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About one third of the world's population suffers from micronutrient deficiencies with short and long-term consequences on individual life.Food fortification is one of the solutions for nutritional optimization to overcome these deficiencies, but the conditions for its maximum effectiveness remain to be defined regarding the actual bioavailability of these micronutrients.The impact of food structure on the kinetics of macronutrient digestion has been widely documented. However, with regard to micronutrients, studies do not always distinguish the matrix structure effect from the composition effect on their bioavailability. The main objective of this thesis is to evaluate the impact of food structure only on the digestion process and on the bioavailability of micronutrients, using real complex foods.Four foods with identical composition but different structures and textures have been designed, and enriched with icronutrients (lutein and vitamins D, B9 and B12). The structure of the food matrix had actually an impact on the bioavailability of lutein, and vitamins D and B9 in adult healthy men, in both quantitative and kinetics terms, thus providing proof of concept. The in vitro studies confirmed the food structure effect observed in vivo and allowed to study in depth the degradation of the food matrix, the release of micronutrients from the matrix, and thus their bioaccessibility.This work highlights the importance of the matrix effect for food digestion. It also suggests that a deep understanding of the digestion mechanisms could enable, in the future, the control over the digestion process with a targeted food design.; Un tiers de la population mondiale souffrirait d’une carence en micronutriments entraînant des conséquences à court et long terme sur la vie des individus. L’enrichissement des aliments est une des pistes de l’optimisation nutritionnelle visant à lutter contre ces carences, mais les conditions de son efficacité maximale restent à définir au regard de la biodisponibilitéréelle de ces micronutriments. L’impact de la structure des aliments sur la cinétique de digestion des macronutriments a été largement démontré. En revanche, en ce qui concerne les micronutriments, les études ne permettent pas toujours de distinguer les effets composition et structure de la matrice sur leur biodisponibilité. L’objectif principal de cette thèse est d’évaluer l’impact de la seule structure d’aliments réels sur le processus de digestion et la biodisponibilité des micronutriments.Quatre aliments de même composition mais de structures et textures variables ont été conçus et enrichis en micronutriments (lutéine et vitamines D, B9 et B12). La structure de la matrice alimentaire a effectivement influencé la biodisponibilité de la lutéine et des vitamines D et B9 chez l’Homme, et ce de manière quantitative et cinétique, apportant ainsi une preuve de concept. Les études in vitro ont permis de confirmer l’effet structure observé in vivo et d’étudier en détail la dégradation de la matrice alimentaire, la libération des micronutriments et donc leur bioaccessibilité.Ce travail souligne l’importance de l’effet matrice dans la digestion des aliments. Il suggère aussi que la compréhension fine des mécanismes de digestion pourrait permettre, à terme, la maîtrise du déroulement de la digestion par un design ciblédes aliments.

