Mass Transport Phenomena in Lipid Oxidation and Antioxidation

Controlled dual release of phenol compounds from phospholipid complexes of short-chain lipophenols

Ethanol evaporation method was applied to synthesize phospholipid complexes from phosphatidylcholine (PC) and short-chain alkyl gallates (A-GAs, a typical representative of lipophenols) including butyl-, propyl- and ethyl gallates. 1H NMR, UV and FTIR showed that A-GAs were interacted with PC through weak physical interaction. Through the analysis of concentrations of A-GAs and gallic acid (GA) by an everted rat gut sac model coupled with HPLC-UV detection, phospholipid complexes were found to gradually release A-GAs. These liberated A-GAs were further hydrolyzed by intestinal lipases to release GA. Both of GA and A-GAs could cross intestinal membrane. Especially, the transmembrane A-GAs could also be hydrolyzed to produce GA. Undoubtedly, the dual release of phenol compounds from phospholipid complexes of short-chain lipophenols will be effective to extend the in vivo residence period of phenol compounds. More importantly, such behavior is easily adjusted by changing the acyl chain lengths of lipophenols in phospholipid complexes.

Mechanism of discoloration of Antarctic krill oil upon storage: A study based on model systems

The reddish-orange color of Antarctic krill oil fades during storage, and the mechanism remains unclear. Model systems containing different combinations of astaxanthin (ASTA), phosphatidylethanolamine (PE), and tocopherol were subjected to accelerated storage. Among all groups containing ASTA, only the ones with added PE showed significant fading. Meanwhile, the specific UV-visible absorption (A470 and A495) showed a similar trend. Peroxide value and thiobarbituric acid reactive substances increased during storage, while ASTA and PE contents decreased. Correlation analysis suggested that oxidized PE promoted fading by accelerating the transformation of ASTA. PE content exceeded the critical micelle concentration (1μg/g) indicating the formation of reverse micelles. Molecular docking analysis indicated that PE also interacted with ASTA in an anchor-like manner. Therefore, it is speculated that amphiphilic ASTA is more readily distributed at the oil-water interface of reverse micelles and captured by oxidized PE, which facilitates oxidation transfer, leading to ASTA oxidation and color fading.

Antioxidant potency and inhibitory mechanism of curcumin and its derivatives in oleogel and emulgel produced by linseed oil

The antioxidant activity of curcumin and curcumin esters was investigated in oleogel and emulgel produced by linseed oil. In the initiation phase, curcumin acetate at 1.086 mM concentration showed the highest antioxidant activity in linseed oil, while curcumin at 2.172 mM concentration showed the highest antioxidant activity in oleogel. In the propagation phase, curcumin and curcumin esters exhibited higher efficiency in linseed oil samples than those of oleogel samples. In the initiation phase, curcumin hexanoate showed higher antioxidant activity than curcumin acetate and curcumin butyrate, while curcumin hexanoate showed lower efficiency than curcumin acetate and curcumin butyrate in the propagation phase. Investigating the mechanism of action of curcumin and curcumin esters in oleogel and emulgel showed that in addition to inhibiting peroxyl radicals, curcumin and curcumin esters were likely to pro-oxidatively attack hydroperoxides. Also, curcumin and curcumin esters radicals were likely to attack lipid substrates in these systems.

β-cyclodextrin inclusion complexes with short-chain phenolipids: An effective formulation for the dual sustained-release of phenolic compounds

The β-cyclodextrin and short-chain alkyl gallates (A-GAs), which are representative of phenolipids, such as butyl, propyl, ethyl, and methyl gallates, were chosen to form inclusion complexes by the use of the freeze-drying process. In the everted rat gut sac model, HPLC-UV analysis demonstrated that the released A-GAs from inclusion complexes were degraded to yield free gallic acid (GA) (sustained-release function 1). The small intestine membrane may be crossed by both the GA and the A-GAs. A-GAs may also undergo hydrolysis to provide GA (sustained-release function 2) following transmembrane transfer. Clearly, a helpful technique for the dual sustained-release of phenolic compounds is to produce β-cyclodextrin inclusion complexes with short-chain phenolipids. This will increase the bioactivities of phenolic compounds and prolong their in vivo residence length. Moreover, changing the carbon-chain length of these β-cyclodextrin inclusion complexes would readily modify the dual sustained-release behavior of the phenolic compounds. Thus, our work effectively established a theoretical foundation for the use of β-cyclodextrin inclusion complexes containing short-chain phenolipids as new source of functional food components to provide the body with phenolic compounds more efficiently.

