Claude Genot

Lipid Oxidation in Oil-in-Water Emulsions: Involvement of the Interfacial Layer

More polyunsaturated fats in processed foods and fewer additives are a huge demand of public health agencies and consumers. Consequently, although foods have an enhanced tendency to oxidize, the usage of antioxidants, especially synthetic antioxidants, is restrained. An alternate solution is to better control the localization of reactants inside the food matrix to limit oxidation. This review establishes the state-of-the-art on lipid oxidation in oil-in-water (O/W) emulsions, with an emphasis on the role of the interfacial region, a critical area in the system in that respect. We first provide a summary on the essential basic knowledge regarding (i) the structure of O/W emulsions and interfaces and (ii) the general mechanisms of lipid oxidation. Then, we discuss the factors involved in the development of lipid oxidation in O/W emulsions with a special focus on the role played by the interfacial region. The multiple effects that can be attributed to emulsifiers according to their chemical structure and their location, and the interrelationships between the parameters that define the physicochemistry and structure of emulsions are highlighted. This work sheds new light on the interpretation of reported results that are sometimes ambiguous or contradictory.

Dietary oxidized n-3 PUFA induce oxidative stress and inflammation: role of intestinal absorption of 4-HHE and reactivity in intestinal cells

Dietary intake of long-chain n-3 PUFA is now widely advised for public health and in medical practice. However, PUFA are highly prone to oxidation, producing potentially deleterious 4-hydroxy-2-alkenals. Even so, the impact of consuming oxidized n-3 PUFA on metabolic oxidative stress and inflammation is poorly described. We therefore studied such effects and hypothesized the involvement of the intestinal absorption of 4-hydroxy-2-hexenal (4-HHE), an oxidized n-3 PUFA end-product. In vivo, four groups of mice were fed for 8 weeks high-fat diets containing moderately oxidized or unoxidized n-3 PUFA. Other mice were orally administered 4-HHE and euthanized postprandially versus baseline mice. In vitro, human intestinal Caco-2/TC7 cells were incubated with 4-hydroxy-2-alkenals. Oxidized diets increased 4-HHE plasma levels in mice (up to 5-fold, P < 0.01) compared with unoxidized diets. Oxidized diets enhanced plasma inflammatory markers and activation of nuclear factor kappaB (NF-κB) in the small intestine along with decreasing Paneth cell number (up to −19% in the duodenum). Both in vivo and in vitro, intestinal absorption of 4-HHE was associated with formation of 4-HHE-protein adducts and increased expression of glutathione peroxidase 2 (GPx2) and glucose-regulated protein 78 (GRP78). Consumption of oxidized n-3 PUFA results in 4-HHE accumulation in blood after its intestinal absorption and triggers oxidative stress and inflammation in the upper intestine.

Multiscale structures of lipids in foods as parameters affecting fatty acid bioavailability and lipid metabolism.

On a nutritional standpoint, lipids are now being studied beyond their energy content and fatty acid (FA) profiles. Dietary FA are building blocks of a huge diversity of more complex molecules such as triacylglycerols (TAG) and phospholipids (PL), themselves organised in supramolecular structures presenting different thermal behaviours. They are generally embedded in complex food matrixes. Recent reports have revealed that molecular and supramolecular structures of lipids and their liquid or solid state at the body temperature influence both the digestibility and metabolism of dietary FA. The aim of the present review is to highlight recent knowledge on the impact on FA digestion, absorption and metabolism of: (i) the intramolecular structure of TAG; (ii) the nature of the lipid molecules carrying FA; (iii) the supramolecular organization and physical state of lipids in native and formulated food products and (iv) the food matrix. Further work should be accomplished now to obtain a more reliable body of evidence and integrate these data in future dietary recommendations. Additionally, innovative lipid formulations in which the health beneficial effects of either native or recomposed structures of lipids will be taken into account can be foreseen.

Contribution of the Interfacial Layer to the Protection of Emulsified Lipids against Oxidation

The oxidative stability of oil-in-water (O/W) emulsions is highly dependent on the type of emulsifier. The purpose of this work was to investigate the specific role of the adsorbed emulsifiers on lipid oxidation of O/W emulsions. Emulsions of similar droplet size distribution stabilized by minimum amounts of proteins or surfactants were oxidized at 25 °C in the presence of equimolar iron-EDTA complex. The pH and the amount of emulsifier in the aqueous phase were also varied to investigate the role of the droplet charge and the emulsifier in the aqueous phase. Oxygen uptake, conjugated dienes (CD), and volatile compound formation demonstrated that the protein-stabilized interfaces are less efficient at protecting emulsified lipids against oxidation than surfactant-stabilized interfaces. The antioxidant effect of unadsorbed proteins was also confirmed.

