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Acid milk gels with fat (3.5 or 10%) or without fat containing 0.2–1% of whey proteins (WP) or 0.2–1.5% of protein aggregates (fractal aggregates, microgels and mixed casein/WP aggregates with an 80/20 ratio) were investigated. The fat-containing systems were homogenized and the systems were preheated (90 °C, 11 min) and acidified to a pH of 4.6 by adding glucono-delta-lactone. The protein composition of the fat droplet interface was characterized by SDS-PAGE and the textural and rheological properties, microstructure, and whey separation of acid networks were determined. WP and fractal aggregates showed the best ability to improve the textural properties and microstructure of all acid milk gels and reduce whey separation. Increasing the concentrations in microgels and mixed aggregates did not lead to an increase in gel firmness or generate a strong impact on the protein network, but a high concentration in mixed aggregates could reduce whey separation. The fat droplet interface was made almost exclusively of caseins, even if the fractal aggregates could also be adsorbed when the interfacial surface was increased either through fat content or through an increase in homogenization pressure. Adding proteins changes the textural properties of the acid gels in all the systems, mainly due to their role in the continuous phase.

International audience; Background: Since the early 1990s, major health and environmental concerns have developed and driven the emergence of diets involving a lower consumption of animal products. However, the transition towards greener diets is being hampered by the poor acceptance of vegan foodstuffs among western consumers. Mixed animal/ plant alternatives to familiar dairy or egg products offer a new field of innovation. Scope and approach: This review focuses on innovative mixes of egg or milk with plant ingredientsespecially legumesto develop products in which interactions between animal and plant are not usually expected, such as dairy or egg gels, emulsions or foams. The opportunities offered by such products in terms of consumer acceptance, nutrition, digestibility and techno-functional properties are reviewed and discussed with respect to their risk-benefit ratios. Key findings and conclusions: In many cases, animal/plant mixes offer enhanced protein stability and synergistic interfacial or textural properties that make them a flexible tool for food design. Fermentation offers important prospects for the nutritional and sensorial enhancement of animal/plant mixes, through the multi-criteria application of microbial consortia. Animal/plant mixes enable reduction in animal protein consumption while preserving amino acid and micronutrient intakes and sensory properties. However, their acceptability to consumers and society will also depend on controlled safety, especially regarding allergies or contaminants, on affordability, their degree of novelty or (ultra)processing, their actual environmental footprint and whether they meet consumer expectations for innovative foods in the transition towards greener diets.

International audience; A process of dry heating alkaline powder containing whey protein (WP) and lactose is used to produce micro-particles that can trap large amounts of water and thus be used in many food applications as a thickening agent. The objective of this study was to optimise the yield of particles formed and the amount of water they trap as well as to minimise the heating duration. The parameters studied were the contents of WP and lactose, the pH, storage time at that pH, water activity (a w) of the powder, and the temperature and duration of dry heating. The best parameters to reach the objective were WP at 100 g/kg with 0.5 g lactose/10 g protein, adjusted and stored at pH 10 for 3 h, and dry heating at 120 °C for ca. 30 min at a w ¼ 0.33. Approximately 70% of the WP converted into wet particles that contained 96% water. This result can help advance large-scale production of particles in a multi-stage spray-dryer that uses an in-line heating fluidised bed.

International audience; Background: Today's consumers demand natural and healthy functional food products with clean labels and less added ingredients and exogenous hydrocolloids. The goal is to produce dairy foods only made by using milk ingredients, while maintaining good sensory properties. Thanks to their multifunctional properties, dairy proteins are used to enhanced the texture of dairy products. However, their addition into dairy products can also have a great influence on taste and aroma perception. Scope and approach: This review concentrates on recent information regarding the impact of dairy proteins in dairy products with a focus on yogurts. The aim of the review is to highlight recent findings relating the composition and the physico-chemical properties of yogurts to their sensory properties. Key findings and conclusions: The addition of dairy proteins in yogurts induces changes in their microstructure, which can explain the modifications of their texture properties. Modifying the protein content also tends to decrease the release of most flavor compounds, which can impact the overall aroma balance and change aroma perception. Modifications of texture and aroma perceptions can also be due to cognitive interactions. Dairy protein aggregates are particularly promising as dairy texture enhancers, however almost no sensory studies have been performed to investigate their impact on texture and aroma perception. More studies focusing on the impact of dairy protein aggregates on the organoleptic qualities of yogurts and dairy products are needed to obtain natural and low-fat products while maintaining a desirable texture quality.

This study aimed to perform Temporal Dominance of Sensations by modality (M-TDS) combined with a multi-intake approach to investigate texture and flavor perception in semi-solid products. Trained panelists (n = 15) evaluated fat-free strawberry yogurts enriched with functional proteins involving texture modifications. As yogurt is a semi-solid product, its in-mouth residence time is short. A multi-intake approach was therefore expected to give more reliable information about the sensory properties perceived by panelists. The two modalities of texture and flavor were analyzed separately to characterize the effect of added proteins. Trials were made according to an experimental design with two factors (protein type and concentration) and three levels each. Different statistical treatments, taking or not the temporality of attributes into account, were performed on standardized and non-standardized data. The implementation of M-TDS was essential to highlight differences of flavor perception in addition to the more evident texture modifications. The study of sensory trajectories evidenced that texture modifications, induced by the use of different whey proteins, slightly modified the perception of flavor and sweetness. The global flavor perception of the samples varied with the number of spoons, which particularly impacted the taste attributes. This study highlighted the importance of using M-TDS when studying texture and flavor in semi-solid products, and the relevance of the multi-intake approach to characterize flavor perception. This methodology enabled panelists to evidence both marked texture differences and subtler flavor modifications, and these useful data were emphasized by combining different statistical treatments.

Hydrophobisation of whey proteins, followed by erythritol addition into the hydrophobised protein dispersion, enables formation of water-in-water (W/W) emulsions of the proteins and alginate. In this study, we investigated the interfacial and gel rheology of whey proteins as affected by hydrophobisation, heat denaturation and erythritol addition. Additionally, the gel rheology of the resultant W/W emulsion was assessed. Hydrophobisation shortened the linear viscoelastic region and decreased the surface storage modulus ( G s ' ), the flow stress and the flow strain of protein layer at the air-liquid interface. Erythritol addition into the hydrophobised protein caused a further reduction of G s ' . In accordance with interfacial rheology, protein hydrophobisation and erythritol addition decreased the dynamic moduli of acid-induced protein gels. Frequency sweep tests indicated that the gelled emulsion had higher dynamic moduli than all WPI gels. The higher firmness of the emulsion gel was ascribed, based on microstructural images, to micro-phase separation of alginate droplets.

Whey protein products are of widespread use as food ingredients because of their high nutritional, biological and functional properties. Whey proteins are important structural components in many foods as used in their native form, for example for their heat-induced gelation abilities. Furthermore, they also offer reliable functionalities when modified by heating processes as denatured or aggregated proteins. Heat treatment of whey proteins in a liquid state has received much attention in recent years. While dry heating of whey proteins, say heating whey proteins in the dry state, is frequently cited in the literature as a potential and efficient means to improve the functional properties of proteins, it has received very little attention. We report first on the dry heating of whey products as applied to promote glycation of whey proteins with a low denaturation, and second, to promote their denaturation and aggregation and on their consequences on the functional properties of whey proteins.

