Association Colloids Research Articles

The change rule of lipid oxidation and hydrolysis driven via water in Antarctic krill oil: Based on association colloid formation

The residual water and amphiphilic compounds such as phospholipids in bulk oil can form reverse micelles, which affect oxidative stability. In this study, the Antarctic krill oil (AKO) samples with different water contents were subjected to accelerated storage. During storage, AKO exhibited oxidative changes, manifested as increased POV, TBARS values, and volatile compound levels but decreased PUFA percentages. Meanwhile, AKO underwent hydrolysis, evidenced by decreased PC, PE, and TG contents but increased FFA contents. Moreover, the degree of lipid oxidation and hydrolysis is dose-dependent with water added. Cryogenic scanning electron microscopy imaging and micelle size distribution measurement proved the presence of reverse micelle, and their size and interfacial area improved with increased water contents. Correlation analysis suggested that lipid oxidation and hydrolysis positively correlated with the size and interfacial area of reverse micelle. Therefore, it is speculated that the oil-water interface may be the site of lipid oxidation and hydrolysis.

Effect of combinations of 3,4‐dihydroxyphenylacetic acid and its esters on the oxidative stability of fish oil–containing trace water

AbstractThe current study aims to comprehend the effect of the various combinations of 3,4‐dihydroxyphenylacetic acid (3,4‐DHPA) and its esters in varying molar ratios on retarding oxidation in bulk refined fish oil in the presence of 0.3% w/w water. All the esters and 3,4‐DHPA exhibited better performance than the synthetic antioxidant butylated hydroxytoluene. In the presence of trace water, the parent compound was found to have a synergistic effect with hexyl ester when used at a molar ratio of 2:1, respectively, exhibiting a higher percent reduction among all the esters and their combinations. The study also showed that the presence of extraneous water can significantly accelerate the oxidation (twofold) in a bulk fish oil system. This suggests that the microenvironment of the oil is altered when water is present and that association colloids play a key role in enhancing the rate of oxidation. Thus, while designing a competent mixture of antioxidants, the specific site of oxidation involved and the surface‐active components should be taken into consideration to efficiently retard oxidation.Practical Applications: Analyzing the impact of trace amounts of water on the efficiency of natural antioxidants, including 3,4‐DHPA and its lipophilic esters, helps to comprehend the required optimal antioxidant concentrations for such a dynamic bulk oil system. The study finds application in controlling oxidation in PUFA‐rich oils containing surface‐active minor components that can accelerate oxidation. The results of the study show that 3,4‐DHPA and its esters could be a potential replacement for the synthetic antioxidant BHT in all aspects.

Removal of Minor Components From Vegetable Oils by a Multistage Chromatography Column in a Specific Order

ABSTRACTThe purpose of this study was to investigate the effects of different chromatographic column absorbents (activated clay, silica gel, and activated aluminum oxide) on the adsorption and removal of minor components (sterols, tocopherols, β‐carotene, free fatty acids (FFAs), secondary oxidation products, and peroxides) in vegetable oils. For single absorbents, activated aluminum oxide was the most effective material for removing tocopherols and FFAs from oil. All the adsorbents used have the capacity to remove β‐carotene from edible oils, and activated clay has the strongest ability, with removal rates reaching 99.8%. The brassicasterol, campesterol, β‐sitosterol, γ‐tocopherol, and δ‐tocopherol in vegetable oil can be completely removed by silica gel. Using a combination of these absorbents, a multistage optimized method was developed to maximize the removal of various minor components from vegetable oils. After multistage purification, free sterols, tocopherols, FFAs, β‐carotene, and secondary oxidation products were completely removed, whereas peroxides were also removed at concentrations less than 0.71 mmol/kg. The purified oils could be used as standard samples for in‐depth study of the effects of minor components on formation of association colloids and their influence on oil oxidation, as well as for evaluating the antioxidant potential of novel antioxidants or extracts.

Mini review: recent advances in biosurfactant-based association colloids–formation of microemulsions

In the context of a more sustainable economy, bio-surfactants become increasingly important, due to their independence of petrol-based chemistry, their usually mild synthesis conditions, and in certain cases their pharmacological activity. We have recently discussed self-assembly studies in binary systems of bio-surfactants of microbial origin, or saponins extracted from plants (Hellweg et al., Frontiers in Soft Matter, 2023, 2). In the present review, we focus on the formation of microemulsions based on these molecules. We review the formation and structure of microemulsion systems formed by oil, water, and biosurfactants, with a particular focus on Quillaja saponins and rhamnolipids.

