/g, the average droplet size of the emulsion decreased from 92.2 ± 5.1 µm to 34.0 ± 5.4 µm. Too low (e.g. ≤ 1 mg/g) or too high (e.g. ≥25 mg/g) concentration of BC in the oil phase yielded an insufficient coverage or flocculation of the droplets. By enriching onto the interface, the color intensity of BC were enhanced apparently at the reflectance wavelength ranging from 500 nm to 700 nm, compared with that of the BC encapsulated within the emulsion droplets. This enhancement was due to the higher availability of incident light for the BC particles on the interface than that of the BC particles buried inside the droplets.

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.

Nanochemoprevention with therapeutic benefits: An updated review focused on epigallocatechin gallate delivery.

Epigallocatechin gallate (EGCG) is a natural phenolic compound found in many plants, especially in green tea, which is a popular and restorative beverage with many claimed health benefits such as antioxidant, anti-cancer, anti-microbial, anti-diabetic, and anti-obesity activities. Despite its great curative potential, the poor bioavailability of EGCG restricts its clinical applcation. However, nanoformulations of EGCG are emerging as new alternatives to traditional formulations. This review focuses on the nanochemopreventive applications of various EGCG nanoparticles such as lipid-based, polymer-based, carbohydrate-based, protein-based, and metal-based nanoparticles. EGCG hybridized with these nanocarriers is capable of achieving advanced functions such as targeted release, active targeting, and enhanced penetration, ultimately increasing the bioavailability of EGCG. In addition, this review also summarizes the challenges for the use of EGCG in therapeutic applications, and suggests future directions for progress.

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.

Effect of sodium alginate on the stability of natural soybean oil body emulsions.

In this work, the influence of an anionic polysaccharide, sodium alginate (ALG), on the stability of soybean oil body (OB) emulsions under different environmental conditions, including NaCl, pH and freeze-thaw cycling, was studied by analyzing the particle electric charge, particle size and distribution, and using optical and fluorescence microscopy. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the proteins on the surface of oil bodies were mainly oleosins. It was found that ALG can be adsorbed to the surface of oil bodies by strong electrostatic interactions at pH 4.5 and the optimal concentration of ALG was 0.35 wt% for 1 wt% OB emulsions. At pH 4-8, ALG-coated OB emulsions were more stable than uncoated OB emulsions with smaller particle size and more uniform size distribution due to the interaction between OB and ALG. The ALG-coated OB emulsions were also all stable against NaCl within the concentration range of 0-250 mM at pH 7 while uncoated OB emulsions aggregated gradually with the increase of NaCl concentration. For OB emulsions with higher concentration of 10-40 wt% which are frequently used in the food industry, the minimal concentration of ALG required to make stable emulsions was found to be 0.5-1 wt%, correspondingly. Coating oil bodies with ALG also significantly improved the stability of natural oil body emulsions against freeze-thaw cycling, which is of great significance to the further development of natural oil body-based products in food industry.

Stability and Oil Migration of Oil-in-Water Emulsions Emulsified by Phase-Separating Biopolymer Mixtures.

Oil-in-water (O/W) emulsions with varying concentration of oil phase, medium-chain triglyceride (MCT), were prepared using phase-separating gum arabic (GA)/sugar beet pectin (SBP) mixture as an emulsifier. Stability of the emulsions including emulsion phase separation, droplet size change, and oil migration were investigated by means of visual observation, droplet size analysis, oil partition analysis, backscattering of light, and interfacial tension measurement. It was found that in the emulsions prepared with 4.0% GA/1.0% SBP, when the concentration of MCT was greater than 2.0%, emulsion phase separation was not observed and the emulsions were stable with droplet size unchanged during storage. This result proves the emulsification ability of phase-separating biopolymer mixtures and their potential usage as emulsifiers to prepare O/W emulsion. However, when the concentration of MCT was equal or less than 2.0%, emulsion phase separation occurred after preparation resulting in an upper SBP-rich phase and a lower GA-rich phase. The droplet size increased in the upper phase whereas decreased slightly in the lower phase with time, compared to the freshly prepared emulsions. During storage, the oil droplets exhibited a complex migration process: first moving to the SBP-rich phase, then to the GA-rich phase and finally gathering at the interface between the two phases. The mechanisms of the emulsion stability and oil migration in the phase-separated emulsions were discussed.

