Effects of emulsifier charges on the oxidative stability in oil-in-water emulsions under riboflavin photosensitization

Effects of association colloidal structures on the oxygen solubility in oil-in-water emulsion matrix

Although association colloidal structures are believed as major oxidation places, relationship of oxygen molecules with association colloids have not been evaluated in oil-in-water (O/W) emulsion. Oxygen solubility was determined in O/W emulsion containing dispersed phases with different charges of emulsifiers, numbers of dispersed droplets, and surface areas of dispersed droplets. The rates of lipid oxidation were also examined. O/W emulsion made of positively charged emulsifier had higher oxygen solubility than negatively charged and neutral emulsifiers. As number and surface area of oil droplet in O/W emulsion increased, higher oxygen solubility was observed, implying that dispersed phases could be places for oxygen molecules. O/W emulsion made of positively charged emulsifier had higher lipid oxidation than neutral emulsifier. O/W emulsion with more interfaces had lower oxidative stability, implying interfaces of association colloids could affect rates of lipid oxidation. Dispersed phase in O/W emulsion can be places for oxygen molecules.

Efficiency of δ-Tocopherol in Inhibiting Lipid Oxidation in Emulsions: Effects of Surfactant Charge and of Surfactant Concentration

Charged interfaces may play an important role in the fate of chemical reactions. Alterations in, for instance, the interfacial acidity of emulsions induced by the charge of the surfactant head group and associated counterions may change the ionization status of antioxidants, modifying their effective concentrations. The chemical reactivity between interfacial reactants and charged species of opposite charge (protons, metallic ions, etc.) is usually interpreted in terms of pseudophase ion-exchange models, treating the distribution of charged species in terms of partitioning and ion exchange. Here, we focus on analyzing the effects of charged interfaces on the oxidative stability of soybean oil-in-water (o/w) emulsions prepared with anionic (sodium dodecyl sulfate, SDS), cationic (cetyltrimethylammonium bromide, CTAB) and neutral (Tween 20) surfactants, and some of their mixtures, in the presence and absence of δ-tocopherol (δ-TOC). We have also determined the effective concentrations of δ-TOC in the oil, interfacial and aqueous regions of the intact emulsions. In the absence of δ-TOC, the relative oxidative stability order was CTAB < TW20 ~ TW20/CTAB < SDS. Surprisingly, upon the addition of δ-TOC, the relative order was SDS ≈ TW20 << TW20/CTAB < CTAB. These apparently surprising results can be rationalized in terms of the nice correlation that exists between the relative oxidative stability and the effective interfacial concentrations of δ-TOC in the various emulsions. The results emphasize the importance of considering the effective interfacial concentrations of antioxidants in interpreting their relative efficiency in emulsions.

The impact of pH on mechanical properties, storage stability and digestion of alginate-based and soy protein isolate-stabilized emulsion gel beads with encapsulated lycopene

In alginate-based emulsion gels containing protein-coated droplets, pH can influence the gelation mechanism of alginate gels, and the interactions between alginate molecules and protein-coated droplets, and thus properties of emulsion gels. This study investigated the impact of pH 3-7 on the properties (e.g., surface structures of droplets, mechanical properties, storage stability, digestion behavior) of alginate gel beads containing soy protein isolate(SPI)-stabilized oil droplets. Emulsion droplets were SPI-coated droplets at pH 6-7 and alginate/SPI-coated droplets at pH 3-5. Emulsion droplet flocculation only occurred in emulsions at pH 7.0. Emulsion gel beads at pH 3.0 had lower mechanical strength, higher storage stability, faster release of encapsulated lycopene during in-vitro digestion, and higher bioaccesibility of lycopene after 2 h of intestinal digestion than those at pH 7.0 and 5.0. The findings of this study are crucial to emulsion gel beads with controlled release and improved storage stability of encapsulated compounds by changing the pH of emulsions.

