Food Structure Modulates the Bioavailability of Triglycerides and Vitamin D, and Partly That of Lutein: A Randomized Trial with a Crossover Design in Adults.

SCOPE: The specific effect of the food matrix structure on fat-soluble micronutrient bioavailability is only partly understood. Evaluating fat-soluble micronutrient bioavailability after consumption of foods displaying similar composition but different structure is aimed at. METHODS AND RESULTS: Twelve healthy subjects are enrolled in a randomized, open label, crossover postprandial trial. Four different model foods are tested: custard, pudding, sponge cake, and biscuit. Vitamin D3 , lutein, and triglyceride chylomicron responses, evaluated as postprandial areas under the curve, are then assayed. Custard triglyceride response is higher than pudding and biscuit responses (up to +122.7%, p < 0.0001). Sponge cake vitamin D3 response is higher than biscuit response (+26.6%, p = 0.047). No difference between the model foods are observed regarding lutein responses. Triglyceride responses peak at 3 h for all conditions, while vitamin D3 and lutein peaks are delayed by 1 h with the biscuit matrix compared to other model foods. CONCLUSION: Food structure can significantly impact on triglyceride and vitamin D3 bioavailability in terms of absorbed amounts and/or maximum absorption time. The data highlight positive correlations between triglyceride, vitamin D, and lutein nutrient responses. These results are of particular interest to develop functional foods for population subgroups such as the elderly.

Impact of onions in tomato-based sauces on isomerization and bioaccessibility of colorless carotenes: phytoene and phytofluene.

Onions as an interesting ingredient have been proved to promote Z-isomerization of lycopene and increase bioaccessibility of total-lycopene. Phytoene (PT) and phytofluene (PTF), the precursors of lycopene, are colorless carotenes, which are attracting much attention and are also abundant in tomatoes. Therefore, onions might also affect the distribution and bioaccessibility of PT and PTF isomers during heating tomato (hot-break and cold-break purees)-onion-extra virgin olive oil (EVOO) sauces. The addition of onions (or diallyl disulfide present in onions) into tomato purees did not cause degradation of PT or PTF; however it favored E/Z-isomerization of PT and PTF by reducing the proportions of their natural Z-isomers (Z-15-PT and Z2,3-PTF) and decreased the bioaccessibility of total-PT and total-PTF. Simultaneously, a complex picture was obtained for the effect of onions on the bioaccessibility of individual PT and PTF isomers, depending on the precise isomer. Bioaccessibility of PT and PTF isomers in tomato-based sauces decreased in the order: 15-Z-PT > all-E-PT; Z2,3-PTF > all-E-PTF > Z4 or Z5-PTF; total-PT > total-PTF. E-isomerization of PT and PTF enhanced by onions during heating tomato-onion purees decreased their bioaccessibility.

Mechanisms Governing the Transfer of Pure and Plant Matrix Carotenoids Toward Emulsified Triglycerides.

SCOPE: The study aims to assess the role of factors assumed to be involved in the transfer of carotenoids from plant matrices to dietary emulsions in the upper digestive tract. METHODS AND RESULTS: Transfer is first measured as a function of time of pure ß-carotene (ßC), lutein (LUT), and lycopene (LYC) to triglyceride (TG) droplets dispersed in water. Then the transfer to TG droplets stabilized with either bovine serum albumin (BSA), phospholipids (PL), or both is measured. Finally, transfer of tomato and spinach puree carotenoids to these emulsions is measured. The maximal transfer efficiency of the pure carotenoids to uncoated emulsions is very efficient, ranging from 59% to 77%. However, it is dramatically impaired, ranging from 0.5% to 31% (p < 0.05), when emulsions are stabilized by the emulsifiers. Conversely, when LUT, and to a less extent ßC, but not LYC, is provided by the vegetable purees, its maximal transfer efficiency is significantly higher for the coated emulsions than for the uncoated one. CONCLUSIONS: Emulsifiers can dramatically impair the transfer of pure carotenoids to emulsion TG while they can facilitate the transfer of carotenoids from plant matrices. This suggests that specific interactions between plant matrix compounds and emulsifiers can enhance the transfer efficiency of carotenoids.

