Effect of calcium on bioaccessibility of milk fat during digestion of Cheddar-type cheeses

Le fromage cheddar est reconnu comme une excellente source de calcium. Outre son intérêt nutritionnel intrinsèque, le calcium favorise la lipolyse lors de la digestion. Cet effet s’explique par la formation de savons de calcium avec les acides gras saturés à longue chaîne, ce qui entraîne l’exposition de nouveau substrat à l’interphase huile-eau des gouttelettes de gras laitier, permettant à la lipase de continuer son action. En contrepartie, les savons de calcium limitent l'absorption des acides gras impliqués. D’un point de vue technologique, le calcium joue un rôle clé dans la structure du fromage car il participe à la formation du gel de paracaséine. Ayant un effet sur la matrice fromagère et sur la digestion des lipides, le calcium peut alors modifier la biodisponibilité du gras laitier. L’objectif de ce projet était de mieux comprendre l’effet du calcium sur la biodisponibilité du gras laitier à partir de fromages de type cheddar avec le but éventuel de développer des aliments pouvant contrôler la digestion et l’absorption des lipides. Dans un premier temps, des fromages de type cheddar enrichis en calcium par l’ajout de CaCl₂ ont été soumis à une digestion in vitro. L’analyse des chymes a permis de démontrer que les fromages enrichis se désintégraient plus lentement que leur contrôle sans calcium ajouté. D’une autre part, la libération d’acides gras des fromages enrichis progressait plus rapidement, mettant en évidence l’effet du calcium sur les mécanismes impliqués dans la lipolyse. Dans un second temps, des fromages de type cheddar ont été fabriqués à partir de lait standardisé avec des huiles de beurre contrôle, oléine et stéarine et salés avec ou sans CaCl₂. Les fromages ont été digérés in vitro pour étudier l’effet du calcium sur la lipolyse et la formation de savons de calcium avec les huiles de beurre ayant différents profils d’acides gras. Les fromages préparés avec la fraction stéarine (avec le rapport le plus élevé d’acides gras saturés à longue chaîne) étaient plus résistants à la désintégration physique et présentaient une lipolyse plus lente que les autres fromages, en raison du point de fusion élevé de cette matière grasse. Les fromages enrichis en calcium présentaient des taux de lipolyse supérieurs aux fromages sans enrichissement. Cette lipolyse accrue a été expliquée par la formation de savons de calcium avec des acides gras à longue chaîne. Ces composés insolubles pourraient toutefois réduire la biodisponibilité des acides gras impliqués en empêchant leur absorption. Pour confirmer l’effet du calcium et du type de matière grasse sur la biodisponibilité des lipides, les fromages ont été utilisés par la suite pour une étude chez le rat. La lipémie postprandiale des animaux a été mesurée suite à l’ingestion du fromage. Les matières fécales ont été analysées pour quantifier les acides gras excrétés sous forme de savons de calcium. Les fromages ont eu des effets différents au niveau de la lipémie postprandiale. L'enrichissement en calcium a entraîné une augmentation de la lipémie avec les fromages à l'oléine, alors qu'un pic différé a été observé avec les fromages à stéarine. Ceci s'explique par la formation de savons de calcium avec des acides gras saturés à longue chaîne, favorisant indirectement une lipolyse plus rapide de ceux à courtes et à moyennes chaînes. Le retard du pic pour les fromages à base de stéarine s’expliquait par leur teneur plus élevée en acides gras saturés à longue chaîne, qui formaient des savons avec le calcium et se retrouvaient dans les fèces. Les résultats confirment que le calcium affecte la digestion intestinale des lipides laitiers en augmentant le taux de lipolyse. Cependant, il limite également la bioaccessibilité des acides gras en produisant, au pH intestinal, des savons de calcium insolubles avec des acides gras saturés à longue chaîne. Ce projet démontre que la biodisponibilité des lipides peut être régulée par le calcium présent dans le fromage cheddar. Cette étude met en évidence l'interaction en cours de digestion du calcium et des lipides présents dans la matrice laitière et confirme sa répercussion physiologique. Ces effets sur la digestion et l'absorption des lipides sont d’intérêt pour la conception de matrices alimentaires pour la libération contrôlée de nutriments et bioactifs liposolubles. D'autres recherches dans ce domaine permettront de mieux comprendre le rôle joué par les aliments sur la santé humaine et d’habiliter le développement de produits laitiers pour contrôler la libération de nutriments afin de moduler les réponses métaboliques. Mots clés : fromage, gras laitier, digestion, lipolyse, savons de calcium.Cheddar cheese is recognized as an excellent source of calcium. In addition to its intrinsic nutritional value, calcium promotes lipolysis during digestion. This lipolysis enhancing effect is explained by the formation of calcium soaps with saturated long-chain fatty acids, resulting in the exposure of new substrate to the oil-water interphase of the milk fat droplets, thus enabling lipase to continue its action. On the other hand, the formation of calcium soaps reduces the absorption of saturated long-chain fatty acids. From a technological point of view, calcium plays a key role in the cheese structure as it participates in the formation of the paracasein gel. By such effects on the cheese matrix and the digestion of lipids, calcium can modify the bioavailability of the dairy fat. The objective of this project was to better understand the effect of calcium on the bioavailability of dairy fat from Cheddar cheeses, in aim to developing food matrices for controlled digestion and absorption of lipids. In a first step, Cheddar cheeses enriched with calcium by the addition of CaCl₂ were subjected to digestion in vitro. Chyme analysis showed that calcium-enriched cheeses disintegrated less rapidly than the non-enriched control but that their lipolysis progressed more rapidly, demonstrating the effect of calcium on the factors that influence lipolysis. In a second step, Cheddar cheeses were made from standardized milk with control, olein and stearin butter oils and salted with or without CaCl₂. The cheeses were digested in vitro to study the effect of calcium on lipolysis and the formation of calcium soaps from butter oils with different fatty acid profiles. Cheeses prepared with the stearin fraction (with the highest ratio of saturated long-chain fatty acids) were more resistant to physical disintegration and presented slower lipolysis than the other cheeses because of the high melting point of this fat. Cheeses enriched with calcium had higher levels of lipolysis than cheeses without enrichment. This increased lipolysis was due to the formation of calcium soaps with saturated long-chain fatty acids. These insoluble compounds could reduce the bioavailability of the fatty acids involved by preventing their absorption. To confirm the effect of calcium and type of fat on lipid bioavailability, the cheeses were subsequently used for an in vivo study. Postprandial lipemia of Wistar rats was monitored following ingestion of the cheese. The feces were analyzed to quantify the fatty acids excreted as calcium soaps. The cheeses had different effects in postprandial lipemia. Calcium enrichment led to a higher lipemic peak for the cheeses with olein, while a delayed peak was observed for cheeses with the stearin. This was explained by the increased affinity of calcium for saturated long-chain fatty acids, indirectly allowing faster lipolysis of other fatty acids, such as those with short- and medium-chains. The delay for stearin cheeses was due to their high content of saturated long-chain fatty acids, which formed soaps with calcium, thus reducing their absorption and ending up in feces. The results confirm that calcium plays an important role in intestinal digestion of dairy lipids by increasing the rate of lipolysis. However, it also limits the bioaccessibility of fatty acids by producing insoluble calcium soaps with saturated long-chain fatty acids at intestinal pH conditions. This project demonstrates that the bioavailability of lipids can be regulated by calcium in Cheddar cheese. This study demonstrates the interaction of calcium and lipids present in the dairy matrix during digestion and confirms its physiological repercussion. These effects on digestion and lipid absorption are of interest for the design of food matrices for the controlled release of liposoluble nutrients or bioactive molecules. Further research in this area will provide a better understanding of the role of foods in human health and enable the development of dairy products to control the release of nutrients to modulate metabolic responses. Keywords: Cheese, milk fat, digestion, lipolysis, calcium soaps

