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

Revealing the oxidation mechanism of Antarctic krill oil induced by metal ion: Focusing on the influence of reverse micelles

Water-soluble copper (CuSO4), oil-soluble copper and different amount of water were added to demetallized and dehydrated Antarctic krill oil (AKO) for accelerated storage. The results showed that water-soluble copper (100 μmol/kg oil) could not significantly promote the oxidation of dehydrated AKO. While water-soluble copper (100 μmol/kg oil) exhibited stronger prooxidative property than oil-soluble copper (100 μmol/kg oil) in AKOs adding water. Meantime, with prolonged storage time of AKO adding water, the size of reverse micelle increased, the electronegativity and surface tension of the oil-water interface decreased, and adding water-soluble copper ions aggravated the above changes. Therefore, it was speculated that Cu2+ is adsorbed to the oil-water interface by the action of electric charge to promote the oxidation of phospholipids containing unsaturated fatty acids (UFAs) and free UFAs present at the interface by initiating the free radical chain reaction, thereby accelerating the oxidation of AKO.

Evaluation of antioxidant efficacy of quercetin encapsulated in micelles, mixed micelles, or liposomes in oil-in-water emulsions

Quercetin was encapsulated in polyoxyethylene laurylether (Brij 35®) micelles, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes and Brij 35®/DMPC mixed micelles. These obtained formulations were then physically characterized for their particle size, morphology, physical stability and polydispersity index. All quercetin formulations were evaluated for their antioxidant efficiency in two oil-in-water emulsion systems and compared to the one of free quercetin. In short-term assays, results showed that among the tested formulations, quercetin liposomal form offered superior antioxidant protection, in comparison with polymer micelles or mixed micelles form or free quercetin. These results were attributed to a better synergistic effect of liposomal quercetin formulation with tocopherols present in the oil phase of the emulsion. However, in long-term assay, the loaded quercetin showed chemical degradation over the long term in the liposomal form, thus limiting its long-term antioxidant effectiveness in food emulsions.

Physical and oxidative stability of 5 % fish oil-in-water emulsions stabilized with lesser mealworm (Alphitobius diaperinus larva) protein hydrolysates pretreated with ultrasound and pulsed electric fields

Lesser mealworm (Alphitobius diaperinus larva) meal was pretreated with ultrasound (US) or pulsed electric fields (PEF) and hydrolyzed using Alcalase or Trypsin enzymes. The resulting hydrolysates were evaluated for their ability to maintain physical and oxidative stability of 5 % fish oil-in-water emulsions. The effects of the pretreatment on enzymatic hydrolysis were assessed by measuring the degree of hydrolysis (DH), protein yield, and molecular weight distribution. Hydrolysates with 19-28 % DH were produced. Physical stability was evaluated in terms of creaming index, Turbiscan stability index, ζ-potential, and droplet size. Emulsions stabilized with US-pretreated Trypsin hydrolysates presented the smallest droplet sizes (0.626 μm). Primary and volatile secondary oxidation products were measured during storage. However, none of the hydrolysate-stabilized emulsions exhibited greater oxidative stability than sodium caseinate, the reference protein. These results suggest that although US-pretreated Trypsin hydrolysates exhibit potential as emulsifiers, additional antioxidants are needed to effectively control lipid oxidation.

The oxidative stability of sunflower oleosomes depends on co-extracted phenolics and storage proteins

Unsaturated triacylglycerols (TAGs) are highly oxidatively stable when extracted as part of the natural lipid droplets (oleosomes) from seeds. This study investigates whether this protection is inherent to oleosomes or derives from phenolics (PHE) and storage proteins (PRO), which are commonly co-extracted with oleosomes. Oleosome extracts with low (PHE <0.7 mmol/kg TAGs, PRO <4 wt% on DM) or high (PHE >10 mmol/kg TAGs, PRO >9 wt% on DM) amounts of phenolics and storage proteins were obtained from sunflower seeds and then dispersed to create 10 wt% oil-in-water emulsions at pH 3 that were stored at 40 °C for 120 days. No triacylglycerol oxidation occurred in emulsions with high amounts of phenolics, while a high amount of storage proteins reduced the lipid oxidation rate. Our findings evidence that the oxidative stability of triacylglycerols in oleosomes derives primarily from the co-extracted phenolics and storage proteins and not only from the architecture of oleosomes.