Approaches of lipid oxidation mechanisms in oil matrices using association colloids and analysis methods for the lipid oxidation.

Lipid oxidation is one of the key chemical reactions in foods containing fats and oils during production and storage. For several decades, many researchers have tried to understand the mechanisms of lipid oxidation and ways to control the rates of lipid oxidation. Theories of autoxidation or free radical chain reaction have been developed to successfully explain the phenomenon observed in oxidized lipids. Many studies have been conducted to explain the other factors that can affect the lipid oxidation such as food matrix, oxidation time and temperature, transition metal ions, pigments with sensitizing abilities, and surface-active compounds such as phospholipids, free fatty acids, monoacylglycerols, and diacylglycerols. Several strategies were developed to evaluate the degree of oxidation and oxidative stability. This review provides crucial information on the mechanism of lipid oxidation affected amphiphilic compounds and association colloids. This review article will extensively discuss about the methods for determining the oxidative stability.

Recent advances in biosurfactant-based association colloids—Self-assembly in water

Recent studies of self-assembly in binary systems of bio-surfactants, either of microbial origin or saponins extracted from plants, are reviewed. Saponins in water reported in the first section include aescin, glycyrrhizin, and quillaja saponins, while rhamnolipids are discussed in the second section on microbial surfactants. Studies of surface activities are a natural starting point of the characterization of surfactants, but here we focus mainly on physico-chemical and structural properties of self-assembled bulk structures in solution, often characterized by scattering techniques. When quantitative modelling is performed, self-assembly parameters like aggregation numbers, head group areas, and resulting shapes can be followed as a function of physical-chemical parameters like concentration, composition, temperature, or pH. Morphologies include micelles and their structural evolution with addition of other bio- or synthetic surfactants, co-surfactants, proteins or phospholipids.

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.

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.

Water content, critical micelle concentration of phospholipids and formation of association colloids as factors influencing autoxidation of rapeseed oil.

The exact mechanism of lipid autoxidation in vegetable oils, taking into account physical aspects of this phenomenon, including the role of association colloids, is still not fully understood. The purpose of this study was to consider changes in moisture content and DOPC phospholipid (1,2-dioleoyl-sn-glycero-3-phosphocholine) critical micelle concentration (CMC) in rapeseed oil during autoxidation as well as to find the relationship between these parameters and the accumulation of primary and secondary lipid oxidation products. The experiments were performed at initial oil humidity 220 ppm and 700 ppm, with DOPC below and above CMC. The increase in water concentration was favored by the presence of phospholipids above CMC and, at the same time, high initial water level, which favored oxidation processes and the creation of amphiphilic autoxidation products. At relatively high water level and low amphiphilic DOPC concentration, the growth of water content does not affect the concentration of oxidation products. Amphiphilic substances play a significant role in increasing the water content of oil. Autoxidation products may reduce CMC of DOPC, but water is able to compensate for the CMC-reducing effect of oxidation products. The presence of association colloids and initial water content play a crucial role in the oxidation process of rapeseed oil. The increase in water concentration does not cause a sufficiently large increase in the number of micelles or sufficiently significant changes in their structure to effect an increase in the level of oxidation products. The formation of micelles requires an appropriate content of both water and amphiphilic substances derived from seeds (phospholipids). © 2021 Society of Chemical Industry.

PH Changes in the Micelle-Water Interface of Surface-Active Ionic Liquids Dictate the Stability of Encapsulated Curcumin: An Insight Through a Unique Interfacial Reaction between Arenediazonium Ions and t-Butyl Hydroquinone.

The chemical kinetic (CK) method, which involves the reduction of 4-hexadecylbenzenediazonium ions (16-ArN2+) by antioxidants (in the present case, TBHQ) occurring exclusively at the interface of the association colloids, was employed to establish the changes in the chemical reactivity of anionic surface-active ionic liquids (SAILs) as a function of the concentration and the composition in their mixed states. We used sodium dodecyl sulfate and different SAILs based on the dodecylsulfate surfactant containing 1-alkyl-3-methylimidazolium cations as counterions having a varying alkyl chain length of 4 (bmim), 8 (omim), and 12 (ddmim) carbon atoms. The structural transitions of aggregates of the SAILs from the micellar to vesicular form were observed as a function of concentration in single surfactant systems and as a function of composition in mixed surfactant systems. Results of the reduction kinetics of 16-ArN2+ at the interface of such aggregates, which depends on the acid/base equilibria at the interface, gave an insight into the changes in the interfacial H+ ions with the change in the hydrophobicity of the counterions of SAILs and the morphological changes from micelles to vesicles as a function of concentration or composition. These changes in the interfacial pH correlate very well with the stability of curcumin within these self-assemblies, which exclusively depends on the pH of the medium and highlights the importance of the results obtained from the CK method in selecting the appropriate medium/conditions for the stabilization of the bioactive molecules.

