Influence of AO chain length, droplet size and oil to water ratio on the distribution and on the activity of gallates in fish oil-in-water emulsified systems: Emulsion and nanoemulsion comparison

Effect of High-Pressure Homogenization and Wall Material Composition on the Encapsulation of Polyunsaturated Fatty Acids from Fish Processing

Fish oil, a rich source of omega-3 polyunsaturated fatty acids (PUFA), is a vital nutritional component, but considering its susceptibility to oxidation, it could benefit from an effective encapsulation system. This study aims to optimize high-pressure homogenization (HPH) parameters (pressure, number of passes) and wall material composition to maximize the encapsulation efficiency (EE) of fish oil, using different concentrations of maltodextrin with Arabic gum or sodium alginate. Key metrics such as emulsion droplet size, encapsulation efficiency, color, and oxidation in the final freeze-dried product were evaluated. Optimal values were achieved at 60 MPa, resulting in the lowest mean droplet diameter (369.4 ± 3.8 nm) and narrow distribution (0.197 ± 0.011) of the fish oil micelles prepared with a mixture of Tween80 and sodium caseinate as an emulsifier, without significant oxidation after four cycles of homogenization, while 80 MPa led to the highest EE (up to 95.6%), but increased oxidation. The combination of 10% w/w Arabic gum or 1% w/w sodium alginate with 20% w/w maltodextrin achieved the highest EE (79.1-82.9%) and whiteness index (82.5-83.0), indicating neutral-colored well-encapsulated fish oil without oxidation, which is desirable for product stability. Selecting optimal HPH conditions and wall material is crucial for the encapsulation efficiency and oxidation stability of omega-3 PUFA delivered in dehydrated forms.

Antioxidant mechanism of ferulic acid and γ-oryzanol in emulsion and emulgel based on black seed oil

The aim of this research was to compare the antioxidant mechanism of ferulic acid and γ-oryzanol in emulsion with that of emulgel. In the initiation phase, ferulic acid at 2.32 mM concentration exhibited the best efficiency in emulgel samples, while in emulsion samples, γ-oryzanol at 2.32 mM concentration exhibited the best efficiency. γ-Oryzanol was more effective than ferulic acid in emulsion and emulgel samples in the propagation phase. The γ-oryzanol and ferulic acid participated in side reactions of initiation chain in addition to participating in the major termination reaction. In both of the emulgel and emulsion samples, ferulic acid showed higher consumption rate constant and extent of participation in side reactions of initiation chain than that of γ-oryzanol. In conclusion, ferulic acid showed higher efficiency in emulgel in the initiation phase, while γ-oryzanol showed higher efficiency in emulsion and emulgel in the propagation phase.

Low-Calorie Cookies Enhanced with Fish Oil-Based Nano-ingredients for Health-Conscious Consumers

This study explored the effectiveness of fish oil (FO)-loaded nanoemulsions, averaging 197 nm in diameter, as fat substitutes in creating low-calorie cookies. The cookies' diameter, thickness, and spread ratio were measured, ranging from 46.33 to 57.15 mm, 6.45 to 7.51 mm, and 6.16 to 8.86, respectively. Notably, cookies containing nanoemulsions exhibited a significant increase in the spread ratio compared to the control. The control sample had the highest hardness value at 43.81 N, while the nanoemulsion group had the lowest at 26.98 N. The energy value, which was 508 kcal/100 g in the control group, decreased to 442 kcal/100 g in the group containing the nanoemulsion. The total n-3 fatty acid content in cookies rose from 0.46% in the control cookies to 3.90% in the cookies containing nanoemulsion. Sensory evaluations showed that cookies containing fish ol-loaded nanoemulsion received the highest scores, indicating that the fat reduction did not compromise the desired ″greasy″ sensation. This is especially noteworthy, as it showed that the fat content could be reduced by half without compromising the sensory quality. Utilizing FO-loaded nanoemulsions as a fat replacement in fat-reduced baked goods could provide valuable insights for other food products. The findings have significant implications for the food industry, suggesting that healthier, low-calorie baked goods can be developed without sacrificing physical quality and texture. This approach can cater to the growing market demand for health-conscious food options, potentially leading to new product innovations and enhanced nutritional profiles in a variety of food products.