Effect of calcium enrichment of Cheddar cheese on its structure, in vitro digestion and lipid bioaccessibility

The nutritional role of cheese is usually reduced to its composition, often neglecting the effect that the matrix can have on digestion. The purpose of this study was to establish a link between the characteristics of Cheddar cheeses with different calcium levels and the impact on cheese in vitro digestion. Curds were enriched with CaCl2 during the salting step to produce control, high-calcium, and very high-calcium cheeses. Cheese composition, texture and structure were characterized, and physical disintegration and lipolysis were monitored during in vitro digestion. Cheese hardness increased with higher calcium content. This resulted in a slower disintegration during in vitro digestion. Despite showing faster disintegration, the control cheese had the slowest lipolysis progression. The results suggest that lipolysis depends on calcium content and the matrix modulating the access of enzymes to their substrates. Further studies should provide a better understanding of the calcium–matrix interaction affecting lipid bioaccessibility

Postprandial lipemia and fecal fat excretion in rats is affected by the calcium content and type of milk fat present in Cheddar-type cheeses

The aim of this study was to better understand the effect of calcium on the bioavailability of milk lipids from a cheese matrix using a rat model. Cheddar-type cheeses were manufactured with one of three types of anhydrous milk fat, control, olein or stearin, and salted with or without CaCl₂. The cheeses were fed to rats and postprandial lipemia was monitored. Feces were analyzed to quantify fatty acids excreted as calcium soaps. Higher calcium concentration in cheese caused a higher and faster triacylglycerol peak in blood, except for cheeses containing stearin. Furthermore, calcium soaps were more abundant in feces when the ingested cheese had been enriched with calcium and when the cheese was prepared with stearin. Increased lipid excretion was attributable to the affinity of saturated long-chain fatty acids for calcium. Results showed that lipid bioaccessibility can be regulated by calcium present in Cheddar cheese. This study highlights the nutritional interaction between calcium and lipids present in the dairy matrix and confirms its physiological repercussions on fatty acid bioavailability