The impact of nanoparticulated whey protein aggregates on the texture of fat-free set-type yoghurts was investigated. Monodisperse (MFA) and polydisperse (PFA) fractal aggregates obtained from heated whey protein isolate (WPI) were added to skimmed milk for yoghurt manufacture at four different concentrations (0.2%–1.5%, w/w). The impact of the concentration and the polydispersity of the aggregates on fat-free set-type yoghurts were studied by instrumental measurements (rheology, penetrometry, syneresis and microscopy) and sensory analysis. Yoghurt gel strength and firmness increased with the concentration of WPI, MFA and PFA. However, yoghurts enriched with PFA clearly differed from the yoghurts enriched with WPI. Indeed, yoghurts enriched with PFA were characterised by a weak gel, a low firmness and a low-density of the protein network. Sensory analysis confirmed the results obtained by instrumental measurements. The whey protein aggregates studied are thus promising tools to modulate fat-free yoghurt texture while using milk-derived ingredients.

Dry heating (DH) at 100 °C of a whey protein isolate powder conditioned at pH 9.5 leads to the formation of stable, large and porous whey protein microparticles (WPM), resulting from crosslinking of proteins in the powder. The Maillard reaction (MR) is probably involved in the formation of these WPM. To confirm the role played by the MR and understand the protein changes occurring during particle formation, we analyzed the properties of the powders (such as their water activity (aw) and color) and characterized the WPM formed after 3 and 36 h of DH in powders with increasing amounts of added lactose. Adding lactose and prolonging the time of DH increased the extent of protein denaturation and the rate of formation of WPM and the yield of conversion of powder into WPM, but led to decreases in their water content. Addition of lactose also altered the kinetics of the MR, the increase in aw and the formation of WPM. The MR, as followed by powder browning, was complete within 3 h of DH irrespective of the amount of added lactose. In contrast, the increase in aw, thought to be due to progress of the MR, continued to increase from 3 to 36 h of DH. Formation of WPM went on increasing from 3 to 36 h of DH at low to medium levels of lactose, but was complete by 3 h of DH at high levels of lactose. In conclusion, the formation of WPM was not simply related to the MR and needs further investigation.

Dry heating (DH) at 100 °C for 36 h of a whey protein isolate powder conditioned at pH 9.5 leads to the formation of stable, large and porous whey protein microparticles (PMs), resulting from the crosslinking of proteins inside the powder. These PMs could be used as high-viscosity food ingredients. Casein, present as a contaminant in whey protein powders, has been shown to become incorporated into the PMs. In this study, we investigated the effect of adding increasing amounts of sodium caseinate to whey protein powders on the formation of PMs during DH at 100 °C for 36 h. In addition, we studied PM formation during DH of a micellar casein-enriched milk protein powder (Casmic). The browning index of the dry-heated powders, and the size and water content of the microparticles were also characterized. We confirmed that sodium caseinate was incorporated into the PMs. The highest PM D[4,3] values (270 μm) were observed for powders with around 40% caseinate. Powders without added caseinate displayed D[4,3] values of 150 μm. The yield of conversion of proteins into PMs increased from 0.6 to 0.8 g/g with caseinate addition, whereas the amount of water entrapped in the PMs decreased from around 30 to 20 g/g. PMs were also formed by DH of the Casmic powder, but these particles were smaller, with sizes of around 80 μm. In conclusion, our study shows that the process of DH at pH 9.5 could be applied to all milk proteins to obtain PMs with functional properties that could be used in the food industry.

Modification of whey protein isolate (WPI) powders is used in the food industry to enhance the functional properties of WPI. We investigated the impact of severe dry heating (DH) at 100 °C for up to 36 h on an alkaline-treated (pH 9.5), spray dried (water activity of ~0.24) WPI powder. Dry heated powders and their reconstituted suspensions were analysed. DH for 0–6 h led to 47% loss of native proteins, increases in the levels of soluble aggregates (×2.2) and of advanced glycation end-products of the Maillard reaction (at least ×2.7) and to powder browning (at least ×3) with a 95% decrease in free lactose content. DH for at least 12 h led to a decrease in soluble aggregates with concomitant formation of large, stable and insoluble microparticles. These microparticles had a microsphere structure, contained 98% of water phase and were made of insoluble powder particles resulting from protein cross-links during DH. Microparticle size could be altered by varying the pH of the suspension: at pH 6.5, microsphere size was 3–5 times larger than powder particle size, but decreased as the suspension pH neared the isoelectric point. DH could be a useful method for producing functional protein ingredients as these microparticles had very high water retention properties and high viscosity values.

International audience; We investigated the effect of dry heating (DH) a whey protein powder (water activity 0.24) at pH 3.5, 6.5 and 9.5 for up to 36 hat 100 degrees C on the structural properties of proteins. Powder browning, particle structures in suspensions reconstituted from the dry-heated powders (DHP), residual native protein content and Maillard reaction markers were studied. The browning index of the DHP rapidly increased after 6-10 h of DH and then levelled off at all pH values. beta-Lactoglobulin, alpha-lactalbumin and bovine serum albumin were denatured by DH at all pH values. In contrast to pH 3.5 and 6.5, DH at pH 9.5 led to abundant production of microparticles. The highly heterogeneous size of these particles was related to the initial powder particle size. One g of DHP in suspension led to 20 g of hydrated microparticles made from 0.5 g of dry material. Maillard reactions at pH 9.5 were probably involved in microparticle formation. (C) 2017 Elsevier Ltd. All rights reserved.

Conference Paper in AIP Conference Proceedings · February 2018 DOI: 10.1063/1.5021215Conference Paper in AIP Conference Proceedings · February 2018DOI: 10.1063/1.5021215; International audience; The current paper describes the formation of whey protein microbeads (WPM) having a spherical shapeand a monodispersed size distribution. A microfluidic flow-focusing geometry was used to control the production of whey protein microdroplets in a hydrophobic phase. The microfluidic system consists of two inlet channels where the WPI solution and the lipophilic phase were separately injected towards the flow-focusing (FF) junction where they eventually meet, then co-flow. A whey protein isolate (WPI) solution of 150 g/kg protein and two types of hydrophobic phases, i.e. sunflower oil and n-dodecane, were tested as the continuous phase. The formation of WPM was observed microscopically. The aim of the present study was to describe the production of stable monodisperse WPM in suspension in milk ultrafiltrate using a microfluidic system. Hints to perform the control of the running parameters, i.e. choice of the hydrophobic phase or fluids flowrates, are provided. The results showed that in the sunflower oil, microdroplets had a large polydisperse size distribution, while in n-dodecane, microdroplets with narrow size distribution were obtained. Stabilization of the whey protein microdroplets through heat-gelation at 75 °C for 20 min in n-dodecane produced WPM and no change in shape nor size is observed. Meanwhile replacing the n-dodecane by MUF using centrifugation and washing caused the swelling of the WPM, but dispersity remained low. From this study, microfluidic system seemed to be a suitable method to be used for producing small quantities of monodisperse WPM.

In acidified dairy products, the size of the whey protein particles could play a key role in the final structure of the gel. In the present study, small (SM; 2.5 ± 1.2 μm), medium (MM; 4.2 ± 2.2 μm), and large (LM; 18.4 ± 7.2 μm) whey protein microbeads were produced by mixing a 150 g.kg−1 whey protein isolate (WPI) solution and n-dodecane in the presence of polyglycerolpolyricinoleate (PGPR) surfactant at different shear rates and were then stabilized through heat gelation. The microbeads were then washed by centrifugation, dispersed at 70 or 90 g.kg−1 in milk ultrafiltrate, and acidification was performed at 35 °C by adding glucono-δ-lactone to achieve the final pH of ~4.5 in 6 h. Acid gelation was monitored using small deformation rheology, while the gel microstructure was investigated microscopically. The results showed that smaller size of microbeads promoted gels with a higher stiffness and a smaller pore size distribution. The effects were particularly significant at SM microbeads as the number of particles in this system was higher than in LM or MM, hence more connectivity between particles.

