Antioxidant potential of non-modified and glycated soy proteins in the continuous phase of oil-in-water emulsions

Antioxidant potential and protective effect of modified sea cucumber peptides against H2O2-induced oxidative damage in vitro HepG2 cells and in vivo zebrafish model

In this study, modified sea Cucumber Peptides (SCP) were prepared by reacting with xylooligosaccharide (XOS) and alginate oligosaccharides (AOS) via glycation. Free radical inhibitory and inhibition of oxidative stress of modified SCP was evaluated using human hepatocellular carcinoma (HepG2) cells and zebrafish embryos. LC-MS analysis revealed that SCPs mainly consist of 40 active peptides, with an average molecular weight of 1122.168 Da and an average length of 11 amino acid residues. For amino acid composition, L-Asparagine, L-Methionine, and L-Aspartic Acid were dominant amino acids in SCP. The result showed that the antioxidant ability of SCP against 2,2-Diphenyl-1-picrylhydrazyl (DPPH), superoxide anion radical (O-2), and Hydroxyl Radical (OH) was significantly improved after modification. In HepG2 cells, the modified SCP showed stronger protection than native SCP native against H2O2-induced oxidative stress by enhancing cell viability and reducing radical oxygen species (ROS) generation. The inhibition effect of SCP was increased after modification with XOS and AOS by 13 % and 19 % respectively. Further studies displayed that the activity of antioxidative enzymes, including Superoxide dismutase (SOD), Glutathione Peroxidase (GPx), and catalase (CAT), was remarkably enhanced, whereas malondialdehyde (MDA) level was reduced compared with native SCP and H2O2-treated groups, thus, improving the intracellular antioxidant defenses. The gene expression analysis showed that the mechanism underlying the modified SCP protective effect may be linked with the capability to regulate Nuclear factor-erythroid factor 2-related factor 2 (NRF2) gene expression. The protective effect of modified SCP against H2O2 in vitro was confirmed in vivo by reduced toxicity in zebrafish embryos via improvement of mortality rate, hatching rate, heart beating rate, and deformities of the zebrafish model. However, SCPAOS conjugate displayed greater antioxidant potentials compared to the SCPXOS, the different effects between SCPAOS and SCPXOS could be due to their different antioxidant activity. Thus, modified SCP could be potentially used as a novel nutraceutical in the preparation of anti-aging food and medicine.

Effect of Nonprotein Components for Lipid Oxidation in Emulsions Stabilized by Plant Protein Extracts

Plant protein ingredients are rich in non-protein components of which the antioxidant and pro-oxidant effects are expected to be considerable. In this paper, commercial soy and pea protein isolates and concentrates were selected by using their soluble fractions to prepare oil-in-water (O/W) emulsions. Emulsions stabilized with soy protein isolates were more prone to lipid oxidation than those with soy protein concentrate or pea protein isolate. Compositional analysis revealed that the soluble fraction of soy protein isolates contained higher concentrations of phenolic compounds and metals (iron and copper) but lower mineral and ash contents than those of soy protein concentrate and pea protein isolate. Correlating the composition to oxidation in emulsions highlighted the significant role of non-protein components, alongside the protein's oxidative state. These findings are relevant for the use of alternative proteins in food formulation, a practice often promoted as sustainable yet that may come with repercussions for oxidative stability.

Lipid oxidation in emulsions: New insights from the past two decades

Lipid oxidation constitutes the main source of degradation of lipid-rich foods, including food emulsions. The complexity of the reactions at play combined with the increased demand from consumers for less processed and more natural foods result in additional challenges in controlling this phenomenon. This review provides an overview of the insights acquired over the past two decades on the understanding of lipid oxidation in oil-in-water (O/W) emulsions. After introducing the general structure of O/W emulsions and the classical mechanisms of lipid oxidation, the contribution of less studied oxidation products and the spatiotemporal resolution of these reactions will be discussed. We then highlight the impact of emulsion formulation on the mechanisms, taking into consideration the new trends in terms of emulsifiers as well as their own sensitivity to oxidation. Finally, novel antioxidant strategies that have emerged to meet the recent consumer's demand will be detailed. In an era defined by the pursuit of healthier, more natural, and sustainable food choices, a comprehensive understanding of lipid oxidation in emulsions is not only an academic quest, but also a crucial step towards meeting the evolving expectations of consumers and ensuring the quality and stability of lipid-rich food products.