Colmatage des membranes par les minéraux et les protéines en cours d'électrodialyse conventionnelle

Cette étude avait comme objectif l’étude de l’effet de la composition en calcium et carbonate d’une solution modèle de protéine de lactosérum et de l’influence du pH du concentrat sur le colmatage des membranes en électrodialyse conventionnelle. L’intégrité des membranes a été évaluée en fonction des paramètres de fonctionnalité comme l’épaisseur et la conductivité électrique. Le colmatage formé sur les membranes échangeuses d’anions (MEA) et de cations (MEC) a été caractérisé à l’aide de la microscopie optique, de l’ATR-FTIR et de la microscopie électronique couplée à une caractérisation élémentaire de surface par rayons-X. Un colmatage protéique sur les AEM a été observé sous conditions acides du concentrat, tandis qu’un colmatage minéral s’est formé sous conditions alcalines sur les MEC et les MEA. Suite à ces résultats, une nouvelle configuration concernant la circulation des fluides et la valeur de pH des concentrats a été proposée afin d’éviter la formation des colmatages observés.The aim of this project was to investigate the effect of the composition in calcium, and carbonate of a model whey protein solution to be treated by electrodialysis on the fouling of ion-exchange membranes. The pH of the concentrate was also controlled at different values to study its influence on membrane fouling. Membrane integrity was determined by membrane parameters and completed with fouling characterization by macroscopic and microscopic pictures, ATR-FTIR analyses and electron microscope images coupled to elementary X-ray mapping to identify the deposits. A protein layer was formed when the pH of the concentrate compartment was acidic, while a mineral deposit occurred when pH was basic. From these results, a stack arrangement is proposed to prevent the formation of mineral and protein fouling

Effect of calcium on fatty acid bioaccessibility during in vitro digestion of Cheddar-type cheeses prepared with different milk fat fractions

Calcium plays an important role in intestinal lipid digestion by increasing the lipolysis rate, but also limits fatty acid bioaccessibility by producing insoluble Ca soaps with long-chain fatty acids at intestinal pH conditions. The aim of this study was to better understand the effect of Ca on the bioaccessibility of milk fat from Cheddar-type cheeses. Three anhydrous milk fats (AMF) with different fatty acid profiles (olein, stearin, or control AMF) were used to prepare Cheddar-type cheeses, which were then enriched or not with Ca using CaCl2 during the salting step. The cheeses were digested in vitro, and their disintegration and lipolysis rates were monitored during the process. At the end of digestion, lipids were extracted under neutral and acidic pH conditions to compare free fatty acids under intestinal conditions in relation to total fatty acids released during the digestion process. The cheeses prepared with the stearin (the AMF with the highest ratio of long-chain fatty acids) were more resistant to disintegration than the other cheeses, owing to the high melting temperature of that AMF. The Ca-enriched cheeses had faster lipolysis rates than the regular Ca cheeses. Chromatographic analysis of the digestion products showed that Ca interacted with long-chain fatty acids, producing Ca soaps, whereas no interaction with shorter fatty acids was detected. Although higher Ca levels resulted in faster lipolysis rates, driven by the depletion of reaction products as Ca soaps, such insoluble compounds are expected to reduce the bioavailability of fatty acids by hindering their absorption. These effects on lipid digestion and absorption are of interest for the design of food matrices for the controlled release of fat-soluble nutrients or bioactive molecules

Ultrathin Sicopion Composite Cation-Exchange Membranes: Characteristics and Electrodialytic Performance following a Conditioning Procedure

The aim of this work was to investigate the properties of Sicopion membranes: an ultrathin (≈20 μm) composite cation-exchange membrane (CEM) made from sulphonated poly(ether-ether-ketone) (SPEEK) containing different levels of sulphonic-functionalized silica particles (SFSPs). Sicopion membranes were conditioned according to the French Normalization Association procedure, consisting in a series of acid and alkaline washes, and their electrodialytic characteristics were compared to an existent commercial food-grade membrane (CMX-SB). Electrical conductivity of Sicopion membranes was higher than that of CMX-SB membranes (9.92 versus 6.98 mS/cm), as well as their water content (34.0 versus 27.6%). As the SFSP level was reduced, the ion-exchange capacity (IEC) of Sicopion membranes increased. Concerning their electrodialytic performances, Sicopion membranes presented a lower demineralization rate than CMX-SB membranes (35.9 versus 45.5%), due to an OH− leakage through the pores created by dislodging the SFSP particles during the conditioning procedure