Solvent Selectivity Governs the Emergence of Temperature Responsiveness in Block Copolymer Self-Assembly.

In highly selective solvents, block copolymers (BCPs) form association colloids, while in solvents with poor selectivity, they exhibit a temperature-controlled (de)mixing behavior. Herein, it is shown that a temperature-responsive self-assembly behavior emerges in solvent mixtures of intermediate selectivity. A biocompatible poly-ethylene(oxide)-block-poly-ε-caprolactone (PEO-PCL) BCP is used as a model system. The polymer is dissolved in solvent mixtures containing water (a strongly selective solvent for PEO) and ethanol (a poorly selective solvent for PEO) to tune the solvency conditions. Using synchrotron X-ray scattering, cryogenic transmission electron microscopy, and scanning probe microscopy, it is shown that a rich temperature-responsive behavior can be achieved in certain solvent mixtures. Crystallization of the PCL block enriches the phase behavior of the BCP by promoting sphere-to-cylinder morphology transitions at low temperatures. Increasing the water fraction in the solvent causes a suppression of the sphere-to-cylinder morphology transition. These results open up the possibility to induce temperature-responsive properties on demand in a wide range of BCP systems.

100th Anniversary of Macromolecular Science Viewpoint: Attractive Soft Matter: Association Kinetics, Dynamics, and Pathway Complexity in Electrostatically Coassembled Micelles.

Electrostatically coassembled micelles constitute a versatile class of functional soft materials with broad application potential as, for example, encapsulation agents for nanomedicine and nanoreactors for gels and inorganic particles. The nanostructures that form upon the mixing of selected oppositely charged (block co)polymers and other ionic species greatly depend on the chemical structure and physicochemical properties of the micellar building blocks, such as charge density, block length (ratio), and hydrophobicity. Nearly three decades of research since the introduction of this new class of polymer micelles shed significant light on the structure and properties of the steady-state association colloids. Dynamics and out-of-equilibrium processes, such as (dis)assembly pathways, exchange kinetics of the micellar constituents, and reaction-assembly networks, have steadily gained more attention. We foresee that the broadened scope will contribute toward the design and preparation of otherwise unattainable structures with emergent functionalities and properties. This Viewpoint focuses on current efforts to study such dynamic and out-of-equilibrium processes with greater spatiotemporal detail. We highlight different approaches and discuss how they reveal and rationalize similarities and differences in the behavior of mixed micelles prepared under various conditions and from different polymeric building blocks.

Antioxidant activity and synergism of canolol and α-tocopherol in rapeseed oil is affected by the presence of phospholipid association colloids

Interactions of canolol and α-tocopherol (α-T) with reverse micelles made from DOPC phospholipid (1,2-dioleoyl-sn-glycero-3-phosphocholine) in rapeseed oil were investigated in the current study. Furthermore, the antioxidant efficiency of canolol and α-T as well as the phenomenon of synergism between them in the oil containing association colloids has been determined. As demonstrated by fluorescence measurements, canolol may be incorporated into the structure of DOPC reverse micelles. This antioxidant may also accumulate in bulk oil at oil/water interface. In turn, no interactions of α-T with phospholipid association colloids were observed.The presence of DOPC association colloids affects antioxidant efficiency of canolol and α-T. Simultaneously, at the concentration 100 μmol of both substances, decreasing of their antioxidant activity effectiveness over time was observed. Formed during autoxidation amphiphilic compounds probably influence the structure of reverse micelles, modifying effectiveness of antioxidants. Antioxidant synergism of canolol and α-T occurs only in DOPC reverse micelles. Synergism phenomenon allows eliminating adverse effect of autoxidation products on the effectiveness of antioxidants. The presence of canolol may eliminate prooxidative action of α-T.

