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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.

The Maillard conjugation of proteins and reducing saccharides is used to modify the technological functionality of whey proteins. In this study, whey protein isolate (WPI) was conjugated with maltodextrin (at 1:1 ratio and two total solid contents of 100 and 200 mg mL−1) through the Maillard reaction and used to form cold-set gels. The glycation reaction increased the strength of hydrogen bonding of whey proteins and preferentially modified α-lactalbumin, in comparison with β-lactoglobulin. It also increased the reducing power of binary protein-saccharide solution and allowed formation of self-standing cold-set WPI gel at a low protein content (i.e., ≈50 mg mL−1). Microscopic imaging showed micro-phase separated maltodextrin domains, interrupting the protein network, in gels made of protein-maltodextrin physical mixtures, whereas Maillard conjugation resulted in more homogenous microstructures at both total solid contents. The Maillard reaction increased gel firmness and water-holding capacity and caused a reduction in the extent of gel swelling.

International audience; Heat treatments induce changes in the protein structure in infant milk formulas (IMFs). The present study aims to investigate whether these structural modifications affect protein digestion. Model IMFs (1.3% proteins), with a bovine or a human whey protein profile, were unheated or heated at 67.5°C or 80°C to reach 65% of denaturation, resulting in six protein structures. IMFs were submitted to in vitro static gastro-intestinal digestion simulating infant conditions. During digestion, laser light scattering was performed to analyze IMF destabilization and SDS-PAGE, OPA assay and cation exchange chromatography were used to monitor proteolysis. Results showed that, during gastric digestion, α-lactalbumin and β-lactoglobulin were resistant to hydrolysis in a similar manner for all protein structures within IMFs (p > 0.05), while the heat-induced denaturation of lactoferrin significantly increased its susceptibility to hydrolysis. Casein hydrolysis was enhanced when the native casein micelle structure was modified, i.e. partially disintegrated in the presence of lactoferrin or covered by heat-denatured whey proteins. The IMF destabilization at the end of the gastric digestion varied with protein structures, with larger particle size for IMF containing native casein micelles. During intestinal digestion, the kinetics of protein hydrolysis varied with the IMF protein structures, particularly for IMFs containing denatured lactoferrin, exhibiting higher proteolysis degree (67.5°C and 80°C vs. unheated) and essential amino acid bioaccessibility (67.5°C vs. unheated). Overall, the protein structures, generated by modulating the whey protein profile and the heating conditions , impacted the IMF destabilization during the gastric phase and the proteolysis during the entire simulated infant digestion.

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.

International audience; In the industrialized world, dairy products constitute an important part of the diet, especially in northern Europe and North America. In these regions, milk products contribute around 30% of the total dietary protein supply and represent about 65% of the intake of animal protein. The protein content of cow’s milk ranges from 32 to 35 g/L. There are two major types of milk protein: the caseins (80%), which are represented by four distinct proteins (αs1-,αs2-, β-, and κ-caseins), and the whey proteins (20%), which are represented by proteins such as β-lactoglobulin, α-lactalbumin, and lactoferrin. These two families of proteins are opposite in terms of structure. Caseins exhibit a loose and highly flexible structure and are associated into a supramolecular structure called the micelle, whereas whey proteins have a globular, well-defined three-dimensional structure. These structural differences between the two families markedly affect the behavior of these proteins in the gastrointestinal tract and particularly their susceptibility to hydrolysis by the digestive enzymes. The nutritive value of proteins, including milk proteins, is generally associated with their capacity to provide two components: nitrogen (related to protein quantity) and essential amino acids (related to protein quality). The overall nutritional efficiency of protein is most commonly measured via nitrogen retention, which assesses protein retention. In terms of protein quality, the nutritive value is related to the amino acid composition and the bioavailability of these amino acids. The content and the bioavailability of indispensable amino acids, that is, those that cannot be synthesized in the body and consequently must be supplied through the diet, are of particular concern.

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.

Dehydration by spray drying is a valuable technique for water evaporation, using hot air to stabilize the majority of dairy ingredients. In view of the increased development of filtration processes, the dairy industry requires greater understanding of the effects of spray drying on the quality of protein powders. Several publications have reported that the proteins have an important role in the mechanisms of water transfer during drying and rehydration. The residence time of the droplet and then the powder is so short that it is very difficult to study the mechanisms of the structural change in the protein without fundamental research into relationships with the process/product interactions. Following an introduction to spray drying, this chapter on the effects of drying on milk proteins covers seven areas: the world dairy powder situation, the properties of spray-dried milk products, the principles of spray drying, drying of proteins, reactions of dried proteins during storage, the rehydration of dried protein powders, and the characterization of insolubility formation.