About one third of the world's population suffers from micronutrient deficiencies with short and long-term consequences on individual life.Food fortification is one of the solutions for nutritional optimization to overcome these deficiencies, but the conditions for its maximum effectiveness remain to be defined regarding the actual bioavailability of these micronutrients.The impact of food structure on the kinetics of macronutrient digestion has been widely documented. However, with regard to micronutrients, studies do not always distinguish the matrix structure effect from the composition effect on their bioavailability. The main objective of this thesis is to evaluate the impact of food structure only on the digestion process and on the bioavailability of micronutrients, using real complex foods.Four foods with identical composition but different structures and textures have been designed, and enriched with icronutrients (lutein and vitamins D, B9 and B12). The structure of the food matrix had actually an impact on the bioavailability of lutein, and vitamins D and B9 in adult healthy men, in both quantitative and kinetics terms, thus providing proof of concept. The in vitro studies confirmed the food structure effect observed in vivo and allowed to study in depth the degradation of the food matrix, the release of micronutrients from the matrix, and thus their bioaccessibility.This work highlights the importance of the matrix effect for food digestion. It also suggests that a deep understanding of the digestion mechanisms could enable, in the future, the control over the digestion process with a targeted food design.; Un tiers de la population mondiale souffrirait d’une carence en micronutriments entraînant des conséquences à court et long terme sur la vie des individus. L’enrichissement des aliments est une des pistes de l’optimisation nutritionnelle visant à lutter contre ces carences, mais les conditions de son efficacité maximale restent à définir au regard de la biodisponibilitéréelle de ces micronutriments. L’impact de la structure des aliments sur la cinétique de digestion des macronutriments a été largement démontré. En revanche, en ce qui concerne les micronutriments, les études ne permettent pas toujours de distinguer les effets composition et structure de la matrice sur leur biodisponibilité. L’objectif principal de cette thèse est d’évaluer l’impact de la seule structure d’aliments réels sur le processus de digestion et la biodisponibilité des micronutriments.Quatre aliments de même composition mais de structures et textures variables ont été conçus et enrichis en micronutriments (lutéine et vitamines D, B9 et B12). La structure de la matrice alimentaire a effectivement influencé la biodisponibilité de la lutéine et des vitamines D et B9 chez l’Homme, et ce de manière quantitative et cinétique, apportant ainsi une preuve de concept. Les études in vitro ont permis de confirmer l’effet structure observé in vivo et d’étudier en détail la dégradation de la matrice alimentaire, la libération des micronutriments et donc leur bioaccessibilité.Ce travail souligne l’importance de l’effet matrice dans la digestion des aliments. Il suggère aussi que la compréhension fine des mécanismes de digestion pourrait permettre, à terme, la maîtrise du déroulement de la digestion par un design ciblédes aliments.

IntroductionLuminal pH is a key determinant of food disintegration in the stomach, acting both on their biochemicalstructures and on the activity of digestive enzymes.ObjectiveThe present study aimed at monitoring postprandial intragastric pH variation after ingestion of fourplant-based meals having the same macronutrients content: two liquids (soymilk and a pea emulsion)and two solids (seitan and tofu).MethodologyFour mini-pigs fitted with a gastric cannula located on the stomach greater curve were used. Threerecording methods were compared: chyme sampling from cannula, a classic pH meter-catheterequipped with two probes or a wireless pH sensor directly put inside the stomach through the canula.Gastric emptying was also investigated using indigestible markers sampled from duodenal cannulaon six other mini-pigs. In vitro multi-scale characterization in gastric condition were assessed inin vitro conditions in order to explain intragastric pH differences observed in vivo.Main findingsDistribution of variation coefficients allowed us to detect the method inducing the less interindividualvariability. The average values obtained from the catheter system and the wireless sensor wereconsistent with each other, while sampling method gave less meaningful results. Food effect washighlighted: an exponential decrease occurred with solids while liquids observed a plateau at pH 7that lasted about 2h before a sigmoid-type decrease. The seitan appeared to empty faster from thestomach than the other foods, that could explain the quick pH decrease observed in the stomach. Itwas not the case for tofu explained probably by aggregation, buffering capacity or nitrogen solubility.Finally, entire gastric pH curves were modeled for each meal, that will be useful for implementing invitro dynamic digestion in relevant conditions.ConclusionIn conclusion, pH recording with catheter remained better than other methods and food macrostructureappeared to impact significantly gastric pH.

In situ disintegration of protein gels (egg white) by pepsin based on time-lapse confocal microscopy . Première réunion plénière du GDR SLAMM (Solliciter LA Matière Molle)