Meat processing and colon carcinogenesis: cooked, nitrite-treated, and oxidized high-heme cured meat promotes mucin-depleted foci in rats.

Processed meat intake is associated with colorectal cancer risk, but no experimental study supports the epidemiologic evidence. To study the effect of meat processing on carcinogenesis promotion, we first did a 14-day study with 16 models of cured meat. Studied factors, in a 2 × 2 × 2 × 2 design, were muscle color (a proxy for heme level), processing temperature, added nitrite, and packaging. Fischer 344 rats were fed these 16 diets, and we evaluated fecal and urinary fat oxidation and cytotoxicity, three biomarkers of heme-induced carcinogenesis promotion. A principal component analysis allowed for selection of four cured meats for inclusion into a promotion study. These selected diets were given for 100 days to rats pretreated with 1,2-dimethylhydrazine. Colons were scored for preneoplastic lesions: aberrant crypt foci (ACF) and mucin-depleted foci (MDF). Cured meat diets significantly increased the number of ACF/colon compared with a no-meat control diet (P = 0.002). Only the cooked nitrite-treated and oxidized high-heme meat significantly increased the fecal level of apparent total N-nitroso compounds (ATNC) and the number of MDF per colon compared with the no-meat control diet (P < 0.05). This nitrite-treated and oxidized cured meat specifically increased the MDF number compared with similar nonnitrite-treated meat (P = 0.03) and with similar nonoxidized meat (P = 0.004). Thus, a model cured meat, similar to ham stored aerobically, increased the number of preneoplastic lesions, which suggests colon carcinogenesis promotion. Nitrite treatment and oxidation increased this promoting effect, which was linked with increased fecal ATNC level. This study could lead to process modifications to make nonpromoting processed meat. Cancer Prev Res; 3(7); 852–64. ©2010 AACR.

The antioxidant activity of carnosine and its consequences on the volatile profiles of liposomes during iron/ascorbate induced phospholipid oxidation

Abstract The natural dipeptide L-carnosine (β-Ala-His) exhibits antioxidative properties and can be used as an antioxidant in food products. Its antioxidant activity and its effect on the volatile compounds produced during lipid oxidation was studied in a meat-related model system (liposomes of muscle phospholipids). Oxygen uptake, conjugated dienes, trienes and ketodienes, thiobarbituric acid reactive substances (TBARS) and volatile compounds were measured after induction of oxidation by equimolar Fe(III)/ascorbate (45 μM). Inclusion of carnosine (2–10 mM) lead to a decrease in all indices of lipid oxidation, except for the initial rate of oxygen uptake, which increased, and the rates of oxygen uptake 5 or more min after catalyst injection, which remained constant. The decrease varied as a function of carnosine concentration, method of measurement and incubation time. When carnosine was added to previously oxidised liposomes, TBARS, t-2-undecenal, total 2-alkenals and hexanol amounts decreased significantly. Carnosine antioxidant activity is multifunctional: it has a buffering effect; it interferes in the initiation step of oxidation; it decreases the amount of preformed peroxides; it reacts with some secondary products.

Quantification of unadsorbed protein and surfactant emulsifiers in oil-in-water emulsions

Unadsorbed emulsifiers affect the physical and chemical behaviour of oil-in-water (O/W) emulsions. A simple methodology to quantify unadsorbed emulsifiers in the aqueous phase of O/W emulsions has been developed. Emulsions were centrifuged and filtered to separate the aqueous phase from the oil droplets and the concentration of unadsorbed emulsifiers in the aqueous phase determined. The quantification of unadsorbed surfactants based on the direct transesterification of their fatty acids was validated for Tween 20, Tween 80, citric acid ester (Citrem), Span 20 and monolauroyl glycerol. To determine unadsorbed proteins, results obtained with Folin-Ciocalteu reagent or UV-spectrophotometry were compared on emulsions stabilized by β-lactoglobulin (BLG), β-casein (BCN) or bovine serum albumin (BSA). The first method gave more accurate results especially during aging of emulsions in oxidative conditions. The whole methodology was applied to emulsions stabilized with single or mixed emulsifiers. This approach enables optimization of emulsion formulations and could be useful to follow changes in the levels of unadsorbed emulsifiers during physical or chemical aging processes.

n-3 PUFA added to high-fat diets affect differently adiposity and inflammation when carried by phospholipids or triacylglycerols in mice