Effects of rosmarinic acid esters on the oxidation kinetic of organogel and emulsion gel

Rosmarinic acid was esterified with ethanol, butanol, and hexanol to produce ethyl rosmarinate, butyl rosmarinate, and hexyl rosmarinate, respectively. The antioxidant capacities of the rosmarinic acid esters were evaluated in linseed oil, organogel, and emulsion gel during the initiation and propagation phases of peroxidation. Organogel control sample showed higher induction period and propagation period than those of linseed oil and emulsion gel control samples. Among linseed oil and organogel samples containing antioxidants, samples containing rosmarinic acid exhibited the highest antioxidant activity during the initiation phase, while rosemary extract containing butyl rosmarinate showed the highest antioxidant activity in the propagation phase. In emulsion gel, rosemary extract containing butyl rosmarinate showed higher antioxidant activity than those of rosemary extract containing ethyl rosmarinate or hexyl rosmarinate in the initiation and propagation phases. In addition, the investigated antioxidants showed lower efficiency in organogel and emulsion gel samples than those in linseed oil samples.

Comparative study on the enzymatic degradation of phenolic esters: The HPLC-UV quantification of tyrosol and gallic acid liberated from tyrosol acyl esters and alkyl gallates by hydrolytic enzymes

HPLC-UV analysis was used to evaluate the enzymatic degradation characteristics of tyrosol acyl esters (TYr-Es) and alkyl gallates (A-GAs). Among various hydrolytic enzymes, TYr-Es can be hydrolyzed by pancrelipase, while A-GAs cannot be hydrolyzed by pancrelipase. Interestingly, carboxylesterase-1b (CES-1b), carboxylesterase-1c (CES-1c) and carboxylesterase-2 (CES-2) are able to hydrolyze TYr-Es and A-GAs, and thus to liberate tyrosol (TYr) and gallic acid (GA). By contrast, the degrees of hydrolysis (DHs) of TYr-Es and A-GAs by CES-1b and CES-1c were significantly higher than those by CES-2. Meanwhile, the DHs of TYr-Es were much higher than those of A-GAs. Especially, the DHs firstly increased and then decreased with the increasing alkyl chain length. Besides, DHs positively correlated with the unsaturation degree at the same chain length. Through regulating carbon length, unsaturation degree and the ester bond structure, controlled-release of phenolic compounds and fatty acids (or fatty alcohols) from phenolic esters will be easily achieved.

Analysis of the Efficiency of Antioxidants in Inhibiting Lipid Oxidation in Terms of Characteristic Kinetic Parameters

In this work, we aim to find physical evidence demonstrating the crucial role that the effective concentration of antioxidants (AOs) present at the interfacial region of emulsions has in controlling the inhibition of the lipid oxidation reaction. We prepared a series of antioxidants of different hydrophobicities derived from chlorogenic and protocatechuic acids. We first monitored, in intact emulsions, the (sigmoidal) production of conjugated dienes and determined the corresponding induction times, tind. Independently, we determined the effective concentrations of the antioxidants in the same intact emulsions. Results show that both the length of the induction periods and the antioxidant interfacial concentrations parallel each other, with a maximum at the octyl-dodecyl derivatives. The ratio between the interfacial antioxidant concentrations and the induction periods remains constant for all AOs in the same series, so that the rates of initiation of lipid oxidation are the same regardless of the hydrophobicity of the antioxidant employed. The constancy in the rate of initiation provides strong experimental evidence for a direct relationship between interfacial concentrations and antioxidant efficiencies. Results suggest new possibilities to investigate lipid peroxidation under non-forced conditions and are of interest to formulators interested in preparing emulsions with antimicrobial properties.

Response to "Liposome vesicle cannot be formed in non-aqueous phase"

In a recent letter to the editor Prof Khosravi-Darani responded to our paper ''Unravelling mechanisms of protein and lipid oxidation in mayonnaise at multiple length scales''. In our work, we observed liposomes in the continuous phase of mayonnaise. In the letter the objection was made that liposomes cannot be formed in a non-aqueous phase which, however, was not argued in our publication. As mayonnaise is an oil-in-water (O/W) emulsion and its continuous phase is aqueous, liposomes may be observed in this phase. Therefore, the objection from Prof Khosravi-Darani does not apply to our work.

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.