Encapsulation of antioxidants with colloidal lipid particles for enhancing the photooxidation stability of phytosterol in Pickering emulsions

In order to prevent the photooxidation of phytosterols, a new type of Pickering emulsion was developed by regulating the oriented distribution of antioxidants in colloidal lipid particles (CLPs) at the oil-water interface. High-melting-point and low-melting-point lipids were tested to modulate their protective effect against phytosterols photooxidation. Results showed that CLPs could stabilize Pickering emulsion and encapsulate antioxidants, providing a dual functional delivery system for phytosterols protection. The Pickering emulsion formed had a particle size of around 350-820 nm, and the crystallization and melting temperatures of tripalmitin particles were approximately 32 °C and 63.8 °C, respectively. The addition of tributyrin or tricaprylin reduced the crystallization and melting temperatures of Pal CLPs and improved the photooxidation emulsion stability. The prepared Pickering emulsion remained stable for a maximum of 12 days under accelerated light-induced oxidation. Among all formulations, the emulsion primarily composed of tripalmitin CLPs, with added tributyrin and resveratrol, exhibited the highest photooxidation stability.

Recent Advancements in Gallic Acid-Based Drug Delivery: Applications, Clinical Trials, and Future Directions

Gallic acid (GA) is a well-known herbal bioactive compound found in many herbs and foods like tea, wine, cashew nuts, hazelnuts, walnuts, plums, grapes, mangoes, blackberries, blueberries, and strawberries. GA has been reported for several pharmacological activities, such as antioxidant, inflammatory, antineoplastic, antimicrobial, etc. Apart from its incredible therapeutic benefits, it has been associated with low permeability and bioavailability issues, limiting their efficacy. GA belongs to BCS (Biopharmaceutics classification system) class III (high solubility and low probability). In this context, novel drug delivery approaches played a vital role in resolving these GA issues. Nanocarrier systems help improve drug moiety's physical and chemical stability by encapsulating them into a lipidic or polymeric matrix or core system. In this regard, researchers have developed a wide range of nanocarrier systems for GA, including liposomes, transfersomes, niosomes, dendrimers, phytosomes, micelles, nanoemulsions, metallic nanoparticles, solid lipid nanoparticles (SLNs), nanoparticles, nanostructured lipid carriers, polymer conjugates, etc. In the present review, different search engines like Scopus, PubMed, ScienceDirect, and Google Scholar have been referred to for acquiring recent information on the theme of the work. Therefore, this review paper aims to emphasize several novel drug delivery systems, patents, and clinical updates of GA.

Formation mechanism of off-flavor and the inhibition regulatory strategies in the algal oil-loaded emulsions-a review

Algal oil rich in docosahexaenoic acid is easily oxidized and degraded to produce volatile short-chain compounds, leading to the deterioration of product flavor. Currently, the emulsion delivery of algal oil provides a promising approach to minimize oxidative deterioration and conceal its off-flavor. However, algal oil emulsions would also experience unanticipated oxidation as a result of the large specific surface area between the aqueous phase and the oil phase. The current paper offers a mechanism overview behind off-flavor formation in algal oil emulsions and explores corresponding strategies for the inhibition regulation. Additionally, the paper delves into the factors influencing lipid oxidation and the perception of off-flavors in such emulsions. To mitigate the development of off-flavors in algal oil emulsions resulting from oxidation, it is crucial to decline the likelihood of lipid oxidation and proactively prevent the creation of off-flavors whenever possible. Minimizing the release of volatile off-flavor compounds that are inevitably generated is also considered effective for weakening off-flavor. Moreover, co-encapsulation with particular desirable aroma substances could improve the overall flavor characteristics of emulsions.

Unravelling the effect of droplet size on lipid oxidation in O/W emulsions by using microfluidics

Lipid oxidation in emulsions is hypothesised to increase with decreasing droplet size, as this increases the specific oil-water interfacial area, where lipid oxidation is expected to be initiated. In literature, however, contradictory results have been reported, which can be caused by confounding factors such as the oil droplet polydispersity and the distribution of components between the available phases. In this work, monodisperse surfactant-stabilised emulsions with highly controlled droplet sizes of 4.7, 9.1, and 26 µm were produced by microfluidic emulsification. We show that lipid oxidation increases with decreasing droplet size, which we ascribe to the increased contact area between lipids and continuous phase prooxidants. Besides, a significant amount of oxygen was consumed by oxidation of the surfactant itself (Tween 20), an effect that also increased with decreasing droplet size. These insights substantiate the importance of controlling droplet size for improving the oxidative stability of emulsions.

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.

Semisolid medium internal phase emulsions stabilized by dendritic-like mushroom cellulose nanofibrils: Concentration effect and stabilization mechanism

Emulsions with reduced fat and natural stabilizers are currently prevalent. Herein, semisolid emulsions with an oil phase of 50 % were successfully prepared using cellulose nanofibrils from mushroom stipes as stabilizers. Cellulose nanofibrils obtained by high-pressure homogenization were dendritic-like and possessed a contact angle of 70.50 ± 0.41°. The rheological properties and stability of emulsions increased significantly as nanocellulose concentrations increased from 5 to 20 mg/mL, while nanocellulose at 25-30 mg/mL significantly reduced the storage stability and anti-lipid oxidation ability of emulsions. The microstructure of semisolid emulsions demonstrated that nanocellulose fibers at 20 mg/mL could stabilize emulsions by forming compact interfacial films around droplets and creating intensive bridging networks between neighboring droplets, while nanofibers at concentrations over 20 mg/mL easily clustered in the aqueous phase, making the droplets more susceptible to aggregation and demulsification. The results demonstrate that cellulose nanofibrils from mushroom byproducts have the potential to stabilize semisolid food-grade emulsions.