The most common hypothesis to explain the influence of food structure on digestion rates is that the proteolysis may be first limited in the stomach by the pepsin activity within the protein structures, as formed during food processing and possibly modified during gastric digestion. It is known that the gastric juice penetrates the food matrix and assists in digestion, but how the acidity and enzyme of the gastric juice affect disintegration of food is still far from being fully understood. There is, indeed, a real lack of methods that allow monitoring the evolution of food micro and nanostructure in the course of digestion. A novel time-lapse synchrotron deep-UV microscopy methodology was developed that made use of the natural tryptophan fluorescence of proteins. It enabled the monitoring in situ of the microstructural changes of protein small gel particles ( 1mm) during simulated gastric digestion. Two dairy gels with an identical composition, but differing by the coagulation mode, were submitted to static in vitro gastric digestion. The kinetics of gel particle breakdown were quantified by image analysis and physico-chemical analyses of digesta. In parallel, the fluorescence recovery after photobleaching (FRAP) technique in confocal microscopy was adapted to investigate the diffusion behaviour of fluorescently labelled pepsin in casein gels of increasing protein concentrations, allowing to form protein networks with different microstructures. The results confirm the tendency of rennet gels, but not acid gels, to form compact protein aggregates under acidic conditions of the stomach. Consequently, the kinetics of proteolysis were much slower for the rennet gel, confirming the hypothesis of a reduced pepsin accessibility to its substrate. Indeed, pepsin diffusivity was quantified (by FRAP) as significantly lower in stronger gels, because of the increasing steric hindrance in the gel microstructure as the protein concentration increased. Moreover, the proteolysis kinetics of the gel particles followed an exponential trend, and while the particle size decreased progressively, their morphology remained unchanged, suggesting that external erosion was the predominant mechanism of the enzymatic breakdown of dairy gels in these experimental conditions.

The food matrix structure is one of the key drivers to control the fate of food in the digestive tract. The behaviour in the gastrointestinal tract of milk protein matrices of identical composition but different micro and macrostructures was investigated in vivo. Six multi-canulated and catheterized mini-pigs were fed 6 different dairy matrices (raw and heat-treated milks, acid and rennet gels). Effluents from the duodenum and mid-jejunum as well as plasma from the abdominal aorta were collected over 7h. Structure was shown to drive the time of residence of food in the stomach. Liquid matrices generated a fast and intense peak of proteins in the intestine and amino acids in the bloodstream whereas the behaviour of rennet gels was opposite. Controlling the time of residence of food in the stomach by playing on its structure allows to design products with a fast/slow release of nutrients.

Food structure affects the kinetics of food digestion and the bioavailability of nutrients. Rencontre Université de Suzhou et industriels chinois COFCO

Recent findings have demonstrated that the food matrix structure is one of the key drivers to control the fate of food in the digestive tract and, consequently, the kinetics of nutrient release. As an example, the behaviour in the gastrointestinal tract of milk protein matrices of identical composition but different micro and macrostructures was investigated in vivo. Six multi-canulated and catheterized mini-pigs were fed 6 different dairy matrices (raw and heat-treated milks, acid and rennet gels). Effluents from the duodenum and mid-jejunum as well as plasma from the abdominal aorta were collected over 7h. Structure was shown to drive the time of residence of food in the stomach. The liquid-gel transition led to a significant increase in the gastric emptying time. Liquid matrices generated a fast and intense peak of proteins in the intestine and amino acids in the bloodstream. Peptidomic analysis showed different patterns between intestinal samples. Finally, rennet gels had a different behaviour than the acid ones forming a compact coagulum in the stomach that slowed down the gastric emptying and delayed the release of amino acids. A similar experiment was performed with DHA-enriched egg products. Once again, food structure drove the bioavailability of this fatty acid. Controlling the time of residence of food in the stomach by playing on its structure should allow to design products with a fast release of nutrients particularly adapted for elderlies, athletes etc… whereas foods persisting in the stomach should induce satiety and be dedicated to overweight people. Ongoing experiments using biophysical methods will help us to understand the mechanisms of gel particle breakdown in the stomach in order to design foods of new generation perfectly adapted to the nutritional needs of specific populations.