Recent advances in understanding the interfacial activity of antioxidants in association colloids in bulk oil

The chemical stability of edible oils rich in polyunsaturated fatty acids (PUFAs) is a major challenge within the food and supplement industries, as lipid oxidation reduces oil quality and safety. Despite appearing homogeneous to the human eye, bulk oils are actually multiphase heterogeneous systems at the nanoscale level. Association colloids, such as reverse micelles, are spontaneously formed within bulk oils due to the self-assembly of amphiphilic molecules that are present, like phospholipids, free fatty acids, and/or surfactants. In bulk oil, lipid oxidation often occurs at the oil-water interface of these association colloids because this is where different reactants accumulate, such as PUFAs, hydroperoxides, transition metals, and antioxidants. Consequently, the efficiency of antioxidants in bulk oils is governed by their chemical reactivity, but also by their ability to be located close to the site of oxidation. This review describes the impact of minor constituents in bulk oils on the nature of the association colloids formed. And then the formation of mixed reverse micelles (LOOH, (co)surfactants, or antioxidations) during the peroxidation of bulk oils, as well as changes in their composition and structure over time are also discussed. The critical importance of selecting appropriate antioxidants and surfactants for the changes of interface and colloid, as well as the inhibition of lipid oxidation is emphasized. The knowledge presented in this review article may facilitate the design of bulk oil products with improved resistance to oxidation, thereby reducing food waste and improving food quality and safety.

Antioxidant functions of caffeic acid and allylpyrocatechol in supramolecular oxidation of bulk oil: Role of acidic group in the mass transfer network

Antioxidant activities of caffeic acid (CFA) and allylpyrocatechol (APC) were measured in bulk oil and in emulsion (oil/water) to evaluate the effects of the carboxylic group on the antioxidant function. As an emulsifier, polyglycerol polyricinoleate (PGPR) was added to the bulk oil to assist in promoting the interfacial activity of antioxidants. The antioxidant activity of CFA in the bulk oil was 186.5% higher than that of APC. In the emulsion, however, APC showed 150.3% higher antioxidant activity. PGPR showed a synergistic effect on CFA (>31%) and APC (<18%) which arose from organizing and supporting the formation of oxidation-microreactors. Water molecules were generated as an oxidation byproduct throughout the oxidation course, and they facilitated the formation of supramolecular structures. Polar imbalance became more prominent in the molecular structure of CFA, due to the presence of the carboxyl group, thereby increasing the effective collisions between the antioxidant molecules and free radicals.

Mechanistic kinetic modelling of lipid oxidation in vegetable oils to estimate shelf-life

Estimating the shelf-life of vegetable oils is important to develop solutions to reduce spoilage by lipid oxidation. Typically, the shelf-life is predicted by detecting secondary oxidation markers in accelerated shelf-life tests, which are time-consuming. Existing numerical approaches using early primary oxidation products as predictive markers do not account for variations in fatty acid types, antioxidants, or storage conditions. A mechanistic kinetic model was developed incorporating these factors as a step towards shelf-life prediction for vegetable oils. Specific kinetic constants for the reactions of each unsaturated fatty acid type account for variations in fatty acid composition, and oxygen mass transfer accounts for variations in oxygen conditions. A second acceleration of lipid oxidation observed in long-term storage experiments was described by a multiplication factor for the kinetic constants related to oxidation products. Our model accurately extrapolates short-time experimental data to estimate long term formation of oxidation products under the same conditions.

Hydrolysis and Transport Characteristics of Phospholipid Complex of Alkyl Gallates: Potential Sustained Release of Alkyl Gallate and Gallic Acid

Phospholipid complexes of alkyl gallates (A-GAs) including ethyl gallate (EG), propyl gallate (PG), and butyl gallate (BG) were successfully prepared by the thin film dispersion method. HPLC-UV analysis in an everted rat gut sac model indicated that A-GAs can be liberated from phospholipid complexes, which were further hydrolyzed by intestinal lipase to generate free gallic acid (GA). Both A-GAs and GA are able to cross the membrane, and the hydrolysis rate of A-GAs and the transport rate of GA are positively correlated with the alkyl chain length. Especially, compared with the corresponding physical mixtures, the phospholipid complexes exhibit slower sustained-release of A-GAs and GA. Therefore, the formation of phospholipid complexes is an effective approach to prolong the residence time in vivo and additionally enhance the bioactivities of A-GAs and GA. More importantly, through regulating the carbon skeleton lengths, controlled-release of alkyl gallates and gallic acid from phospholipid complexes will be achieved.

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.