Thermosensitive injectable in-situ forming carboxymethyl chitin hydrogel for three-dimensional cell culture.

Injectable hydrogels have gained great attentions for cell therapy and tissue regeneration as a result of the applications in minimally invasive surgical procedures with the ease of handling and complete filling of the defect area. Here, a novel biodegradable, thermosensitive and injectable carboxymethyl chitin (CMCH) hydrogel was developed for three-dimensional (3D) cell culture. The obtained CMCH solution remained transparent liquid flowing easily at low temperatures and gelled rapidly at 37°C. The gelation time of CMCH hydrogels could be easily tuned by varying temperature and the degree of carboxymethylation, which facilitates the cell encapsulation process at room temperature and in-situ forming hydrogel at body temperature. Moreover, the CMCH-14 hydrogels in PBS buffer remained stable and continuous porous structure and could be degraded in the presence of lysozyme or hyaluronidase. HeLa cells proliferated sustainably and self-assembled to form 3D multicellular spheroids with high cell activity on the surface of CMCH-14 hydrogel. Encapsulation of COS-7 cells within the in-situ forming CMCH hydrogel demonstrated that CMCH hydrogels promoted cell survival and proliferation. In vivo mouse study of the CMCH hydrogels showed good in-situ gel formation and tissue biocompatibility. Thus, the biodegradable thermosensitive injectable CMCH hydrogels hold potential for 3D cell culture and biomedical applications. STATEMENT OF SIGNIFICANCE: Biodegradable hydrogels have been widely studied for cell therapy and tissue regeneration. Herein, we report a novel thermosensitive injectable carboxymethyl chitin (CMCH) hydrogel for 3D cell culture, which was synthesized homogeneously from the bioactive natural chitin through the "green" process avoiding using organic solvent. The CMCH solutions exhibited rapid thermoresponsive sol-to-gel phase transition behavior at 37°C with controllable gelation times, which facilitates the cell encapsulation process at room temperature and in-situ forming hydrogel at body temperature. Importantly, in vitro 3D cell culture and in vivo mouse study of the CMCH hydrogel showed promotion of cell survival and proliferation, good in-situ gel formation and biocompatibility. We believe that such thermosensitive injectable CMCH hydrogels would be very useful for biomedical applications, such as tumor model for cancer research, post-operative adhesion prevention, the regeneration of cartilage and central nervous system and so on.

Protein/Polysaccharide Electrostatic Complexes and Their Applications in Stabilizing Oil-in-Water Emulsions.

Consumers are becoming increasingly fastidious in demanding food products with improved quality and functionality. This largely relies on rational design of food structures. As the two key food ingredients, protein and polysaccharides play important roles in food structuring. The combination of protein and polysaccharide provides rich opportunities for food structure and function designs through molecular interaction and assembly. This paper provides a brief review on the formation and characterization of protein/polysaccharide electrostatic complexes and their applications in stabilizing oil-in-water emulsions, particularly those containing polyunsaturated fatty acids.

Aggregation behaviour and stability of maize germ oil body suspension.

To utilize maize germ oil bodies as ingredients in the food industry, zeta potential determination and particle diameter analysis were used in this study as indicators of the stability of maize germ oil body suspensions. The stability and aggregation properties of maize germ oil body suspensions were studied at different pH and ion strength conditions, and different thermal treatments. Zeta potential measurement, mean particle size determination, and confocal laser scanning microscopy were also performed. The zeta potential and mean particle diameter of the oil bodies were easily affected by salt (7.05 mV and d32=1.43 µm at 100mM NaCl) and pH (23.30, 15.00, -16.43 mV and d32=1.02, 2.55, and 0.95 µm at pH 3, pH 4, and pH 7, respectively). Results demonstrated that aggregation and instability of the oil bodies were promoted by high salt concentrations and acidic pH but not by heating. The association between oil bodies and surfactant properties resulted in the disruption of hydrophobic interactions among oil body surface proteins because of the smaller mean particle sizes and the reduced negative charges (-75.73 mV and d32=0.46 µm at pH 3). Thus, the oil body aggregation behavior and stability of proteins are based on hydrophobic interactions present on the surface of the oil bodies.