Tiny, yet impactful: Detection and oxidative stability of very small oil droplets in surfactant-stabilized emulsions

HYPOTHESIS

The shelf life of multiphase systems, e.g. oil-in-water (O/W) emulsions, is severely limited by physical and/or chemical instabilities, which degrade their texture, macroscopic appearance, sensory and (for edible systems) nutritional quality. One prominent chemical instability is lipid oxidation, which is notoriously complex. The complexity arises from the involvement of many physical structures present at several scales (1-10,000 nm), of which the smallest ones are often overlooked during characterization.

EXPERIMENTS

We used cryogenic transmission electron microscopy (cryo-TEM) to characterize the coexisting colloidal structures at the nanoscale (10-200 nm) in rapeseed oil-based model emulsions stabilized by different concentrations of a nonionic surfactant. We assessed whether the oxidative and physical instabilities of the smallest colloidal structures in such emulsions may be different from those of larger colloidal structures.

FINDINGS

By deploying cryo-TEM, we analyzed the size of very small oil droplets and of surfactant micelles, which are typically overlooked by dynamic light scattering when larger structures are concomitantly present. Their size and oil content were shown to be stable over incubation, but lipid oxidation products were overrepresented in these very small droplets. These insights highlight the importance of the fraction of "tiny droplets" for the oxidative stability of O/W emulsions.

Extraction and Emulsification of Carotenoids from Carrot Pomaces Using Oleic Acid

This study aimed to use oleic acid-based ultrasonic-assisted extraction (UAE) to recover carotenoids from carrot pomace and emulsify the enriched-carotenoid oleic acid using spontaneous and ultrasonic-assisted emulsification. The extraction performance of oleic acid was compared with traditional organic solvents, including hexane, acetone, and ethyl acetate. The one-factor experiments were employed to examine the impact of UAE conditions, including liquid-to-solid ratios, temperature, ultrasonic power, and time, on the extraction yield of carotenoids and to find the conditional ranges for the optimization process. The response surface methodology was employed to optimize the UAE process. The second-order extraction kinetic model was used to find the mechanism of oleic acid-based UAE. After that, the enriched-carotenoid oleic acid obtained at the optimal conditions of UAE was used to fabricate nanoemulsions using spontaneous emulsification (SE), ultrasonic-assisted emulsification (UE), and SE-UE. The effect of SE and UE conditions on the turbidity of nanoemulsion was determined. Then, the physiochemical attributes of the nanoemulsion from SE, UE, and spontaneous ultrasonic-assisted emulsification (SE-UE) were determined using the dynamic light scattering method. The extraction yield of carotenoids from carrot pomace by using sonication was the highest. The adjusted optimal conditions were 39 mL/g of LSR, 50 °C, 12.5 min, and 350 W of ultrasonic power. Under optimal conditions, the carotenoid content attained was approximately 163.43 ± 1.83 μg/g, with the anticipated value (166 μg/g). The particle sizes of nanoemulsion fabricated at the proper conditions of SE, UE, and SE-UE were 31.2 ± 0.83, 33.8 ± 0.52, and 109.7 ± 8.24 nm, respectively. The results showed that SE and UE are suitable methods for fabricating nanoemulsions. The research provided a green approach for extracting and emulsifying carotenoids from carrot pomace.

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.

Partitioning of Antioxidants in Edible Oil-Water Binary Systems and in Oil-in-Water Emulsions

In recent years, partitioning of antioxidants in oil-water two-phase systems has received great interest because of their potential in the downstream processing of biomolecules, their benefits in health, and because partition constant values between water and model organic solvents are closely related to important biological and pharmaceutical properties such as bioavailability, passive transport, membrane permeability, and metabolism. Partitioning is also of general interest in the oil industry. Edible oils such as olive oil contain a variety of bioactive components that, depending on their partition constants, end up in an aqueous phase when extracted from olive fruits. Frequently, waste waters are subsequently discarded, but their recovery would allow for obtaining extracts with antioxidant and/or biological activities, adding commercial value to the wastes and, at the same time, would allow for minimizing environmental risks. Thus, given the importance of partitioning antioxidants, in this manuscript, we review the background theory necessary to derive the relevant equations necessary to describe, quantitatively, the partitioning of antioxidants (and, in general, other drugs) and the common methods for determining their partition constants in both binary (PWOIL) and multiphasic systems composed with edible oils. We also include some discussion on the usefulness (or not) of extrapolating the widely employed octanol-water partition constant (PWOCT) values to predict PWOIL values as well as on the effects of acidity and temperature on their distributions. Finally, there is a brief section discussing the importance of partitioning in lipidic oil-in-water emulsions, where two partition constants, that between the oil-interfacial, POI, and that between aqueous-interfacial, PwI, regions, which are needed to describe the partitioning of antioxidants, and whose values cannot be predicted from the PWOIL or the PWOCT ones.