Emergence of (hydro)persulfides as suppressors of lipid peroxidation and ferroptotic cell death

Recognition of the prevalence of hydropersulfides (RSSH) and characterization of their enhanced two-electron reactivity relative to thiols have led to their implication in maintaining cellular redox homeostasis, in addition to other potential roles. Recent attention on the one-electron reactivity of RSSH has uncovered their potent radical-trapping antioxidant activity, which enables them to inhibit phospholipid peroxidation and associated cell death by ferroptosis. Herein, we briefly review key aspects of the reactivity and underlying physicochemical properties of RSSH. We emphasize their reactivity to radicals-particularly lipid peroxyl radicals that propagate the lipid peroxidation chain reaction-and the recent recognition that this results in ferroptosis suppression. We highlight open questions related to recent developments in this area and, given that all living organisms possess the ability to synthesize persulfides endogenously, suggest they may be primordial radical scavengers that occurred early in evolution and still play a role today.

Comparison of the antioxidant capacity of sesamol esters in gelled emulsion and non-gelled emulsion

The antioxidant capacity of sesamol esters in gelled emulsion was investigated in comparison with non-gelled emulsion to assess the role of mass transfer on their antioxidant capacity. Initiation phase and propagation phase kinetic parameters of peroxidation was calculated using a sigmoidal model. Sesamol esters showed higher antioxidant activity than sesamol in gelled emulsion and non-gelled emulsion. Sesamyl acetate, sesamyl butyrate, and sesamyl hexanoate had no synergistic effect with sesamol in gelled emulsion, while in non-gelled emulsion sesamyl butyrate exhibited a slight synergistic effect with sesamol. The antioxidant activity of sesamyl acetate and sesamyl hexanoate in non-gelled emulsion samples were higher than those of gelled emulsion samples, while sesamyl butyrate exhibited higher antioxidant activity in gelled emulsion than that of non-gelled emulsion. The cut-off effect hypothesis was observed in gelled emulsion, while this hypothesis was disappeared in non-gelled emulsion. During propagation phase, sesamol esters remained active and exhibited inhibitory effect.

Comparing the antioxidant activity of gallic acid and its alkyl esters in emulsion gel and non-gelled emulsion

In this study, antioxidant capacity of gallic acid and its alkyl esters in emulsion gel was compared with non-gelled emulsion to determine the role of mass transport on their efficiency. Lauryl gallate exhibited higher antioxidant activity than gallic acid and ethyl gallate in emulsion gel and non-gelled emulsion. In emulsion gel, the synergistic effects in the initiation stage for gallic acid + ethyl gallate, gallic acid + lauryl gallate, and ethyl gallate + lauryl gallate were 78.28 %, 68.46 %, and 60.04 %, respectively. In non-gelled emulsion, the synergistic effects were 52.78 %, 39.02 %, and 22.30 %, respectively. In both emulsion gel and non-gelled emulsion, the longest induction period and propagation period was observed in samples containing gallic acid + lauryl gallate. The effectiveness of antioxidants in emulsion gel was lower than non-gelled emulsion. This reduction in antioxidant activity can be due to the limited ability of antioxidants to be transferred to the interfacial area.

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.

Recent Trends in Improving the Oxidative Stability of Oil-Based Food Products by Inhibiting Oxidation at the Interfacial Region

In recent years, new approaches have been developed to limit the oxidation of oil-based food products by inhibiting peroxidation at the interfacial region. This review article describes and discusses these particular approaches. In bulk oils, modifying the polarity of antioxidants by chemical methods (e.g., esterifying antioxidants with fatty alcohol or fatty acids) and combining antioxidants with surfactants with low hydrophilic–lipophilic balance value (e.g., lecithin and polyglycerol polyricinoleate) can be effective strategies for inhibiting peroxidation. Compared to monolayer emulsions, a thick interfacial layer in multilayer emulsions and Pickering emulsions can act as a physical barrier. Meanwhile, high viscosity of the water phase in emulsion gels tends to hinder the diffusion of pro-oxidants into the interfacial region. Furthermore, applying surface-active substances with antioxidant properties (such as proteins, peptides, polysaccharides, and complexes of protein-polysaccharide, protein-polyphenol, protein-saponin, and protein-polysaccharide-polyphenol) that adsorb at the interfacial area is another novel method for enhancing oil-in-water emulsion oxidative stability. Furthermore, localizing antioxidants at the interfacial region through lipophilization of hydrophilic antioxidants, conjugating antioxidants with surfactants, or entrapping antioxidants into Pickering particles can be considered new strategies for reducing the emulsion peroxidation.