Understanding how food structure impacts the availability of target molecules such as nutrients and bioactives during digestion is of crucial interest to strengthen the relationships between food and human health. This presentation gives an overview of the work conducted at INRA during the last 6 years on in vitro and in vivo digestion of milk and egg proteins. Our main objectives are to elucidate the mechanisms of protein structures disintegration in the GI tract and to determine if the laws driving native protein digestion can be applied to complex food matrices. At the molecular scale, the kinetics of native protein digestion are mainly driven by the 3D-structure of the biopolymer. Compact and globular proteins like β-lactoglobulin exhibit a high resistance towards the action of pepsin whereas the flexible caseins are rapidly hydrolysed. Local side chain dynamics may explain preferential cleavage of certain peptide bonds. At the supramolecular scale, linear fibril-like aggregates of ovalbumin are more prone to proteolysis than branched or spherical aggregates and the peptidome released in the small intestine is directly connected to the type of aggregate. At the micro/macroscopic scale, egg white gels made with linear aggregates form a dense network that seems to limit pepsin diffusion and increases resistance to in vitro digestion. In contrast, gels formed with large spherical aggregates exhibit spaced clusters surrounded by an aqueous phase that is favorable to pepsin diffusion increasing the susceptibility of these gels to digestion. Finally, complex dairy matrices of identical composition but different physical state (liquid, gel, solid) submitted to in vivo digestion in multi-canulated mini-pigs showed that the matrix structure affects the time of residence in the stomach and drives the kinetics of protein digestion and amino acids bioavailability in the bloodstream. The knowledge generated will help to design novel foods with controlled nutrient release.

Beyond nutritional composition, food structure is increasingly recognized to play a role in food health potential, notably in satiety and glycemic responses. Food structure is also highly dependent on processing conditions. The hypothesis for this study is, based on a data set of 98 ready-to-eat foods, that the degree of food processing would correlate with the satiety index (SI) and glycemic response. Glycemic response was evaluated according to two indices: the glycemic index (GI) and a newly designed index, the glycemic glucose equivalent (GGE). The GGE indicates how a quantity of a certain food affects blood glucose levels by identifying the amount of food glucose that would have an effect equivalent to that of the food. Then, foods were clustered within three processing groups based on the international NOVA classification: (1) raw and minimally processed foods; (2) processed foods; and (3) ultra-processed foods. Ultra-processed foods are industrial formulations of substances extracted or derived from food and additives, typically with five or more and usually many (cheap) ingredients. The data were correlated by nonparametric Spearman's rank correlation coefficient on quantitative data. The main results show strong correlations between GGE, SI and the degree of food processing, while GI is not correlated with the degree of processing. Thus, the more food is processed, the higher the glycemic response and the lower its satiety potential. The study suggests that complex, natural, minimally and/or processed foods should be encouraged for consumption rather than highly unstructured and ultra-processed foods when choosing weakly hyperglycemic and satiating foods.

The microstructure of milk fat in processed dairy products is poorly known despite its importance in their functional, sensorial and nutritional properties. However, for the last 10 years, several research groups including our laboratory have significantly contributed to increasing knowledge on the organization of lipids in situ in dairy products. This paper provides an overview of recent advances on the organization of lipids in the milk fat globule membrane using microscopy techniques (mainly confocal microscopy and atomic force microscopy). Also, this overview brings structural information about the organization of lipids in situ in commercialized milks, infant milk formulas and various dairy products (cream, butter, buttermilk, butter serum and cheeses). The main mechanical treatment used in the dairy industry, homogenization, decreases the size of milk fat globules, changes the architecture (composition and organization) of the fat/water interface and affects the interactions between lipid droplets and the protein network (concept of inert vs active fillers). The potential impacts of the organization of lipids and of the alteration of the milk fat globule membrane are discussed, and technological strategies are proposed, in priority to design biomimetic lipid droplets in infant milk formulas.

This concept paper intends to define four new paradigms for improving nutrition research. First, the consequences of applying a reductionist versus a holistic approach to nutrition science will be discussed. The need for a more focused preventive nutrition approach, as opposed to a curative one, will then be presented on the basis of the ‘healthy core metabolism’ concept. This will lead us to propose a new classification of food products based on processing for future epidemiological studies. As a result of applying the holistic approach, health food potential will be redefined based on both food structure and nutrient density. These new paradigms should help define a more ethical preventive nutrition for humans to improve public recommendations while preserving the environment.

