Relationship between the Physiochemical Properties of Cocoa Procyanidins and Their Ability to Inhibit Lipid Oxidation in Liposomes

Concentration-dependent dual roles of proanthocyanidins on oxidative stress and docosahexaenoic acid production in Schizochytrium sp. ATCC 20888

Antioxidant addition is an effective strategy to achieve docosahexaenoic acid (DHA) overproduction in oleaginous microorganisms. Nevertheless, antioxidants like phenolic compounds sometimes exert pro-oxidant activity. In this work, effects of proanthocyanidins (PAs) on fermentation performance and oxidative stress in Schizochytrium sp. were investigated. Low PAs addition (5 mg/L) reduced reactive oxygen species and enhanced lipogenic enzymes activities and NADPH, resulting in significant increase in lipid (20.3 g/L) by 33.6 % and DHA yield (9.8 g/L) by 53.4 %. In contrast, high PAs addition (500 mg/L) exerted pro-oxidant effects, aggravated oxidative damage and lipid peroxidation, leading to sharp decrease in biomass (21.3 g/L) by 35.1 %, lipid (8.2 g/L) by 46.0 %, and DHA (2.9 g/L) by 54.8 %. Therefore, the antioxidant concentration is especially crucial in DHA production. This study is the first to report concentration-dependant dual roles of PAs in oxidative stress and DHA production in Schizochytrium sp., providing new insights into microbial DHA production.

Apple Pomace Compositional Data Highlighting the Proportional Contribution of Polymeric Procyanidins

Recent years have seen an increase in research focusing on the amelioration of apple pomace waste for use in the food and nutraceutical industries. Much of this work has concentrated on the characterisation of the polyphenol composition of apple pomace materials to determine their role in conferring nutritional and health benefits. Although apples contain substantial quantities of polymeric procyanidins (condensed tannins), this class of compounds has received limited attention in apple research. This study quantified the polymeric procyanidins in apple pomace extracts using a rapid, methyl-cellulose precipitation (MCP) approach for the first time. In addition, a non-targeted metabolomics approach was applied to determine the most abundant phenolic classes present. Polymeric procyanidins were found to be the most abundant type of polyphenol in apple pomace extracts and were generally oligomeric in nature. Multivariate statistical analysis revealed that the ferric-reducing antioxidant power (FRAP) was most strongly correlated with the polymeric procyanidin concentration. Noting that polymeric procyanidins may not cross the cell layer to exert antioxidant activity in vivo, their presence in apple pomace extracts may therefore overestimate the FRAP. This work highlights the importance of polymeric procyanidins in the phenolic diversity of apple pomaces, and it is proposed that in future studies, rapid MCP assays may be used for their quantification.

Natural carriers: Recent advances in their use to improve the stability and bioaccessibility of food active compounds

In the last decades, the incorporation of bioactive compounds in food supplements aroused the attention of scientists. However, these ingredients often exhibit both low solubility and stability and their poor bioaccessibility within the gastrointestinal tract limits their effectiveness. To overcome these drawbacks, many carriers have been investigated for encapsulating nutraceuticals and enhancing their bioavailability. It is note that several different vegetable wall materials have been applied to build delivery systems. Considering their encapsulation mechanism, lipid and protein-based carriers display specific interaction patterns with bioactives, whereas polysaccharidic-based carriers can entrap them by creating porous highly stable networks. To maximize the encapsulation efficiency, mixed systems are very promising. Following the current goal of using natural and sustainable ingredients, only a limited number of studies about the isolation of new ingredients from agro-food waste are available. In this review, a comprehensive overview of the state of art in the development of innovative natural lipid-, protein- and polysaccharide-based plant carriers is presented, focusing on their application as food active compounds. Different aspects to be considered in the design of delivery systems are discussed, including the carrier structure and chemical features, the interaction between the encapsulating and the core material, and the parameters affecting bioactives entrapment.

Encapsulation of tannins and tannin-rich plant extracts by complex coacervation to improve their physicochemical properties and biological activities: A review

As a major class of dietary polyphenols, tannins are demonstrated to have various health-promoting properties. Although tannins have been widely utilized in food, pharmaceutical and many other industries, the applications of tannins are quite limited due to their poor stability, sensory attributes and bioavailability. Encapsulation helps improve all of these properties. Complex coacervation, one of the most effective encapsulation techniques, is known for its simplicity, low cost, scalability and reproducibility in encapsulation of functional components. In recent years, complex coacervation has been successfully used for encapsulation of tannins and tannin-rich plant extracts. In this article, the research progress in encapsulating tannins and tannin-rich plant extracts by complex coacervation to improve their physicochemical properties and biological activities is critically reviewed for the first time. Encapsulation of tannins and tannin-rich plant extracts can effectively improve their sensory characteristics, stabilities, bioavailability, anti-hypercholesterolemia, anti-diabetic, antioxidant, anticancer and antimicrobial activities. In particular, the enhancement of biological activities of tannins and tannin-rich plant extracts is usually correlated to their improved physicochemical properties imparted by the encapsulation technique. Moreover, we introduce the issues that need to be further resolved in future studies on encapsulation of tannins and tannin-rich plant extracts by complex coacervation.