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.

Interfacial effects of gallate alkyl esters on physical and oxidative stability of high fat fish oil-in-water emulsions stabilized with sodium caseinate and OSA-modified starch

Effects of sodium caseinate (SC) and its combination with OSA-modified starch (SC-OS; 1:1) alone and with n-alkyl gallates (C0-C18) on the physical and oxidative stability of high-fat fish oil-in-water emulsion were evaluated. SC emulsion contained the smallest droplets and highest viscosity due to the fast adsorption at droplet surfaces. Both emulsions had non-Newtonian and shear-thinning behavior. A lower accumulation of lipid hydroperoxides and volatile compounds was found in SC emulsion due to its better Fe²⁺ chelating activity. The incorporated short-chain gallates (G1 > G0 ∼ G3) in SC emulsion had a strong synergistic effect against lipid oxidation compared to that of SC-OS emulsion. The better antioxidant efficiency of G1 can be related to its higher partition at the oil-water interface, while G0 and G3 had a higher partition into the aqueous phase. In contrast, G8, G12, and G16 added emulsions indicated higher lipid oxidation due to their internalization inside the oil droplets.

Olive oil oleogels as strategy to confer nutritional advantages to burgers

The effect of bovine back fat replacement by oleogels containing pork skin and olive oil on the oxidative stability, physicochemical, technological, nutritional, and sensory parameters of burgers was evaluated. Four different hamburger (H) were manufactured: with 90 % of lean beef and 10 % of bovine back fat (control, HC), or with 10 % of pork skin/water/virgin olive oil (HVOO), stripped olive oil added of an olive leaf extract (HESOO) or stripped olive oil (HSOO) oleogels, at 20:60:20 ratio. Physical-chemical stability was assessed after storage for 7 days at 4 °C and for 90 days at -20 °C, under non-vacuum and vacuum packaging. A reduction in the fat content by 80 % and in the energy content by 35 %, an increase in the protein content by 15 % and a better fatty acid profile were achieved in the oleogel containing burgers. After processing at 180 °C (grill), hardness, chewiness, sensory parameters and overall acceptability were high and comparable to control. All burgers were oxidative stable during 7 days at 4 °C. After storage for 90 days at -20 °C, only HSOO samples stored under non-vacuum packaging were oxidized. The antioxidant content in samples HVOO and HESOO efficiently prevented the oxidation of these samples.

Review on the Regulation of Plant Polyphenols on the Stability of Polyunsaturated-Fatty-Acid-Enriched Emulsions: Partitioning Kinetic and Interfacial Engineering

The plant polyphenols are normally presented as natural functional antioxidants, which also possess the potential ability to improve the physicochemical stability of polyunsaturated fatty acid (PUFA)-enriched emulsions by interface engineering. This review discussed the potential effects of polyphenols on the stability of PUFA-enriched emulsions from the perspective of the molecular thermodynamic antioxidative analysis, the kinetic of interfacial partitioning, and the covalent and non-covalent interactions with emulsifiers. Recently, research studies have proven that the interfacial structure of emulsions can be concurrently optimized via promoting interfacial partitioning of polyphenols and further increasing interfacial thickness and strength. Moreover, the applied limitations of polyphenols in PUFA-enriched emulsions were summarized, and then some valuable and constructive viewpoints were put forward in this review to provide guidance for the use of polyphenols in constructing PUFA-enriched emulsions.

Advances in the control of lipid peroxidation in oil-in-water emulsions: kinetic approaches†

Large efforts have been, and still are, devoted to minimize the harmful effects of lipid peroxidation. Much of the early work focused in understanding both the lipid oxidation mechanisms and the action of antioxidants in bulk solution. However, food-grade oils are mostly present in the form of oil-in-water emulsions, bringing up an increasing complexity because of the three-dimensional interfacial region. This review presents an overview of the kinetic approaches employed in controlling the oxidative stability of edible oil-in-water emulsions and of the main outcomes, with particular emphasis on the role of antioxidants and on the kinetics of the inhibition reaction. Application of physical-organic chemistry methods, such as the pseudophase models to investigate antioxidant partitioning, constitute a remarkable example on how kinetic methodologies contribute to model chemical reactivity in multiphasic systems and to rationalize the role of interfaces, opening new opportunities for designing novel antioxidants with tailored properties and new prospects for modulating environmental conditions in attempting to optimize their efficiency. Here we will summarize the main kinetic features of the inhibition reaction and will discuss on the main factors affecting its rate, including the determination of antioxidant efficiencies from kinetic profiles, structure-reactivity relationships, partitioning of antioxidants and concentration effects.