Impact of processing on the oxidative stability of oil bodies

Plant lipids are stored as emulsified lipid droplets also called lipid bodies, spherosomes, oleosomes or oil bodies. Oil bodies are found in many seeds such as cereals, legumes, or in microorganisms such as microalgae, bacteria or yeast. Oil Bodies are unique subcellular organelles with sizes ranging from 0.2 to 2.5 μm and are made of a triacylglycerols hydrophobic core that is surrounded by a unique monolayer membrane made of phospholipids and anchored proteins. Due to their unique properties, in particular their resistance to coalescence and aggregation, oil bodies have an interest in food formulations as they can constitute natural emulsified systems that does not need the addition of external emulsifier. This manuscript focuses on how extraction processes and other factors impact the oxidative stability of isolated oil bodies. The potential role of oil bodies in the oxidative stability of intact foods is also discussed. In particular, we discuss how constitutive components of oil bodies membranes are associated in a strong network that may have an antioxidant effect either by physical phenomenon or by chemical reactivities. Moreover, the importance of the selected process to extract oil bodies is discussed in terms of oxidative stability of the recovered oil bodies.

Hydropersulfides inhibit lipid peroxidation and ferroptosis by scavenging radicals

Ferroptosis is a type of cell death caused by radical-driven lipid peroxidation, leading to membrane damage and rupture. Here we show that enzymatically produced sulfane sulfur (S⁰) species, specifically hydropersulfides, scavenge endogenously generated free radicals and, thereby, suppress lipid peroxidation and ferroptosis. By providing sulfur for S⁰ biosynthesis, cysteine can support ferroptosis resistance independently of the canonical GPX4 pathway. Our results further suggest that hydropersulfides terminate radical chain reactions through the formation and self-recombination of perthiyl radicals. The autocatalytic regeneration of hydropersulfides may explain why low micromolar concentrations of persulfides suffice to produce potent cytoprotective effects on a background of millimolar concentrations of glutathione. We propose that increased S⁰ biosynthesis is an adaptive cellular response to radical-driven lipid peroxidation, potentially representing a primordial radical protection system.

Bacterial Cellulose Nanofibril-Based Pickering Emulsions: Recent Trends and Applications in the Food Industry

The Pickering emulsion stabilized by food-grade colloidal particles has developed rapidly in recent decades and attracts extensive attention for potential applications in the food industry. Bacterial cellulose nanofibrils (BCNFs), as green and sustainable colloidal nanoparticles derived from bacterial cellulose, have various advantages for Pickering emulsion stabilization and applications due to their unique properties, such as good amphiphilicity, a nanoscale fibrous network, a high aspect ratio, low toxicity, excellent biocompatibility, and sustainability. This review provides a comprehensive overview of the recent advances in the Pickering emulsion stabilized by BCNF particles, including the classification, preparation method, and physicochemical properties of diverse BCNF-based particles as Pickering stabilizers, as well as surface modifications with other substances to improve their emulsifying performance and functionality. Additionally, this paper highlights the stabilization mechanisms and provides potential food applications of BCNF-based Pickering emulsions, such as nutrient encapsulation and delivery, edible coatings and films, fat substitutes, etc. Furthermore, the safety issues and future challenges for the development and food-related applications of BCNFs-based Pickering emulsions are also outlined. This work will provide new insights and more ideas on the development and application of nanofibril-based Pickering emulsions for researchers.

Review on the Antioxidant Activity of Phenolics in o/w Emulsions along with the Impact of a Few Important Factors on Their Interfacial Behaviour

This review paper focuses on the antioxidant properties of phenolic compounds in oil in water (o/w) emulsion systems. The authors first provide an overview of the most recent studies on the activity of common, naturally occurring phenolic compounds against the oxidative deterioration of o/w emulsions. A screening of the latest literature was subsequently performed with the aim to elucidate how specific parameters (polarity, pH, emulsifiers, and synergistic action) affect the phenolic interfacial distribution, which in turn determines their antioxidant potential in food emulsion systems. An understanding of the interfacial activity of phenolic antioxidants could be of interest to food scientists working on the development of novel food products enriched with functional ingredients. It would also provide further insight to health scientists exploring the potentially beneficial properties of phenolic antioxidants against the oxidative damage of amphiphilic biological membranes (which link to serious pathologic conditions).

Gastrointestinal Digestion and Microbial Hydrolysis of Alkyl Gallates: Potential Sustained Release of Gallic Acid

Phenolipids such as alkyl gallates (A-GAs) have been approved by the food industry as non-toxic antioxidant additives, which are also regarded as an emerging source of functional food ingredients. However, comprehensive understanding of their digestive absorption is needed. Thus, the models of live mice and anaerobic fermentation were used to clarify the distribution and microbial hydrolysis characteristics of A-GAs in the gastrointestinal tract. HPLC-UV results demonstrated that A-GAs could be hydrolyzed by intestinal lipases and gut microorganisms including Lactobacillus to produce free gallic acid (GA). Through regulating the chain length of the lipid part in A-GAs, the sustained and controllable release of the GA can be easily achieved. Furthermore, A-GAs were also able to reach the colon and the cecum, which would lead to potential gastrointestinal protective effects. Therefore, A-GAs may be applied as possible ingredient for functional foods.

