Exploring accessibility of pretreated poplar cell walls by measuring dynamics of fluorescent probes

Background: The lignocellulosic cell wall network is resistant to enzymatic degradation due to the complex chemical and structural features. Pretreatments are thus commonly used to overcome natural recalcitrance of lignocellulose. Characterization of their impact on architecture requires combinatory approaches. However, the accessibility of the lignocellulosic cell walls still needs further insights to provide relevant information. Results: Poplar specimens were pretreated using different conditions. Chemical, spectral, microscopic and immunolabeling analysis revealed that poplar cell walls were more altered by sodium chlorite-acetic acid and hydrothermal pretreatments but weakly modified by soaking in aqueous ammonium. In order to evaluate the accessibility of the pretreated poplar samples, two fluorescent probes (rhodamine B-isothiocyanate-dextrans of 20 and 70 kDa) were selected, and their mobility was measured by using the fluorescence recovery after photobleaching (FRAP) technique in a full factorial experiment. The mobility of the probes was dependent on the pretreatment type, the cell wall localization (secondary cell wall and cell corner middle lamella) and the probe size. Overall, combinatory analysis of pretreated poplar samples showed that even the partial removal of hemicellulose contributed to facilitate the accessibility to the fluorescent probes. On the contrary, nearly complete removal of lignin was detrimental to accessibility due to the possible cellulose-hemicellulose collapse. Conclusions: Evaluation of plant cell wall accessibility through FRAP measurement brings further insights into the impact of physicochemical pretreatments on lignocellulosic samples in combination with chemical and histochemical analysis. This technique thus represents a relevant approach to better understand the effect of pretreatments on lignocellulose architecture, while considering different limitations as non-specific interactions and enzyme efficiency

The Hypotriglyceridemic Effect of Sciadonic Acid is Mediated by the Inhibition of Δ9-Desaturase Expression and Activity.

International audienceScope: Sciadonic acid (Scia; 20:3Δ5,11,14) is a distinctive fatty acid (FA) with a polymethylene-interrupted double bond at C5. It is specifically found in seeds from gymnosperms such as pine nuts. Published papers describe a decrease in liver and plasma triacylglycerols in rats fed with this nutriment. The present study sought to identify the action mechanism of Scia on triacylglycerol synthesis. In this way, its nutritional effect on FA metabolism involving the Stearoyl-CoA Desaturase 1 (SCD1) was investigated.Methods and results: Scia was discerned in trace amount in various tissues of rats and in human serum. It was produced by Δ5-desaturation of 20:2n-6 in human transfected SH-SY5Y cell lines and also in rat hepatocytes. When Scia was incubated with cultured hepatocytes as a nutrient, the cellular FA profile was modified. In particular, the proportion of the monoenes (18:1n-9, 18:1n-7, 16:1n-7) were all decreased, correlating to the reduction of triacylglycerol amounts. This effect was mediated by the inhibition of SCD1 expression. Furthermore, Scia, as well as 20:3n-6 and 20:3n-9 but not 20:3n-3, strongly inhibited the SCD1 activity measured on liver microsomes.Conclusion: Overall this study showed that Scia, despite its unusual structure, contributes to the FA metabolism and reduced triacylglycerol release by inhibiting SCD1 activity

In vitro lipolysis kinetics of human milks is dependent from fat globule structure

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In vitro lipolysis kinetics of human milks is dependent from fat globule structure

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In vitro lipolysis kinetics of human milks is dependent from fat globule structure

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In vitro dynamic gastrointestinal digestion of model infant formulas

International audienceConsidering the frequent need of developing new formulations that contain functional appeal to meet the scientific and technological demands, this study describes the influence of different model infant formulas composition on their behaviour under the simulated conditions of the infant gastrointestinal tract. To achieve this objective, rehydrated model infant formulas, produced with different types of proteins (whey protein isolate (WPI) or WPI+Lactoferrin (LF)) and oils (high oleic sunflower oil (HOSO), or a mixture of HOSO with medium chain triacyclglycerols (MCT)), were submitted to an in vitro dynamic gastrointestinal digestion system. During the digestion process the lipolysis, proteolysis and structural disintegration of the samples were evaluated. To perform that, analyses such as free fatty acids by gas chromatography, SDS-PAGE, confocal laser scanning microscopy and droplet size distribution were conducted. Changes in the microstructural properties at different digestion steps depended on the emulsifier (protein) properties and were attributed to pH changes and protein hydrolysis. For samples containing LF, lesser proteolysis was observed in the gastric phase and also less lipolysis in the intestinal phase. Thus, the protein remaining in the oil droplets surface may have hindered lipase access and consequently leading to a lower release of free fatty acids. However, for samples containing MCT, there was a considerable increase in the free fatty acids released. LF and MCT showed to be promising ingredients for the development of functional infant formulas. Furthermore, these results may be useful for controlled release applications and for modulating satiety responses to food ingestio

Sciadonic acid derived from pine nuts as a food component to reduce plasma triglycerides by inhibiting the rat hepatic Δ9-desaturase