Unexpected Antioxidant Efficiency of Chlorogenic Acid Phenolipids in Fish Oil-in-Water Nanoemulsions: An Example of How Relatively Low Interfacial Concentrations Can Make Antioxidants to Be Inefficient

Selecting effective antioxidants is challenging since their efficiency in inhibiting lipid oxidation depends on the rate constants of the chemical reactions involved and their concentration at the reaction site, i.e., at the interfacial region. Accumulation of antioxidants at the interface of emulsions is key to modulate their efficiency in inhibiting lipid oxidation but its control was not well understood, especially in emulsions. It can be optimized by modifying the physicochemical properties of antioxidants or the environmental conditions. In this work, we analyze the effects of surfactant concentration, droplet size, and oil to water ratio on the effective interfacial concentration of a set of chlorogenic acid (CGA) esters in fish oil-in-water (O/W) emulsions and nanoemulsions and on their antioxidant efficiency. A well-established pseudophase kinetic model is used to determine in the intact emulsified systems the effective concentrations of the antioxidants (AOs). The relative oxidative stability of the emulsions is assessed by monitoring the formation of primary oxidation products with time. Results show that the concentration of all AOs at the interfacial region is much higher (20–90 fold) than the stoichiometric one but is much lower than those of other phenolipid series such as caffeic or hydroxytyrosol derivatives. The main parameter controlling the interfacial concentration of antioxidants is the surfactant volume fraction, Φ_I, followed by the O/W ratio. Changes in the droplet sizes (emulsions and nanoemulsions) have no influence on the interfacial concentrations. Despite the high radical scavenging capacity of CGA derivatives and their being concentrated at the interfacial region, the investigated AOs do not show a significant effect in inhibiting lipid oxidation in contrast with what is observed using other series of homologous antioxidants with similar reactivity. Results are tentatively interpreted in terms of the relatively low interfacial concentrations of the antioxidants, which may not be high enough to make the rate of the inhibition reaction faster than the rate of radical propagation.

Polyphenols as Antioxidants for Extending Food Shelf-Life and in the Prevention of Health Diseases: Encapsulation and Interfacial Phenomena

Toxicity caused by the exposure to human-made chemicals and environmental conditions has become a major health concern because they may significantly increase the formation of reactive oxygen species (ROS), negatively affecting the endogenous antioxidant defense. Living systems have evolved complex antioxidant mechanisms to protect cells from oxidative conditions. Although oxidative stress contributes to various pathologies, the intake of molecules such as polyphenols, obtained from natural sources, may limit their effects because of their antioxidant and antimicrobial properties against lipid peroxidation and against a broad range of foodborne pathogens. Ingestion of polyphenol-rich foods, such as fruits and vegetables, help to reduce the harmful effects of ROS, but the use of supramolecular and nanomaterials as delivery systems has emerged as an efficient method to improve their pharmacological and therapeutic effects. Suitable exogenous polyphenolic antioxidants should be readily absorbed and delivered to sites where pathological oxidative damage may take place, for instance, intracellular locations. Many potential antioxidants have a poor bioavailability, but they can be encapsulated to improve their ideal solubility and permeability profile. Development of effective antioxidant strategies requires the creation of new nanoscale drug delivery systems to significantly reduce oxidative stress. In this review we provide an overview of the oxidative stress process, highlight some properties of ROS, and discuss the role of natural polyphenols as bioactives in controlling the overproduction of ROS and bacterial and fungal growth, paying special attention to their encapsulation in suitable delivery systems and to their location in colloidal systems where interfaces play a crucial role.