Structure-Dependent Eco-Toxicity of Vegetable Tannin

Vegetable tannin is widely applied in various industries, in agriculture, and in water treatment as a natural polyphenolic compound; however, little data has been collected concerning the relationship between structure and eco-toxicity. Here, the toxicity of six commercial tannin and three model chemicals was assessed using Photobacterium phosphoreum. Two kinds of hydrolyzed tannin displayed higher bioluminescence inhibition than four kinds of condensed tannin, and the model chemical of hydrolyzed tannin also showed greater toxicity than those of condensed tannin, indicating the structure dependent eco-toxicity of vegetable tannin. The reactive toxicity mechanism was proposed, which was illustrated by molecular simulations based on the model chemicals and luciferase.

Active sites of peptides Asp-Asp-Asp-Tyr and Asp-Tyr-Asp-Asp protect against cellular oxidative stress

The protective effects of the peptides Asp-Asp-Asp-Tyr (DDDY) and Asp-Tyr-Asp-Asp (DYDD) against AAPH-induced HepG2 cells are unclear. Our objective was to investigate the active sites of these peptides and their cellular antioxidant mechanism. DDDY and DYDD show a direct free radical scavenging effect in reducing ROS levels and maintained cellular antioxidant enzymes at normal levels. The quantum chemistry analysis of the electronic properties of antioxidant activity showed that DYDD has a greater energy in the highest occupied molecular orbital than DDDY, and O₅₈-H₅₉ and N₁₀-H₁₂ were identified as the active antioxidant sites in DYDD and DDDY, respectively, indicating that the inconsistent arrangement of amino acids affects the distribution of the highest occupied orbital energy as well as the active sites; thus, influences the antioxidant activity of peptides. It provide valuable insights into the antioxidant active sites of peptides.

Towards Oxidatively Stable Emulsions Containing Iron-Loaded Liposomes: The Key Role of Phospholipid-to-Iron Ratio

To encapsulate soluble iron, liposomes were prepared using unsaturated phospholipids (phosphatidylcholine from egg yolk), leading to high encapsulation efficiencies (82–99%). The iron concentration affected their oxidative stability: at 0.2 and 1 mM ferrous sulfate, the liposomes were stable, whereas at higher concentrations (10 and 48 mM), phospholipid oxidation was considerably higher. When applied in oil-in-water (O/W) emulsions, emulsions with liposomes containing low iron concentrations were much more stable to lipid oxidation than those added with liposomes containing higher iron concentrations, even though the overall iron concentration was similar (0.1 M). Iron-loaded liposomes thus have an antioxidant effect at high phospholipid-to-iron ratio, but act as pro-oxidants when this ratio is too low, most likely as a result of oxidation of the phospholipids themselves. This non-monotonic effect can be of crucial importance in the design of iron-fortified foods.

Build-Up of a 3D Organogel Network within the Bilayer Shell of Nanoliposomes. A Novel Delivery System for Vitamin D3: Preparation, Characterization, and Physicochemical Stability

The inherent thermodynamic instability of liposomes during production and storage has limited their widespread applications. Therefore, a novel structure of food-grade nanoliposomes stabilized by a 3D organogel network within the bilayer shell was developed through the extrusion process and successfully applied to encapsulate vitamin D₃. A huge flocculation and a significant reduction of zeta potential (-17 mV) were observed in control nanoliposomes (without the organogel shell) after 2 months of storage at 4 °C, while the sample with a gelled bilayer showed excellent stability with a particle diameter of 105 nm and a high negative zeta potential (-63.4 mV), even after 3 months. The development of spherical vesicles was confirmed by TEM. Interestingly, the gelled bilayer shell led to improved stability against osmotically active divalent salt ions. Electron paramagnetic resonance confirmed the higher rigidity of the shell bilayer upon gelation. The novel liposome offered a dramatic increase in encapsulation efficiency and loading of vitamin D₃ compared to those of control.