Advancing the assessment of oxidative stability in co-stabilized zein nanoparticles and xanthan gum Pickering emulsions using isothermal calorimetry

This study aims to apply isothermal calorimetry to investigate the oxidative stability of Pickering emulsions made with zein nanoparticles (ZNPs) and xanthan gum. The ZNPs were fabricated using an anti-solvent precipitation method, resulting in nanoparticles with a particle size of 168.4 ± 38.9 nm and a zeta potential of +27.8 ± 7.3 mV. Xanthan gum was incorporated to enhance the physical stability by increasing the viscosity of the continuous phase. The emulsions oil phase consisted of different plant-based oils such as sunflower, corn, olive, and soy. Pickering emulsions physical stability was characterized using a multiple light scattering technique. Kinetic parameters of emulsions oxidative stability, including induction time (τ), rates of inhibited (Rinh) and uninhibited (Runi) periods, and oxidizability index (O.I.) were determined by isothermal calorimetry. Pickering emulsions exhibited a different oxidative stability depending on the oils used, with olive oil-based emulsions showing the longest induction time, highest antioxidant efficiency (A.E. = 9.35 ± 0.07), and lowest oxidizability index (2.25 ± 0.02 (M·h)-0.5). The results correlated with the total phenolic content and antioxidant activity of the oils. The findings provide valuable insights into designing emulsion-based formulations, emphasizing the role of oil type in enhancing Pickering emulsion oxidative stability.

Use of emulsifying plant protein hydrolysates from winery, whiskey and brewery by-products for the development of echium oil delivery emulsions

This study investigates the production of plant protein hydrolysates from defatted grape seed flour and barley spent grains, by-products of wine, beer and whiskey industries, using limited hydrolysis with subtilisin or trypsin. The hydrolysates were characterized by protein content, molecular weight, antioxidant capacity, interfacial adsorption, dilatational rheology, and interfacial conformational changes using synchrotron radiation circular dichroism. Physical and oxidative stability of 5 % echium oil-in-water emulsions (pH 7), stabilized by the hydrolysates, were studied during seven days of storage. The trypsin-derived hydrolysate from brewers' spent grains resulted in the most physically stable emulsion due to enhanced interfacial adsorption and higher dilatational modulus. Alternatively, the trypsin-treated grape seed flour hydrolysate provided the emulsion with the highest oxidative stability, aligning with its superior in vitro antioxidant capacity. These results show the potential of wine and brewery industry side streams as a sustainable source of plant-based emulsifiers with application in omega-3 delivery systems.

Lipid-Derived Electrophiles Modify Proteins and Alter Their Interfacial Behavior: The Distinct Mediating Role of the Interface

In interface-dominated systems (IDSs), lipid peroxidation (LPO) and interfacial protein arrangement commonly coexist. Although lipid-derived electrophiles (LDEs), especially α,β-unsaturated aldehydes, extensively modify proteins, the specific role of interfaces in promoting such modification and its effect on protein behavior remains unclear. Here, we synthesized a yne-ACR probe to simulate LDEs and investigated its modification effect on whey protein (WP) in an IDS model comprising n-hexadecane (Hex) and water. Interface hydromechanics results reveal that the interface distinctly mediates protein modification by yne-ACR in the IDS model. Both the yne-ACR concentration and interfacial properties significantly affect protein interfacial behavior. The interface offers a unique environment for protein modification by yne-ACR, differing from homogeneous systems and producing varied aggregation behaviors between interfacial and nonadsorbed proteins. Chemical proteomic profiling identified 209 modified proteins at the interface compared to 156 in nonadsorbed systems, highlighting increased susceptibility of interfacial proteins to yne-ACR modification and subsequent changes in aggregation patterns. All-atom molecular dynamics (MD) simulations indicate that yne-ACR modification disrupts the stability of protein aggregates at interfaces, promoting redistribution between the interface and the bulk phases and modifying interfacial activity. These findings clarify how LDEs modify proteins in IDSs and their subsequent effects on interfacial behavior.