International audience; Hydrophobised whey protein particles were prepared through successive acetylation and heat treatment practices, and the particle characteristics were modulated by CaCl 2 supplementation. Then, the usefulness of the hydrophobised protein particles for emulsification of a docosahexaenoic acid-rich oil was compared with that of heat-denatured whey protein. Addition of CaCl 2 into hydrophobised whey protein resulted in smaller protein particles and lower z-potential and interfacial tension values. It also decreased the creaming stability of the consequent emulsions. It was argued that besides Ca 2þ-protein charge interactions, Cl e anions bind to the hydrophobised particles, and the Pickering stabilisation of oil does not rely on interfacial tension reduction. Compared with heat-denatured whey protein, hydrophobised whey protein afforded a lower protection to oil against oxidation; the peroxide value of the oil emulsified using hydrophobised protein was higher during storage.

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.

Part of special issue: The 5th International Conference on Food Digestion - Edited by Didier Dupont, Pasquale Ferranti, Alan Mackie 5. International Conference on Food Digestion (INFOGEST) ; Rennes (France) - (2017-04-04 - 2017-04-06) / Conférence; In the frame of the COST action INFOGEST, a static in vitro digestion protocol has been elaborated aiming at the improvement of data comparability by harmonizing the experimental conditions. The success in harmonization was confirmed with inter-laboratory trials using skim milk powder as a standardized model food. Moreover, the physiological relevance of the gastric and intestinal endpoints of the static digestion protocol was demonstrated in a pig in vivo trial, with the same skim milk powder and samples collected from different sections of the digestive tract, as well as in a human study with from jejunal effluents. In vivo, digestion is a dynamic process influenced by peristalsis and by the gradual secretion of enzymes and juices and the dwell time of the food. To mimic these physiological mechanisms, dynamic in vitro digestion protocols are widely used. Until now, the differences of protein hydrolysis taking place during dynamic and static in vitro digestion have not been investigated.In this study, the gradual hydrolysis of the main milk proteins present in skim milk powder was digested with the dynamic DIDGI®-system using adult digestion protocol and the static harmonized INFOGEST method. Protein hydrolysis was analyzed by gel electrophoresis, peptide patterns were measured with mass spectrometry, and free amino acids with high pressure liquid chromatography. The peptide patterns at the gastric and intestinal endpoints of in vitro digestion showed a good approximation to the in vivo results from pigs. Moreover, gradual peptide generation was comparable in both in vitro digestion conditions. However, the dynamic protocol reflected the physiological situation better at the level of free amino acid release. Nonetheless, in both in vitro digestion protocols, absorption of free amino acids is not simulated, and they are therefore limited in reflecting the in vivo situation at this level.

The rheological properties and microstructure of dairy gels involve the connectivity between milk fat globules (MFG) and casein micelles that is affected by technological processes such as milk homogenization and heat treatment. The underlying mechanisms require further quantification of the interactions at the nanoscale level to be fully understood and controlled. In this study, we examined the adhesion of homogenized MFG to milk proteins and evaluated the role of ultra-high temperature (UHT) heat treatment and pH. The combination of physico-chemical analysis, rheology and microscopy observations at different scale levels associated to atomic force microscopy (AFM) force spectroscopy were used. AFM experiments performed at the particle scale level showed that adhesion of individual homogenized MFG to milk proteins (1) is increased upon acidification at pH 4.5: 1.4 fold for unheated samples and 3.5 fold for UHT samples, and (2) is enhanced by about 1.7 fold at pH 4.5 after UHT heat treatment of milk, from 176 pN to 296 pN, thanks to highly-reactive heat-denatured whey proteins located at the surface of MFG and caseins. The increased inter-particle adhesion forces accounted for more connected structures and stiffer UHT milk acid gels, compared to unheated-milk gels. Using a multiscale approach, this study showed that heat treatment of milk markedly affected the interactions occurring at the particle’s surface level with consequences on the bulk structural and rheological properties of acid gels. Such findings will be useful for manufacturers to modulate the texture of fermented dairy products through the tailoring of heat-induced complexation of proteins and the connectivity of homogenized MFG with the protein network. This work will also contribute in a better understanding of the impact of process-induced changes on the digestibility and metabolic fate of proteins and lipids.