The Effect of an Iron Supplement on Lycopene Metabolism and Absorption During Digestion in Healthy Humans.

SCOPE: To investigate the formation and absorption of lycopene (LYC) metabolites in the human upper gastrointestinal lumen, in the absence and presence of iron. METHODS: Healthy males (n = 7) consumed test meals that deliver ≈22 mg LYC + ≈0.3 mg apo-lycopenals from oleoresin without (-FeSO4 ) and with ferrous sulfate (160 mg, +FeSO4 ). Subjects were intubated with a naso-gastric/naso-duodenal tube. Digesta, blood plasma, and the triglyceride-rich lipoprotein (TRL) fractions of plasma were analyzed using LC-MS/MS, to measure LYC and apo-lycopenoids. RESULTS: Digesta LYC concentrations increased with time (p = 1.2 × 10-7 ), decrease with time × iron (p = 1.1 × 10-5 ), and remain ≈200× higher than apo-lycopenals/lycopenone. Digesta apo-8'-, -10'-, -12'-, -14'-, -15-lycopenal, and apo-13-lycopenone concentrations increased with time (p < 0.01), apo-12'-, -14'-, -15-lycopenal, apo-13-lycopenone increase with iron (p < 0.05), and time × iron decrease apo-8'-, -10'-, -12'-, -14'-, -15-lycopenal, apo-13-lycopenone concentrations (p < 0.01). A 1.9-fold decrease in LYC TRL area-under-the-time-concentration-curve is observed after the test meal +FeSO4 versus the test meal -FeSO4 (p = 0.02). Apo-lycopenals were detected in later TRL fractions, and no apo-lycopenols or apo-lycopenoic acids were observed in any samples. CONCLUSIONS: FeSO4 reduces LYC absorption. Apo-lycopenals appear to be absorbed from foods, and not made in significant quantities during digestion.

Heating tomato puree in the presence of lipids and onion: The impact of onion on lycopene isomerization.

Z-lycopene isomers are more bioavailable than all-E-lycopene, especially 5-Z-lycopene. Based on our observations, the addition of unblanched onion could favor Z-isomerization of lycopene (by more than 94%) during heating tomato-onion-extra virgin olive oil (EVOO) purees at 90 °C for 2 h. The increase in Z-lycopene was correlated linearly with the addition of unblanched onion, with R2 > 0.92, and increased rates of 5-Z-lycopene were 3-4 times higher than for 9-Z-lycopene and 13-Z-lycopene. Diallyl disulfide (DADS), formed by alliinase-catalyzed breakdown of non-volatile precursors in onion, contributed to these increases and correlated linearly (R2 > 0.79, 0-0.50 mg/g puree) with increased Z-lycopene. Increased rates of 5-Z-lycopene were also 3-4 times higher than for 9-Z-lycopene and 13-Z-lycopene. However, blanching of onion, in tomato-onion-EVOO purees, before heating, significantly decreased the effect of onion on Z-isomerization of lycopene.

A D-optimal mixture design of tomato-based sauce formulations: effects of onion and EVOO on lycopene isomerization and bioaccessibility.

A D-optimal mixture design was used to study the effects of onion and extra virgin olive oil (EVOO) on lycopene Z-isomerization, lycopene diffusion into oil (expressed as a partition factor between tomato-based puree and oil) and in vitro bioaccessibility of lycopene isomers after thermal treatment of tomato-based puree consisting of tomato (75-100%), onion (0-20%) and EVOO (0-5%). A decrease of tomato puree could improve lycopene Z-isomerization, lycopene diffusion and lycopene bioaccessibility. The component interactions had an important influence on the Z-isomerization of lycopene, besides the linear mixtures of components. However, only linear mixtures of components appeared to have significant effects on the diffusion and bioaccessibility of lycopene, in which EVOO had the highest positive effect followed by onion. The bioaccessibility of lycopene isomers in every tomato-based sauce formulation decreased in the order: 13-Z-lycopene > 9-Z-lycopene > 5-Z-lycopene > all-E-lycopene. The bioaccessibility of total-Z-lycopene was at least 10 times higher than that of all-E-lycopene. Proportions of total-Z-lycopene were correlated positively with the partition factor and bioaccessibility of total-lycopene, with an r over 0.730 (p = 0.0031). Therefore, increased Z-lycopene proportions probably contributed to enhanced lycopene diffusion and bioaccessibility. The positive effects of components, especially onion, on total-lycopene diffusion and bioaccessibility were probably because the components increased the Z-isomerization of lycopene during heating of tomato-based puree.