A model lipoproteic matrix able to mimic hard-type cheese was produced with controlled structural and textural properties. Changes in the microstructural and rheological properties of these model cheeses made from different milk concentrate powder, anhydrous milk fat, salt contents and pH values at renneting were characterised. Rheological properties were measured by texture profile analysis, fat globule and protein aggregate size distributions by laser light scattering. Microstructural properties of the model matrices were studied by confocal laser scanning and scanning electron microscopy. Significant differences between the matrices were found for the structural, physico-chemical and rheological parameters measured. Cheeses with higher dry matter content were significantly harder and contained more insoluble proteins than cheeses with lower dry matter content. The salt concentration and the pH at renneting had significant influence on cheese hardness and adhesiveness of rheological parameters. The model lipoproteic matrix presented air bubbles and powder aggregates which could not be avoided during the manufacture of products. However, compared with classic cheese making with rennet or acid coagulation, the technology used here allows model cheeses to be produced rapidly with a good reproducibility of texture.

International audience; The ripening of industrial soft cheeses manufactured using a liquid pre-cheese produced from the ultrafiltration (UF) of milk was observed to be slow in comparison to that of cheese manufactured by a traditional process. Moreover, in the UF-cheeses investigated in this study, which were produced using Penicillium camemberti as the surface flora, several surface defects were observed: the texture was 'carton' like and the rind frequently detached from the cheese. To gain a fuller understanding of the development of these surface defects in UF-cheeses, the migration of different minerals and ions, and the study of the rind microstructure by scanning electron microscopy and X-ray mapping were performed. The results suggest that the slower diffusion of lactate, possibly due to the mineral layer at the surface of cheeses, acting as a barrier to its diffusion, may have caused an alteration in the metabolism and growth of the surface mould and may explain the surface defects of these UF-cheeses.; Les fromages à pâte molle industriels produits par ultrafiltration (UF) à partir d'un pré-fromage liquide présentent un affinage retardé par rapport à des fromages produits à l'aide d'un procédé traditionnel. De plus, des fromages UF modèles produits avec seulement Penicillium camemberti comme flore de surface montrent une texture de carton et la croûte se détache souvent du fromage. La caractérisation des migrations des minéraux et des ions et l'étude de la microstructure de la croûte de ces fromages modèles par microscopie électronique à balayage et micro-analyse X ont été réalisées afin de comprendre l'origine de ces défauts. La diffusion retardée du lactate, peut-être due à la présence d'une couche minérale à la surface des fromages, pourrait être à l'origine de changements de métabolisme et de la croissance de la moisissure et pourrait expliquer la moindre qualité des fromages.

The objective of this work was to investigate the effect of heat treatment of sweet creams on the physicochemical properties of sweet industrial buttermilks. Creams with three different heat treatments: low, medium and high, were churned and the corresponding buttermilks were characterised. Furthermore, buttermilks were renneted and centrifuged to obtain insoluble pellets and supernatants. The physicochemical properties such as the particle size measured by laser light scattering and composition of creams, buttermilks, pellets and supernatants were determined and compared. Buttermilk had a composition close to that of skim milk but it contained more phospholipids (PL): 958 (± 137) mg·kg−1, compared with 120 mg·kg−1 in milk. The heat treatment induced a significant decrease in soluble protein contents in creams, buttermilks and soluble fractions as well as an increase in the buttermilk PL/fat ratio, and an increase in supernatant protein and total solids. Buttermilk and supernatant particle sizes ranged from 0.03 to 200 μm, with a maximum at 130 nm, which may correspond to small milk fat globules, phospholipid vesicles or protein aggregates. Fat and PL in buttermilks were recovered in supernatants. The use of buttermilk enzymatic coagulation combined with centrifugation may constitute a means to fractionate milk PL.

The native whey proteins have been intensively used in a multitude of food applications due to their high nutritional, biological, and versatile technofunctional properties. The range of applications of whey proteins has further been extended in the last decades by the use of whey protein aggregates offering new technofunctional properties. These properties are directly dependent on the structure of whey protein aggregates, i.e., their size, shape, density, surface properties, and the type of bonds maintaining proteins together in the aggregates. In this review, after a brief description of the major whey proteins, we examine the most important advances reported to date pertaining to the available approaches to modify the structure of whey proteins for specific functionalities. Our laboratory, Science and Technology of Milk and Eggs, has contributed significantly to the advancement of knowledge on the structure-function relationships of whey proteins either in the native or denatured/aggregated forms. Our expertise and research approaches are highlighted throughout some selected results accumulated during the last decade in comparison with results from the literature.

The effect of heat treatment of milk on the formation of acid gels was investigated using model protein systems. Protein systems contained micellar casein alone (35 g kg −1 ) (systR) or in the combination with either β -lactoglobulin ( β LG) (4 g kg −1 ; systB) or egg ovalbumin (4 g kg −1 ; systO). Proteins in a milk ultrafiltrate (UF) were heat-treated at 90°C for 24 min. The same heat-treated systems without casein were also prepared: the UF alone (systUFR), with β LG (4 g kg −1 ; systUFB) and with ovalbumin (4 g kg −1 ; systUFO). Proteins in pellet and supernatant fractions were analysed using reverse-phase high-pressure liquid chromatography and sodium dodecyl sulphate polyacrylamide gel electrophoresis. The solubility of globular proteins in heated systUFB and heated systUFO was determined at pH 1.6–6.5 by absorbance measurements. Rheological changes during gelation with a starter at 42°C were determined and microstructures of gels by scanning electron microscopy. High quantities of κ -casein and β LG in the form of complexes (disrupted by 2-mercaptoethanol) were found in supernatant of heated systB and not in that of systO. The gelation pH was related to the solubility of the globular proteins, and the gelation pattern for systB and systO resembled that of heated milk and the systR pattern resembled that of unheated milk. The gels of systR were coarse and consisted of large particles. Particles in gels from systB and systO were smaller and less clustered. Although the two globular proteins behave differently during heating, they both confer to the casein micelles their solubility properties as a function of pH. A model is presented where both soluble and colloidal complexes including the globular protein interact at pH 5.5 and initiate the acid gelation.

Le comportement du lait ecreme traite thermiquement au cours de l'acidification par des bacteries lactiques est etudie a 30 et 42 °C. Les modifications rheologiques par oscillations dynamiques et le temps de relaxation T2 en RMN du proton sont etudies en fonction du temps et du pH. La fluorescence frontale intrinseque etudiee conjointement avec l'analyse en composantes principales a ete suivie au cours de la fermentation. La gelification du lait apparait a un temps plus court et un pH plus eleve a 42 °C (5,53 ± 0,01) qu'a 30 °C (5,24 ± 0,13). Le pic de maximum de tan δ etait plus marque a 42 qu'a 30 °C, mais le G t a pH 4,6 avait la meme valeur aux deux temperatures. Les changements de T2 au cours de l'acidification etaient peu differents aux deux temperatures etudiees, mais les courbes dT2/dpH montrent quelques differences entre 42 et 30 °C. Les changements de T2 sont dus a des changements de structure de la particule provoques par la fermentation et sont correles a la solubilisation du calcium. La fluorescence frontale detecte un premier decalage des spectres vers des longueurs d'onde plus petites puis un decalage vers des longueurs d'onde plus grandes. Le point associe a l'inversion de l'environnement des tryptophanes des chaines proteiques correspond au point de gel. Ces resultats et les differences avec des gels acides obtenus par l'addition de GDL sont discutes en terme de limitation des transferts d'acides et de protons de la phase aqueuse vers la phase colloidale et de l'heterogeneite du gel qui en decoule.