Magnetic imprinted nanoparticles with synergistic tailoring of covalent and non-covalent interactions for purification and detection of procyanidin B2

A synergistic imprinting strategy of covalent and non-covalent interactions is proposed to prepare magnetic molecularly imprinted polymers (DI-MMIPs) for highly selective separation of procyanidin B2 (PC) from grape seed samples. Dopamine and 3-amino-phenylboronic acid as cooperative functional monomers endow the imprinted sites with synergistic tailoring. Benefiting from the synergistic effect, the DI-MMIPs exhibit enhanced imprinting performance with high adsorption capacity (27.71 mg g^-1), fast kinetic equilibrium time (within 30 min), outstanding selectivity (IF = 5.8, SC > 3.2), and satisfactory regeneration ability. In addition, the DI-MMIPs possess good magnetism, uniform morphology with typical core-shell structure, and stable crystallization. Furthermore, the established DI-MMIPs coupled with HPLC-UV (~ 280 nm) method has a wide linearity range of 0.05-200 μg mL^-1 with correlation coefficient of 0.9997, high recoveries (> 93.1%) with RSDs from 2.9 to 5.5%, and low LOD (0.0008 μg mL^-1). Consequently, this work provides an effective and easily tailored way to fabricate magnetic imprinted nanomaterials with both rapid recognition rate and high selectivity and thus holds great promise to realize the extraction and detection of PC from real samples.

Chitosan decoration improves the rapid and long-term antibacterial activities of cinnamaldehyde-loaded liposomes

In this work, cinnamaldehyde-loaded liposomes decorated with different concentrations of chitosan (0, 0.25, 0.5, 1, 2, 3, and 4 mg/mL) were prepared and their physical and antibacterial properties were evaluated. The results showed that the physical decoration of chitosan improved the encapsulation efficiency and storage stability of the liposomes. Liposomes decorated with chitosan at the concentration of 0.25 to 4 mg/mL were able to achieve an obvious antibacterial efficiency against Staphylococcus aureus after only 10 min of incubation. The antibacterial efficiency of chitosan-decorated liposomes was still higher than 90% after being stored for 28 d when the chitosan concentration was greater than 1 mg/mL. Besides, increasing the chitosan concentration significantly decreased the minimum inhibitory concentration of the liposomes. The comparison of the antibacterial activities and mechanisms of cinnamaldehyde-loaded liposomes decorated with chitosan at a concentration of 4 mg/mL (CH-CL), cinnamaldehyde-loaded liposomes (CL), cinnamaldehyde, and chitosan revealed that chitosan and cinnamaldehyde exerted a cumulative and synergistic bacteriostatic effect in the liposomes. This led to damage to the cell membrane integrity, causing cell death by inducing leakage of intracellular components. These results can potentially provide guidance for the preparation and application of natural preservatives with rapid and long-term bacteriostatic effects.

Discovering active sites in peptide Ala-Val-Thr-Phe that counter 2,2-azobis(2-methylpropanimidamidine)dihydrochloride-induced oxidative stress in HepG2 cells

The Ala-Val-Thr-Phe (AVTF) peptide derived from edible Dendrobium aphyllum was co-incubated with Lactobacillus amylolyticus in a previous study. The aim of the present study was to further examine the antioxidative and protective effects of the AVTF peptides through the analysis of free-radical quenching in HepG2 cells subjected to 2,2-azobis(2-methylpropanimidamidine)dihydrochloride (AAPH)-induced oxidative stress and to determine the active sites within the peptide. Variations in intracellular malondialdehyde levels indicated that these peptides protect HepG2 cells by preventing ROS attack and lipid peroxidation. Antioxidant enzymes and Nrf2 were downregulated in AVTF-treated but not in AAPH-treated HepG2 cells, whereas the electrically sensitive Keap1 was not susceptible to free radical-induced damage after AVTF treatment. However, this did not result in the activation of the Nrf2/Keap1 signaling pathway, thus indicating that one potential mechanism by which AVTF maintains homeostasis in HepG2 cells is by directly scavenging free radicals. Furthermore, quantum chemical calculations and the assessment of electronic-related properties associated with antioxidant activity revealed that the active sites of AVTF included N9-H11, which was further confirmed by the assessment of ROS levels in methylated AVTF-treated cells. The results of this study provide valuable insights into the active site N9-H11 in the Ala residue of AVTF, which influences the antioxidant activity of the peptide.