Increased diffusivity of lycopene in hot break vs. cold break purees may be due to bioconversion of associated phospholipids rather than differential destruction of fruit tissues or cell structures.

Lycopene bioaccessibility is enhanced by processing, as explained by the destructuration of plant tissues, making diffusion easier. However, in tomato, the relationship between grinding intensity and lycopene release from purees suffers from uncertainty. In particular, hot break puree exhibited twice as much diffusible lycopene as compared to cold break, while both were processed with the same grinding intensity. To explain the difference, we systematically studied the diffusivity of particles according to their size and integrity, and used microscopic and physical analyses to reveal structural differences. Neither particle size distribution, nor cell destruction, nor plastid transformation exhibited any correlation to the differences in diffusivity. However, Raman microspectroscopy combined with a chemometric analysis revealed significant changes in lycopene spectra and a putative linkage to phospholipid transformation. Phospholipid profiling of five pairs of contrasted purees revealed that, during the cold break, a transition from complex phospholipids to more simple phosphatidic acid molecules systematically occurred.

Production, separation, and characterization of apo-luteinoids by LC-MS/MS.

It has been postulated that chemical or enzymatic catabolism of carotenoids could produce apo­carotenoids which have biological activity. Our objective was to generate and chemically characterize a series of apo­luteinoids (i.e. products resulting from the catabolism of lutein) which could putatively be found in vivo. Lutein was oxidized using potassium permanganate to produce a series of apo­luteinals/luteinone of subsequently shorter chain lengths, from apo­8'­luteinal to apo­11­luteinal. Sodium borohydride reduced this mixture into the corresponding alcohols (i.e. apo­luteinols). Similarly, Tollens' reagent was employed to oxidize the aldehyde series into carboxylic acids (i.e. apo­luteinoic acids). Mixtures of products were separated via HPLC and characterized in-line using photodiode array (PDA) and tandem mass spectrometry (MS-MS). A global HPLC-PDA-MS/MS method was developed to separate the products, and application of the methods to the symmetric xanthophyll zeaxanthin further confirmed the ε- and ß-ring species. These methods can be employed for the study of lutein oxidation products in plants, foods and biological samples.

Production of asymmetric oxidative metabolites of [13C]-ß-carotene during digestion in the gastrointestinal lumen of healthy men.

Background: Asymmetric ß-apo-carotenoids (nonvitamin A-active metabolites) of provitamin A carotenoids have been observed in humans, but no study has investigated their formation during digestion. Objective: The aim of this study was to follow the formation and absorption of asymmetric ß-apo-carotenoids during digestion. Design: Healthy men were intragastrically and intraduodenally intubated, and randomly assigned to consume a lipid-rich control meal (n = 3) or a lipid-rich test meal containing 20 mg [13C-10]-ß-carotene (n = 7). Digesta samples were collected over 5 h, and blood collected over 7 h. The triglyceride-rich lipoprotein (TRL) fractions of plasma were also isolated. Lipophilic extracts of digesta, plasma, and TRL were analyzed via a high-performance liquid chromatography-tandem mass spectrometry method developed to identify [13C]-labeled ß-apo-carotenals/carotenone, [13C]-ß-apo-carotenols, and [13C]-ß-apo-carotenoic acids. Results: Relative to [13C]-ß-carotene, [13C]-ß-apo-carotenal levels remained ∼3 orders of magnitude lower throughout digestion (no [13C]-ß-apo-carotenols, or [13C]-ß-apo-carotenoic acids were observed). A mixed model determined relative influence of digesta type and time on digesta metabolite level. Increasing time significantly increased the model levels of digesta [13C]-ß-apo-10',12',14',15-carotenal and [13C]-ß-apo-13-carotenone (P < 0.05) and trended toward decreased [13C]-ß-apo-8'-carotenal (P = 0.0876). Gastric digesta were associated with a significantly higher level of [13C]-ß-apo-8'-carotenal (P = 0.0289), and lower levels of [13C]-ß-apo-12',14',15-carotenal (P < 0.05), relative to duodenal digesta. Anticipated retinoids, but no asymmetric [13C]-ß-apo-carotenals, [13C]-ß-apo-carotenols, or [13C]-ß-apo-carotenoic acids, were observed in the blood or TRL samples. Conclusions: ß-Carotene appears to be robust to digestion, with minor amounts of ß-apo-carotenals/carotenone formed. Absence of asymmetric [13C]-ß-apo-carotenals in plasma and TRL suggests lack of absorption, levels below the limit of detection, lack of stability, or further conversion during the digestive process to as-yet unidentified products. Lack of asymmetric [13C]-ß-apo-carotenals in plasma also suggests a lack of postprandial intestinal BCO2 activity in healthy humans. This trial was registered at clinicaltrials.gov as NCT03492593.