Synergistic iron single/diatomic nanozyme-based colorimetric filtration valve for real-time detection and degradation of kitchen wastewater contaminants

Conventional single-atom nanozyme materials often exhibit limited enzyme-like activities and substrate specificity, making it challenging to meet the integrated demands for simultaneous detection and purification in environmental applications. In this study, we developed a novel nanozyme system featuring single/diatomic synergistic iron active sites (sdsFeN@G). sdsFeN@G exhibits superior multi-enzyme activities (POD, OXD, Laccase), outperforming natural enzymes in catalytic efficiency. Density functional theory (DFT) calculations revealed that the Fe-N four-coordination bonding shifted the d-band center of Fe closer to the Fermi level, enhancing the catalytic activity of the single/diatomic synergistic active sites. The colorimetric sensor platform integrating sdsFeN@G as the active component exhibited a detection limit as low as 0.992 μM and, leveraging its Laccase-like activity, achieved effective degradation of these antioxidants with a maximum degradation rate of 80 % for kitchen wastewater. To meet the real-time detection and purification needs in practical kitchen wastewater discharge processes, a convenient detection/purification integrated kitchen wastewater filtration valve was designed based on the sdsFeN@G nanozyme. This work advances the development of multi-enzyme active nanozyme materials, providing a promising strategy for addressing real-world environmental protection challenges.

A high-dose coenzyme Q10-emulgel for chronic oral therapy of deficient patients with secondary dysphagia

Coenzyme Q10 (CoQ10) is the major endogenously fat-soluble antioxidant synthesized in the mitochondrion inner membrane as the electron carrier in the respiratory chain. In CoQ10-deficient patients, early high-oral doses (5-50 mg/kg/day) can constrain renal dysfunction and neurological signs. CoQ10, a typical class IV drug, with low bulk density, was dissolved at high-dose (1 g) in the oil phase (20:80 O/W) of a novel emulgel of small serving size (25 g) for its chronic administration in deficient patients with secondary dysphagia, as an alternative to maintain therapy adherence. The novelty is that CoQ10 remained dissolved in 5 g of oil phase (MCT and coconut oils) per 25 g of alginate-emulgel. This was physically stable for 9 months at 25 °C as a "weak gel" type network, with high zeta potential (‒80 mV) being then the oil droplet size (5.0 μm) successfully maintained. The emulgel showed pseudoplastic behavior and four times lower viscosities than those of a contrast fluid used for swallow studies in dysphagic patients. Chemical stability of CoQ10 was 100 % for 12 months. Emulgel administration (25 g/day) for 2 weeks increased CoQ10 plasma concentration in 3.9 times. The number of doses for high CoQ10 therapy can then be reduced, without swallowing discomfort.

Metal-Phenolic Networks Enable Biomimetic Antioxidant Interfaces Through Nanocellulose Engineering

Metal-phenolic networks (MPNs) integrated with functionalized cellulose nanofibers present a promising platform for stabilizing oxidation-sensitive compounds. Here, a novel antioxidant pickering emulsion system utilizing MPN-decorated carboxyl-functionalized pulp cellulose nanofibers (MPN-PCNF) is demonstrated. The system exhibits exceptional interfacial stability through synergistic effects of MPN coating and alkyl functionalization, validated by DLVO theoretical modeling and rheological characterization. MPN-PCNF demonstrates remarkable antioxidant efficacy, achieving 94% α-tocopherol retention over 50 days and 80% reduction in cellular reactive oxygen species. In reconstructed human skin models, the system significantly attenuates UV-induced oxidative stress, evidenced by preserved stratum corneum integrity and suppressed matrix metalloproteinase-1 expression. This biocompatible platform represents a versatile solution for protecting oxidation-sensitive compounds across pharmaceutical, cosmetic, and food applications, offering a sustainable alternative to conventional synthetic antioxidant systems.

