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.

Exploiting the Native Microorganisms from Different Food Matrices to Formulate Starter Cultures for Sourdough Bread Production.

The use of sourdough for bread production involves fermentation, which is dominated by lactic acid bacteria (LAB) and yeast. Sourdough can be inoculated with a starter culture or through a food matrix containing microorganisms to initiate sourdough fermentation. Sourdough is used as leavening agent for bread making, and metabolites produced by LAB and yeast confer a specific aroma and flavor profile to bread, thus improving its sensory attributes. However, few publications report the effect of microorganisms from different food products and by-products on sourdough fermentation. This review focuses on using different starter cultures from various food sources, from wheat flour to starter cultures. Additionally, included are the types of sourdough, the sourdough fermentation process, and the biochemical transformations that take place during the sourdough fermentation process.

Investigation on the Double CutOff Phenomenon Observed in Protocatechuic Acid and Its Alkyl Esters under Various CAT-Based Assays.

A strange cutoff phenomenon of a series of protocatechuic acid alkyl esters had been noticed using the conjugated autoxidizable triene (CAT) assay. Two parabolic shapes of antioxidant activities of protocatechuic acid alkyl esters described as ″the double cutoff effect″ have been speculated as a result of an oxidative driving force generated in the aqueous phase. The aim of this research was to investigate the double cutoff effect using various types of oxidation driving forces in different CAT-based assays. To further explain the phenomenon, the natural oxidation of conjugated autoxidizable triene (NatCAT) assay has been developed for the first time by relying solely on only the lipid autoxidation of tung oil-in-water (O/W) emulsions. In conclusion, NatCAT exhibited different antioxidant and oxidation patterns from both CAT and apolar radical-initiated CAT assays, and only one cutoff point was obtained. This discovery would lead to a greater understanding of the complexity of antioxidant/lipid oxidation dynamics in O/W emulsion systems.

Identification and quantification of phytoprostanes and phytofurans of coffee and cocoa by- and co-products.

Phytoprostanes (PhytoPs) and phytofurans (PhytoFs) are isoprostanoids that result from the peroxidation of α-linolenic acid and are biomarkers of oxidative stress in plants and humans. These compounds exhibit several interesting biological activities (e.g. neuroprotection and anti-inflammatory activities). The aim of this research was to add value to coffee pulp (CP), cocoa husk (CH) and cocoa pod husk (CPH) by identifying and quantifying PhytoPs and PhytoFs by liquid chromatography-tandem mass spectrometry. The contents of PhytoPs and PhytoFs in CP, CH, and CPH were, respectively, 654.6, 474.3 and 179.9, and 543.2, 278.0 and 393.8 ng per g dry weight (dw). The main PhytoP found in CP (171.37 ng per g dw) and CPH (37.12 ng per g dw) was 9-epi-9-F1t-PhytoP, while ent-9-L1t-PhytoP was the most abundant in CH (109.78 ng per g dw). The main PhytoF found in all sources was ent-16(RS)-13-epi-ST-Δ14-9-PhytoF, at 196.56, 126.22, and 207.57 ng per g dw in CP, CH, and CPH, respectively. We provide the first complete profile of PhytoPs and PhytoFs for these agro-residues, which could be used in the functional food industry for enriching food or as nutritional supplements.

Theoretical Characterization by Density Functional Theory (DFT) of Delphinidin 3-O-Sambubioside and Its Esters Obtained by Chemical Lipophilization.

Anthocyanins are water-soluble phenolic pigments. However, their poor solubility in lipidic media limits their use. This hurdle can be overcome with the lipophilization of anthocyanins, which consists of adding an aliphatic chain to a hydrophilic compound, in order to increase its solubility in lipids. Still, the unspecific chemical lipophilization of anthocyanin-esters produces molecules with different properties from their precursors. In this work, experimental changes of anthocyanin-esters obtained by chemical lipophilization are investigated in silico aiming specifically at observing their molecular behavior and comparing it with their anthocyanin precursor. Thus, the analysis of delphinidin 3-O-sambubioside and its esters employing Density Functional Theory (DFT) methods, such as the hybrid functional B3LYP in combination with the 6-31++G(d,p) Pople basis set, provides the ground state properties, the local reactivity and the molecular orbitals (MOs) of these compounds. Excited states properties were analyzed by TD-DFT with the B3LYP functional, and the M06 and M06-2X meta-GGA functionals. Local reactivity calculations showed that the electrophilic site for all the anthocyanin-esters was the same as the one for the anthocyanin precursor, however the nucleophilic site changed depending localization of the esterification. TD-DFT results indicate that the place of esterification could change the electronic transitions and the MOs spatial distribution.

Eleostearic phospholipids as probes to evaluate antioxidants efficiency against liposomes oxidation.