Skim milk supplemented with calcium caseinate (Ca-Cas) and whey protein isolate (WPI) at different ratios was preheated at 72e90 C for 7 min and subsequently acidified for the production of set-style and stirred acid gels. Upon heat-treatment of the suspensions, the native whey protein content decreased and particle size increased with increasing temperature and WPI content. Consequently, the pH of gelation, firmness of the set gel, viscosity and particle size of the stirred gel all increased as the content in denatured whey protein increased. However, for preheating temperatures of 80 or 90 C, the viscosity and firmness of the gels reached a plateau, although almost all whey proteins were denatured and largest particles were formed. These results open perspectives for the production of high-protein yoghurts without unusual firmness properties

In acidified milk, heat-induced whey protein aggregates and casein micelle particles assemble to form a soft gel. The present study was set to evaluate the respective roles of whey protein aggregates (WPIA) and native casein micelles (NMC) during acid gelation by means of changing their ratio in model systems. NMC and WPIA were dispersed in milk permeate at different weight ratios ranging from 0% to 100% NMC for a total protein concentration of ∼45 g kg −1 . Acidification was performed at 35 °C by addition of glucono-δ-lactone to achieve the same final pH of 4.5 in 6 h. Acid-induced gelation of these systems was followed using small deformation rheology followed by large deformation test and whey retention measurement at pH 4.5, while their microstructure was investigated microscopically. The results showed that higher content in WPIA promoted faster gelation and led to more elastic gels with smaller pore size and increased whey retention. The effects were particularly dramatic up to ∼10% w/w WPIA, where the aggregates were about equimolar to the casein micelles and covered ∼8% of the micellar surface. The results were discussed in terms of the physical interactions between two populations of colloids of different abilities for acid gelation. It seemed likely that a preferred interaction exists between the casein micelles and the aggregates, and directs the structural and mechanical properties of the acid gel.

International audience; The kinetics of whey drainage of Camembert soft cheese was studied using an instrumented drainage device to record the pH and the weight of the whey with a variation coefficient amounting to 1.8% during the first 100 min and 0.34% at the end of drainage. Drainage data were fit with a two step equation to obtain a descriptive model of the drainage kinetics. The effect of the pH at renneting, the casein concentration and the ionic strength on the drainage kinetics was investigated with a 2 level experimental design. Milk was modified by a combination of ultrafiltration and dilution with a lactose solution. The pH at renneting had a negative effect on the amount of whey expelled in the early drainage (up to 100 min) and a positive one after 400 min. The effect of the casein concentration was negative on the amount of whey expelled and on the rate of drainage. The ionic strength had a slight positive effect on drainage. An equation was obtained allowing the prevision of whey drainage kinetics according to the milk composition. Calculated values fit experimental data with a correlation coefficient of $r = 0.994$.; Caractérisation des cinétiques d'égouttage au cours de la fabrication d'un fromage type pâte molle en relation avec les facteurs physico-chimiques et technologiques : effet du pH d'emprésurage, de la teneur en caséine et de la force ionique des laits. L'égouttage du fromage à pâte molle de type Camembert a été étudié à l'aide d'un prototype d'égouttage instrumenté qui permettait d'enregistrer le poids de sérum et son pH. Le coefficient de variation était de 1,8 % pendant les 100 premières minutes et de 0,34 % à la fin de l'égouttage. Les cinétiques d'égouttage obtenues ont été ajustées à l'aide d'un modèle mathématique descriptif à deux phases. L'effet sur l'égouttage du pH à l'emprésurage et de modifications de la composition du lait, telle la concentration en caséine et la force ionique, ont été testés à l'aide d'un plan d'expérience à deux niveaux. La composition des laits était modifiée en combinant une concentration par ultrafiltration et une dilution par une solution de lactose. L'effet du pH sur le poids de sérum expulsé était négatif au début de l'égouttage puis devenait positif. L'effet de la concentration en caséine était négatif sur la quantité de sérum obtenue et sur la vitesse d'égouttage. La force ionique avait un léger effet positif sur l'égouttage. Une équation a été obtenue permettant de prévoir la cinétique d'égouttage en fonction de la valeur des trois facteurs étudiés. Les valeurs calculées s'ajustaient aux valeurs expérimentales avec un coefficient de corrélation $r=0,994$.

Gels from milk concentrates [milk and caseinate powder, ultrafiltration (UF) and microfiltration (MF)] and whey concentrates (UF) were obtained with high pressure (200 and 400 MPa, 10 and 30 min). The effects of protein concentration (66–114gkg −1 for milk and 97–127g kg −1 for whey), NaCl addition (0–8 g kg −1 ), sodium citrate addition (0–4 g kg −1 ) and pH (5.2–6.6 for milk and 7–9 for whey) were studied with a Box-Behnken design. Milk supplemented with casemate powder did not lead to gel formation by pressure. For UF or MF milk concentrates, a pH decrease towards 5.9 and a protein content increase led to firmer pressure-set gels. Gels of whey concentrates were obtained only at pH 9. A pressure increase from 200 to 400 MPa led to firmer gels, while a protein content increase did not.

Summary The role of thiol/disulphide exchanges during acid gelation of preheated milk was studied with milk samples with or without N-ethylmaleimide (NEM), a thiol-blocking agent, and acidified to pH 4 by the addition of glucono-delta-lactone at 20 °C. Active or total thiol groups, particle size with light scattering measurements in a dissociating solvent or by SDS-agarose electrophoresis were determined on acidified milk samples. Diffusing wave spectroscopy and rheology in low strain were applied during acidification of sample, while rheology in large strain was applied on final acid gels. The only effect of the presence of NEM was a reduced firmness of acid gels as measured at large strain and a reduced tendency to form large aggregates at pH

This study aimed to determine the kinetics of milk protein digestion and amino acid absorption after ingestion of four dairy matrices by six minipigs: unheated or heated skim milk and corresponding rennet gels. Digestive contents and plasma samples were collected over a 7 h-period after meal ingestion. Gelation of milk slowed down the outflow of the meal from the stomach and the subsequent absorption of amino acids, and decreased their bioavailability in peripheral blood. The gelled rennet matrices also led to low levels of milk proteins at the duodenum. Caseins and b-lactoglobulin, respectively, were sensitive and resistant to hydrolysis in the stomach with the unheated matrices, but showed similar digestion with the heated matrices, with a heat-induced susceptibility to hydrolysis for b-lactoglobulin. These results suggest a significant influence of the meal microstructure (resulting from heat treatment) and macrostructure (resulting from gelation process) on the different steps of milk proteins digestion.

SummaryPreparation, physicochemical characterization and stability of iron-supplemented caseins were studied. When ferrous iron (final concentrations of 0·25, 0·5, 1·0 and 1·5 mM) was added to sodium caseinate (final casein concentration 25 g/l), iron binding to caseins was complete. In parallel, an increase in absorbance at 280 nm, a decrease in fluorescence intensity, modifications of reversed-phase HPLC profile, a decrease in pH and an increase in free sodium concentration were observed. Moreover, no release of iron from iron-casein complexes was found between pH 6·5 and 3·7 or after heat treatments or in the presence of inorganic phosphate. Only EDTA disodium salt and trisodium citrate had significant effects on the release of iron bound to caseins.