Carotenoids: Experimental Ionization Energies and Capacity at Inhibiting Lipid Peroxidation in a Chemical Model of Dietary Oxidative Stress.

Carotenoids are important natural pigments and micronutrients contributing to health prevention by several mechanisms, including their electron-donating (antioxidant) activity. In this work, a large series of carotenoids, including 11 carotenes and 14 xanthophylls, have been investigated by wavelength-resolved atmospheric pressure photoionization mass spectrometry (DISCO line of SOLEIL synchrotron), thus allowing the experimental determination of their ionization energy (IE) for the first time. On the other hand, the carotenoids have been also investigated for their ability to inhibit the heme iron-induced peroxidation of linoleic acid in mildly acidic micelles, a simple but relevant chemical model of oxidative stress in the gastric compartment. Thus, the carotenoids can be easily classified from IC50 concentrations deduced from the time dependence of the lipid hydroperoxide concentration. With a selection of two carotenes and three xanthophylls a quantitative analysis is also provided to extract stoichio-kinetic parameters. The influence of the carotenoid structure (number of conjugated carbon-carbon double bonds, presence of terminal six-membered rings, hydroxyl, keto, and/or epoxy groups) on the IE, IC50, and stoichio-kinetic parameters is discussed in details. The data show that the antioxidant activity of carotenes is well correlated to their electron-donating capacity, which itself largely depends on the length of the conjugated polyene chain. By contrast, the IE of xanthophylls is poorly correlated to the polyene chain length because of the strong, and sometimes unexpected, electronic effects of the O-atoms. Although IE remains an approximate predictor of the antioxidant activity of xanthophylls, other factors (interaction with the aqueous phase, competing radical-scavenging mechanisms, the residual activity of the antioxidant's oxidation products) probably play a significant role.

Opposite Effects of the Spinach Food Matrix on Lutein Bioaccessibility and Intestinal Uptake Lead to Unchanged Bioavailability Compared to Pure Lutein.

SCOPE: Food matrix is generally believed to alter carotenoid bioavailability, but its effect on xanthophylls is usually limited. This study thus aims to decipher the digestion-absorption process of lutein in the presence or not of a food matrix. METHODS: Lutein transfer to gastric-like lipid droplets or artificial mixed micelles was assessed when lutein was added to test meals either as a pure molecule ((all-E)-lutein) or in canned spinach ((Z) + (all-E)-lutein). The obtained mixed micelles were delivered to Caco-2 cells to evaluate lutein uptake. Finally postprandial plasma lutein responses were compared in minipigs after the two test meals. RESULTS: Lutein transfer to gastric-like lipid droplets and to mixed micelles was higher when lutein was added in spinach than when it was added as pure lutein (+614% and +147%, respectively, p < 0.05). Conversely, lutein uptake was less effective when micellar lutein was from a meal containing spinach than from a meal containing its pure form (-55%, p < 0.05). In minipigs, postprandial lutein response was delayed with spinach but not significantly different after the two test meals. CONCLUSION: Opposite effects at the micellarization and intestinal cell uptake steps explain the lack of effect of spinach matrix on lutein bioavailability.