Nanoencapsulation and crosslinking of trans-ferulic acid in whey protein isolate films: A comparative study on release profile and antioxidant properties

Despite extensive research on incorporating nanocapsules into films, the efficiency of active compounds in affecting food and maintaining long-term packaging functionality remains a major challenge. Our study reports the fabrication of whey protein isolate (WPI) films via crosslinking and nanoencapsulation of trans-ferulic acid (TFA), respectively. Nanocapsules were prepared by ultrasonication, and their particle size and polydispersity index were determined. Results demonstrate that the incorporation of nanoencapsulated TFA significantly improves the antioxidant capacity of WPI films (5.18 %) during storage, maintaining up to 40 %, which is higher than crosslinking. The crosslinked TFA-WPI film exhibited enhanced oxygen barrier properties by 50 % owing to increased polymer density and crystallinity. The water vapor permeability significantly decreased by 77 % for both crosslinked and nanoencapsulated films owing to their polymer density and hydrophobicity, respectively. A controlled release test revealed nanoencapsulation of TFA in WPI film was beneficial for a higher released ratio of phenolic acids (99.55 %) and sustained antioxidant activity than crosslinking (73.77 %). The Higuchi model suggests that TFA are diffused from a homogeneous film matrix. Nanoencapsulation improved the water vapor barrier of WPI film and the long-term stability of TFA. Furthermore, improved oxygen barrier properties of WPI were observed due to the crosslinking while maintaining a mechanical strength higher than that of nanoencapsulation. Consequently, the WPI film demonstrates exceptional potential for food packaging applications due to its advanced gas barrier properties, the robust and sustained antioxidant activity of TFA, and the efficient release of TFA, without compromising functionality during storage.

Utilizing carboxymethyl cellulose to assist soy protein isolate in the formation of emulsion to deliver β-carotene: Exploring the correlation between interfacial behavior and emulsion stability

This study investigated the effects of carboxymethyl cellulose (CMC) adsorption on the interfacial properties of soy protein isolate (SPI) and its correlation with emulsion stability. The findings revealed that SPI-CMC emulsions exhibited reduced zeta potential and particle size compared with SPI emulsion alone. Molecular docking analysis suggested that the enhanced stability of SPI-CMC emulsions was primarily due to hydrogen bonding and electrostatic interactions between SPI and CMC. Notably, the encapsulation efficiency of β-carotene in SPI-CMC emulsions increased by 47.74 % at pH 4.0 with 0.4 % CMC and by 39.55 % at pH 5.0 with 0.5 % CMC compared to SPI emulsion. Stability analyses demonstrated that at pH 4.0, the SPI-CMC interfacial layer formed by hydrogen bonding and electrostatic interactions effectively protected β-carotene from external degradation factors. At pH 5.0, steric hindrance facilitated the formation of a SPI-CMC network structure, increasing the path length for oxidants to reach the oil droplet interface. These distinct binding mechanisms in SPI-CMC emulsions effectively prolonged oil droplet digestion and regulated the release of free fatty acids. The resulting emulsion exhibited slow and sustained lipid release and digestion kinetics, making it a suitable model for designing sustained-release nutritional supplements.

Innovative applications of medium- and long-chain triacylglycerol in nutritional support: Current perspectives and future directions

As a unique structured lipid, medium- and long-chain triacylglycerol (MLCT) is characterized by the combination of medium- and long-chain fatty acids in a single triacylglycerol molecule. In recent years, MLCT, as a nutritional lipid, has gradually emerged as a research hot topic in the fields of food science and nutrition. This paper innovatively provides a comprehensive review of the current application status and development prospects of MLCT in nutritional support. First, the basic principles defining characteristics and selection basis of both enteral and parenteral nutrition are analyzed, elucidating the differences between the two modalities in terms of nutrient delivery pathway, absorption mechanisms, and physiological effects. Subsequently, the natural sources and artificial synthetic pathways of MLCT along with its metabolic behavior in vivo are elaborated. On this basis, the latest research advancements in the application of MLCT in both nutritional models are reviewed, with a particular emphasis on current research hotspots. Finally, the challenges encountered in the practical application of MLCT are discussed, and the future trajectory of MLCT as a functional lipid is predicted. In particular, the innovative potential of MLCT in functional foods, food for special medical purposes, personalized nutrition, and other aspects is emphasized, which provides beneficial ideas and directions for further research and industrial applications of MLCT.