Digestion provides nutrients and energy essential to the survival and growth of the organisms. But little is known about the influence of food structure and of interactions between food components during processing on their digestibility and nutritional properties. Our objectives are to understand how dairy products are disintegrated in the gastrointestinal tract, identify the potentially bioactive molecules (peptides, amino acid, fatty acid...) released during digestion and demonstrate the physiological effect of these molecules on the host. In a first experiment, six dairy matrices (raw and heat - treated milk, stirred and non - stirred acid gels, rennet gels made of raw or heat - treated milk) of similar composition but with different micro and macrostructures were manufactured in a pilot plant. Each sample was given to six multi- canulated adult mini- pigs. Effluents were collected in the duodenum and mid-jejunum during 7h after the meal and characterized by SDS-PAGE, LC -MS-MS and ELISA. Free amino acids were quantified in plasmas. More than 16000 peptides released in the lumen during digested were identified. Among those, several are known for carrying biological activities. Compares to liquid milks, acid gels showed a delayed gastricemptying and a slower release of caseins and β-lactoglobulin in the duodenum. In a secondexperiment, two infant formulas adapted to reac h the nutritional requirement of piglets were manufactured using either vegetable fat (STD) or a combination of milk and vegetable fats stabilized by a mixture of proteins and milk fat globule membrane fragments (EXP). The formulas were distributed with an automatic milk feeder to piglets until slaughter at 28 days. Intestinal contents and tissues as well as mesenteric lymph nodes (MLN) were collected. Microbiota diversity and composition was assessed using DHPLC and metasequencing analysis. The immunoreact ivity of β-lg and Cns, as determined by ELISA, was higher in EXP than in STD intestinal contents. The secretory activity of MLN cells was modified by the formula composition, the highest IFNγ secretion was obtained in EXP piglets. Microbiota clustering successfully discriminated infant formulas according to the nature of fat. Differences in proteobacteria and firmicutes phyla were observed. These data emphasize the crucial role played by the food composition but also its structure on the digestion mechanisms, the kinetics of nutrient release and the physiological response of the host

International audience; This study aimed at identifyingmilk peptides released in the gastrointestinal tract ofmini-pigs during the digestion of dairy matrices and determining the effect of the matrix structure on the gut lumen peptidome. Six dairy matrices (raw and heated milk, the corresponding rennet gels, and a non-stirred or a stirred acid gel prepared from the heated milk) of similar composition but with different structures were ingested by four mini-pigs. Duodenal effluentswere collected over a 5 h-period and analyzed by tandemmass-spectrometry.More than 16,000 peptideswere sequenced and unambiguously identified. The structure of dairy products had only little influence on the location of cleavage sites on the protein sequences.However, it strongly impacted the number of identified peptides andmore especially for rennet gels which led to about 3 times less detected peptides than for the other matrices. This effect was attributed to greater extents of dilution by digestive secretions associated with longer gastric retentions for the rennet gels. Potential bioactive peptides were also produced over time and are all reported to contribute to document the literature originating from in vivo experiments. Our results indicate that the structure of dairymatrices strongly affects the kinetics ofmilk protein digestion in vivo, more than themechanism of proteolysis itself.

This study aimed at identifying milk peptides released in the gastrointestinal tract of mini-pigs during the digestion of dairy matrices and determining the effect of the matrix structure on the gut lumen peptidome. Six dairy matrices (raw and heated milk, the corresponding rennet gels, and a non-stirred or a stirred acid gel prepared from the heated milk) of similar composition but with different structures were ingested by four mini-pigs. Duodenal effluents were collected over a 5 h-period and analyzed by tandem mass-spectrometry. More than 16,000 peptides were sequenced and unambiguously identified. The structure of dairy products had only little influence on the location of cleavage sites on the protein sequences. However, it strongly impacted the number of identified peptides and more especially for rennet gels which led to about 3 times less detected peptides than for the other matrices. This effect was attributed to greater extents of dilution by digestive secretions associated with longer gastric retentions for the rennet gels. Potential bioactive peptides were also produced over time and are all reported to contribute to document the literature originating from in vivo experiments. Our results indicate that the structure of dairy matrices strongly affects the kinetics of milk protein digestion in vivo, more than the mechanism of proteolysis itself.