Are lutein, lycopene, and ß-carotene lost through the digestive process?

The bioavailability of many carotenoids has been assessed, but little attention has been given to the metabolism of these antioxidant compounds during digestion. The isomerization and loss of lutein, lycopene, and ß-carotene incorporated into a lipid-rich liquid meal was determined in vitro through the gastric, duodenal, and jejunal phases in the presence and absence of digestive enzymes, and in the presence and absence of known oxidizing agents often found in mixed meals (metmyoglobin in red meat and ferrous sulfate in supplemental iron). Carotenoids were quantitated using HPLC-PDA. In the absence of enzymes, lutein and lycopene were lost during earlier phases of the digestive process. In the presence of enzymes, lutein and lycopene were robust through the gastric and duodenal phases, with statistically significant losses of 40% and 20%, respectively, observed only during the jejunal phase. Regardless of the presence or absence of enzymes, an initial 25% of ß-carotene was lost during the gastric phase, but no further loss was observed. Ferrous sulfate had no significant impact on any carotenoid level. Metmyoglobin had no impact on lutein, but significantly reduced lycopene and ß-carotene levels by 30% and 80%, respectively, by the end of the jejunal phase. No significant isomerization was observed between the initial and jejunal phases for any of the carotenoids.

Lycopene and Its Antioxidant Role in the Prevention of Cardiovascular Diseases-A Critical Review.

The present review is based mainly on papers published between 2000 and 2011 and gives information about the properties of the carotenoid lycopene in chemical and biological systems and its possible role in preventing cardiovascular diseases (CVD). The main aim of this report is to highlight its role as an antioxidant, also reported are bioactive properties that may influence the development of foam cells and protection against endothelial cell damage. The paper will also examine recent observations that lycopene may improve blood flow and reduce inflammatory responses. Lycopene possesses antioxidant properties in vitro, and some epidemiological studies have reported protective effects against the progression of CVD. The oxidation of human low density lipoproteins (LDL) is a fundamental mechanism in the initiation of atherosclerosis. A beneficial role of lycopene as antioxidant in the prevention of CVD is suggested but the data are still controversial. Lycopene is believed to be the most potent carotenoid antioxidant in vitro. Tissue culture experiments and animal studies support potential cardioprotective effects for lycopene and other carotenoids in the blood. Most studies showed beneficial effects of lycopene to individuals who are antioxidant-deficient like elderly patients, or humans exposed to higher levels of oxidative stress like smokers, diabetics, hemodialysis patients and acute myocardial infarction patients. By defining the right population and combining antioxidant potentials of lycopene with vitamins and other bioactive plant compounds, the beneficial role of lycopene in CVD can be clarified in future studies.

A Review About Lycopene-Induced Nuclear Hormone Receptor Signalling in Inflammation and Lipid Metabolism via still Unknown Endogenous Apo-10´-Lycopenoids.

Lycopene is the red pigment in tomatoes and tomato products and is an important dietary carotenoid found in the human organism. Lycopene-isomers, oxidative lycopene metabolites and apo-lycopenoids are found in the food matrix. Lycopene intake derived from tomato consumption is associated with alteration of lipid metabolism and a lower incidence of cardiovascular diseases (CVD). Lycopene is mainly described as a potent antioxidant but novel studies are shifting towards its metabolites and their capacity to mediate nuclear receptor signalling. Di-/tetra-hydro-derivatives of apo-10´-lycopenoic acid and apo-15´-lycopenoic acids are potential novel endogenous mammalian lycopene metabolites which may act as ligands for nuclear hormone mediated activation and signalling. In this review, we postulate that complex lycopene metabolism results in various lycopene metabolites which have the ability to mediate transactivation of various nuclear hormone receptors like RARs, RXRs and PPARs. A new mechanistic explanation of how tomato consumption could positively modulate inflammation and lipid metabolism is discussed.

Interactions between Carotenoids from Marine Bacteria and Other Micronutrients: Impact on Stability and Antioxidant Activity.