Self-assembly embedding of curcumin by alkylated rice bran protein

Lysine-rich rice bran protein (RBP) can be used as raw material for alkylation modification to improve the self-assembly performance of protein. The results of 1H NMR, degree of alkylation, and DSC analysis showed that the alkyl chain was successfully attached to the RBP. The surface hydrophobicity and absolute ζ-potential increased. The three-dimensional structure of the alkylated RBP (ARBP) become more porous and ARBP-2 was selected as the material for embedding curcumin. The XRD results revealed that curcumin induced self-aggregation of ARBP-2 and the inclusion of curcumin was attained. The maximum encapsulation efficiency of curcumin was 82.67 % and the maximum loading amount was 171.37 g/100 g RBP. The results of atomic force microscopy (AFM), particle size, and polydispersity index (PDI) analyses revealed that the particles in the system were aggregated after curcumin was added. Curcumin was well protected by encapsulation in the self-assembled particles. Thus, this study provides a new strategy for the embedding and delivery of curcumin.

Waxy maize starch incorporated (-)-epigallocatechin-3-gallate can stabilize emulsion gel and improve antioxidant activity

A food-grade emulsion gel was stabilized using waxy maize starch (WS) incorporated (-)-epigallocatechin-3-gallate (EGCG) at different ratio (from 5 % to 20 %, w/w). The microstructure, rheological behavior, physical stability and antioxidant activity of emulsion gels were investigated using confocal laser scanning microscopy (CLSM), cryo-scanning electron microscopy (cryo-SEM), and rheometer, etc. The results suggested that incorporated EGCG obviously affected the spatial configuration of WS hydrogel. The WS/EGCG hydrogels presented an excellent lipophilic capacity characterized by tightly adhering to linseed oil droplets in the emulsion gels. Moreover, the viscosity, viscoelasticity and physical stability of the emulsion gels stabilized by the WS/EGCG hydrogel matrices were significantly enhanced. The emulsion gel stabilized by the WS/EGCG hydrogel matrix (15 % EGCG) had long-term emulsifying stability because its emulsified phase volume fraction (77.14 %) remained stable for 30 days. Compared with typical natural and synthetic antioxidants in food and pharmaceutical processing, the emulsion gels stabilized by the WS/EGCG hydrogel matrices showed significant stronger DPPH (97.45 %) and ABTS•+ (97.97 %) free radical scavenging activity. These results demonstrate that WS/EGCG hydrogels can not only be used in food-grade matrix materials to stabilize emulsion gels but also improve the antioxidant activity of the emulsion gels.

Stability and Digestive Properties of a Dual-Protein Emulsion System Based on Soy Protein Isolate and Whey Protein Isolate

The stability and digestive properties of a dual-protein emulsion consisting of soy protein isolate (SPI) and whey protein isolate (WPI) have been systematically studied. The results showed that the particle size and viscosity of the dual-protein emulsion system decreased continuously with the increase in WPI, and this might be related to the large amount of electric charge on the surface of the emulsion droplets. Dual-protein emulsions with ratios of 3:7 and 5:5 showed the highest emulsion activity, while emulsion stability increased with the increase in WPI. The thicker adsorption layer formed at the interface might have contributed to this phenomenon. After in-vitro-simulated digestion, the emulsion droplet particle size increased substantially due to the weakened electrostatic repulsion on the droplet surface, especially for the intestinal digestion phase. Meanwhile, WPI accelerated the release of free fatty acids in the digestion process, which played a positive role in the nutritional value of the dual-protein emulsion. In accelerated oxidation experiments, WPI also improved the antioxidant properties of the dual-protein emulsion system. This study will provide a new insight and necessary theoretical basis for the preparation of dual-protein emulsions.

Avocado seed by-product uses in emulsion-type ingredients with nutraceutical value: Stability, cytotoxicity, nutraceutical properties, and assessment of in vitro oral-gastric digestion

The avocado industry obtains 20-30% of the total by-products (peels and seeds). However, byproducts can be uses as sources of economic nutraceutical ingredients with functional potential. This work developed emulsion-type ingredients from avocado seed to evaluate its quality, stability, cytotoxicity, and nutraceutical properties before/after in vitro oral-gastric digestion. Ultrasound lipid extraction achieved an extraction yield of up to 95.75% compared with Soxhlet conventional extraction (p > 0.05). Six ingredients' formulations (E1-E6) were stable for up to day 20 during storage, preserving their antioxidant capacity and displaying low in vitro oxidation compared to control. None of the emulsion-type ingredients were considered cytotoxic according to the shrimp lethality assay (LC₅₀ > 1000 µg/mL). Ingredients E2, E3, and E4 generated low lipoperoxides' concentrations and high antioxidant capacity during the oral-gastric stage. The 25 min-gastric phase showed the highest antioxidant capacity and low lipoperoxidation. Results suggested avocado seed-derived could be used to develop functional ingredients with nutraceutical properties.