Présentation orale : session "Structure des aliments et effets santé"; National audience

National audience; Beside differences in composition, infant formula and human milk exhibit structural differences. Native milk fat globule is a 4–5 μm particle composed by a core of triglycerides surrounded by a tri-layer of phospholipids. Fat in infant formula appears as small droplets stabilized by milk proteins. Similarly, type of proteins and casein micelle size differ between these two foods. Two infant formulas and human milk were submitted to a simulated in vitro dynamic digestion mimicking the gastro-intestinal tract of a 1-month old baby. Digested samples were collected and characterized at different scales. Structure of the native human milk fat globule persisted in the stomach during the first 2 h of digestion. Kinetics of proteolysis and lipolysis presented some differences with casein being digested more rapidly in the formula than in the human milk. It now needs to determine whether these differences have some physiological consequences on the neonate.; Outre des différences de composition, les formules infantiles présentent des différences structurales avec le lait maternel. Le globule gras natif du lait maternel correspond à une particule de 4–5 μm de diamètre constituée d’un cœur de triglycérides entouré d’une tri-couche de phospholipides. La matière grasse des formules infantiles apparaît sous forme de petites gouttelettes stabilisées par des protéines. De même, le type de protéines et la taille des micelles de caséines diffèrent entre ces deux aliments. Deux formules infantiles et un lait maternel ont été soumis à un protocole de digestion in vitro en conditions dynamiques simulant le tractus gastro-intestinal d’un enfant d’un mois. Les digestas ont été collectés et caractérisés à différents niveaux d’échelle. La structure du globule gras natif du lait maternel persiste dans l’estomac lors des deux premières heures de digestion. Les cinétiques de protéolyse et lipolyse sont différentes avec des caséines digérées plus rapidement dans les formules que dans le lait maternel. Il reste cependant à déterminer si ces différences ont des conséquences physiologiques pour le nourrisson.

L’impact de la structure de l’aliment sur ses propriétés nutritionnelles est encore mal connu. L’objectif de ce travail était de voir si des gels laitiers de composition identique obtenus par des procédés de gélification différents présentaient des cinétiques de digestion des protéines et de mise à disposition d’acides aminés plasmatiques différentes. A partir d’un lait écrémé traité thermiquement (90°C/10 min), un gel acide et un gel présure de composition identique ont été conçus. Ces deux gels présentent des microstructures similaires (diamètre des pores 0.8 μm) et des propriétés rhéologiques voisines (facteur de perte tan δ identiques). Ces deux matrices ont été données à des mini-porcs adultes équipés de canules duodénale et jéjunale et d’un cathéter sanguin. Il ressort que les cinétiques de digestion des protéines laitières dépendent directement du temps de résidence de ces aliments dans l’estomac, luimême piloté par la structure du gel. Les gels acides présentent un temps de résidence plus court dans l’estomac que les gels présure. Le nombre de peptides identifiés dans la lumière intestinale tout au long des 7h de digestion était 3 fois supérieur pour le gel acide que pour le gel présure (4349 vs 1443). Le gel acide provoque l’apparition d’un pic précoce et massif d’acides aminés essentiels dans le plasma. Le gel présure semble induire plus de satiété que le gel acide. Des données supplémentaires obtenues in vitro et in silico ont permis de mettre en évidence une forte agglomération de particules de caséines dans l’estomac pour le gel présure entrainant un temps de séjour supérieur ainsi qu’une contraction du réseau protéique suivie d’une expulsion de lactosérum (synérèse) provoquant une vidange rapide des protéines sériques., Little is known about the effect of the structure on the nutritional properties of food. The objective of this work was to determine if dairy gels of identical composition but obtained through different gelation process exhibited different protein kinetics of digestion and amino acid release in plasma. Using a heattreated milk (90°C/10 min), an acid and a rennet gel were manufactured. These two gels exhibited similar microstructure (mean pore diameter of 0.8μm) and rheological properties (identical loss factor tan δ). Multi-canulated (duodenum and jejunum) adult mini-pigs bearing blood catheters were fed these matrices. Milk protein kinetics of digestion were directly related to the time of residence of the matrices in the stomach that was driven itself by the gel structure. Acid gels showed a lower time of residence in the stomach than the rennet one. Number of peptides identified in the intestinal lumen throughout the 7h of digestion was 3 times higher for the acid gel (4349 vs 1443). The acid gel caused a fast and sharp increase of essential amino acids in the plasma. Rennet gel induced more satiety than acid ones. Supplementary data obtained in vitro and in silico showed a strong casein particle aggregation in the stomach for rennet gel leading to a higher time of residence and a contraction of the protein network followed by an expulsion of whey (syneresis) causing a rapid gastric emptying of the whey proteins.