Evaluation of the effects of aldehydes on association colloid properties and oxidative stability in bulk oils

The effects of amphiphilic aldehydes, including propanal, hexanal, and nonanal, on the critical micelle concentration (CMC) of phospholipids, moisture content, and oxidative stability in soybean oil were evaluated. The selected aldehydes are typical secondary oxidation products from unsaturated fatty acids. Moisture content increased as aldehydes were added to soybean oil during thermal oxidation at a storage temperature of 50 or 100 °C. The CMC of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) increased as propanal and hexanal were added, whereas nonanal decreased the CMC of DOPC, which implies that aldehydes participate in forming association colloids in bulk oils. The addition of aldehydes increased the rates of lipid oxidation significantly in both 50 and 100 °C treatments (p < 0.05), with the effect being more evident in oils treated at 50 °C than at 100 °C. Therefore, aldehydes formed from lipid oxidation affected the association colloidal structures and oxidative stability in a bulk oil matrix.

Amphiphilic Block Copolymers: A Novel Substance for Bitter-Masking in Aqueous Solutions.

It is a challenging task to suppress the bitterness of liquid preparations, especially for children. Bitter molecules are highly dispersible in liquids, leading to a strong and instant stimulation of the bitter receptors. At present, there is no effective way to correct this issue except for adding sweeteners, resulting in an unsatisfying taste. Based on the three-point contact theory, which is a universally accepted mechanism of bitterness formation, a new idea and application of amphiphilic block copolymers (ABCs) for bitterness suppression was proposed for the first time. We found that ABCs could widely inhibit the bitterness of four typical bitter substances. The mechanism is that ABCs self-assemble to form association colloids, which attract bitter components and reduce their distribution in the molecular form in solution. The bitter components were demonstrated to automatically embed in the spiral hydrophobic cavity of the hydrophobic chain of the ABCs, and their special interaction dispersed the positive electrostatic potential of bitter groups. The combination did not affect the pharmacokinetic parameters and pharmacodynamics of bitter drugs. These findings highlight the novel application of ABCs for the inhibition of bitterness and illuminate the underlying inhibition mechanisms.

Formation of Phospholipid Association Colloids in Rapeseed Oil and Their Effect on Lipid Autoxidation in the Presence of Sinapic and Ferulic Acid

AbstractThis study describes the formation of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) association colloids (reverse micelles) in rapeseed oil and interactions of sinapic and ferulic acids with these structures. Furthermore, the process of oil autoxidation in the presence of DOPC is characterized and the antioxidant efficiency of phenolic acids in the oil containing reverse micelles is determined. Formation of DOPC reverse micelles above the phospholipid critical micelle concentration (51.13 µmol kg–1) is observed. The fluorescence probe emission parameters confirm the interactions of sinapic and ferulic acids with reverse micelles and changes of their structure (reduced rigidity) as a result of phenolic acid incorporation. In the analyzed rapeseed oil, an evident prooxidative effect of DOPC reverse micelles is found, as their presence accelerates decomposition of hydroperoxides to hexanal. The antioxidant effect of sinapic acid is strongly influenced by the presence of DOPC reverse micelles. Ferulic acid shows a concentration‐dependent antioxidant effect in relation to the formation of hexanal.Practical Applications: Understanding the influence of sinapic and ferulic acids on the structure of association colloids and rapeseed oil autoxidation in the presence of reverse micelles should facilitate extension of shelf life and reduce oil quality deterioration during storage. This knowledge may also be used to optimize industrial oil refining to provide the desired amount of amphiphilic minor components and native antioxidants. Thus, developed refining using mild conditions or even minimizing the degree of refining is attractive in view of greater retention of health‐promoting compounds in vegetable oil, reduction of processing costs, and increased sustainability of the oil‐refining process.

Microencapsulation of pink pepper essential oil: Properties of spray-dried pectin/SPI double-layer versus SPI single-layer stabilized emulsions

Microencapsulation by spray drying of hydrophobic materials, such as pink pepper essential oil (Schinus terebinthifolia Raddi), relies on the efficient stabilization of the oil-in-water emulsion to be dried. Association colloids resulting from electrostatic interactions between proteins and polysaccharides are able to provide higher interfacial activity when compared to proteins alone. The main purpose of this work was to examine the role of pectin in the physicochemical properties of powders produced by spray-drying emulsions stabilized by protein single-layer or by protein/pectin double-layer. Oil retention, water activity, hygroscopicity, reconstitution, flow behavior, particle size and morphological properties were evaluated. Powders produced from double-layer emulsions had higher oil retention and, despite presenting higher water activity, were less hygroscopic (0.280, 8.5%) when compared to single-layer powders (0.176, 9.3%). Double-layer powders also showed higher contact angle and higher wetting time in water. Both powders had good water solubility (about 70%) and good dissolution in water and in oil. Powder flowability was affected by formulation, with single-layer powders presenting greater cohesion than double-layer ones. Addition of pectin allowed a more homogeneous distribution of particle sizes, preventing formation of oversized particles and agglomerates. Scanning electron microscopy showed spherical particles with absence of pores, which is desirable for greater preservation of the volatile compounds. Based on the complete set of results, double-layer powders presented higher oil retention and better shelf life properties than single-layers ones, showing the ability of association colloids between soy proteins and pectin to enhance the possibilities of applying pink pepper essential oil in the food industry.