Comprehensive quantitative profiling of vegetable oil oxidation products by NMR-based oxylipidomics

Lipid oxidation is one the major causes of food deterioration. Current advancement in mechanistic understanding is limited by the lack of high-throughput methods that can simultaneously quantify a wide range of oxidation product classes, such as lipid hydroperoxides, epoxides, ketones, hydroxides, and aldehydes. Here, we introduce an NMR-based 'oxylipidomics' platform by providing the annotation of 42 substructures formed during lipid oxidation in vegetable oils. The annotated substructures accounted for respectively 93, 90 and 70% of the oxidation products of triolein, trilinolein, and trilinolenin. The spectral assignments allowed for quantification of lipid oxidation products in vegetable oil at class (e.g., epoxides) and substructure level (e.g., trans-epoxides) at the commonly available field strength of 14.1 T (600 MHz). We anticipate that our workflow will enable rapid assessment of health risks, unravelling of precursor-sensory relationships, rational design of antioxidant strategies, and in-depth mechanistic studies into food lipid oxidation.

Dynamics and Stability Mechanism of Lactoferrin-EPA During Emulsification Process: Insights from Macroscopic and Molecular Perspectives

Although eicosapentaenoic acid (EPA) as a functional fatty acid has shown significant benefits for human health, its susceptibility to oxidation significantly limits its application. In this study, we developed a nanoemulsion of the lactoferrin (LTF)-EPA complex and conducted a thorough investigation of its macro- and molecular properties. By characterizing the emulsion with different LTF concentrations, we found that 1.0% LTF formed the most stable complex with EPA, which benefited the formation and stability of the emulsion against storage and freezing/thawing treatment. As the foundation block of the emulsion structure, the binding mechanism and the entire dynamic reaction process of the complex have been fully revealed through various molecular simulations and theoretical calculations. This study establishes a comprehensive picture of the LTF-EPA complex across multiple length scales, providing new insights for further applications and productions of its emulsion.

How lipids, as important endogenous nutrient components, affect the quality of aquatic products: An overview of lipid peroxidation and the interaction with proteins

As the global population continues to grow and the pressure on livestock and poultry supply increases, the oceans have become an increasingly important source of quality food for future generations. However, nutrient-rich aquatic product is susceptible to lipid oxidation during storage and transport, reducing its nutritional value and increasing safety risks. Therefore, identifying the specific effects of lipid oxidation on aquatic products has become particularly critical. At the same time, some lipid oxidation products have been found to interact with aquatic product proteins in various ways, posing a safety risk. This paper provides an in-depth exploration of the pathways, specific effects, and hazards of lipid oxidation in aquatic products, with a particular focus on the interaction of lipid oxidation products with proteins. Additionally, it discusses the impact of non-thermal treatment techniques on lipids in aquatic products and examines the application of natural antioxidants in aquatic products. Future research endeavors should delve into the interactions between lipids and proteins in these products and their specific effects to mitigate the impact of non-thermal treatment techniques on lipids, thereby enhancing the safety of aquatic products and ensuring food safety for future generations.

A mechanistic kinetic model for lipid oxidation in Tween 20-stabilized O/W emulsions

Models predicting lipid oxidation in oil-in-water (O/W) emulsions are a requirement for developing effective antioxidant solutions. Existing models do, however, not include explicit equations that account for composition and structural features of O/W emulsions. To bridge this gap, a mechanistic kinetic model for lipid oxidation in emulsions is presented, describing the emulsion as a one-dimensional three phase (headspace, water, and oil) system. Variation in oil droplet sizes, overall surface area of oil/water interface, oxidation of emulsifiers, and the presence of catalytic transition metals were accounted for. For adequate predictions, the overall surface area of oil/water interface needs to be determined from the droplet size distribution obtained by dynamic and static light scattering (DLS, SLS). The kinetic model predicted well the formation of oxidation products in both mono- and polydisperse emulsions, with and without presence of catalytic transition metals.