Food structure can have a major impact on digestion in the gastrointestinal tract. Moreover, the structure of food proteins, which are typically consumed within complex food matrices, can be modified during food processing. Protein aggregation is one such modification and in the present study, the relationship between thermally-induced aggregated structures and in vitro digestion was explored using ovalbumin (the majoregg white protein) as a food protein model. In order to explore the relationship between the structure of ovalbumin aggregates with their behavior during in vitro digestion, four different thermally-induced ovalbuminaggregates were prepared. The digestion of the latter aggregates and the resulting peptides profiles of the digests were investigated using an in vitro two-step model (stomach and small intestine mimicking the adult gastrointestinal tract). Different combinations of pH and ionic strength (IS; pH 5/IS 0.8M, pH 7/IS 0.3M, pH7/IS 0.03M, pH 9/IS 0.03M) were used to generate different aggregate structures. These structures were characterized using light scattering methods, transmission electronic microscopy (TEM) and SDS-PAGE electrophoresis. Aggregate structures varied from random to linear, with particle size distributions (D[4;3]) ranging from 16nm to 90μm for linear and random aggregates, respectively. After in vitro simulated gastrointestinal tract digestion, the degree of hydrolysis of the linear aggregates was almost twice that of the random aggregates or the native ovalbumin. The overall peptide profiles of the digests of the untreated OVA and the random and linear OVA aggregate preparations were compared using spectral principal componentanalysis of reverse-phase HPLC chromatograms for each sample. Three distinct clusters were identified which corresponded to untreated OVA, linear aggregates and random aggregates treatments respectively.Consequently, based on an in vitro digestion model, it would appear that the type of protein aggregates present in a processed food may impact the extent and the nature of protein digestion in the gastrointestinal tract.

Structure and properties of milk lipids. Congrès FIL/IDF

Crystallisation properties and polymorphism of triacylglycerols (TG) in natural milk fat globules are studied with an apparatus permitting the coupling of time-resolved synchrotron X-ray diffraction (XRD) and high-sensitivity differential scanning calorimetry (DSC) for cooling rates 0.1 < Rcooling < 1000 ◦C·min−1. We showed that the fat phase of dairy products displays a complex polymorphism. For the first time, six different types of crystals were identified, several of them in coexistence, and their time- and temperature-dependent evolutions were quantitatively monitored. They correspond to lamellar structures with double-chain length (2L: 40.5–48 Å) and triple-chain length (3L: 54–72 Å) organisations of TG. Depending on the cooling rate, at least five crystalline subcell species were observed at wide angles: α and sub-α, two β’ and one β. All these crystalline structures coexist with a liquid phase even at low temperatures. Thermal events recorded by DSC were related to the structural information on the organisation of TG obtained by XRD. Moreover, we showed that crystallisation in fat globules induces a higher disorder and a smaller size of crystals than in bulk, i.e. in anhydrous milk fat. Furthermore, XRD permitted the identification of different crystallisation behaviour in natural milk fat globules with different sizes, which could be implicated in the manufacture of dairy products involving tempering periods in the technological process (e.g. butter, ice cream, whipped products). The increased knowledge of milk fat crystallisation in waterdispersed and highly complex food products might have a certain value for technical applications as well as for the development of new processes and dairy products.