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.

Raw Milk: Balance Between Hazards and Benefits provides an in-depth nutritional and safety analysis of raw milk. This high-quality reference is comprised of contributions from global researchers highly specialized in the field. The book is divided into five sections that address the characteristics of raw milk, production guidelines and concerns, the benefits and hazards of raw milk, and the current market for raw milk. Topics include production physiology and microbiology, rules and guidelines for production, the world market for raw milk and its products, and consumer acceptance. A final section identifies future trends and research needs related to raw milk. Provides current information related to raw milk’s characteristics Presents worldwide coverage of raw milk production and government guidelines Addresses the benefits and hazards related to raw milk consumption Analyzes the worldwide economic impact of raw milk production and consumption

Beyond nutrient composition matrix plays an important role on food health potential, notably acting on the kinetics of nutrient release, and finally on their bioavailability. This is particularly true for dairy products that present both solid (cheeses), semi-solid (yogurts) and liquid (milks) matrices. The main objective of this narrative review has been to synthesize available data in relation with the impact of physical structure of main dairy matrices on nutrient bio-accessibility, bioavailability and metabolic effects, in vitro, in animals and in humans. Focus has been made on dairy nutrients the most studied, i.e., proteins, lipids and calcium. Data collected show different kinetics of bioavailability of amino acids, fatty acids and calcium according to the physicochemical parameters of these matrices, including compactness, hardness, elasticity, protein/lipid ratio, P/Ca ratio, effect of ferments, size of fat globules, and possibly other qualitative parameters yet to be discovered. This could be of great interest for the development of innovative dairy products for older populations, sometimes in protein denutrition or with poor dentition, involving the development of dairy matrices with optimized metabolic effects by playing on gastric retention time and thus on the kinetics of release of the amino acids within bloodstream.

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.

International audience; Infant formulas (IFs) can be defined as substitutes for human milk, which are mostly based on cow milk proteins. For sustainability reasons, alternative to animal proteins in food have to be considered. Plant proteins offer interesting nutritional and functional benefits for the development of innovative IFs. However, the behaviour of these proteins during processing and storage must ensure the physical stability and ability to reconstitution of IF powders, and that needs to be tested. This work aimed to study how a partial substitution of dairy proteins by plant proteins may influence the functional properties of 1st age IFs. Three IFs were developed at a semiindustrial scale using two different processing routes. The IFs composition was identical, except that 50% of the proteins were whey proteins in the “reference IF” (RIF), and pea or faba bean proteins in the “plant IFs” (PIF and FIF, respectively). After reconstitution, the three IFs result in similar stable emulsions with equivalent free fat release. In comparison to RIF, PIF and FIF were difficult to disperse, conducting to remaining insoluble particles. Thus, the protein source greatly influences IFs properties, and process parameters need to be adapted for each formulation to meet IFs quality criteria.

International audience; Lactose hydrolyzed milk powder production remains a challenge for the dairy industry because of specific technological problems, such as stickiness and caking during drying. The molecular mechanisms that lead to these problems are poorly understood. The aim of this study was to provide a better understanding of how galactose and glucose affect the organization and physicochemical behavior of milk powder molecules. In order to do so, we analyzed the organization and dynamics of lactose hydrolyzed milk powder particles after lactose hydrolyzed milk had been processed under anti-caking conditions. In general, the structure of the lactose hydrolyzed milk powder sample was characterized by a greater number of monosaccharides around proteins compared to those found in the lactose of a traditional milk powder sample. This difference can be explained by a combination of greater repulsive interactions between proteins as well a stronger attractive interaction between proteins and monosaccharides. Our data indicated that this difference in the molecular organization impacted milk powder’s hydration kinetics.

The antibacterial activity of camel milk b-casein and its peptic hydrolysate was investigated. The hydrolysatewas fractionated by ultrafiltration successively through membranes with a 10 kDa and a 1 kDacut-off, sequentially. Antibacterial activity assays against Staphylococcus aureus CNRZ 3, Listeria innocuaATCC 33090 and Escherichia coli ATCC 25922 were performed. The growth of S. aureus and L. innocuastrain was not inhibited by b-casein; E. coli strain growth was slightly inhibited. All fractions of hydrolysatesexhibited some anti-bacterial activity and molecular mass fraction

Understanding the mechanism of whey protein fouling along a plate heat exchanger is a challenging issue in the dairy industry. The influence of the calcium/protein molar ratio on β-lactoglobulin (β-LG) denaturation and its consequence both on fouling mass along the plate heat exchanger and the structure of the fouling layer were studied. The experimental design was defined by varying the calcium/protein molar ratio from 2.3 to 22.9 and fixing the total concentration of calcium at 100 ppm. Results established that both the β-LG denaturation rate constants and the distribution of fouling in the plate heat exchanger were strongly impacted by the calcium/protein molar ratio. Structural analysis provided evidence that the fouling layer evolved from a thin and dense structure at low calcium/protein molar ratio towards a thicker and more open structure at higher calcium/protein molar ratio.