Regardless of the applications: therapeutic vehicle or membrane model to mimic complex biological systems; it is of a great importance to develop simplified, reproducible and rapid model assays allowing for a relevant assessment of the liposomal membrane oxidation and therefore antioxidant activity of selected molecules. Here, we describe a new and high-throughput assay that we called "Vesicle Conjugated Autoxidizable Triene (VesiCAT)". It is based on specific UV absorbance spectral properties of a new phospholipid probe, synthesized with natural conjugated eleostearic acid extracted from Tung oil. The VesiCAT assay has been developed with two different radical generators (2,2'-azobis(2-amidinopropane) dihydrochloride; AAPH and 2,2'-azobis(2,4-dimethylvaleronitrile); AMVN), producing a constant flux of oxidant species, either in membrane or in aqueous phase. This method appears very efficient in assessing the effect of various pure antioxidant molecules in their ability to preserve liposomes from oxidative degradation. In addition, the AAPH- and AMVN-induced oxidations offer the possibility of extracting different but complementary information with respect to the antioxidants efficacy.

Comparison of Antioxidant Evaluation Assays for Investigating Antioxidative Activity of Gallic Acid and Its Alkyl Esters in Different Food Matrices.

The addition of antioxidants is one of the strategies to inhibit lipid oxidation, a major cause of lipid deterioration in foods leading to rancidity development and nutritional losses. However, several studies have been reported that conventional antioxidant assays, e.g., TPC, ABTS, FRAP, and ORAC could not predict antioxidant performance in several foods. This study aimed to investigate the performance of two recently developed assays, e.g., the conjugated autoxidizable triene (CAT) and the apolar radical-initiated conjugated autoxidizable triene (ApoCAT) assays to predict the antioxidant effectiveness of gallic acid and its esters in selected food models in comparison with the conventional antioxidant assays. The results indicated that the polarities of the antioxidants have a strong impact on antioxidant activities. In addition, different oxidant locations demonstrated by the CAT and ApoCAT assays influenced the overall antioxidant performances of the antioxidants with different polarities. To validate the predictability of the assays, the antioxidative performance of gallic acid and its alkyl esters was investigated in oil-in-water (O/W) emulsions, bulk soybean oils, and roasted peanuts as the lipid food models. The results showed that only the ApoCAT assay could be able to predict the antioxidative performances in O/W emulsions regardless of the antioxidant polarities. This study demonstrated that the relevance of antioxidant assays to food models was strongly dependent on physical similarities between the tested assays and the food structure matrices.

Lipophilization and MS characterization of the main anthocyanins purified from hibiscus flowers.

Hibiscus sabdariffa flowers represent an interesting source of anthocyanins, one of the most important plant pigments, which are responsible of the intense red color of the calyces, and have potential as natural colorants for food applications. Nevertheless, anthocyanins are highly hydrosoluble and unstable compounds. On this basis, the aim of this work was to increase the lipophilicity of the hibiscus anthocyanins by lipophilization, in order to obtain amphiphilic colorants, which could be easily incorporated in lipid-rich food matrices. Octanoyl derivatives of delphinidin-3-O-sambubioside and cyanidin-3-O-sambubioside were chemically obtained for the first time, and characterized by means of HPLC-ESI-MS data.

Application of Deep Eutectic Solvents (DES) for Phenolic Compounds Extraction: Overview, Challenges, and Opportunities.

The green chemistry era has pushed the scientific community to investigate and implement new solvents in phenolic compounds (PC) extraction as alternatives to organic solvents, which are toxic and may be dangerous. Recently, deep eutectic solvents (DES) have been applied as extraction solvents for PC. They have the advantages of biodegradability and ease of handling with very low toxicity. Nevertheless, the extraction process is affected by several factors: affinity between DES and the target compounds, the water content, the mole ratio between DES' starting molecules, the liquid/solid ratio between the DES and sample, and the conditions and extraction method. On the other hand, PC recovery from DES is a challenge because they can establish a strong hydrogen bond network. Alternatively, another possibility is to use DES as solvent extraction as well as formulation medium. In this way, DES can be suitable for cosmetics, pharmaceutical, or food applications.

Antioxidant activity of protocatechuates evaluated by DPPH, ORAC, and CAT methods.