Physical and chemical stability of gum arabic-stabilized conjugated linoleic acid oil-in-water emulsions.

Oil-in-water (O/W) emulsions have been used as a delivery system to protect conjugated linoleic acid (CLA), a polyunsaturated fatty acid, from oxidation. Conventional gum arabic (GA) and two matured gum arabic samples (EM2 and EM10) were used as emulsifiers to prepare CLA-in-water emulsions. The emulsions have optimal physical and chemical stability at gum concentrations of 5% for all three gums. Emulsions with higher gum concentrations are more susceptible to lipid oxidation. This is attributed to reduced physical stability at higher gum concentrations because of the coalescence and depletion-induced flocculation of the emulsion droplets. The prooxidants iron and copper intrinsically contained in the gums could also contribute to this instability. Among the three gums, EM10 provides the most effective protection for CLA both physically and chemically, because of its superior interfacial properties over GA and EM2.

Competitive adsorption between sugar beet pectin (SBP) and hydroxypropyl methylcellulose (HPMC) at the oil/water interface.

The emulsification performance, stability and competitive adsorption of two natural food emulsifiers, sugar beet pectin (SBP) and hydroxypropyl methylcellulose (HPMC) have been investigated. Both can reduce the surface tension and emulsify oil in water. However, due to their different structure and conformation they operate via different mechanisms. Using 15% middle chain triglycerides (MCTs) oil, the amounts of SBP and HPMC adsorbed in emulsions made with these individually and in mixtures were determined. The interfacial concentration (Γ) for SBP stabilized emulsion was ∼1.25mg/m(2) and for HPMC 3.5mg/m(2). The higher adsorption of HPMC was due to multilayer adsorption, whereas SBP adsorbed as a monolayer. Competitive adsorption between SBP and HPMC was also investigated. When the HPMC concentration approached that of adsorbed SBP, the effect of HPMC became dominant and at 1.5wt.% controlled the behavior of the mixed emulsions, which were then almost independent of SBP. The minor role of SBP was mainly to decrease the proportion of large droplets in the emulsion. A model to describe the competitive adsorption between SBP and HPMC is proposed.

Complexation of bovine serum albumin and sugar beet pectin: stabilising oil-in-water emulsions.

In a previous study (Langmuir 28 (2012) 10164-10176.), we investigated the complexation of bovine serum albumin (BSA) with sugar beet pectin (SBP). A pH-composition phase diagram was established and structural transitions in relation to the phase diagram during complexation were identified. The present study examines the implications of these interactions on the emulsifying performance of BSA/SBP mixtures. Middle-chain triglycerides (MCTs) in water emulsions were prepared using conditions corresponding to different regions of the phase diagram. At high pHs and in the stable region of mixed individual soluble polymers where complexation is absent, there is no improved emulsifying performance, compared with the individual protein and polysaccharide. For these mixtures, the emulsion characteristics are controlled by the major component in the solutions, as determined by the competitive adsorption of the two components at the oil-water interface. At low pHs and low BSA/SBP ratios, and so mainly within the stable region of intramolecular soluble complexes, BSA/SBP mixtures greatly improve the stability of emulsions. Here, stabilisation is controlled by the cooperative adsorption of the two components at the oil-water interface. Through electrostatic complexation BSA promotes the adsorption of SBP on to interfaces to form a thick steric layer around emulsion droplets and thus providing better stability. At low pHs and high BSA/SBP ratios, that is, mainly within the unstable region of intermolecular insoluble complexes, emulsions prepared are extremely unstable due to bridging flocculation between emulsion droplets.