L'effet du pH sur les evolutions physicochimiques de suspensions de micelles de caseine, ainsi que sur les temps de coagulation presure, a ete etudie sur une poudre de phosphocaseinate natif reconstituee dans de l'eau, une solution 0,1 mol L -1 en NaCI et un ultrafiltrat de lait. L'augmentation de force ionique entre l'eau et NaCl provoque une augmentation des teneurs en calcium et en phosphore diffusibles, une plus grande voluminosite des micelles, et une augmentation de la solubilisation des caseines et des mineraux intervenant lors de l'acidification. La solubilisation du phosphocaseinate natif dans l'ultrafiltrat conduit a un comportement proche du lait. L'acidification peut etre divisee en cinq phases successives. Les relations entre les evolutions physicochimiques sont discutees, ainsi que la diminution des temps de coagulation presure avec la baisse du pH et de la force ionique.

The formation of whey protein complexes during heating enhances the acid gelation of milk; hydrophobic interactions may play an important role in this acid gelation. To investigate this, the surface hydrophobicity of model heat-induced whey protein complexes was modified using acylation with various carbon chain lengths. It was determined that the size and thiol/disulfide distribution of the complexes were unaffected, and that the change in their apparent isoelectric point could be restricted within 0.5 pH unit. These complexes were added to whey protein-free skim milk systems and the resulting acid-gelation behaviour of the milk samples was measured. Increasing the hydrophobicity of the heat-induced whey protein complexes significantly increased the pH of gelation of the milk samples and strongly affected the final properties of the acid gels, demonstrating both the importance of the heat-induced complexes and the relevance of hydrophobic interactions in the acid-induced gelation of preheated milk.

The diffusion of small solutes in cheese is of key importance for most enzymatic reactions involved in the ripening process. However, only a limited amount of data is available on salt diffusion and practically none on peptide diffusion. Nisin, a bacteriocin peptide, migrated in model cheeses made from ultrafiltered (UF) retentate. A profile concentration device and an enzyme-linked immunosorbent assay (ELISA), specifically developed for nisin quantification in cheese, were used to model the apparent diffusion coefficients for nisin according to Fick's law. This average coefficient was 49.5 μm(2)/s in UF cheese (n = 2). When 10% gelatin was added to the retentate, this value decreased to 34.4 μm(2)/s (n = 2). The two cheeses differed in their macrostructure (rheology) and microstructure (confocal microscopy). This study provides the first apparent diffusion coefficients for a peptide in cheese and supports the hypothesis that composition and structure influence the diffusion of small solutes such as peptides.

The heat treatment of milk greatly improves the acid gelation of milk and is therefore largely applied in yoghurt manufacture. During the heat treatment, soluble and micelle-bound whey protein/κ-casein complexes are produced in milk. The complexes and their physico-chemical properties have been held responsible for the early gelation point, the increased final firmness and for the serum retention capacity of the acid gels made of heated milk. They are suspected to bring new functionalities to the casein micelles and to help the formation of interactions when building the gel network. In order to investigate the type of interactions that the complexes can affect throughout the acid gelation of milk, an original strategy would be to control the physico-chemical properties of the whey protein/κ-casein soluble complexes and to use them as vectors to modify the possible interactions in the milk. In that perspective, the different physico-chemical properties of the whey protein/κ-casein soluble complexes that are thought to significantly affect the acid gelation behaviour of the casein micelles are listed. Then, the physical, chemical and biological means that could possibly be applied to the formation of complexes in order to modulate each of the targeted property are reviewed and evaluated. In order to open a large choice for future investigation, these methods were found in a larger literature resource than milk, including other protein systems like model whey protein solutions or non-dairy globular protein systems. The food-compatible character of some of these means is indicated, for their potential technological interest.

Heat treatment of milk at 85–95 °C has long been reported to increase the pH of gelation and firmness of acid milk gels; hence its wide application in yoghurt manufacture. These changes have been attributed to the formation of heat-induced whey protein/κ-casein complexes in the milk, to which heat-denatured whey protein ingredients may be substituted. However, variations in resulting gels show that a possible role of κ-casein in determining the functional acid-gelation property of the complexes needs investigating. Model heat-induced whey protein/κ-casein complexes were produced of κ-casein content from 0 to 40% (w/w), but of similar size, secondary structure, surface hydrophobicity and thiol/disulphide distribution. These complexes were added to whey protein-free skim milk systems and the resulting acid-gelation behaviour of the milks was evaluated. The results showed a modification of the pH of gelation that was explained more by variation of the pI of complexes than by the κ-casein content.

Separation and size measurement of protein particles are a relevant approach to monitor heat-induced changes in skim milk. Unfortunately, no method is currently available at low cost and without excessive preparation of the samples. Therefore, the present study aimed at evaluating the interest of asymmetrical flow field-flow fractionation (AFlFFF) coupled with multiangle laser light scattering (MALLS) for this purpose. Unheated and heated skim milk samples at pH 6.5 and 7.2 were prepared and comparatively analyzed using AFlFFF-MALLS, size exclusion chromatography (SEC-MALLS) and dynamic light scattering. The results showed that AFlFFF could evidence the conversion of the native whey proteins of unheated milk into heat-induced whey protein/κ-casein complexes in the serum phase of milk and possibly on the surface of the casein micelles. The pH-induced changes in the partition of the complexes between the serum and the micellar phases could also be observed. The results therefore showed the interest of AFlFFF-MALLS to monitor the heat-induced changes in particle sizes in skim milk and to separate the different protein components of unheated and heated skim milk.

The effect of heat treatment of milk on the formation of acid gel was examined using confocal scanning laser microscopy and low-amplitude dynamic oscillation throughout acidification. Milk samples were reconstituted by mixing colloidal phase from unheated or preheated skim milk, labeled with rhodamine B isothiocyanate, with the aqueous phase from unheated or preheated milk, labeled with fluorescein isothiocyanate. Gels were made by acidification with glucono-delta-lactone. The presence of material from preheated milk, that is, either the colloidal or the aqueous phase or both, led to an increase in the gelation pH and in the final elastic modulus and to a more branched network with larger pores. During acidification, the heat-induced serum complexes and the casein micelles did not appear to form separated gels with time or in space. Moreover, the colocalization in the final network of serum heat-induced complexes and casein micelles is particularly well observed in the presence of an aqueous phase obtained from preheated milk. Finally, because the rheological and microstructural properties of acid gels containing either micelle-bound or serum heat-induced complexes were similar, it was suggested that the serum heat-induced complexes interacted with the casein micelles early in the course of acidification and that formation of the network did not differ significantly whether the heat-induced complexes were initially found in the aqueous phase of milk or bound to casein micelles.