Hibiscus sabdariffa L. is a worldwide consumed plant, principally after infusion of its dried sepals and calyces, which are usually discarded. Nevertheless, they represent a potential source of natural bioactive compounds, e.g. polyphenols, which could add value to this under-exploited plant. Protocatechuic acid (PA) was chosen as a model of the phenolic acids that can be extracted from H. sabdariffa. In order to modify PA hydrophilic character, which limits its use in lipid-rich food products, PA was esterified to C1-C18 alcohols, and the impact of lipophilization on its antioxidant activity was evaluated in both, an homogeneous (DPPH and ORAC methods) and an heterogeneous (CAT method) system. Results herein obtained showed that, depending on the grafted alkyl chain length, lipophilization could positively affect the antioxidant activity of PA in heterogeneous media; therefore, support its use as an innovative way to synthesize molecules with an improved antioxidant capacity and potential to be used as multifunctional preservatives in food.

Grape seed and apple tannins: emulsifying and antioxidant properties.

Tannins are natural antioxidants found in plant-based foods and beverages, whose amphiphilic nature could be useful to both stabilize emulsions and protect unsaturated lipids from oxidation. In this paper, the use of tannins as antioxidant emulsifiers was studied. The main parameters influencing the stability of emulsions (i.e. tannins structure and concentration, aqueous phase pH, and ionic strength) were identified and optimized. Oil in water emulsions stabilized with tannins were compared with those stabilized with two commercial emulsifying agents, poly(vinyl alcohol) (PVA) and polyoxyethylene hydrogenated castor oil. In optimized conditions, the condensed tannins allowed to obtain a stability equivalent to that of PVA. Tannins presented good antioxidant activity in oil in water emulsion, as measured by the conjugated autoxidizable triene (CAT) assay.

Relationship between hydrophobicity and antioxidant ability of "phenolipids" in emulsion: a parabolic effect of the chain length of rosmarinate esters.

The polar paradox predicts that hydrophobic antioxidants are more active in emulsions than their hydrophilic homologues, thus assuming a linear dependency between hydrophobicity and antioxidant capacity. In contrast, we formulate in this paper an alternative hypothesis assuming a possible nonlinear dependency. To verify this so-called "nonlinear hypothesis", the antioxidant capacity of a homologous series of rosmarinic acid and its alkyl esters (methyl, butyl, octyl, dodecyl, hexadecyl, octadecyl, and eicosyl) was evaluated using a newly developed conjugated autoxidizable triene (CAT) assay. It appeared that the antioxidant capacity increases as the alkyl chain is lengthened, with a maximum for the octyl chain, after which further chain extension leads to a collapse in antioxidant capacity. This nonlinear effect was discussed in relation to the "cutoff effect" generally observed in studies using cultured cells. This new hypothesis may provide a better understanding of the antioxidant behavior of phenolics in emulsion which is a key to develop new antioxidant strategies to protect lipid substrates from oxidation. Moreover, the lipophilization with medium chain appeared as a promising way to enhance the antioxidant capacity of phenolics since octyl rosmarinate was three times more effective than rosmarinic acid which is already one of the most powerful known phenolic antioxidant. Finally, this work paves the way for systematic investigation of the chain length effect to design new "phenolipids" in a rational fashion.

Chain length affects antioxidant properties of chlorogenate esters in emulsion: the cutoff theory behind the polar paradox.

Twenty years ago, Porter et al. (J. Agric. Food Chem. 1989, 37, 615 - 624) put forward the polar paradox stating among others that apolar antioxidants are more active in emulsified media than their polar homologues. However, some recent results showing that not all antioxidants behave in the manner proposed by this hypothesis led us to investigate the relationship between antioxidant property and hydrophobicity. With a complete homologous series of chlorogenic acid esters (methyl, butyl, octyl, dodecyl, hexadecyl, octadecyl, and eicosyl), we observed in emulsified medium that antioxidant capacity increases as the alkyl chain is lengthened, with a threshold for the dodecyl chain, after which further chain extension leads to a drastic decrease in antioxidant capacity. The antioxidant capacity evaluation in emulsion was possible using a newly developed conjugated autoxidizable triene (CAT) assay, which allows the assessment of both hydrophilic and lipophilic antioxidants. The nonlinear behavior was mainly explained in terms of antioxidant location since it was found from partition analysis that the dodecyl ester presented the lowest concentration in the aqueous phase and also that the quantity of emulsifier drastically changes the partition of antioxidant. In addition, this nonlinear influence was connected to the so-called cutoff effect largely observed in studies using cultured cells. Taken together, these different results allow one to make the proposal of a new scenario of the behavior of phenolic compounds in emulsified systems with special emphasis on the micellization process. Finally, in the CAT system, the polar paradox appeared to be the particular case of a far more global nonlinear effect that was observed here.

Kinetic and stoichiometry of the reaction of chlorogenic acid and its alkyl esters against the DPPH radical.