An Overview on the Use of Extracts from Medicinal and Aromatic Plants to Improve Nutritional Value and Oxidative Stability of Vegetable Oils

Oil oxidation is the main factor limiting vegetable oils' quality during storage, as it leads to the deterioration of oil's nutritional quality and gives rise to disagreeable flavors. These changes make fat-containing foods less acceptable to consumers. To deal with this problem and to meet consumer demand for natural foods, vegetable oil fabricators and the food industry are looking for alternatives to synthetic antioxidants to protect oils from oxidation. In this context, natural antioxidant compounds extracted from different parts (leaves, roots, flowers, and seeds) of medicinal and aromatic plants (MAPs) could be used as a promising and sustainable solution to protect consumers' health. The objective of this review was to compile published literature regarding the extraction of bioactive compounds from MAPs as well as different methods of vegetable oils enrichment. In fact, this review uses a multidisciplinary approach and offers an updated overview of the technological, sustainability, chemical and safety aspects related to the protection of oils.

Systematic comparison of structural and lipid oxidation in oil-in-water and water-in-oil biphasic emulgels: effect of emulsion type, oil-phase composition, and oil fraction

BACKGROUND

Because many common foods are emulsions (mayonnaise, margarine, salad dressing, etc.), a better understanding of lipid oxidation is crucial for the formulation, production, and storage of the relevant consumer products. We prepared oil-in-water (O/W) and water-in-oil (W/O) emulgels, and their architecture was characterized before monitoring lipid oxidation under thermally accelerated conditions to systematically compare the effect of emulsion type, oil composition, and oil fraction on the structure and lipid oxidation in thee biphasic emulgel systems.

RESULTS

Higher susceptibility of lipids to oxidation (>2.5 times) was observed in the biphasic O/W and W/O emulgels than in soybean oil owing to an interfacial region. In the heterogeneous emulsion systems, W/O emulgels had oxidation resistance than O/W emulgels did. Compared with the oil-phase composition of high oleic sunflower, soybean, and flaxseed oils, oxidation sensitivity of emulsified lipids was significantly raised as the degree of unsaturation increased from 100.72 to 203.07. Moreover, increasing oil fraction from 75% to 85% led to an obvious increase in total oxidation in O/W emulgels but a decrease in W/O emulgels. In addition to emulsion size and oil unsaturation, viscoelasticity had a remarkable effect on the low-unsaturated oil oxidation (e.g. high oleic sunflower oil).

CONCLUSION

Physical and structural phenomena played important roles in lipid oxidation based on a mass transport principle. These findings provide novel information for designing the structures of emulsion gels for controlling lipid oxidation through the cooperation of both formulation and architecture principles. © 2022 Society of Chemical Industry.

The Prognostic Value of Derivatives-Reactive Oxygen Metabolites (d-ROMs) for Cardiovascular Disease Events and Mortality: A Review

Oxidative stress participates in the development and exacerbation of cardiovascular diseases (CVD). The ability to promptly quantify an imbalance in an individual reductive-oxidative (RedOx) state could improve cardiovascular risk assessment and management. Derivatives-reactive oxygen metabolites (d-ROMs) are an emerging biomarker of oxidative stress quantifiable in minutes through standard biochemical analysers or by a bedside point-of-care test. The current review evaluates available data on the prognostic value of d-ROMs for CVD events and mortality in individuals with known and unknown CVD. Outcome studies involving small and large cohorts were analysed and hazard ratio, risk ratio, odds ratio, and mean differences were used as measures of effect. High d-ROM plasma levels were found to be an independent predictor of CVD events and mortality. Risk begins increasing at d-ROM levels higher than 340 UCARR and rises considerably above 400 UCARR. Conversely, low d-ROM plasma levels are a good negative predictor for CVD events in patients with coronary artery disease and heart failure. Moreover, combining d-ROMs with other relevant biomarkers routinely used in clinical practice might support a more precise cardiovascular risk assessment. We conclude that d-ROMs represent an emerging oxidative-stress-related biomarker with the potential for better risk stratification both in primary and secondary cardiovascular prevention.