Targeting Interfacial Location of Phenolic Antioxidants in Emulsions: Strategies and Benefits

It is important to have larger proportions of health-beneficial polyunsaturated lipids in foods, but these nutrients are particularly sensitive to oxidation, and dedicated strategies must be developed to prevent this deleterious reaction. In food oil-in-water emulsions, the oil-water interface is a crucial area when it comes to the initiation of lipid oxidation. Unfortunately, most available natural antioxidants, such as phenolic antioxidants, do not spontaneously position at this specific locus. Achieving such a strategic positioning has therefore been an active research area, and various routes have been proposed: lipophilizing phenolic acids to confer them with an amphiphilic character; functionalizing biopolymer emulsifiers through covalent or noncovalent interactions with phenolics; or loading Pickering particles with natural phenolic compounds to yield interfacial antioxidant reservoirs. We herein review the principles and efficiency of these approaches to counteract lipid oxidation in emulsions as well as their advantages and limitations.

Physical and Oxidative Stabilization of Oil-In-Water Emulsions by Roasted Coffee Fractions: Interface- and Continuous Phase-Related Effects

Emulsions fortified with polyunsaturated fatty acids are highly relevant from a nutritional perspective; however, such products are prone to lipid oxidation. In the current work, this is mitigated by the use of natural antioxidants occurring in coffee. Coffee fractions with different molecular weights were extracted from roasted coffee beans. These components were positioned either at the interface or in the continuous phase of emulsions where they contributed to emulsion stability via different pathways. Coffee brew as a whole, and its high-molecular-weight fraction (HMWF), was able to form emulsions with good physical stability and excellent oxidative stability. When added post-homogenization to the continuous phase of dairy protein-stabilized emulsions, all coffee fractions were able to slow down lipid oxidation considerably without altering the physical stability of emulsions, though HMWF was more effective in retarding lipid oxidation than whole coffee brew or low-molecular-weight fraction. This is caused by various effects, such as the antioxidant properties of coffee extracts, the partitioning of components in the emulsions, and the nature of the phenolic compounds. Our research shows that coffee extracts can be used effectively as multifunctional stabilizers in dispersed systems leading to emulsion products with high chemical and physical stability.

Food protein glycation: A review focusing on stability and in vitro digestive characteristics of oil/water emulsions

Recently, increasing studies have shown that the functional properties of proteins, including emulsifying properties, antioxidant properties, solubility, and thermal stability, can be improved through glycation reaction under controlled reaction conditions. The use of glycated proteins to stabilize hydrophobic active substances and to explore the gastrointestinal fate of the stabilized hydrophobic substances has also become the hot spot. Therefore, in this review, the effects of glycation on the structure and function of food proteins and the physical stability and oxidative stability of protein-stabilized oil/water emulsions were comprehensively summarized and discussed. Also, this review sheds lights on the in vitro digestion characteristics and edible safety of emulsion stabilized by glycated protein. It can further serve as a research basis for understanding the role of structural features in the emulsification and stabilization of glycated proteins, as well as their utilization as emulsifiers in the food industry.

Oxidation and oxidative stability in emulsions

Emulsions are implemented in the fabrication of a wide array of foods and therefore are of great importance in food science. However, the application of emulsions in food production is restricted by two main obstacles, that is, physical and oxidative stability. The former has been comprehensively reviewed somewhere else, but our literature review indicated that there is a prominent ground for reviewing the latter across all kinds of emulsions. Therefore, the present study was formulated in order to review oxidation and oxidative stability in emulsions. In doing so, different measures to render oxidative stability to emulsions are reviewed after introducing lipid oxidation reactions and methods to measure lipid oxidation. These strategies are scrutinized in four main categories, namely storage conditions, emulsifiers, optimization of production methods, and antioxidants. Afterward, oxidation in all types of emulsions, including conventional ones (oil-in-water and water-in-oil) and uncommon emulsions in food production (oil-in-oil), is reviewed. Furthermore, the oxidation and oxidative stability of multiple emulsions, nanoemulsions, and Pickering emulsions are taken into account. Finally, oxidative processes across different parent and food emulsions were explained taking a comparative approach.