Casein micelle dispersions have been concentrated through osmotic stress and examined through rheological experiments. In conditions where the casein micelles are separated from each other, i.e., below random-close packing, the dispersions have exactly the flow and dynamic properties of the polydisperse hard-sphere fluid, demonstrating that the micelles interact only through excluded volume effects in this regime. These interactions cause the viscosity and the elastic modulus to increase by three orders of magnitude approaching the concentration of random-close packing estimated at Cmax[approximate]178 g/l. Above Cmax, the dispersions progressively turn into “gels” (i.e., soft solids) as C increases, with elastic moduli G[prime] that are nearly frequency independent. In this second regime, the micelles deform and/or deswell as C increases, and the resistance to deformation results from the formation of bonds between micelles combined with the intrinsic mechanical resistance of the micelles. The variation in G[prime] with C is then very similar to that observed with concentrated emulsions where the resistance to deformation originates from a set of membranes that separate the droplets. As in the case of emulsions, the G[prime] values at high frequency are also nearly identical to the osmotic pressures required to compress the casein dispersions. The rheology of sodium caseinate dispersions in which the caseins are not structured into micelles is also reported. Such dispersions have the behavior of associative polymer solutions at all the concentrations investigated, further confirming the importance of structure in determining the rheological properties of casein micelle systems. ©2009 American Institute of Physics

Abstract – This study aimed at understanding the role of colloidal calcium phosphate (CCP) in acid gelation of milk. Milks were depleted in Calcium (Ca) by dialysis against milk permeate containing a cation-exchange resin. Dialysed milks were then heated (90 °C-10 min) and acidgelled at 42 °C with a yoghurt culture. Minerals, total and soluble protein contents, pH and optical density were measured in unheated and heated dialysed milk, together with diameters and ζ-potentials of particles. Dialysis of milk led to a dissociation of 45% total Ca and 30% total phosphorus, to an increase in sodium content and pH of milk, to lower turbidity and ξ-potential, but did not change the casein particle size. Soluble Ca and casein-bound Ca were removed from milk, CCP being removed increasingly, while Ca removed from the phosphoserine residues increased very little during the dialysis experiments. Maximal dissociation of αs1- and αs2-casein was 20%, while that of β- and κ-casein was 35–40% of total at the end of dialysis, and it increased after heating, especially for κ-casein. The pH value at which the milk sample begins to gel increased for low mineral depletion rates but decreased for higher depletion levels. This was due to the increase in the pH value of milk and in the κ-casein dissociation. The elastic modulus decreased in samples at the lowest depletion and then levelled off, which suggested that the phosphoserine-bound Ca played a critical role in the formation of acid gels.

The rheological properties of stirred yoghurt were studied as a function of the delay between milk heat-treatment and inoculation (0, 1 and 2 days), of pH in the acid gel on stirring (4.4, 4.7, and 5.0), of the storage temperature (4, 12, and 20 °C) for 24 h following stirring and of over-acidification (allowed or inhibited). At low pH values, the gels exhibited higher elastic modulus ( G ′) and fracture strength. They yielded stirred yoghurts with higher G ′ and viscosity, and higher increase in G ′ and viscosity during storage (“rebodying”). Rebodying was only partially explained by over-acidification and cooling. Changing the storage temperature had no impact on the evolution of G ′ after stirring; hydrophobic interactions were therefore probably not involved in rebodying. Electrostatic interactions seemed to play a major role in rebodying, as pH on stirring was the significant factor.

In the first part of the paper (Floury, J., Camier, B. Rousseau, F., Lopez, C., Tissier, J. P., & Famelart, M. H. (2009) Reducing salt level in food: Part 1. controlled manufacture of model cheese systems and their structure-texture relationships. LWT – Food Science and Technology 49(10) , 1611–1620), a model cheese matrix presenting different textural properties was developed in order to further study the factors implied in the salt release in mouth during food chewing. The present work consists in physical and modelling approaches to better understand the mass transfer phenomena occurring in the product during its consumption in the mouth. Concentration profiles of several ionic species were measured during the release of salt from the different model matrices into artificial saliva. Apparent diffusion coefficients of the sodium chloride were determined by fitting the experimental data to the second Fick's law. Apparent diffusion coefficients were included between 2.81 and 3.43 × 10 −10 m 2 s −1 at 15 °C and 75% HR. D -value decreased strongly when the dry matter content decreased. Microstructure of the matrices with the lower protein concentration was coarser and fluffier, facilitating the diffusion of the solutes. The D -value increased with the pH at renneting, probably because of the chemical changes of the structure of the casein micelles and significant differences in textural characteristics of cheeses. The diffusion coefficient also significantly decreased with the initial salt concentration, due to the tightening of the matrix microstructure.

Abstract – The aim of this study was to compare the rheological properties of stirred acid milk gels, acidified using two different acidification procedures. Pre-heated milks were acidified either by means of glucono-δ-lactone (GDL gel) at 20 ◦C or by incubation with lactic acid bacteria (lactic gel)at 38 ◦C. The latter procedure gave a harder acid set gel with a more heterogeneous structure. Once formed, the gels were filtered and stirred, then immediately characterised using the low-amplitude dynamic oscillation method for 20 h at 4 ◦C or creep measurement at 4 ◦C. The stirred gels were stored at 4 ◦C for 28 d, during which the pH and the viscosity at 64 s−1 were measured. After stirring, the lactic gel made at 38 ◦C had a higher instantaneous elastic modulus, a higher viscosity and showed a greater increase in the elastic modulus over 20 h compared with the stirred GDL gel. The viscosity of both stirred gels progressively increased during storage at 4 ◦C, but that of GDL acidified gels increased 3.5 times more than that of lactic gels. The procedure used to prepare the set acid gels had notable effects on the interactions formed within 20 h and 28 d of storage of stirred gels.

The aim of the present study was to identify the nature of bonds established between protein particles after stirring that are responsible for the texture improvement of stirred yoghurts, called rebodying. Using a constant model yoghurt at pH 4·4, the effects of changes in the physicochemical conditions at stirring were studied on the subsequent rebodying. Short term rebodying was measured as the changes in viscoelastic properties at 4°C during 20 h after stirring, while long-term rebodying was measured as the viscosity changes during 28 d storage at 4°C. Moreover, stirred gels obtained from either set gels that were allowed time or not for ionic equilibration were compared. Increasing or decreasing ionic strength did not change the properties of stirred gels. Calcium chloride addition significantly decreased G′0 h, G′20 h and tan20 h but did not induce changes in the gel microstructure as observed by confocal scanning microscopy. Yoghurt rebodying could not be explained by fulfilling ionic equilibrium. Moreover, N-ethyl maleimide addition had no effect on the stirred yoghurt. Attractive electrostatic and disulphide interactions were not involved in the gel rebodying and increasing calcium concentration in the set gel limited rebodying.

International audience; Emmental cheeses were produced with control native milk fat globules (CFG) or smaller ones (SFG) selected from the same milk by microWltration. Either the same regular technology was used for both cheeses (so-called SFGreg and CFGreg), or two diVerent adapted technologies to obtain cheeses with the same moisture (so-called SFGadapt and CFGadapt). SFGreg cheeses were more humid and presented lower Wrmness and longness than CFGreg cheeses. Yellow index was greater for SFGadapt than CFGadapt cheeses while melting coeYcient and extrusion force were similar. SFGadapt cheeses exhibited improved sensory characteristics. Stretching and elasticity increase were always greater for SFG than for the corresponding CFG cheeses; eyes were always smaller in SFG cheeses. Confocal micrographs revealed larger inclusions of non-globular fat in CFG cheeses; there were more fat globules and aggregates in SFG cheeses. The ultrastructure of milk fat played a role in the functional and sensory properties of Emmental cheese and the use of smaller native globules may be advantageous.