Caffeic acid phenolipids in the protection of cell membranes from oxidative injuries. Interaction with the membrane phospholipid bilayer

Caffeic acid (CA) has demonstrated a strong intracellular antioxidant ability by scavenging ROS, contributing to the maintenance of cell membrane structural integrity and to reduce oxidative injuries in other cell components. Nevertheless, caffeic acid has limited usage, due to its hydrophilic character. In this work, the introduction of alkyl chains in the caffeic acid molecule by esterification (methyl - C1, ethyl - C2, butyl - C4, hexyl - C6, octyl - C8 and hexadecyl - C16), significantly increased its lipophilicity. All caffeates tested showed a much higher protective activity than caffeic acid against red blood cells (RBCs) AAPH-induced oxidative stress; this protection was heavily dependent on the length of the alkyl chain of the esters, and on their concentration. At 2.5 and 5 μM, the more lipophilic compounds (C8 and C16) showed a remarkable antioxidant activity, inhibiting hemolysis; probably, their better location within the membrane leads to a better antioxidative protection; however, at 50 μM, the more hydrophilic compounds (C1-C4) showed a better activity against hemolysis than the more lipophilic ones (C8-C16). At this higher concentration, the better interaction of the more lipophilic compounds with the membrane seems to cause changes in RBC membrane fluidity, disturbing membrane integrity. Our data show that the antioxidant activity of these compounds could play an important role for the protection of different tissues and organs, by protecting cell membranes from oxidative injuries.

Effects of Surfactant Volume Fraction on the Antioxidant Efficiency and on The Interfacial Concentrations of Octyl and Tetradecyl p-Coumarates in Corn Oil-in-Water Emulsions

Surfactants have been used for decades in the food industry for the preparation of lipid-based emulsified food stuffs. They play two main roles in the emulsification processes: first they decrease the interfacial tension between the oil and water, facilitating droplet deformation and rupture; second, they reduce droplet coalescence by forming steric barriers. However, addition of surfactants to binary oil-water mixtures also brings up the formation of three-dimensional interfacial layers, surrounding each emulsion droplet, that significantly alter chemical reactivity. This is the case, for instance, in the inhibition reaction between antioxidants and the lipid radicals formed in the course of the spontaneous oxidation reaction of unsaturated lipids, which are commonly employed in the preparation of food-grade emulsions. The rate of the inhibition reaction depends on the effective concentrations of antioxidants, which are mostly controlled by the amount of surfactant employed in the preparation of the emulsion. In this work, we analyze the effects of the surfactant Tween 20 on the oxidative stability and on the effective concentrations of two model antioxidants derived from cinnamic acid, determining their interfacial concentrations in the intact emulsions to avoid disrupting the existing equilibria and biasing results. For this purpose, a recently developed methodology was employed, and experimental results were interpreted on the grounds of a pseudophase kinetic model.

Modeling Chemical Reactivity at the Interfaces of Emulsions: Effects of Partitioning and Temperature

Bulk phase chemistry is hardly ever a reasonable approximation to interpret chemical reactivity in compartmentalized systems, because multiphasic systems may alter the course of chemical reactions by modifying the local concentrations and orientations of reactants and by modifying their physical properties (acid-base equilibria, redox potentials, etc.), making them-or inducing them-to react in a selective manner. Exploiting multiphasic systems as beneficial reaction media requires an understanding of their effects on chemical reactivity. Chemical reactions in multiphasic systems follow the same laws as in bulk solution, and the measured or observed rate constant of bimolecular reactions can be expressed, under dynamic equilibrium conditions, in terms of the product of the rate constant and of the concentrations of reactants. In emulsions, reactants distribute between the oil, water, and interfacial regions according to their polarity. However, determining the distributions of reactive components in intact emulsions is arduous because it is physically impossible to separate the interfacial region from the oil and aqueous ones without disrupting the existing equilibria and, therefore, need to be determined in the intact emulsions. The challenge is, thus, to develop models to correctly interpret chemical reactivity. Here, we will review the application of the pseudophase kinetic model to emulsions, which allows us to model chemical reactivity under a variety of experimental conditions and, by carrying out an appropriate kinetic analysis, will provide important kineticparameters.

Interfacial kinetics in olive oil-in-water nanoemulsions: Relationships between rates of initiation of lipid peroxidation, induction times and effective interfacial antioxidant concentrations

HYPOTHESIS

A detailed quantitative description of the effects of antioxidants in inhibiting lipid peroxidation in oil-in-water emulsions can be achieved by determining the relationships between the rates of initiation of the lipid peroxidation reaction, the length of the induction period preceding the propagation step of the radical oxidation process and the effective antioxidant interfacial concentrations.

EXPERIMENTS

We successfully prepared and characterized a series of olive oil-in-water nanoemulsions and allowed them to spontaneously oxidize. Their oxidative stability was evaluated by carrying out in the presence, and absence, of antioxidants derived from gallic acid, by monitoring the formation of primary oxidation products with time, by determining the corresponding induction periods, and by determining the effective interfacial concentrations of the antioxidants in the intact emulsions.

FINDINGS

Results show that both, the length of the induction periods and the antioxidant interfacial concentrations change concomitantly, increasing with the hydrophobicity of the antioxidant up to a maximum at the octyl derivative; longer aliphatic chains decrease their efficiency. The ratio between the interfacial antioxidant concentration and the induction period remains constant independently of the antioxidant, demonstrating that the effective concentrations of antioxidant at the interface control their efficiencies in emulsions.