During heat treatment, whey proteins (WP) are denatured and form different kinds of whey protein aggregates (WPA) depending on the physico-chemical conditions. In the presence of casein micelles, mixed aggregates (MA), resulting from the interaction of κ-casein and WP, are formed. The aim of this study is to understand the effect of pH on the WPA structure and the impact of the casein/whey proteins (Cas/WP) ratio on MA morphology. In this work, WP solutions were heated at pH 5.8 or 7 to produce WPA. On the other hand, aqueous mixtures containing three Cas/WP ratios (82/18, 56/44 and 30/70) were heated at 80 °C during 1 h at pH 6.3 to obtain MA. Milk protein aggregates were analyzed by Transmission Electron Microscopy (TEM) and Asymmetrical Flow Field-Flow Fractionation coupled with Multiangle Laser Light Scattering and Differential Refractometer (AF4-MALLS-DRi). Dense and spherical WPA were formed at pH 5.8 whereas branched and fractal aggregates were obtained at pH 7. Regarding MA, results suggested that they were mainly produced with the 82/18 Cas/WP ratio whereas a majority of WPA was obtained with the 30/70 ratio. At intermediate ratio, the mixture was composed of small MA and WPA that did not interact with κ-casein. Moreover, WP seem to interact preferentially with larger casein micelles. Thereby, AF4-MALLS-DRi proved to be a powerfull technique to characterize the complex structure of milk protein aggregates and an interesting alternative to size exclusion chromatography especially for MA and casein micelles which interact with the stationary phase and are retained in the column.

Milk is often subjected to technological treatments which have impacts on the structure of milk constituents and the characteristics of rennet curds. In this paper, the influence of the dairy fat structure on the biochemical and textural characteristics of curds coagulated by an extract of Calotropis procera leaves was studied. Standardized milks were reconstituted with the same contents in protein (35 g·kg− 1) and fat (35 g·kg− 1) but with different structures of fat i.e. homogenized anhydrous milk fat (HAMF), homogenized cream (HC) and non-homogenized cream (NHC). As expected, the size distributions of fat globules in the different milks were different. After their coagulations by the plant extract, the physico-chemical characteristics of the curds and respective wheys were determined. No difference was observed in the coagulation time between the three milks but the whey removed more quickly from HAMF and HC curds than NHC-curd. The biochemical analyses of curds revealed a lower content in dry matter and fat in the NHC-curd compared to HAMF- and HC-curds. Otherwise, the NHC-whey exhibited the highest amount of fat. Observations by confocal microscopy showed that the fat globules were homogenously distributed and well trapped in the protein networks of HAMF- and HC-curds. In the NHC-curd, the fat globules were located in whey pockets, with less connectivity with the protein network. The textural analysis showed that the NHC-curd was more elastic, soft and adhesive than HAMF- and HC-curds. Homogenization significantly reduced the loss of fat during cheese manufacturing and conferred specific textural characteristics to the curds coagulated by an extract of Calotropis procera.

Iron deficiency is usually the result of insufficient dietary intake of iron, poor utilization of iron from ingested food, or a combination of the two. Cow milk and dairy products are considered as poor in iron. Addition of supplementary iron to milk or dairy products might be an effective mean of increasing the dietary intake of iron for the population. This presentation reviews information on the iron fortification of milk and dairy products. It will be described the different possible iron sources with their advantages and inconvenient. Different results from the scientific literature will be reported showing that iron fortification of milk or dairy products induces several changes. Among the changes, special attentions will be paid on the 1. Bio-physico-chemical modifications of dairy constituents with the location of added iron after enrichment, the formations of iron-casein, iron-phosphopeptides, iron-whey-proteins and iron-phosphate. The oxidations of lipids and iron will be also described. 2. Modifications of some technological properties of milk enriched in iron (thermal stability of casein micelles, properties of acid and rennet gels made with milk); 3. Quality (composition, colour, flavour…) of some dairy products enriched in iron such as yoghurts, cheeses… and 4. Nutritional interest of iron enrichment. The last part of this presentation will show different dairy products fortified in iron and commercialised.