Lipid oxidation in emulsions and bulk oils: a review of the importance of micelles

Lipid oxidation is a major cause of quality deterioration in food products. In these foods, lipids are often present in a bulk or in emulsified forms. In both systems, the rate, extent and pathway of oxidation are highly dependent on the presence of colloidal structures and interfaces because these are the locations where oxidation normally occurs. In bulk oils, reverse micelles (association colloids) are present and are believed to play a crucial role on lipid oxidation. Conversely, in emulsions, surfactant micelles are present that also play a major role in lipid oxidation pathways. After a brief description of lipid oxidation and antioxidants mechanisms, this review discusses the current understanding of the influence of micellar structures on lipid oxidation. In particular, is discussed the major impact of the presence of micelles in emulsions, or reverse micelles (association colloids) in bulk oil on the oxidative stability of both systems. Indeed, both micelles in emulsions and associate colloids in bulk oils are discussed in this review as nanoscale structures that can serve as reservoirs of antioxidants and pro-oxidants and are involved in their transport within the concerned system. Their role as nanoreactors where lipid oxidation reactions occur is also commented.

Bacteria biohybrid oral vaccines for colorectal cancer treatment reduce tumor growth and increase immune infiltration

Bacteria biohybrid-based vaccine delivery systems, which integrate a vaccine carrier with live non-pathogenic bacteria, are hypothesized to have improved immunostimulating potential. The aim of this study was to develop oral bacteria biohybrid-based vaccines to treat a mouse model of colorectal cancer. E. coli were combined with tumor antigen- and adjuvant-containing emulsions or liposomes. Emulsion and liposome biohybrid vaccines demonstrated in vitro and in vivo therapeutic potential. Bacteria biohybrid vaccines significantly increased the expression of CD40⁺, CD80⁺ and CD86⁺ on murine bone marrow-derived dendritic cells. Mice vaccinated with emulsion biohybrid vaccines had an increased CD8⁺ T cell infiltration into tumors and developed three-fold smaller tumors compared to the mice that received emulsion vaccine without E. coli.

Effect of emulsifiers on linseed oil emulsion structure, lipolysis and oxidation during in vitro digestion

Health benefits have been associated with the consumption of omega-3 polyunsaturated fatty acids (PUFA). Linseed oil is rich in long chain omega-3 PUFA, but can generate toxic compounds due to its high susceptibility to oxidation. The nature of the emulsifier can affect both lipolysis and oxidation during digestion since these phenomena occur at the oil-water interface. The objective of this study was to compare the effect of low-molecular weight surfactants (cetyltrimethylammonium bromide (CTAB), Citrem), protein (sodium caseinate, fish gelatin) and polysaccharides (gum arabic, modified starch) on the structure of linseed oil emulsions, lipolysis and formation of reactive oxidation species during in vitro digestion. The emulsion stabilized with Citrem underwent extensive coalescence in the gastric phase, which strongly decreased the extent of lipid digestion and reduced the formation of oxidation markers relative to other emulsions. Emulsions stabilized by proteins and modified starch showed aggregation with partial coalescence in the gastric phase, but protein-stabilized emulsions showed better resistance to oxidation. This study shows that emulsifier properties affect the susceptibility of the emulsion to aggregation and coalescence in the gastrointestinal environment, and strongly influence the extent of lipid digestion and the formation of reactive oxidation products. These findings point out the importance of the choice of the emulsifier to control the lipid digestibility and the protection of sensible lipids thus promoting optimal nutritional properties in omega-3-enriched foods.