The effects of heat treatment and limited kappa-casein hydrolysis on the micelle/serum distribution of the heat-induced whey protein/kappa-casein aggregates were investigated as a possible explanation for the gelation properties of combined rennet and acid gels. Reconstituted skim milk was submitted to combinations of 0-67% hydrolysis of the kappa-casein at 5 degrees C and heat treatment at 90 degrees C for 10 min. The protein composition of the ultracentrifugal fractions was obtained by reverse-phase high-performance liquid chromatography (RP-HPLC). The aggregates contained in each phase were isolated by size-exclusion chromatography and analyzed by RP-HPLC and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Upon heating only, 20-30% of the total kappa-casein dissociated, while 20-30% of the total whey protein attached to the micelles. When heated milk was renneted, little changes were observed in the distribution and composition of the aggregates. Conversely, the heat treatment of partially renneted milk induced the formation of essentially micelle-bound aggregates. The results were discussed in terms of the preferred interaction between hydrophobic para-kappa-casein and denatured whey proteins.

peer-reviewed This paper takes a new approach to determining which sulfhydryl groups are exposed during the heat denaturation of bovine β-lactoglobulin A. The sulfhydryl groups exposed after heating were blocked with 5-((((2-iodoacetyl)amino)ethyl)amino)naphthalene-1-sulfonic acid (IAEDANS). The results show that IAEDANS is a suitable blocking agent, and its absorbance at 336 nm enabled the quantification of exposed sulfhydryl groups in a mixture of protein species by gel permeation chromatography. Combined with the specific fragmentation of bound IAEDANS by matrix-assisted laser desorption ionization (MALDI) MS/MS in negative ionization mode, this facilitated the identification of peptides that contained blocked cysteines after enzymatic digestion of the protein. During MALDI MS/MS of the peptides, in positive ionization mode, the IAEDANS molecule remained bound to the cysteines, making it possible to identify exactly which cysteine had been exposed after heating. In β-lactoglobulin A it was found that cysteine 66 and cysteine 160 were predominantly exposed regardless of the length of exposure to heat. Travel costs associated with exchanges of scientists between the authors’ laboratories were co-funded by the Enterprise Ireland / French Ministry for Foreign Affairs Ulysses Exchange Research Program. The cost of project work was supported by the Food Institutional Research Measure (FIRM) of the National Development Plan 2000-2006 (Ireland). J. Kehoe was funded by the Teagasc Walsh Fellowship Scheme

– In an attempt to improve the acid gelation properties of heated milk, or to reduce the heat load necessary to obtain significant acid gelation properties, skim milk adjusted at pH values ranging from 6.7 to 10.5 was heat-treated for 10 min at temperatures ranging from 25 to 95 °C then neutralised to pH 6.7. Protein composition of the serum and micellar phases of milk and separation of the protein particles present in the serum phase of milk indicated that formation of micelle-bound heat-induced whey protein/κ-casein aggregates was prevented from pH 7.5 upward, to the benefit of serum aggregates. Aggregates were formed in milk at pH 9.5 and 10.5 even at mild heating temperature (65–75 °C), while temperatures of 85 or 95 °C were necessary at lower pH values. Size of the aggregates decreased as pH of heat-treatment increased. Quality of the results was however reduced because of the extensive dissociation of caseins on alkaline treatment and of side mechanisms like Maillard reaction at high pH and temperature. However, some relationships could be found between the occurrence of aggregated whey protein and κ-casein and higher elastic modulus of the acid gels after heating at low temperature/high pH or high temperature/low alkaline pH values of skim milk.; Dans l'objectif d'améliorer l'aptitude à la gélification acide du lait traité thermiquement ou de réduire la charge thermique nécessaire à l'obtention d'une aptitude significative, du lait écrémé a été ajusté à des pH variant de 6,7 à 10,5, traité thermiquement pendant 10 min à des températures variant de 25 à 95 °C puis neutralisé. La composition en protéines des phases sérique et micellaire du lait et la séparation des particules présentes dans le sérum indiquaient que la formation d'agrégats thermo-induits de protéines sériques et de caséine k dans la fraction micellaire est inhibée à pH S 7,5 au profit des agrégats sériques. Des agrégats étaient formés à pH 9,5 et 10,5 dès 65 °C, tandis que des températures de 85 ou 95 °C étaient nécessaires à pH moins élevé. La taille des agrégats était inversement proportionnelle au pH de traitement thermique. La qualité des résultats était cependant médiocre du fait de la dissociation importante des caséines à pH alcalin et de la dégradation des protéines à pH et températures élevés (e.g. réaction de Maillard). Cependant, une relation entre la présence d'agrégats et les qualités rhéologiques des gels acides formés a pu être identifiée à basse température/pH élevé et à haute température/pH modéré.

Changes in the acid gelation properties of skim milk as a result of variations in the micelle/serum distribution of the heat-induced whey protein/kappa-casein aggregates, induced by the combination of heat treatment and limited renneting, were investigated. No dramatic change in the zeta potential or the isoelectric point of the casein micelles was suggested, whether the aggregates were all attached to the casein micelle or not. Fluorescence intensity measurement using 8-anilino-1-naphthalenesulfonic acid (ANS) showed that the heat-induced aggregates were highly hydrophobic. Dynamic oscillation viscosimetry showed that acid gelation using glucono-delta-lactone (GDL) started at a higher pH value in prerenneted milk. However, no change in the gelation profile of skim milk could be related to the proportion of aggregates bound to the surface of the casein micelles. The results support the idea of an early interaction between the serum aggregates and the casein micelles on acidification.

Serum heat-induced milk protein aggregates were isolated from heated skim milk. Protein analysis showed that the aggregates were essentially composed of whey protein and κ -casein linked mainly by disulfide bridges. The hydrodynamic diameter of the aggregates, as measured by dynamic light scattering (DLS), was about 70 nm. Multi-angle DLS analysis and electron microscopy indicated that they were almost of spherical shape. Measurement of the turbidity, size and zeta potential of the aggregates in milk permeate at pH 2–9 showed that their apparent isoelectric point was ∼4.5. Surface charge in milk permeate at pH 7.0 was −17 mV. 8-anilino-1-naphthalene sulphonic acid (ANS)-binding indicated that surface hydrophobicity of the aggregates was higher than those of native casein micelles, which suggested that their precipitation on acidification may be initiated before reaching pH 4.5.

The atomization stage in spray drying of a liquid requires a spray of droplets with a high surface-to-mass ratio. Dried products that result from moisture evaporation of atomized spray can be prepared to reach the desired particle size distribution through control of atomization variables. To meet these requirements, many atomization techniques such as pressure nozzles, two-fluid nozzles and rotary atomizers have been used in spray dryers. Many authors have proposed various relationships between droplet size, physical properties (e.g. viscosity of concentrate) and technological parameters (e.g. nozzle pressure). To optimize the moisture content in milk powder, it is necessary to control the thermodynamic parameters of the drying air, the conditions of the atomization and the properties of the concentrate. Droplet size varies in direct relationship with viscosity to the power of 0.17-0.25. There are, in fact, two possible solutions for measuring online viscosity: either an on-line viscometer (direct measurement) or measurement of the amperage of the concentrate extraction pump (indirect measurement). The aim of this study was therefore to develop an indirect method to estimate the viscosity of a concentrate after concentration by filtration or vacuum evaporation and before spray drying. For example, while varying the viscosity of different dairy products (concentrated whey, and whole and skim milk) by changing the parameters of concentration by vacuum evaporation, we obtained a very good correlation between concentrate viscosity and the extraction pump amperage, whatever the product. Concentration parameters can be modified during evaporation to obtain a concentrate of the same viscosity, whatever its temperature or total solid content, just by following the extraction pump amperage., Suivi de la viscosité des concentrés en fonction de l'ampérage. L'étape de pulvérisation de liquide dans le séchage par atomisation exige la formation de gouttelettes ayant un rapport surface / masse élevé. Pour obtenir une taille de poudres maîtrisée, on fait varier les paramètres de séchage des poudres laitières résultant de l'évaporation de l'eau des gouttelettes créées lors de l'atomisation. Plusieurs techniques de pulvérisation peuvent être utilisés pour la création de gouttelettes, tels que l'atomisation par buses haute pression, par buses bi-fluide ou par turbine. De nombreux auteurs ont proposé des relations entre la taille des gouttelettes, les propriétés physiques (telles que la viscosité) et les paramètres technologiques (tels que la pression de pulvérisation). Pour optimiser la teneur en eau dans les poudres, il est nécessaire de contrôler les conditions d'atomisation, les paramètres thermodynamiques de l'air de séchage ainsi que les propriétés du concentré. La taille des gouttelettes varie directement avec la viscosité à la puissance 0,17-0,25. En fait, il existe deux possibilités pour mesurer la viscosité en ligne, soit à l'aide d'un viscosimètre (méthode directe) ou soit par la mesure de l'intensité de la pompe d'extraction (méthode indirecte). L'objectif de ce travail est de développer une méthode indirecte pour estimer la viscosité du concentré après concentration par filtration ou par évaporation sous vide et avant séchage. Par exemple, en faisant varier la viscosité de trois produits laitiers (lactosérum, lait entier et lait écrémé) par variation des paramètres de concentration par évaporation sous vide, nous obtenons une bonne corrélation entre la viscosité du concentré et l'ampérage de la pompe d'extraction quel que soit le produit. Ainsi, les paramètres de concentration pourront être modifiés au cours de l'évaporation afin d'obtenir un concentré à même viscosité quelle que soit sa température ou sa teneur en matière sèche, en suivant uniquement l'ampérage de la pompe d'extraction.