Study on the binding behavior and functional properties of soybean protein isolate and β-carotene

This study focused on the non-covalent interaction between soybean protein isolate (SPI) and β-carotene (BC). The conformational changes of SPI with β-carotene in varying proportions (BC/SPI: 2%, 4%, 6%, 8%, and 10%) were investigated by multi-spectroscopy and molecular docking. Results showed that the quenching mode is static quenching and binding affinity increased with temperature. The stoichiometry was 1:1, indicating there was only one binding site in SPI. The binding was based on entropy and primarily driven by hydrophobic interactions and its binding constant was in the order of 104 L⋅mol–1. The addition of the β-carotene affected the secondary structure of SPI resulting in an increase in α-Helix and a decrease in random coil and β-turn content, indicating protein aggregated and hydrophobic interactions occurred. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) verified that no new larger molecular weight substance was formed and no covalent interaction existed. Molecular docking corroborated that electrostatic and hydrophobic interactions were both involved in the formation of complexes, where hydrophobic interaction was the dominant one. Moreover, β-carotene improved 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, foaming capacity, and emulsifying stability of SPI. These findings provide useful information about the interaction mechanism of SPI and β-carotene, which contributes to the further development and application of SPI products rich in β-carotene in the food industry.

Effects of antioxidant types on the stabilization and in vitro digestion behaviors of silver carp scale gelatin-stabilized fish oil-loaded emulsions

Lipid oxidation is a major challenge in the development and storage of lipid-containing food products. In this work, we extracted aquatic gelatin from silver carp scales and studied the effects of antioxidant types (water-soluble and lipid-soluble types) on the stabilization, lipid oxidation, and in vitro digestion behaviors of silver carp scale gelatin-stabilized fish oil-loaded emulsions. Vitamin C (VC), a water-soluble antioxidant, and vitamin E (VE), a lipid-soluble antioxidant, had no obvious effects on the appearance, droplet size distribution, and droplet stability of the emulsion. VC slowed the liquid-gel transition of the emulsions at room temperature. The emulsion creaming stability decreased with the increase of VC concentration, whereas it increased with the increase of VE concentration. Lipid oxidation hierarchy of emulsion groups at room temperature were VC<VE<control<pure oil. Free fatty acids were mainly released from the silver carp scale gelatin-stabilized emulsions in the simulated intestinal fluid. Moreover, compared with the control group, VC increased the free fatty acid release percentages, whereas VE decreased them. This work provided useful information for developing antioxidants in the field of food science and in value-added utilization research of aquatic by-products.

Macro-Batch and Continuously Operated Microfluidic Emulsification—Differences, Similarities and Optimization

In this work, the emulsification of oil-in-water two-phase systems with three emulsifiers (PEG1500, 6000 and 20000) was studied in a batch macro system and in a continuously operated microfluidic system. The effect of emulsifier concentration, oil concentration and mixing rate on zeta potential and average Feret diameter was analyzed for the macro-batch system, while the effect of emulsifier concentration, oil concentration and total flow rate on zeta potential and average Feret diameter was analyzed for the microfluidic system. The emulsions prepared in batch system were more stable, had smaller droplet diameter but higher values of polydispersity index (PDI) compared to those prepared by continuous method. In both cases, batch and continuous, the use of PEG with higher molecular weight resulted in emulsions with lower zeta potential values. In batch emulsification, all three optimization parameters (emulsifier concentration, oil concentration and mixing rate) had a significant influence on the average Feret diameter and zeta potential (depending on the PEG, used for emulsification), while the emulsifier concentration had the most significant influence on the zeta potential and average Feret diameter of emulsions prepared in the continuous microsystem process.

Characteristics of Soy Protein Prepared Using an Aqueous Ethanol Washing Process

Currently, the predominant process for soy protein concentrate (SPC) production is aqueous ethanol washing of hexane-extracted soy meal. However, the use of hexane is less desired, which explains the increased interest in cold pressing for oil removal. In this study, cold-pressed soy meal was used as the starting material, and a range of water/ethanol ratios was applied for the washing process to produce SPCs. Washing enriched the protein content for the SPCs, regardless of the solvent used. However, we conclude that washing with water (0% ethanol) or solvents with a high water/ethanol ratio (60% and above) can be more advantageous. Washing with a high water/ethanol ratio resulted in the highest yield, and SPCs with the highest protein solubility and water holding capacity. The water-only washed SPC showed the highest viscosity, and formed gels with the highest gel strength and hardness among all the SPCs at a similar protein concentration. The variations in the functionality among the SPCs were attributed to protein changes, although the effects of non-protein constituents such as sugar and oil might also be important. Overall, the aqueous ethanol washing process combined with cold-pressed soy meal created SPCs comparable to commercial SPC in terms of composition, but with varied functionalities that are relevant for novel soy-food developments.