Surface Active Agents and Their Health-Promoting Properties: Molecules of Multifunctional Significance

Surface active agents (SAAs) are molecules with the capacity to adsorb to solid surfaces and/or fluid interfaces, a property that allows them to act as multifunctional ingredients (e.g., wetting and dispersion agents, emulsifiers, foaming and anti-foaming agents, lubricants, etc.) in a widerange of the consumer products of various industrial sectors (e.g., pharmaceuticals, cosmetics, personal care, detergents, food, etc.). Given their widespread utilization, there is a continuously growing interest to explore their role in consumer products (relevant to promoting human health) and how such information can be utilized in order to synthesize better chemical derivatives. In this review article, weaimed to provide updated information on synthetic and biological (biosurfactants) SAAs and their health-promoting properties (e.g., anti-microbial, anti-oxidant, anti-viral, anti-inflammatory, anti-cancer and anti-aging) in an attempt to better define some of the underlying mechanism(s) by which they exert such properties.

Isoflavone profiles and antioxidant properties in different parts of soybean sprout

Sprouting is one of the processing methods to enhance bioavailability of some nutrients of agricultural products. Soybeans were germinated for 6 days and soybean (SB), soybean sprout (SBS), cotyledon of soybean sprout (CSS), and hypocotyl and root of soybean sprout (HRSS) were collected. Isoflavone profiles and in vitro antioxidant activities of 80% ethanol extracts of samples were analyzed. In addition, oxidative stability of the extract was evaluated in corn oils heated at 100 °C. The hypocotyl and root part of soybean sprout contained significantly (P < 0.05) higher content of isoflavone aglycones than the cotyledon part of soybean sprout. Diphenyl-1-picrylhydrazyl radial and 2,2'-azinobis(3-ethylbenzothiazoline-6-sul-fonic acid cation radical scavenging activities of SBS were 1.6 and 1.3 times higher than those of SB, respectively (P < 0.05), whereas those of CSS were 1.1 and 1.8 times higher than those of HRSS, respectively (P < 0.05). CSS had higher ORAC and FRAP values than others. High correlations between contents of total flavonoids and antioxidant activities were observed in all in vitro antioxidant assays. SBS, CSS, and HRSS had significantly higher oxidative stability than SB in 100 °C heated corn oil after 9 hr treatment (P < 0.05). Generally, 80% ethanol extract of CSS had high in vitro antioxidant properties whereas HRSS had high aglycone forms of isoflavones. Isoflavone aglycones may not be major ingredients providing antioxidant activities of soybean sprout. PRACTICAL APPLICATION: Soybeans are important crops for the preparation of tofu, soymilk, and protein sources. Soybean sprout prepared by germinating soybean and growing for several days is one of important food materials used as daily diet in some countries. In this study, antioxidant activities of different parts of soybean sprouts were evaluated using in vitro methods and bulk oil model systems. In addition, isoflavone profiles of soybean sprouts were determined. Enhanced antioxidant activities of soybean sprouts may help consumers choose healthier foods and extend business areas of the soybean food industry.

Oxidative stability of oil-in-water emulsions with α-tocopherol, charged emulsifier, and different oxidative stress

α-Tocopherol is known to show different activity depending on the concentration and food matrix. Effects of α-tocopherol at the concentrations of 0, 0.1, 0.5, and 1.0 mM were determined in oil-in-water (O/W) emulsions containing anionic, neutral, and cationic emulsifiers under different types of oxidative stress including riboflavin photosensitization, photooxidation, and autoxidation. Headspace oxygen depletion, lipid hydroperoxides, and conjugated dienes were analyzed to determine the oxidative stability of O/W emulsions. α-Tocopherol served as an antioxidant in O/W emulsion with a cationic emulsifier irrespective of oxidative stress. α-Tocopherol acted as an antioxidant in O/W emulsion with a neutral emulsifier at riboflavin photosensitization while a prooxidant at photooxidation. However, in samples with an anionic emulsifier, α-tocopherol activity differed from the concentration and types of oxidative stress. Therefore, cationic transition metals or reactive oxygen species generated from RF photosensitization could play key roles of α-tocopherol in O/W emulsion.