Controlled ageing conditions have been applied to two micellar casein (MC) powders and the consequent impact on their rehydration capacity and colorimetric evolution has been reported. Two characteristic times (fragmentation and total rehydration time) and solubility have been determinated to evaluate the evolution of rehydration capacity with controlled ageing conditions. For the two MC powders tested, it was shown that the two characteristic times and the browning index increased with storage duration and temperature applied during ageing, whereas solubility decreased. For each MC powder studied, it was shown that (i) there is a correlation (ageing curves) between the rehydration time (the target variable) and the indicator parameters (fragmentation time, browning index and solubility) and (ii) the shape of each ageing curve is independent of the ageing conditions but dependent on the MC powder studied. These results clearly suggest the (i) possibility to obtain reference ageing curves for each indicator, linking total rehydration time and the following indicators: fragmentation time, browning index and solubility (ii) possibility to identify several ageing similarities between severe and moderate storage conditions (iii) feasibility of applying accelerated ageing conditions to rapidly establish the shape of the reference ageing curves for a given MC powder, and (iv) possibility of predicting the rehydration time of the MC powder studied using reference ageing curves through the measurement of one indicator (fragmentation time, browning index and solubility). This predicting ability of the proposed approach has been ascertained by comparing experimental and predicted values of rehydration time for aged samples having undergone storage accidents. (C) 2017 Institution of Chemical Engineers.

Cow and camel milk proteins before and after heat treatment at 80°C for 60min were identified using LC/MS and LC-MS/MS following monodimensional electrophoresis. The database used for the identification of camel and cow proteins was set from http://www.uniprot.org/. The obtained results showed that, after heating, camel milk at 80°C for 60min, camel α-lactalbumin (α-la) and peptidoglycan recognition protein (PGRP) were not detected while camel serum albumin (CSA) was significantly diminished. When heating cow milk at 80°C for 60min, α-lactalbumin (α-la) and β-lactoglobulin (β-lg) were not significantly detected. Moreover, 19 protein bands from SDS-PAGE were analyzed and a total of 45 different proteins were identified by LC-MS/MS. Casein fractions were kept intact under a heat treatment of 80°C during 60min of both camel and cow milks. Camel and bovine whey proteins were affected by a heat treatment of 80°C for 60min.

This work aims to study the effect of processing on the concentration of TGF-β2, evaluating pasteurization, membrane separation, as well as vacuum evaporation and spray drying. The TGF-β content in each sample of milk taken after each processing step has been quantified by ELISA kit. Furthermore, chemical composition analysis has been performed. TGF-β2 has shown a strong correlation (0.95) with the protein content in the samples. There is no influence of pasteurization on the concentration of TGF-β2, although pasteurization affects the distribution of TGF-β2 in the whey protein fractions and casein, which can be observed in the reduction of TGF-β2 content in whey as heat treatment is applied. This trend is unlike that of microfiltration, where it has been observed that TGF-β2 was equally distributed between casein and whey proteins. The concentration obtained by vacuum evaporation showed a concentration factor less than 1 for TGF-β2 once the constituents other than TGF-β2 became more concentrated. However, spray drying showed values greater than 1, demonstrating that TGF-β2 is concentrated in greater quantities than other solid constituents of the samples.

The gastric digestion is the result of physical disintegration and enzymatic reactions leading to the release of nutrients from the food matrix to be absorbed in the upper intestinal tract. Recent works have shown on mini-pig model that the digestion process may be modulated by the initial structure of dairy matrix and suggested that the gastric phase is the critical step. There is a lack of information concerning the microscopic scale of digestion process and the hypothesis most often invoked is that the proteolysis would be limited by the diffusion of gastric fluid into the food, especially pepsin. Nevertheless, fundamental knowledge of gastric digestion had only focused on acid diffusion from the gastric fluid, but no data are currently available for pepsin diffusion. Using fluorescence recovery after photobleaching technique, diffusion coefficients of inactive isothiocyanate (FITC)-pepsin were measured in rennet gels across a range of casein concentrations, modulating different structures of protein aggregates networks. To investigate the microstructural parameters of native gels, electron microscopy image analysis were performed, and then they were qualitatively related to diffusion behavior of FITC-pepsin in these dairy gels. The diffusion coefficients of FITC-pepsin was reduced by a factor 2.4 as the casein concentration of the rennet gels increased from 32.5 to 130 g/kg. Models of polymer science were successfully applied, allowing the reliable prediction of diffusion coefficients calculated from known size of diffusing solutes and physicochemical properties of the food product, e.g. volume fraction, particle size of the gel network. In a more holistic view of food behavior in the human stomach, the diffusion of pepsin should be now confronted with its activity in acidic environment, in order to be able to define more precisely the food particle disintegration mechanisms.