International audienceSciadonic acid (Scia) is a Δ5-olefinic fatty acid that is particularly abundant in edible pine seeds and that exhibits an unusual polymethylene-interrupted structure. Earlier studies suggested that Scia inhibited the in vitro expression and activity of the Stearoyl-CoA Desaturase 1 (SCD1), the hepatic Δ9-desaturase involved in the formation of mono-unsaturated fatty acids. To confirm this hypothesis, rats were given 10% Scia in diets balanced out with n-6 and n-3 fatty acids. In those animals receiving the Scia supplement, monoene synthesis in the liver was reduced, which was partly attributed to the inhibition of SCD1 expression. As a consequence, the presence of Scia induced a 50% decrease in triglycerides in blood plasma due to a reduced level of VLDL-secreted triglycerides from the liver. In non-fasting conditions, results showed that Scia-induced inhibition of SCD1 led to a decrease in the proportions of 161n-7 and 181n-7 in the liver without impacting on the level of 181n-9, suggesting that only triglycerides with neosynthesized monoenes are marked out for release. In conclusion, this in vivo study confirms that Scia highly inhibits SCD1 expression and activity. The work was performed on normo-triglyceride rats over six weeks, suggesting promising effects on hyper-triglyceridemic models

In vitro dynamic gastrointestinal digestion of model infant formulas

International audienceConsidering the frequent need of developing new formulations that contain functional appeal to meet the scientific and technological demands, this study describes the influence of different model infant formulas composition on their behaviour under the simulated conditions of the infant gastrointestinal tract. To achieve this objective, rehydrated model infant formulas, produced with different types of proteins (whey protein isolate (WPI) or WPI+Lactoferrin (LF)) and oils (high oleic sunflower oil (HOSO), or a mixture of HOSO with medium chain triacyclglycerols (MCT)), were submitted to an in vitro dynamic gastrointestinal digestion system. During the digestion process the lipolysis, proteolysis and structural disintegration of the samples were evaluated. To perform that, analyses such as free fatty acids by gas chromatography, SDS-PAGE, confocal laser scanning microscopy and droplet size distribution were conducted. Changes in the microstructural properties at different digestion steps depended on the emulsifier (protein) properties and were attributed to pH changes and protein hydrolysis. For samples containing LF, lesser proteolysis was observed in the gastric phase and also less lipolysis in the intestinal phase. Thus, the protein remaining in the oil droplets surface may have hindered lipase access and consequently leading to a lower release of free fatty acids. However, for samples containing MCT, there was a considerable increase in the free fatty acids released. LF and MCT showed to be promising ingredients for the development of functional infant formulas. Furthermore, these results may be useful for controlled release applications and for modulating satiety responses to food ingestio

Does encapsulation of DHA with heat-denatured whey proteins in Pickering emulsions improve its bioaccessibility?

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Influence de la texture des aliments sur la digestion des macronutriments et la libération de micronutriments: étude in vitro sur masticateur et digesteur dynamique paramétrés à partir de données in vivo

National audienceIntroduction et but de l’étude: Dans les années à venir, un des défis majeurs de l’optimisation nutritionnelle consistera à lutter contre les carences en micronutriments. Une des stratégies couramment utilisée pour cela est l’enrichissement des aliments, mais sa pertinence reste à prouver au regard de son efficacité réelle. Alors que les caractéristiques structurales des aliments influencent le processus de désintégration pendant la digestion, il semble pertinent d'évaluer l'impact de la structure des aliments sur la biodisponibilité des micronutriments.Matériel et méthodes: Trois aliments enrichis en lutéine et vitamine D ont été conçus à composition strictement identique (sur matière sèche) mais avec des structures et textures différentes (crème anglaise, génoise et biscuit). Lors d’une étude préliminaire in vivochez l’Homme, les caractéristiques des bols alimentaires produits à partir de ces matrices et leurs cinétiques de digestion avaient été étudiées. Après reproduction des bols alimentaires à l’identique des bols in vivopar le simulateur de mastication AM², ceux-ci ont été soumis à une digestion in vitroà l’aide du simulateur de digestion dynamique DIDGI (n=3). Les cinétiques de désintégration de la matrice (protéolyse, lipolyse et amylolyse) et la libération des micronutriments dans la phase soluble (marqueur de la bioaccessibilité) ont été suivies. UneAnalyse en Composantes Principales a ensuite permis de déterminer les corrélations entre variables. Résultats et Analyse statistique: Les cinétiques de désintégration de la matrice sont influencées par l’aliment, en particulier en ce qui concerne la destruction du réseau amylacé: elle est ainsi significativement plus faible pour le biscuit par rapport aux deux autres matrices. En outre, des différences en termes de lipolyse et d’amylolyse ont été observées. Le biscuit montre ainsi une libération d’acidesgras libres et d’oligosaccharides significativement plus faible que les deux autres matrices en phase intestinale de digestion, la génoise présentant quant à elle les valeurs les plus élevées. La structure de la matrice ne semble toutefoisavoir aucun effet sur la protéolyse.Les cinétiques de libération des micronutriments sont également distinctes mais les tendances ne sont pas les mêmes selon le micronutriment considéré. En phase gastrique, les différences entre matrices sont peu marquées que ce soit pour la lutéine ou la vitamine D. En revanche, en phase intestinale, la teneur en lutéine bioaccessible est 6 fois plus importante pour le biscuit que pour la crème après 240 minutes de digestion. La teneur en vitamine D bioaccessible tend à l'inverse à êtremoins élevée pour le biscuit que pour les deux autres matrices en phase intestinale.Conclusion: Les résultats de digestion in vitrodynamique montrent que la structure des aliments module la cinétique de digestion des lipides et de l’amidon, et consécutivement la cinétique de libération des micronutriments