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.

[Bronchial mucoepidermoid carcinoma in a 22 year-old cannabis smoker]. / Carcinome bronchique muco-épidermoïde chez un fumeur de cannabis âgé de 22 ans.

INTRODUCTION: Bronchial mucoepidermoid carcinoma represents less than 0.5% of malignant bronchopulmonary cancers. The factors of risk have not been clearly established. Consumption of cannabis could be incriminated, as is suggested by this case report. OBSERVATION: A 22 year-old man presented with a mucoepidermoid carcinoma of the middle bronchopulmonary lobe. This young man had consumed large quantities of tobacco and cannabis since the age of eleven. DISCUSSION: The relationship between this rare tumour and the addictions in this patient merit further discussion. The oncogenic role of cannabis smoke should be envisaged, and emphasis placed on the possible synergic effects of multiple addiction, in this case tobacco and cannabis.

Evidence that homogenization of BSA-stabilized hexadecane-in-water emulsions induces structure modification of the nonadsorbed protein.

The structural modification of globular proteins (bovine serum albumin, BSA) in the aqueous phase of emulsions produced by homogenization was studied using front-face fluorescence spectroscopy (FFFS). A series of hydrocarbon oil-in-water emulsions (30 wt % n-hexadecane, 0.35 wt % BSA, pH 7.0) were homogenized to differing degrees with a high-speed blender and a high-pressure valve homogenizer. The wavelength of the maximum in the tryptophan emission spectrum (lambda(max)) of serum phases collected from the emulsions by centrifugation was measured and compared to lambda(max) values of BSA solutions subjected to the same homogenization conditions. There was no significant (p < 0.05) change in lambda(max) with homogenization conditions for BSA solutions. In contrast, lambda(max) of serum phases from emulsions blended for 2 min in a high-speed blender was significantly smaller (p < 0.05) than nontreated BSA solutions (Deltalambda(max) = 2 nm). In addition, there was a further significant decrease in lambda(max) of the serum phases with an increasing number of passes of the emulsion through the high-pressure valve homogenizer (e.g., Deltalambda(max) = 4 nm for 12 passes). This study shows that globular proteins present in the aqueous phase of a hexadecane-in-water emulsion after homogenization could be altered, which is probably caused by surface modification of the protein structure during temporary adsorption to emulsion droplet surfaces during homogenization.

Front-face fluorescence spectroscopy study of globular proteins in emulsions: displacement of BSA by a nonionic surfactant.

The displacement of a globular protein (bovine serum albumin, BSA) from the surface of oil droplets in concentrated oil-in-water emulsions by a nonionic surfactant (polyoxyethylene sorbitan monolauarate, Tween 20) was studied using front-face fluorescence spectroscopy (FFFS). This method relies on measurement of the change in intensity (I(MAX)) and wavelength (lambda(MAX)) of the maximum in the tryptophan emission spectrum. A series of oil-in-water emulsions (21 wt % n-hexadecane, 0.22 wt % BSA, pH 7.0) containing different molar ratios of Tween 20 to BSA (R = 0-131) were prepared. As the surfactant concentration was increased, the protein was progressively displaced from the droplet surfaces. At R > or = 66, the protein was completely displaced from the droplet surfaces. There was an increase in both I(MAX) and lambda(MAX) with increasing Tween 20 concentration up to R = 66, which correlated with the increase in the ratio of nonadsorbed to adsorbed protein. In contrast, there was a decrease in I(MAX) and lambda(MAX) with Tween 20 concentration in protein solutions and for R > or = 66 in the emulsions, which was attributed to binding of the surfactant to the protein. This study shows that FFFS is a powerful technique for nondestructively providing information about the interfacial composition of droplets in concentrated protein-stabilized emulsions in situ. Nevertheless, in general the suitability of the technique may also depend on protein type and the nature of the physicochemical matrix surrounding the proteins.

Front-face fluorescence spectroscopy study of globular proteins in emulsions: influence of droplet flocculation.

Measurement of the intensity (I(MAX)) and/or wavelength (lambda(MAX)) of the maximum in the tryptophan (TRP) emission spectrum using front-face fluorescence spectroscopy (FFFS) can be used to provide information about the molecular environment of proteins in nondiluted emulsions. Many protein-stabilized emulsions in the food industry are flocculated, and therefore, we examined the influence of droplet flocculation on FFFS. Stock oil-in-water emulsions stabilized by bovine serum albumin were prepared by high-pressure valve homogenization (30 wt % n-hexadecane, 0.35 wt % BSA, pH 7). These emulsions were used to create model systems with different degrees of droplet flocculation, either by changing the pH, adding surfactant, or adding xanthan. Emulsions (21 wt % n-hexadecane, 0.22 wt % BSA) with different pH (5 and 7) and molar ratios of Tween 20 to BSA (R = 0-131) were prepared by dilution of the stock emulsion. As the surfactant concentration was increased, the protein was displaced from the droplet surfaces, which caused an increase in both I(MAX) and lambda(MAX), because of the change in TRP environment. The dependence of I(MAX) and lambda(MAX) on surfactant concentration followed a similar pattern in emulsions that were initially flocculated (pH 5) and nonflocculated (pH 7). Relatively small changes in FFFS emission spectra were observed in emulsions (21 wt % n-hexadecane, 0.22 wt % BSA, pH 7) with different levels of depletion flocculation induced by adding xanthan. These results suggested that droplet flocculation did not have a major impact on FFFS. This study shows that FFFS is a powerful technique for nondestructively providing information about the molecular environment of proteins in concentrated and flocculated protein-stabilized emulsions. Nevertheless, in general the suitability of the technique may also depend on protein type and the nature of the physicochemical matrix surrounding the proteins.