Effect of polyglycerol polyricinoleate on the inhibitory mechanism of sesamol during bulk oil oxidation

In this study, effects of sesamol on improving the oxidative stability of sunflower oil and its oil-in-water emulsion was investigated. To investigate the kinetic parameters related to the initiation and propagation stages of oxidation, a sigmoidal-model was used. Sesamol exhibited higher antioxidant activity in sunflower oil-in-water emulsion than that of sunflower oil. In both sunflower oil and sunflower oil-in-water emulsion, the inhibitory effect of sesamol against lipid oxidation continued even after the induction period. To improve the efficiency of sesamol in sunflower oil, polyglycerol polyricinoleate (PGPR) was incorporated into the functional environment of the sesamol. Sesamol exhibited a synergistic effect with PGPR during both initiation (synergistic effect of 68.87%) and propagation (synergistic effect of 36.84%) stages. Comparison of the size of reverse micelles in samples containing PGPR with those without PGPR revealed that PGPR can enhance the efficiency of sesamol by increasing the acceptance capacity of lipid hydroperoxides in reveres micelles structures. This can result in enhancing the effective collisions between sesamol and lipid hydroperoxides in the presence of PGPR. The water produced as a major byproduct of oxidation played a key role on the antioxidant activity of sesamol alone or in combination with PGPR during oxidation process.

Effects of Sweet Potato Powder Selected Based on the Polar Paradox Hypothesis on Oil Oxidation in the Preparation of Deep-Fried Croquettes

This study investigated whether sweet potato powder (SPP) and purple SPP (PSPP) could prevent oil oxidation during deep-frying. A volume of soybean oil was repetitively used for deep-frying croquettes coated with either SPP or PSPP. An aliquot of the fried oil was collected (SPP and PSPP oils) before and after each frying to analyze moisture and lipid oxidation products (LOPs). With increasing numbers of frying, the moisture content in oils significantly increased without an appreciable difference between SPP and PSPP oils. The total oxidation values reflecting primary and secondary LOPs also significantly increased. However, the values were higher for PSPP oils despite the much higher antioxidant activity of the polar extracts from PSPP compared to SPP. This was attributed to the presence of transition metals. PSPP oils seemed to have association colloids whose interfaces were occupied more with polar antioxidants, thereby transition metals were easily reduced and their pro-oxidative activity increased. The polar paradox hypothesis stating that polar antioxidants are more effective in preventing lipid oxidation in bulk oil is not always applicable to real foods due to various food matrices.

Alkyl chain length modulates antioxidant activity of gallic acid esters in spray-dried emulsions

Lipid oxidation is a well-recognized issue in dried food emulsions, such as infant milk formula. Antioxidants can be used to mitigate this issue; however, their efficiency in such complex systems is far from understood. In this study, antioxidant polarity is varied through the alkyl chain length of gallic acid esters (0-16 carbon atoms) incorporated to O/W emulsions that are subsequently spray-dried. During processing and subsequent storage of the samples, antioxidants with more than eight carbon atoms are effective. Both for encapsulated fat and surface free fat, we observe a slight cut-off effect, meaning that beyond eight alkyl groups, a more nonpolar antioxidant is slightly less effective. Depending on the antioxidant polarity, lipid oxidation is faster either in the encapsulated or in the surface free fat. The insights obtained contribute to understanding lipid oxidation in low moisture food emulsions, and thus lead to effective antioxidant strategies.

Effect of triacylglycerol structure on the antioxidant activity of γ-oryzanol

In this study, the triacylglycerol structure of vegetable oils was removed and the effects of this removal were observed on the antioxidant efficiency of γ-oryzanol. A sigmoidal-model was used for calculating kinetic parameters relevant to the initiation and propagation phases during the peroxidation of soybean, corn, sesame, and olive oils as well as their fatty acid methyl esters. Removing the triacylglycerol structure caused an increase in the antioxidant activity of γ-oryzanol (26.49%) by affecting both inhibitory mechanisms, i.e. hydrogen-donating (7.80%) and electron-transfer (14.72%). Unexpectedly, the antioxidant performance of γ-oryzanol continued even when the induction period had ended. During the propagation phase, the highest antioxidant activity was observed in the fatty acid methyl esters of soybean oil (3.86) based on hydroperoxides decomposition. An evaluation of how the endergonic activated complexes formed could indicate that the removal of the triacylglycerol structure increased the effective collisions between the γ-oryzanol molecules and free radicals.

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.