Recently isolated spore-forming pigmented marine bacteria Bacillus indicus HU36 are sources of oxygenated carotenoids with original structures (about fifteen distinct yellow and orange pigments with acylated d-glucosyl groups). In this study, we evaluated the stability (sensitivity to iron-induced autoxidation) and antioxidant activity (inhibition of iron-induced lipid peroxidation) of combinations of bacterial HU36 carotenoids with the bacterial vitamin menaquinone MQ-7 and with phenolic antioxidants (vitamin E, chlorogenic acid, rutin). Unexpectedly, MQ-7 strongly improves the ability of HU36 carotenoids to inhibit Fe(II)-induced lipid peroxidation, although MQ-7 was not consumed in the medium. We propose that their interaction modifies the carotenoid antioxidant mechanism(s), possibly by allowing carotenoids to scavenge the initiating radicals. For comparison, ß-carotene and lycopene in combination were shown to exhibit a slightly higher stability toward iron-induced autoxidation, as well as an additive antioxidant activity as compared to the carotenoids, individually. HU36 carotenoids and phenolic antioxidants displayed synergistic activities in the inhibition of linoleic acid peroxidation induced by heme iron, but not by free iron. Synergism could arise from antioxidants interacting via electron transfer through the porphyrin nucleus of heme iron. Overall, combining antioxidants acting via complementary mechanisms could be the key for optimizing the activity of this bacterial carotenoid cocktail.

Effects of high power ultrasound on all-E-ß-carotene, newly formed compounds analysis by ultra-high-performance liquid chromatography-tandem mass spectrometry.

To study effects of high power ultrasound treatment (20 kHz) on ß-carotene degradation, a second-order central composite design (CCD) was performed to investigate maximum ß-carotene loss with three independent factors (ultrasonic intensity, sonication time, and temperature). Results based on variance analysis and Pareto chart have shown that sonication time is the most important factor, followed by ultrasonic intensity level. The evolved degradation products have been tentatively identified using ultra high performance liquid chromatography coupled to both diode array detector and a mass spectrometer (UHPLC-DAD-MS). The main degradation products, tentatively identified, are three Z-isomers of ß-carotene and seven ß-apo-carotenals/ones. Hypothesis on the degradation mechanism of carotenoids are presented.

Stability of bacterial carotenoids in the presence of iron in a model of the gastric compartment - comparison with dietary reference carotenoids.

Recently isolated spore-forming pigmented marine bacteria, Bacillus indicus HU36 and Bacillus firmus GB1 are sources of carotenoids (∼fifteen distinct yellow and orange pigments and ∼thirteen distinct pink pigments, respectively). They are glycosides of oxygenated lycopene derivatives (apo-lycopenoids) and are assumed to be more heat- and gastric-stable than common carotenoids. In this study, the oxidation by O2 of the bacterial carotenoids was initiated by free iron (Fe(II) and Fe(III)) or by heme iron (metmyoglobin) in a mildly acidic aqueous solution mimicking the gastro-intestinal compartment and compared to the oxidation of the common dietary carotenoids ß-carotene, lycopene and astaxanthin. Under these conditions, all bacterial carotenoids appear more stable in the presence of heme iron vs. free iron. Carotenoid autoxidation initiated by Fe(II) is relatively fast and likely involves reactive oxygen-iron species derived from Fe(II) and O2. By contrast, the corresponding reaction with Fe(III) is kinetically blocked by the slow preliminary reduction of Fe(III) into Fe(II) by the carotenoids. The stability of carotenoids toward autoxidation increases as follows: ß-carotene

Intestinal scavenger receptors are involved in vitamin K1 absorption.