BackgroundDietary intake of n-3 polyunsaturated fatty acids (PUFA) is primarily recognized to protect against cardiovascular diseases, cognitive dysfunctions and the onset of obesity and associated metabolic disorders. However, some of their properties such as bioavailability can depend on their chemical carriers. The objective of our study was to test the hypothesis that the nature of n-3 PUFA carrier results in different metabolic effects related to adiposity, oxidative stress and inflammation.Methods4 groups of C57BL/6 mice were fed for 8 weeks low fat (LF) diet or high-fat (HF, 20%) diets. Two groups of high-fat diets were supplemented with long-chain n-3 PUFA either incorporated in the form of phospholipids (HF-ω3PL) or triacylglycerols (HF-ω3TG).ResultsBoth HF-ω3PL and HF-ω3TG diets reduced the plasma concentrations of (i) inflammatory markers such as monocyte chemoattractant protein-1 (MCP-1) and interleukin 6 (IL-6), (ii) leptin and (iii) 4-hydroxy-2-nonenal (4-HNE), a marker of n-6 PUFA-derived oxidative stress compared with the control HF diet. Moreover, in both HF-ω3PL and HF-ω3TG groups, MCP-1 and IL-6 gene expressions were decreased in epididymal adipose tissue and the mRNA level of gastrointestinal glutathione peroxidase GPx2, an antioxidant enzyme, was decreased in the jejunum compared with the control HF diet. The type of n-3 PUFA carrier affected other outcomes. The phospholipid form of n-3 PUFA increased the level of tocopherols in epididymal adipose tissue compared with HF-ω3TG and resulted in smaller adipocytes than the two others HF groups. Adipocytes in the HF-ω3PL and LF groups were similar in size distribution.ConclusionSupplementation of mice diet with long-chain n-3 PUFA during long-term consumption of high-fat diets had the same lowering effects on inflammation regardless of triacyglycerol or phospholipid carrier, whereas the location of these fatty acids on a PL carrier had a major effect on decreasing the size of adipocytes that was not observed with the triacyglycerol carrier. Altogether, these results would support the development functional foods containing LC n-3 PUFA in the form of PL in order to prevent some deleterious outcomes associated with the development of obesity.

Sweetness–texture interactions in model dairy desserts: effect of sucrose concentration and the carrageenan type

Sweetness–texture interactions were investigated in model dairy desserts varying in both sucrose concentration and carrageenan composition (κ-, ι-, λ-carrageenans or an equal-weight mixture of the three). Nineteen panellists evaluated sweetness and five oral texture attributes while instrumental texture was characterised by penetrometry. For each carrageenan composition, sweetness significantly increased with sucrose. Rheological profiles or oral texture attributes allowed to distinguish four matrices. Sweetness–texture interactions were observed but no common rule was applied. On the one hand, firmness of κ-carrageenan desserts, springiness and firmness of ι-carrageenan desserts, unctuousness of λ-carrageenan desserts and brittleness and unctuousness of mix-carrageenan ones increased with sucrose concentration. These changes can be partly attributed to changes in the mechanical profiles. On the other hand, variation of carrageenan composition modified sweetness assessment at higher concentrations, λ-carrageenan desserts being the sweetest and ι-carrageenan desserts the least sweet. A model, which considered carrageenan composition, sucrose concentration and their interactions, was established to relate sweetness and composition of the desserts.

Oxidation of muscle phospholipids in relation to their fatty acid composition with emphasis on volatile compounds

The impact of moderate changes of fatty acid (FA) composition of phospholipids (PL) on their oxidative stability and on volatile profiles remains largely unknown. PL of breast muscle of turkeys fed a diet containing 6% tallow, rapeseed oil or soya oil were purified and prepared as liposomes. After 24 h of incubation at 25 °C with iron/ascorbate, oxidation was quantified by measurement of thiobarbituric acid reactive substances (TBA-RS) and volatile compounds. TBA-RS level was the lowest (21.4 nmole eq MDA mg−1 PL) in PL from tallow-fed animals but was not significantly different (P > 0.05) in soya oil (30.9 nmole eq MDA mg−1 PL) and rapeseed oil (30.3 nmole eq MDA mg−1 PL) batches. ANOVA did not clearly distinguish between the three groups according to the quantities of individual volatiles except for Z,E-2,4-heptadienal. In contrast, principal component analysis (PCA) performed on standardised quantities of volatile compounds distinguished unambiguously the three groups. Axis 1 was positively correlated with volatile compounds arising from oxidation of n-6 fatty acids, and negatively with compounds of n-9 origin. Axis 2 was highly positively correlated with compounds from n-3 origin. Only a few compounds from each origin (n-6, n-3, n-9) had an atypical behaviour. A weak modification of the FA composition of PL led to concomitant modifications of the quantities of volatile compounds generated through oxidation, which were emphasised by multivariate analysis (PCA).