Innovative and Sustainable Technologies to Enhance the Oxidative Stability of Vegetable Oils

To meet consumers’ demand for natural foods, edible oil producers and food processing industries are searching for alternatives to synthetic antioxidants to protect oils against oxidation. Antioxidant compounds extracted from different plant parts (e.g., flowers, leaves, roots, and seeds) or sourced from agri-food industries, including residues left after food processing, attract consumers for their health properties and natural origins. This review, starting from a literature research analysis, highlights the role of natural antioxidants in the protection of edible oils against oxidation, with an emphasis on the emerging and sustainable strategies to preserve oils against oxidative damage. Sustainability and health are the main concerns of food processing industries. In this context, the aim of this review is to highlight the emerging strategies for the enrichment of edible oils with biomolecules or extracts recovered from plant sources. The use of extracts obtained from vegetable wastes and by-products and the blending with oils extracted from various oil-bearing seeds is also pointed out as a sustainable approach. The safety concerns linked to the use of natural antioxidants for human health are also discussed. This review, using a multidisciplinary approach, provides an updated overview of the chemical, technological, sustainability, and safety aspects linked to oil protection.

Tocopherols as antioxidants in lipid-based systems: The combination of chemical and physicochemical interactions determines their efficiency

Lipid oxidation is a major concern in the food, cosmetic, and pharmaceutical sectors. The degradation of unsaturated lipids affects the nutritional, physicochemical, and organoleptic properties of products and can lead to off-flavors and to the formation of potentially harmful oxidation compounds. To prevent or slow down lipid oxidation, different antioxidant additives are used alone or in combination to achieve the best possible efficiency with the minimum possible quantities. In manufactured products, that is, heterogeneous systems containing lipids as emulsions or bulk phase, the efficiency of an antioxidant is determined not only by its chemical reactivity, but also by its physical properties and its interaction with other compounds present in the products. The antioxidants most widely used on the industrial scale are probably tocopherols, either as natural extracts or pure synthetic molecules. Considerable research has been conducted on their antioxidant activity, but results regarding their efficiency are contradictory. Here, we review the known mechanisms behind the antioxidant activity of tocopherols and discuss the chemical and physical features that determine their efficacy. We first describe their chemical reactivity linked with the main factors that modulate it between efficient antioxidant capacity and potential prooxidant effects. We then describe their chemical interactions with other molecules (phenolic compounds, metals, vitamin C, carotenes, proteins, and phospholipids) that have potential additive, synergistic, or antagonist effects. Finally, we discuss other physical parameters that influence their activity in complex systems including their specific interactions with surfactants in emulsions and their behavior in the presence of association colloids in bulk oils.

Fatty Acid Hydroxytyrosyl Esters of Olive Oils Are Bioaccessible According to Simulated In Vitro Gastrointestinal Digestion: Unraveling the Role of Digestive Enzymes on Their Stability

Recently, new bioactive compounds were identified in olive oil, lipophenols, which are composed of a fatty acid (FA) and a phenolic core, such as HT (HT-FA). However, their bioaccessibility remains unknown. Thus, the present study uncovers the impact of the separate phases of gastrointestinal digestion on the release and stability of HT-FAs from oily matrices under in vitro simulated conditions. Accordingly, it was found that the bioaccessibility of HT derivatives is largely dependent on the type of FA that esterifies HT, as well as the food matrix. Also, the generation of HT-FAs during intestinal digestion was observed, with pancreatin being the enzyme responsible, to a higher extent, for the de novo formation of lipophenolic derivatives. These findings prompt us to identify new applications to oily matrices and their byproducts as potential functional ingredients for the promotion of health, where the possible formation of new lipophenols during digestion should be taken into consideration.

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.

Effect of carbon chain length on the hydrolysis and transport characteristics of alkyl gallates in rat intestine

Phenolipids such as alkyl gallates (A-GAs) have been approved by food industry as non-toxic antioxidant additives. However, their digestion and absorption mechanisms in the intestine have not yet been clarified. In this research, the hydrolysis and transport characteristics of A-GAs with fatty alcohols of various chain lengths (C1:0, C2:0, C3:0, C4:0, C8:0, C12:0 and C16:0) were estimated by the everted-rat-gut-sac model (ERGSM) for the first time. High-performance liquid chromatography measurements proved that measurable peaks corresponding to methyl gallate (G-C1:0), ethyl gallate (G-C2:0), propyl gallate (G-C3:0) and butyl gallate (G-C4:0) were discovered in the serosal fluids, which showed the short-chain alkyl gallates can cross the membrane in the form of esters. Besides, all A-GAs were hydrolyzed to GA in the mucosal solution, which contributed evidently to the transport of GA across the membrane of the small intestine. Meanwhile, the hydrolysis rate of A-GAs and transport rate of GA initially increased and then decreased with the chain length, exhibiting a maximum for octyl gallate (G-C8:0). In general, all A-GAs have the behavior of sustained-release. In consequence, the production of A-GAs should be an effective method to extend action time and further increases biological activities of GA.