Preparative Separation of Procyanidins from Cocoa Polyphenolic Extract: Comparative Study of Different Fractionation Techniques

To provide further insight into the antioxidant potential of procyanidins (PCs) from cocoa beans, PC extract was fractionated by several methodologies, including solid phase extraction, Sephadex LH-20 gel permeation, and preparative HPLC using C18 and diol stationary phases. All the isolated fractions were analyzed by UHPLC-QTOF-MS to determine their relative composition. According to our results, classical techniques allowed good separation of alkaloids, catechins, dimers, and trimers, but were inefficient for oligomeric PCs. Preparative C18-HPLC method allowed the attainment of high relative composition of fractions enriched with alkaloids, catechins, and PCs with degree of polymerization (DP) < 4. However, the best results were obtained by preparative diol-HPLC, providing a separation according to the increasing DP. According to the mass spectrometry fragmentation pattern, the nine isolated fractions (Fractions II–X) consisted of exclusively individual PCs and their corresponding isomers (same DP). In summary, an efficient, robust, and fast method using a preparative diol column for the isolation of PCs is proposed. Regarding DPPH^• and ABTS^•+ scavenging activity, it increases according to the DP; therefore, the highest activity was for cocoa extract > PCs > monomers. Thereby, cocoa procyanidins might be of interest to be used as alternative antioxidants.

The Structural Integrity of the Model Lipid Membrane during Induced Lipid Peroxidation: The Role of Flavonols in the Inhibition of Lipid Peroxidation

The structural integrity, elasticity, and fluidity of lipid membranes are critical for cellular activities such as communication between cells, exocytosis, and endocytosis. Unsaturated lipids, the main components of biological membranes, are particularly susceptible to the oxidative attack of reactive oxygen species. The peroxidation of unsaturated lipids, in our case 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), induces the structural reorganization of the membrane. We have employed a multi-technique approach to analyze typical properties of lipid bilayers, i.e., roughness, thickness, elasticity, and fluidity. We compared the alteration of the membrane properties upon initiated lipid peroxidation and examined the ability of flavonols, namely quercetin (QUE), myricetin (MCE), and myricitrin (MCI) at different molar fractions, to inhibit this change. Using Mass Spectrometry (MS) and Fourier Transform Infrared Spectroscopy (FTIR), we identified various carbonyl products and examined the extent of the reaction. From Atomic Force Microscopy (AFM), Force Spectroscopy (FS), Small Angle X-Ray Scattering (SAXS), and Electron Paramagnetic Resonance (EPR) experiments, we concluded that the membranes with inserted flavonols exhibit resistance against the structural changes induced by the oxidative attack, which is a finding with multiple biological implications. Our approach reveals the interplay between the flavonol molecular structure and the crucial membrane properties under oxidative attack and provides insight into the pathophysiology of cellular oxidative injury.

Food-Safe Process for High Recovery of Flavonoids from Cocoa Beans: Antioxidant and HPLC-DAD-ESI-MS/MS Analysis

Considering the increasing interest in the incorporation of natural antioxidants in enriched foods, this work aimed to establish a food-grade and suitable procedure for the recovery of polyphenols from cocoa beans avoiding the degreasing process. The results showed that ultrasound for 30 min with particle sample size < 0.18 mm changed the microstructure of the cell, thus increasing the diffusion pathway of polyphenols and avoiding the degreasing process. The effect of temperature, pH, and concentration of ethanol and solute on the extraction of polyphenols was evaluated. Through a 24 full factorial design, a maximum recovery of 122.34 ± 2.35 mg GAE /g, 88.87 ± 0.78 mg ECE /g, and 62.57 ± 3.37 mg ECE /g cocoa beans, for total concentration of polyphenols (TP), flavonoids (TF), and flavan-3-ols (TF3), respectively, was obtained. Based on mathematical models, the kinetics of the solid-liquid extraction process indicates a maximum equilibrium time of 45 min. Analysis by HPLC-DAD-ESI-MS/MS showed that our process allowed a high amount of methylxanthines (10.43 mg /g), catechins (7.92 mg /g), and procyanidins (34.0 mg /g) with a degree of polymerization >7, as well as high antioxidant activity determined by Oxygen Radical Absorbance Capacity (1149.85 ± 25.10 µMTrolox eq /g) and radical scavenging activity (DPPH•, 120.60 ± 0.50 µM Trolox eq /g). Overall, the recovery method made possible increases of 59.7% and 12.8% in cocoa polyphenols content and extraction yield, respectively. This study showed an effective, suitable and cost-effective process for the extraction of bioactive compounds from cocoa beans without degreasing.