Hydrophilic and lipophilic characteristics of non-fatty acid moieties: significant factors affecting antibacterial activity of lauric acid esters

It has been proposed that the hydrophilic and/or lipophilic characteristics of fatty acid derivatives affect their antibacterial activities according to their ability to incorporate into the bacterial cell membrane. To verify this hypothesis, six kinds of lauric acid derivatives esterified with different non-fatty acid moieties were selected to confirm whether antibacterial activity from their precursor (i.e., lauric acid) is retained or lost. Three compounds, monolaurin, sucrose laurate, and erythorbyl laurate, exerted bacteriostatic and bactericidal effects against Gram-positive bacteria, while the others showed no inhibitory activity. Interestingly, the calculated log P (octanol-water partition coefficient) values of monolaurin, sucrose laurate, and erythorbyl laurate were - 4.122, - 0.686, and 3.670, respectively, relatively lower than those of the other compounds without antibacterial activity. Moreover, the hydrophilic-lipophilic balance values of the three compounds with antibacterial activity were higher than those of the other compounds, corresponding to the log P result.

Antioxidant Properties of Astaxanthin in Oil-in-Water Emulsions with Differently-Charged Emulsifiers Under Chlorophyll Photosensitization

The antioxidative or prooxidative properties of astaxanthin at the concentrations of 0, 10, and 100 μM were determined in oil-in-water (O/W) emulsions containing neutral, anionic, and cationic emulsifiers, which was Tween 20, sodium dodecyl sulfate, cetyltrimethylammonium bromide (CTAB), respectively, under chlorophyll photosensitization. The oxidative parameters and headspace volatiles were analyzed in O/W emulsions. In the 24 h period of visible light irradiation, 100 μM of astaxanthin acted as an antioxidant in O/W emulsions containing neutral and anionic emulsifiers. However, astaxanthin in O/W emulsions with a cationic emulsifier was neither an antioxidant nor a prooxidant. The profiles of volatile compounds showed that astaxanthin served as a singlet oxygen quencher in O/W emulsions containing neutral and anionic emulsifiers. However, in O/W emulsion with a cationic emulsifier, astaxanthin was neither a singlet oxygen quencher nor a free radical scavenger because prooxidant properties of CTAB overwhelmed the antioxidant effects of astaxanthin. Therefore, the antioxidant properties of astaxanthin were influenced by the emulsifier charges in O/W emulsions.

PRACTICAL APPLICATION

Astaxanthin is a lipid-soluble pigment and has antioxidant, anticancer, and anti-inflammatory properties and beneficial effects on cardiovascular diseases. Many lipid-based foods are displayed on the shelves in the markets under fluorescent light. The addition of astaxanthin can extend the shelf life of O/W emulsion type foods such as beverage and dressing products under visible light irradiation. Also, oxidative stability in emulsion type foods containing astaxanthin rich natural ingredients can be predicted.

Interfacial Antioxidants: A Review of Natural and Synthetic Emulsifiers and Coemulsifiers That Can Inhibit Lipid Oxidation

There has been strong interest in developing effective strategies to inhibit lipid oxidation in emulsified food products due to the need to incorporate oxidatively labile bioactive lipids, such as ω-3 fatty acids, conjugated linoleic acids, or carotenoids. Emulsifiers or coemulsifiers can be utilized to inhibit lipid oxidation in emulsions. Both of these molecular types can adsorb to droplet surfaces and inhibit lipid oxidation, but emulsifiers can also stabilize droplets against aggregation whereas coemulsifiers cannot. There are a host of existing emulsifiers, covalent conjugates, or physical complexes that have the potential to inhibit lipid oxidation by a variety of mechanisms. Existing emulsifiers with antioxidant potential consist of surfactants, phospholipids, proteins, polysaccharides, and colloidal particles. Conjugates and complexes are typically formed by covalently or physically linking together a surface-active molecule with an antioxidant molecule. This article reviews the molecular and physicochemical basis for the surface and antioxidant activities of emulsifiers and coemulsifiers, highlights the important properties of interfacial layers that can be engineered to control lipid oxidation, and outlines different kinds of existing emulsifiers, conjugates, and complexes that can be used to inhibit oxidation.