The lipophilization of polar antioxidants such as phenolics is an efficient way to enhance their solubility in apolar media. Thus, in emulsified systems, lipophilized antioxidants are supposed to locate at the lipid/aqueous phase interface and to lead to a better protection of unsaturated lipids. Herein, the antiradical activity of chlorogenic acid (5-CQA) and its corresponding esters with seven fatty alcohols (from methanol to eicosanol) have been achieved using the well-known 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. Hydrophobation was shown to significantly improve the antiradical activity of 5-CQA esters which reached a maximum for butyl- and octyl-chlorogenate. In addition, for both 5-CQA and its esters, it was demonstrated that the global mechanism of DPPH* stabilization proceeded likely by electron transfer (ET), while it appeared that the pathways of DPPH* stabilization were different between 5-CQA and its esters, as confirmed by the LC-MS characterization of reaction products. Finally, strong differences were found between the tested molecules allowing the proposal of different DPPH* stabilization pathways by electron transfer for 5-CQA and its esters.

Ability of surface-active antioxidants to inhibit lipid oxidation in oil-in-water emulsion.

Lipid oxidation in dispersed lipids is prevalent at the oil-water interface where lipid hydroperoxides are decomposed into free radicals by transition metals. Free radical scavenging antioxidants are believed to be most effective in lipid dispersions when they accumulate at the oil-water interface. The surface activity of antioxidants could be increased by their conjugation to hydrocarbon chains. In this study, p-hydroxyphenylacetic acid (HPA) was conjugated with either a butyl or dodecyl group. The HPA conjugates were more effective at decreasing interfacial tension than unconjugated HPA, indicating that they were able to adsorb at lipid-water interfaces. However, free HPA was a more effective antioxidant than butyl and dodecyl conjugates in Menhaden oil-in-water emulsions as determined by both lipid hydroperoxides and thiobarbituric acid reactive substances. The increased antioxidant activity of free HPA could be due to its more effective free radical scavenging activity and its higher concentration in the lipid phase of oil-in-water emulsions in the presence of surfactant micelles where it can act as a chain-breaking antioxidant.

Phenolic acids enzymatic lipophilization.

Lipophilization is the esterification of a lipophilic moiety (fatty acid or fatty alcohol) on different substrates (phenolic acid, sugar, protein, ...), resulting in new molecules with modified hydrophilic/lipophilic balance. This reaction can be obtained chemically or enzymatically using different enzymes. Phenolic acids possess interesting biological properties (antioxidant, chelator, free radical scavenger, UV filter, antimicrobial, ...), but because of their relatively low solubility in aprotic media, their application in oil-based products is limited. Therefore, the esterification of their carboxylic acid function with a fatty alcohol enhances their hydrophobicity and results in a multifunctional amphiphilic molecule. Enzymatic lipophilization of phenolic acids is nowadays studied for potential industrial applications. Different systems have been proposed to perform the reaction yield [free or immobilized enzymes (lipase, feruloyl esterase, tannase, etc.), free or added organic solvent, addition of surfactant, microemulsion system, etc.]. Some of the functional properties of these esters have been demonstrated. This review presents a panorama of the advances in this field.

Enzymatic solubilization of arabinoxylans from native, extruded, and high-shear-treated rye bran by different endo-xylanases and other hydrolyzing enzymes.

The overall objective of this research was to find a new way to valorize rye bran, by producing a gellifier from the enzymatic solubilization of arabinoxylans (AX). The effects of three pure endo-xylanases from Aspergillus niger (Xyl-1), Talaromyces emersonii (Xyl-2), and Bacillus subtilis (Xyl-3) and of Grindamyl S100 (GS100), a commercial enzyme preparation containing a Xyl-1 type endo-xylanase, were tested on rye bran to study the solubilization of water-unextractable arabinoxylans (WUAX). Eight different extrusion-treated rye brans were also used as substrates to find the best physical treatment to facilitate enzymatic arabinoxylan (AX) solubilization. Arabinoxylans were better solubilized from the bran extruded at high temperature using Xyl-3. This enzyme was then tested in combination with pure (1,4)-beta-d-arabinoxylan arabinofuranohydrolase (AXH) and endo-beta-d-glucanase or ferulic acid esterase (FAE), from A. niger. Only beta-glucanase in combination with Xyl-3 improved the AX extraction, but it did not have a marked effect on the viscosity of the extracts. Xyl-3 was then tested on a high-shear-treated rye bran, and results were compared to those obtained with the high-temperature-extruded rye bran. The high-shear treatment did not improve the bran AX enzymatic solubilization. The combination of FAE with Xyl-1 or Xyl-3 did not improve the AX extraction from untreated and high-shear-treated rye bran. Finally, to study the gelation capacity of the enzymatically solubilized AX, the effect of the hydrogen peroxide/horseradish peroxidase (H(2)O(2)/POD) was tested on the Xyl-3 high-temperature-extruded bran extracts. Solubilized AX did not gel in the presence of the oxidizing system.