Microwave Heating Characteristics on Lipid Quality in Sterilized Rainbow Trout (Oncorhynchus mykiss) Using Designed Heating Processing

The aim of this study was to simulate microwave heating characteristics to investigate the lipid quality in rainbow trout, including the impact of the heating rate, maximum temperature, and thermal processing level on the extent of lipid oxidation and on the fatty acid extraction coefficient. Increasing F0 from 3 to 6 min improved fatty acid retention at high heating rates but led to a decrease in the measured results at low heating rates. Elevated thermal processing levels and maximum temperatures were observed to intensify the oxidation. At F0 = 3 min, an increase in maximum temperature led to an increase in the total lipid extraction coefficient but a decrease in the fatty acid extraction coefficient. However, an increase in maximum temperature resulted in a decrease in both extraction coefficients when F0 was 6 min. The coefficient spectra of fatty acid extraction obtained from the microwave and traditional heat treatments showed nonparallel trends, confirming the presence of non-thermal effects during microwave thermal processing. In conclusion, compared to conventional heat treatment methods, microwave processing has significant potential for enhancing the lipid quality of ready-to-eat rainbow trout products and effectively reducing production costs.

Spatiotemporal assessment of protein and lipid oxidation in concentrated oil-in-water emulsions stabilized with legume protein isolates

The growing trend of substituting animal-based proteins with plant-based proteins requires more understanding of the functionality and stability of vegan mayonnaises, especially regarding their susceptibility to lipid and protein oxidation. Here, we investigate the spatial and temporal dynamics of lipid and protein oxidation in emulsions stabilized with legume ((hydrolyzed) soy, pea, and faba bean) protein isolates (hSPI, SPI, PPI, FPI). We assessed lipid oxidation globally by NMR and locally by confocal laser scanning microscopy using the oxidation-sensitive fluorescent dye BODIPY 665/676. Further, we assessed local protein oxidation by employing protein autofluorescence and the fluorescently labeled radical spin-trap CAMPO-AFDye 647. Oxidation of oil in droplets was governed by the presence of tocopherols in the oil phase and pro-oxidant transition metals that were introduced via the protein isolates. Non-stripped oil emulsions stabilized with PPI and hSPI displayed higher levels of lipid hydroperoxides as compared to emulsions prepared with SPI and FPI. We attribute this finding to higher availability of catalytically active transition metals in PPI and hSPI. For stripped oil emulsions stabilized with SPI and FPI, lipid hydroperoxide concentrations were negligible in the presence of ascorbic acid, indicating that this agent acted as antioxidant. For the emulsions prepared with PPI and hSPI, lipid hydroperoxide formation was only partly inhibited by ascorbic acid, indicating a role as prooxidant. Interestingly, we observed protein-lipid aggregates in all emulsions. The aggregates underwent fast and extensive co-oxidation, which was also modulated by transition metals and tocopherols originating from the oil phase. Our study demonstrates the potential of spatiotemporal imaging techniques to enhance our understanding of the oxidation processes in emulsions stabilized with plant proteins.

Thermal oxidation mechanism of palmitic aicd

The oxidation and degradation of fats lead to a decrease in the nutritional value of food and pose safety concerns. Saturated fatty acids also hold a significant position in the field of lipid oxidation. In this study, the oxidation products of methyl palmitate were investigated by using gas chromatography mass spectrometry (GC-MS). Seven monohydroperoxides and 72 secondary oxidation products were detected. Combined with density functional theory (DFT) calculations, the formation mechanisms of oxidation products can be summarized into four stages. The initial stage involved the formation of monohydroperoxides and alkanes, followed by the subsequent stage involving methyl x-oxo(hydroxy)hexadecanoates. The third stage involved the formation of methyl ketones, carboxylic acids, and aldehydes, while the final stage involved lactones. Meanwhile, methyl ketones were the most abundant oxidation product, approximately 25 times more abundant than aldehydes; the calculated results agreed well with the experimental results. The establishment of a comprehensive thermal oxidation mechanism for palmitic acid provided a new foundation for future lipid oxidation analyses.

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.