A comprehensive review on polarity, partitioning, and interactions of phenolic antioxidants at oil-water interface of food emulsions

There has been a growing interest in developing effective strategies to inhibit lipid oxidation in emulsified food products by utilization of natural phenolic antioxidants owing to their growing popularity over the past decades. However, due to the complexity of emulsified systems, the inhibition mechanism of phenolic antioxidants against lipid oxidation is rather complicated and not yet fully understood. In order to highlight the importance of polarity of phenolic antioxidants in emulsified systems according to the polar paradox, this review covers the recent progress on chemical, enzymatic, and chemoenzymatic lipophilization techniques used to modify the polarity of antioxidants. The partitioning behavior of phenolic antioxidants at the oil-water interface, which can be influenced by the presence of synthetic surfactants and/or antioxidant emulsifiers (e.g., polysaccharides, proteins, and phospholipids), is discussed. In addition, the emerging phenolic antioxidants among phenolic acids, flavonoids, tocopherols, and stilbenes applied in food emulsions are elaborated. As well, the interactions of polar-nonpolar antioxidants are stressed as a promising strategy to induce synergistic interactions at oil-water interface for improved oxidative stability of emulsions.

Effects of antioxidants, proteins, and their combination on emulsion oxidation

Lipid oxidation largely determines the quality of emulsion systems as well as their final products. Therefore, an increasing number of studies have focused on the control of lipid oxidation, particularly on its mechanism. In this review, we discuss the factors affecting the efficiency of antioxidants in emulsion systems, such as the free radical scavenging ability, specifically emphasizing on the interfacial behavior and the influence of surfactants on the interfacial distribution of antioxidants. To enhance the antioxidant efficiency of antioxidants in emulsion systems, we discussed whether the combination of antioxidants and proteins can improve antioxidant effects. The types, mixing applications, structures, interface behaviors, effects of surfactants on interfacial proteins, and the location of proteins are associated with the antioxidant effects of proteins in emulsion systems. Antioxidants and proteins can be combined in both covalent and non-covalent ways. The fabrication conditions, conjugation methods, interface behaviors, and characterization methods of these two combinations are also discussed. Our review provides useful information to guide better strategies for providing stability and controlling lipid oxidation in emulsions. The main challenges and future trends in controlling lipid oxidation in complex emulsion systems are also discussed.

Effects of the Reactive Moiety of Phenolipids on Their Antioxidant Efficiency in Model Emulsified Systems

Our previous research was focused on the effects of hydrophobicity on the antioxidant (AO) efficiency of series of homologous antioxidants with the same reactive moieties. In this work we evaluate the antioxidant efficiency of hydrophobic phenolipids in 4:6 olive oil-in-water emulsions, with different phenolic moieties (derived from caffeic, 4-hydroxycinnamic, dihydrocaffeic acids, tyrosol and hydroxytyrosol), with alkyl chains of 8 and 16 carbons, and compare the antioxidant efficiency with that of the parent compounds. All catecholic phenolipids, in particular the C8 derivatives, have proven to be better antioxidants for the oxidative protection of emulsions than their parental compounds with octyl dihydrocafffeate being the most efficient (16-fold increase in relation to the control). To understand the importance of some factors on the antioxidant efficiency of compounds in emulsions, Pearson’s correlation analysis was carried out between antioxidant activity and the first anodic potential (E_pa), reducing capacity (FRAP value), DPPH radical scavenging activity (EC₅₀) and the concentration of antioxidants in each region of the emulsified system. Results confirm the importance of the effective concentration of AOs in the interfacial region (AO_I) (ρ = 0.820) and of the E_pa (ρ = −0.677) in predicting their antioxidant efficiency in olive oil-in-water emulsions.

Polyphenolic Antioxidants in Lipid Emulsions: Partitioning Effects and Interfacial Phenomena

The autoxidation of lipids in complex systems such as emulsions or biological membranes, although known to occur readily and to be associated with important pathological events, is lacking in quantitative data in spite of the huge efforts that have been made in attempting to unravel the complex mechanisms of lipid oxidation and its inhibition by antioxidants. Lipids are present as oil-in-water emulsions in many foods and pharmaceutical formulations, and the prevalent role of the interfacial region is critical to understand the antioxidant behavior and to correctly interpret antioxidant efficiencies. The aim of this review is to summarize the current knowledge on the chemical fate of antioxidants before they react with peroxyl radicals. Many researchers highlighted the predominant role of interfaces, and although some attempts have been made to understand their role, in most instances, they were essentially qualitative and based on putative hypotheses. It is only recently that quantitative reports have been published. Indeed, knowledge on the effects of relevant experimental variables on the effective concentrations of antioxidants is necessary for a successful design of alternate, effective antioxidative solutions.