The quality of cold-pressed rapeseed oil obtained from seeds of Brassica napus L. with increased moisture content.

The basic parameter influencing the quality of cold-pressed oil is the quality of seeds used&nbsp; for pressing. Adverse moisture content and storage temperature of rape seeds may affect the quality of oil obtained from them. This paper presents the effects of increased rapeseed moisture content on the quality of the oil pressed. The material used for the tests was rapeseed (canola) cv. PR 46 W14. The moisture content of the seeds was adjusted to 10%, 12% and 20%, and the seeds were stored at room temperature for 14 days. The samples were then dried to a seed moisture equal to 7% and oil was pressed from them. Acid and peroxide values, as well as the content of water, tocopherols and phenolic acids, were determined. In addition, a sensory analysis of the oil samples was carried out, and structural changes in the association colloids in the oil were determined using a fluorescent probe. With the increase in seed moisture, the increase in peroxide and acid values of the analyzed oils was recorded. A slight decrease in tocopherol content and a significant increase in phenolic acid concentration, depending on the seed moisture content, was observed. Sensory analysis showed odor sensory profile changes that probably indicate microflora development. The rapeseed moisture content has a crucial influence on the quality of oil obtained from them. Along with an increase in seed moisture, the possibility of developing undesirable microflora grows, which results in a deterioration in the quality of the obtained oil.

Column chromatography as a method for minor components removal from rapeseed oil

The purpose of this study was to verify the influence of different chromatographic column beds (silicic acid, activated charcoal, aluminum oxide, silica gel) on the concentration of individual minor components (sterols, tocopherols, carotenoids and chlorophyll) in rapeseed oil. With the use of a combination of these beds, a three-stage optimized method for removing minor components from rapeseed oil was developed. It was demonstrated that the combination of silicic acid and activated charcoal removed about half of the sterols present from the oil. Aluminum oxide turned out to be the most effective bed in removing tocopherols, purifying the oil to their minimum level (2.6 mg/kg). All adsorbents used had similar capacity to purify oil from pigments (carotenoids and chlorophyll). In the three-stage purification process free sterols were almost completely removed (to the level 90.0 mg/kg). Purification of β-carotene and chlorophyll from the oil was also very effective. Tocopherols were completely removed with this method, except for a small amount of α-tocopherol (0.4 mg/kg), which results from its relatively weak interaction with a hydrophilic bed. The developed method may be used in studies on the effect of association colloids on bulk oil autoxidation processes.

Combination of Hydrophilic or Lipophilic Natural Compounds to Improve the Oxidative Stability of Flaxseed Oil

Oxidation of bulk oils involves radical molecules, transitions metals, and association colloids, among other factors. Combining mechanistically different antioxidants is one possible strategy to improve oxidative stability of polyunsaturated fatty acids rich oils. However, antioxidant polarity may play a critical role in the oxidative protection efficacy. Thus, the objective of this study is to formulate a hydrophilic mixture (HM) containing sinapic, ascorbic, and citric acid; and a lipophilic mixture (LM) composed of α‐tocopherol, ascorbyl palmitate, and citric acid; and apply these mixtures in crude, and stripped flaxseed oils. The oxidative stability of crude oil samples containing HM and LM is comparable to that of artificial compounds mixture (ethylenediamine tetraacetic acid [EDTA] and terc‐butyl hydroquinone [TBHQ]). HM is more effective than LM in crude oil, but not in stripped oil, suggesting a strong influence of minor components on antioxidant activity of natural compounds.Practical Applications: The increasing demand for foods containing polyunsaturated fatty acids (PUFA) brings the challenge of their chemical stabilization. Here, a strategic mixture of hydrophilic natural antioxidants is effective to stabilize flaxseed oil, with effectiveness comparable to that of artificial antioxidants. Therefore, this HM constitutes a feasible and efficient option to be applied by food producers, especially in formulations that present a health claim.