Vitamin K1 (phylloquinone) intestinal absorption is thought to be mediated by a carrier protein that still remains to be identified. Apical transport of vitamin K1 was examined using Caco-2 TC-7 cell monolayers as a model of human intestinal epithelium and in transfected HEK cells. Phylloquinone uptake was then measured ex vivo using mouse intestinal explants. Finally, vitamin K1 absorption was compared between wild-type mice and mice overexpressing scavenger receptor class B type I (SR-BI) in the intestine and mice deficient in cluster determinant 36 (CD36). Phylloquinone uptake by Caco-2 cells was saturable and was significantly impaired by co-incubation with α-tocopherol (and vice versa). Anti-human SR-BI antibodies and BLT1 (a chemical inhibitor of lipid transport via SR-BI) blocked up to 85% of vitamin K1 uptake. BLT1 also decreased phylloquinone apical efflux by ∼80%. Transfection of HEK cells with SR-BI and CD36 significantly enhanced vitamin K1 uptake, which was subsequently decreased by the addition of BLT1 or sulfo-N-succinimidyl oleate (CD36 inhibitor), respectively. Similar results were obtained in mouse intestinal explants. In vivo, the phylloquinone postprandial response was significantly higher, and the proximal intestine mucosa phylloquinone content 4 h after gavage was increased in mice overexpressing SR-BI compared with controls. Phylloquinone postprandial response was also significantly increased in CD36-deficient mice compared with wild-type mice, but their vitamin K1 intestinal content remained unchanged. Overall, the present data demonstrate for the first time that intestinal scavenger receptors participate in the absorption of dietary phylloquinone.

Iron-induced oxidation of (all-E)-ß-carotene under model gastric conditions: kinetics, products, and mechanism.

The stability of (all-E)-ß-carotene toward dietary iron was studied in a mildly acidic (pH 4) micellar solution as a simple model of the postprandial gastric conditions. The oxidation was initiated by free iron (Fe(II), Fe(III)) or by heme iron (metmyoglobin, MbFe(III)). Fe(II) and metmyoglobin were much more efficient than Fe(III) at initiating ß-carotene oxidation. Whatever the initiator, hydrogen peroxide did not accumulate. Moreover, ß-carotene markedly inhibited the conversion of Fe(II) into Fe(III). ß-Carotene oxidation induced by Fe(II) or MbFe(III) was maximal with 5-10 eq Fe(II) or 0.05-0.1 eq MbFe(III) and was inhibited at higher iron concentrations, especially with Fe(II). UPLC/DAD/MS and GC/MS analyses revealed a complex distribution of ß-carotene-derived products including Z-isomers, epoxides, and cleavage products of various chain lengths. Finally, the mechanism of iron-induced ß-carotene oxidation is discussed. Altogether, our results suggest that dietary iron, especially free (loosely bound) Fe(II) and heme iron, may efficiently induce ß-carotene autoxidation within the upper digestive tract, thereby limiting its supply to tissues (bioavailability) and consequently its biological activity.

Inhibition of iron-induced lipid peroxidation by newly identified bacterial carotenoids in model gastric conditions: comparison with common carotenoids.

Newly identified spore-forming pigmented marine bacteria, Bacillus indicus HU36 and Bacillus firmus GB1, are sources of carotenoids (mainly 15 yellow and orange pigments and 13 pink pigments, respectively) with original structures. These bacterial carotenoids were evaluated for their ability to inhibit the iron-induced peroxidation of linoleic acid micelles, or sunflower oil-in-water emulsions, in comparison with ß-carotene, lycopene and astaxanthin. Lipid peroxidation was carried out in acidic conditions and initiated by dietary heme or non-heme iron (metmyoglobin or Fe(II), respectively) so as to simply simulate the postprandial gastric medium, a possible site for dietary oxidative stress. Lipid hydroperoxide formation and carotenoid consumption were followed by UV-vis spectroscopy and appropriate indicators of the antioxidant activity were estimated in each model. The bacterial carotenoids were found to be better inhibitors of heme-induced lipid peroxidation than the reference carotenoids as a likely consequence of their location closer to the interface in micelles and lipid droplets. However, this trend was not confirmed in lipid peroxidation induced by non-heme iron, possibly because of the redox recycling of Fe(II) by carotenoids. The quantitative kinetic analysis of the peroxidation curves suggests that the carotenoids mainly inhibit the propagation phase of lipid peroxidation by direct scavenging of the lipid peroxyl radicals, in agreement with independent experiments showing that carotenoids are unable to reduce the one-electron oxidized form of metmyoglobin (ferrylmyoglobin), a model of initiating species in heme-induced lipid peroxidation. Overall, carotenoids from Bacillus indicus HU36 and Bacillus firmus GB1 were found to be interesting antioxidants to fight postprandial oxidative stress in the stomach.