Procyanidins-Loaded Complex Coacervates for Improved Stability by Self-Crosslinking and Calcium Ions Chelation

The purpose of this work was to develop a facile strategy based on self-crosslinking between the core and wall materials in the coacervation system for effective procyanidins (PCs) encapsulation. The coacervates were constructed through the interaction of bioactive PCs, gelatin, and sodium alginate, followed by forming cationic bridge of sodium alginate-calcium ions to improve the stability of PCs. When the concentration of PCs and calcium ions were 6.25 and 0.24 mg/mL, respectively, the PC-loaded coacervates showed spherical shape with a size about 150 nm, and the microcapsulation efficiency and yield was 81.19 ± 1.47 and 87.86 ± 2.67%, respectively. The photothermal stability of PCs was effectively improved by embedding them in coacervates. The decrease of mitochondrial membrane potential in PC-12 cells induced by H₂O₂ was significantly inhibited by PC coacervates, demonstrating an improved protection effect of PCs after being encapsulated in coacervates.

Insight of Stability of Procyanidins in Free and Liposomal Form under an in Vitro Digestion Model: Study of Bioaccessibility, Kinetic Release Profile, Degradation, and Antioxidant Activity

Small unilamellar and multilayered liposomes loaded with polymeric (epi)catechins up to pentamers were produced. The bioaccessibility, kinetic release profile, and degradation under in vitro gastrointestinal conditions were monitored by UHPLC-DAD-QTOF-MS/MS. The results show that all of the procyanidins underwent depolymerization and epimerization into small molecular oligomers and mainly to (epi)catechin subunits. Moreover, all of the liposome formulations presented higher bioaccessibility and antioxidant activity in comparison to their respective counterparts in non-encapsulated form. Similar results were obtained with procyanidins from cocoa extract-loaded liposomes. Namely, the bioaccessibility of dimer, trimer, and tetramer fractions from cocoa-loaded liposomes were 4.5-, 2.1-, and 9.3-fold higher than those from the non-encapsulated cocoa extract. Overall, the procyanidin release profile was dependent on their chemical structure and physicochemical interaction with the lipid carrier. These results confirmed that liposomes are efficient carriers to stabilize and transport procyanidins with the aim of enhancing their bioaccessibility at a controlled release rate.

Development of a rapid ultra performance hydrophilic interaction liquid chromatography tandem mass spectrometry method for procyanidins with enhanced ionization efficiency

Cocoa flavanols (catechins and procyanidins) can exist in various polymerization states and are commonly classified by their degree of polymerization (DP). There is increasing evidence that flavanols of distinct DP possess different biological activities, but separation and quantification of the higher DP procyanidins is challenging and has thus created the need for new methodologies that utilize advancements in columns and LC-MS/MS systems. An aqueous normal phase (hydrophilic interaction liquid chromatography, HILIC), UPLC method with post-column ESI adjuvant infusion was developed to reduce the total analysis time, increase peak separation, and increase detection specificity (compared to traditional fluorescence methods) by coupling with mass spectrometry detection. The total elution time was reduced from 70 to 90 min (typically used for normal phase and HILIC HPLC separation of procyanidins) down to 9 min by employing UPLC. Results indicate that by using a post-column 0.04 M ammonium formate infusion (5 μL/min), ionization of procyanidins was significantly enhanced. Lower limits of detection ranged from 3.19 × 10^-2 to 4.56 pmol-on-column, and lower limits of quantification ranged from 2.79 × 10^-2 to 1.17 × 10² pmol-on-column across compounds DP 1-9. This method builds upon the foundation set by existing analytical methods and employs new technologies to dramatically increase sample throughput and enhance detection limits and specificity, facilitating improved analysis for procyanidins.

Design, Fabrication, Characterization, and In Vitro Digestion of Alkaloid-, Catechin-, and Cocoa Extract-Loaded Liposomes

Liposomes containing theobromine, caffeine, catechin, epicatechin, and a cocoa extract were fabricated using microfluidization and sonication. A high encapsulation efficiency and good physicochemical stability were obtained by sonication (75% amplitude, 7 min). Liposomes produced at pH 5.0 had mean particle diameter ranging from 73.9 to 84.3 nm. The structural and physicochemical properties of the liposomes were characterized by transmission electron microscopy, confocal fluorescence microscopy, and antioxidant activity assays. The release profile was measured by ultra-high performance liquid chromatography coupled to diode array detection. The bioaccessibility of the bioactive compounds encapsulated in liposomes was determined after exposure to a simulated in vitro digestion model. Higher bioaccessibilities were measured for all catechins-loaded liposome formulations as compared to nonencapsulated counterparts. These results demonstrated that liposomes are capable of increasing the bioaccessibility of flavan-3-ols, which may be important for the development of nutraceutical-enriched functional foods.