The pH-dependent behaviour of soluble protein aggregates produced by the pre-heating of reconstituted skim milk at 90 degrees C for 10 min was studied, in order to understand the role of these aggregates in acid gelation of heated milk. The following milk samples were prepared: (1) control (unheated reconstituted milk, pH 6.5); (2) milk heat-treated at pH 6.5 (mHtd6.5) and (3) milk heat-treated at pH 7.2 (mHtd7.2). They were centrifuged and the supernatants (SPNT 1) pH-adjusted to yield a series of pH values ranging from 6.5 or 7.2 to 4.6 using HCl at 20 degrees C or GDL at 20 and 38 degrees C. pH-Adjusted SPNTs 1 were re-centrifuged. The resulting supernatants (SPNTs 2) were analysed by OD (at 600 and 280 nm) and SDS-PAGE in order to characterise proteins still soluble as a function of pH. Particle size in SPNTs 1 was analysed by Steric Exclusion Chromatography. The OD600 nm revealed that during acidification soluble casein in both control and heat-treated samples exhibits variations in its optical properties or size as previously shown with micellar casein. In heat-treated samples, soluble casein and heat-induced covalent soluble aggregates precipitate at the same pH value. A progressive acidification of the soluble phase did not separate them. Increasing the temperature of acidification from 20 to 38 degrees C resulted in an increase in the precipitation pH of the proteins. However choice of acidifier did not have a significant effect on OD profiles. The soluble covalent aggregates from mHtd7.2 were smaller, more numerous, and had a higher content of kappa-casein than mHtd6.5. Both types of aggregates began to precipitate at the same pH value but precipitation occurred over a narrower pH-range for soluble aggregates prepared from mHtd7.2. This may explain the higher gelation pH of mHtd7.2 compared with mHtd6.5.

International audience; Camembert cheeses were produced using either small (~3 mm, SFG) or large (~6 mm, LFG) native milk fat globules obtained by a patented microfiltration process. The composition of the cheese milk did not depend on the fat globule size. Less whey was extracted from the SFG cheeses, that subsequently contained more moisture than LFG cheeses throughout the ripening period. The SFG curds were less rigid and less firm than the LFG ones and underwent greater proteolysis during ripening. Camembert cheeses with small fat globules had a higher melting and elastic texture, a higher flowing aspect and were less yellow. The results were explained (i) by the greater surface area of native milk fat globule membrane for SFG vs. LFG, at a given fat content, and (ii) by the thinner casein strands in SFG cheeses due to the smaller interglobular distance. The use of native milk fat globules with different sizes can thus lead to new products with different technological and sensory properties.; Des propriétés physico-chimiques et sensorielles du Camembert sont affectées par la taille des globules gras natifs du lait. Des camemberts ont été fabriqués en utilisant des globules gras natifs du lait de petit diamètre (~3 mm) ou de grand diamètre (~6 mm), obtenus par un procédé de microfiltration breveté. La composition des laits de fromagerie ne dépend pas de la taille des globules gras. Il s'égoutte moins de sérum des camemberts à petits globules, qui sont ensuite plus humides que les fromages à gros globules au cours de l'affinage. Les caillés à petits globules sont moins fermes et moins rigides que ceux à gros globules et sont plus protéolysés durant l'affinage. Les camemberts à petits globules ont une texture plus fondante et plus élastique, sont plus coulants et moins jaunes. Ces résultats peuvent être expliqués (i) par la plus grande surface de membrane native pour les petits globules par rapport aux gros globules à une teneur donnée en matière grasse et (ii) par la moindre épaisseur des brins de caséine dans les camemberts à petits globules, à cause de la plus faible distance moyenne entre globules. L'utilisation de globules gras natifs du lait de différentes tailles peut donc aboutir à de nouveaux produits présentant des propriétés technologiques et sensorielles différentes.

Solutions of 100 g $\cdot$kg -1 of $\beta$-lactoglobulin ( $\beta$-Lg), $\beta$-Lg + $\alpha$-lactalbumin ( $\alpha$-La), $\beta$-Lg + $\alpha$-La + bovine serum albumin (BSA) or whey protein isolate (WPI) were heated at 75 °C, pH 6.8 in water and in the presence of either 100 mmol $\cdot$L -1 NaCl or 10 mmol $\cdot$L -1 CaCl 2. The subsequent polymerisation-aggregation processes in solution before gelation and the physical properties of the formed gels were determined. The disappearance of native-like proteins, formation of $\beta$-Lg covalent dimer and the nature of the interactions involved in the formed aggregates were addressed. Whatever the protein system, both NaCl and CaCl 2 increased gel strength and decreased gelation time. At gelling time, relatively small aggregates, formed by the contribution of the total initial amount of proteins, were observed in samples without added salts. In contrast, with NaCl or CaCl 2, only part of the initial amount of proteins was aggregated before gel time. Very large aggregates were formed in the presence of calcium. Under these two mineral conditions, as well as in samples without added salt, covalent disulphide bonds were seen to be the major forces involved in the aggregation process at gel time., Modulation de l'agrégation et de la gélification des protéines de lactosérum par les minéraux : de la $\beta$-lactoglobuline pure à l'isolat de protéines sériques. Des gels de différentes solutions de protéines ( $\beta$-lactoglobuline ( $\beta$-Lg), $\beta$-Lg + $\alpha$-lactalbumine ( $\alpha$-La), $\beta$-Lg + $\alpha$-La + sérum albumine bovine (BSA), isolat de protéines sériques) à 100 g $\cdot$kg -1 étaient formés à pH 6.8 dans l'eau ou dans 100 mmol $\cdot$L -1 NaCl ou 10 mmol $\cdot$L -1 CaCl 2. Les propriétés physiques des gels ainsi que les réactions d'agrégation des protéines (disparition des protéines natives, formation de dimères covalents de $\beta$-Lg et nature des liaisons entre protéines agrégées) ont été étudiées. Le NaCl et le CaCl 2 augmentent la force des gels et diminuent les temps de gel (tg). Au tg, sans ajout de sels, les agrégats formés, de petites tailles, impliquent la totalité des protéines présentes en solution. En revanche, en présence de NaCl ou de CaCl 2, seule une partie des protéines est impliquée dans la formation des agrégats au tg. La taille des agrégats formés est plus élevée en présence de CaCl 2. Dans toutes les conditions, les ponts disulfures interprotéiques semblent être les liaisons majoritairement impliquées dans la formation des agrégats au tg.