Scavenging of free radicals, antimicrobial, and cytotoxic activities of the Maillard reaction products of beta-lactoglobulin glycated with several sugars.

The Maillard reaction occurs during many industrial and domestic thermal treatments of foods. It is widely used because of its role in creating colors, flavors, textures, and other functional properties in foodstuffs. Proteins glycated without the use of conventional chemical reagents have improved technofunctional properties such as heat stability, emulsifying, and foaming properties. The present study was carried out to determine the extent to which this reaction can convey antioxidant, antimicrobial, or cytotoxic activities to beta-lactoglobulin (BLG) and to its tryptic and peptic hydrolysates. BLG was modified with six different sugars in solution at 60 degrees C. Antiradical properties were estimated using a radical scavenging activity test. Antimicrobial activities against different bacterial strains were studied with a diffusion disk method. Cytotoxic tests were performed using two cell lines and the 3-(4,5-dimethylthiazoyl-2-yl)-2,5-diphenyltetrazolium bromide (MTT) rapid colorimetric assay. Glycation induced a radical scavenging activity to BLG, the intensity of which depended on the sugar used for modification. Proteins modified with ribose and arabinose showed the highest radical scavenging activities depicted by about 80 and 60% of 2,2-diphenyl-1-picrylhydrazyl (DPPH) absorption decrease at 515 nm. No antimicrobial effect of any glycated form of BLG against Escherichia coli, Bacillus subtilis, Listeria innocua, and Streptococcus mutans was observed. The MTT test showed no enhancement of cytotoxicity by modified proteins and peptides against COS-7 and HL-60 cells. Thus, glycated proteins could be used in formulated food as functional ingredients with a radical scavenging activity able to delay deterioration due to oxidation. This use could be even more advisable considering the lack of toxicity to eukaryotic and prokaryotic cell cultures demonstrated in this work.

Interface characterization and aging of bovine serum albumin stabilized oil-in-water emulsions as revealed by front-surface fluorescence.

This paper is devoted to the application of front-surface fluorescence to the study of aging and oxidation of oil-in-water emulsions. Emulsions with two oil droplet sizes were stabilized with bovine serum albumin (BSA) and stored at 37 or 47 degrees C. Lipid oxidation was demonstrated by measurement of hydroperoxides and headspace pentane. Front-surface fluorescence spectra (excitation wavelength = 355 nm) revealed gradual formation of oxidized lipid-protein adducts during the 4 weeks of storage. Fluorescence (excitation = 290 nm) of BSA tryptophanyl residues (Trp) declined during the first day of aging and then decreased slightly and linearly. Fourth-derivative Trp spectra exhibited peaks at 316 and 332 nm. Their evolution indicated that the ratio of Trp in hydrophobic environments to total Trp increased in small droplet emulsions. This suggests that, during lipid oxidation, the adsorbed and nonadsorbed protein underwent various degrees of Trp degradations, polymerization, and aggregation. Thus, front-surface fluorescence makes it possible to evaluate, noninvasively, protein modification and lipid oxidation end-products during processing and storage of food emulsions.

beta-Lactoglobulin binding properties during its folding changes studied by fluorescence spectroscopy.

The milk protein, beta-lactoglobulin (BLG) exhibits structural and binding properties which vary widely, depending on the medium. These properties of BLG are reflected in fluorescence intensities, steady-state anisotropies and phase lifetimes of BLG tryptophan residues and of retinol and diphenyl hexatriene (DPH) bound to BLG, as functions of pH, ethanol concentration and protein modifications (22% ethylated, 90% methylated and 85% acetylated BLGs). Tryptophan quenching experiments show that retinol and DPH bind to BLG in 1:1 molar ratios with apparent dissociation constants around 10(-7) - 10(-8) M. The strength of retinol binding is pH-dependent in the range 3-8, whereas that of DPH binding is not. Two different binding sites for these two ligands coexist on the protein. Modified BLGs exhibit higher affinities for DPH than the unmodified protein. At all pH values investigated, the fluorescence emission at 480 nm of retinol/BLG mixtures and retinol, DPH and tryptophan anisotropies and lifetimes change dramatically with midpoint at 27% ethanol for the first parameter and 35% for the others, suggesting simultaneous beta-strand to alpha-helix transition and the dissociation of BLG complexes at 35% ethanol. An intermediate state, possibly 'molten globular', occurs around 20% ethanol, as deduced from anisotropy and lifetime measurements.

Conformational changes of bovine serum albumin upon its adsorption in dodecane-in-water emulsions as revealed by front-face steady-state fluorescence.

Front-face fluorescence spectroscopy was used to characterise dodecane-in-buffer (0.1 M phosphate buffer; pH = 7.6) emulsions stabilised by bovine serum albumin (BSA). A 15-nm blue-shift of the emission maximum of the adsorbed protein and a significant increase of its fluorescence quantum yield were observed. The contribution of tyrosyl residues to total fluorescence was tentatively evaluated from different spectra and an R ratio taking into account the stray-light interference; R increased upon BSA absorption but the Tyrosine contribution remained weak in all cases. Thus, conformational changes of the protein take place upon BSA adsorption onto the dodecane-water interface. They involve modifications in the environment of the protein aromatic amino acids especially of the tryptophanyl residues which are displaced to a more hydrophobic location. Moreover, the proportions of absorbed and non-adsorbed BSA in emulsions can be estimated from the position of the emission maximum.