Interfacial Concentrations of Hydroxytyrosol Derivatives in Fish Oil-in-Water Emulsions and Nanoemulsions and Its Influence on Their Lipid Oxidation: Droplet Size Effects

Reports on the effect of droplet size on the oxidative stability of emulsions and nanoemulsions are scarce in the literature and frequently contradictory. Here, we have employed a set of hydroxytyrosol (HT) esters of different hydrophobicity and fish oil-in-water emulsified systems containing droplets of different sizes to evaluate the effect of the droplet size, surfactant, (Φ_I) and oil (Φ_O) volume fractions on their oxidative stability. To quantitatively unravel the observed findings, we employed a well-established pseudophase kinetic model to determine the distribution and interfacial concentrations of the antioxidants (AOs) in the intact emulsions and nanoemulsions. Results show that there is a direct correlation between antioxidant efficiency and the concentration of the AOs in the interfacial region, which is much higher (20–200 fold) than the stoichiometric one. In both emulsified systems, the highest interfacial concentration and the highest antioxidant efficiency was found for hydroxytyrosol octanoate. Results clearly show that the principal parameter controlling the partitioning of antioxidants is the surfactant volume fraction, Φ_I, followed by the O/W ratio; meanwhile, the droplet size has no influence on their interfacial concentrations and, therefore, on their antioxidant efficiency. Moreover, no correlation was seen between droplet size and oxidative stability of both emulsions and nanoemulsions.

A new family of hydroxytyrosol phenolipids for the antioxidant protection of liposomal systems

Hydroxytyrosol (HT) is a well-known olive oil polyphenol for its high antioxidant capacity and important cardio and neuroprotective effects. However, its use in lipidic systems is limited, due to its hydrophilic character. In this study, we approach the particular structure of xanthophylls and synthetize HT esters specially designed for the protection of liposomal systems. These HT esters contain two polyphenolic moieties separated by a lipophilic alkyl spacer of different length (12, 16 or 22 carbons). To evaluate the antioxidant activity of these compounds against the 2,2'-azobis(2-amidinopropane) hydrochloride induced oxidation, soybean phospholipid liposomes were used. Fluorescence quenching studies were used to assess the insertion of the compounds in the liposomes. The synthetized HT derivatives were able to protect liposomes from induced oxidation when added to the suspensions. The rank of activity was severely influenced by the alkyl chain length of the spacer molecule, being the C12 derivative the most active antioxidant, with an increase in the oxidative stability of liposomes of 2.2 times when compared with the control. The incorporation of compounds during liposome preparation improved the antioxidant capacity of all HT derivatives by about 2.8 times, when compared to the control. This is probably due to a similar transmembrane position with both polyphenolic rings located at the phospholipid polar heads. The synthesis of bis-ester derivatives seems to be a promising strategy to fine-tune antioxidant molecules at biomembranes, thus increasing the oxidative stability of liposomal systems by improving the antioxidant activity of hydrophilic phenolic compounds with high free radical scavenging activity.

Improving the Stability of Lycopene from Chemical Degradation in Model Beverage Emulsions: Impact of Hydrophilic Group Size of Emulsifier and Antioxidant Polarity

The chemical stability of the lipophilic bioactives encapsulated in emulsions can be influenced by emulsion droplet interfacial characteristics as well as by the ability of antioxidants incorporated in emulsion to prevent the degradation of the encapsulated compounds. Therefore, this study evaluated the effects of the interfacial characteristics of emulsions and the polarity of antioxidants on the storage stability of lycopene in emulsions. Emulsions with 5% (w/w) oil containing lycopene (30 µmol/kg emulsion) were prepared using a series of polyethylene glycol acyl ether-type emulsifiers through microfluidization. Change in lycopene content in emulsions was monitored by high performance liquid chromatography. Our findings show that the hydrophilic group size (or length) of emulsifiers and the emulsifier concentration at the interfacial film play a role, albeit minor, in controlling the storage stability of lycopene encapsulated in emulsions. Lipophilic (tert-butylhydroquinone (TBHQ)) and amphiphilic (lauryl gallate) antioxidants similarly improved the storage stability of lycopene in emulsions from acid- and radical-mediated degradation, independent of the characteristics of interfacial films of emulsions. However, TBHQ inhibited the degradation of lycopene in emulsions more effectively than lauryl gallate under conditions intended to accelerate the acid-mediated degradation of lycopene. Therefore, our findings can provide helpful information about what type of emulsifiers and antioxidants can be chosen for preparing food emulsions capable of maximizing the stability of lycopene encapsulated therein.