in press; SCOPE: One strategy to manage malnutrition in older patients is to increase protein and energy intake. Here we evaluate the influence of protein quality during refeeding on improvement in muscle protein and energy metabolism.METHODS AND RESULTS: Twenty-month-old male rats (n = 40) were fed 50% of their spontaneous intake for 12 weeks to induce malnutrition, then refed ad libitum with a standard diet enriched with casein or soluble milk proteins (22%) for 4 weeks. 13C-valine was infused to measure muscle protein synthesis and expression of MuRF1, and MAFbx was measured to evaluate muscle proteolysis. mTOR pathway activation and mitochondrial function were assessed in muscle. Malnutrition was associated with a decrease in body weight, fat mass and lean mass, particularly muscle mass. Malnutrition decreased muscle mTOR pathway activation and protein FSR associated with increased MuRF1 mRNA levels, and decreased mitochondrial function. The refeeding period partially restored fat mass and lean mass. Unlike the casein diet, the soluble milk protein diet improved muscle protein metabolism and mitochondrial function in old malnourished rats.CONCLUSIONS: These results suggest that providing better-quality proteins during refeeding may improve efficacy of renutrition in malnourished older patients. This article is protected by copyright. All rights reserved.

The drying process for dairy products is based on rapid removal of water, quickly concentrating milk components to finally form dry particles. The change in concentration may have a considerable effect on the product structure and influence the final characteristics of the dry material. The aim of this study was to investigate the drying behaviour of a major milk protein, i.e. caseins. The droplet – particle conversion was investigated through a single droplet system and by combining complementary methods. Our results showed that the drying process for caseins comprised three stages involving different evaporation rates and droplet dynamics. A thin layer was formed in the early stage of drying that underwent surface instabilities such as buckling and invagination of the droplet. The drying of caseins led to the formation of a deflated and wrinkled particle shape. These results suggest particular mechanical properties of the casein shell leading to a predictable and a characteristic particle shape.

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 spray drying of milk proteins usually leads to dry particles of which the final shape can influences physical and functional properties of powders. The aim of this study was to understand the mechanisms of particle formation by considering the mechanical properties of materials making up the two main classes of milk proteins: whey proteins and casein micelles. The progressive solidification of the interface of the droplet during drying time was studied by high speed camera and fluorescence microscopy, in different experimental conditions. The mechanical properties of the final protein materials were then characterized by micro indentation testing. The drying dynamics of whey protein and casein micelle droplets showed different timescales and mechanical lengths, whatever the drying conditions and the droplet configurations, leading to typical mechanical instability at the surface i.e. buckling and fracture. The interface of casein micelles reached sol–gel transition earlier estimated at around 156 g.L −1 following by elastic and plastic regimes in which the shell distorted and buckled to form a final wrinkled particle. In contrast, the interface of whey proteins became elastic at only half the drying time estimated at around 414 g.L −1 , retaining a spherical shape, which finally fractured at the end of drying. The mechanical difference between the two plastic shells might be explained by the behaviour of proteins in jamming conditions. Analogous behaviour could be discussed between the casein micelles and soft and deformable colloids on the one hand, and between whey proteins and hard spheres on the other.

Fouling and cleaning with a whey protein concentrate solution in a plate heat exchanger were investigated with a varying calcium concentration (from 70 to 87.5 mg L−1) and under a wide range of hydrodynamic conditions for a bulk fouling fluid temperature, ranging from 60 and 96 °C. This work demonstrates that increasing the calcium concentration in whey protein concentrate contributes to the amount of fouling and affects the thermal conductivity of the deposit. It was also observed that the fluid flow regime during fouling, impacts the deposit growth, modifies the structure of fouled layers and has a significant consequence on cleaning behaviour. Finally, a dimensional analysis together with experimental measurements, allowed a relationship to be established enabling prediction of the amount of dry mass deposited locally as a function of the known calcium content, Reynolds number and bulk fluid temperature.

A new thin film concentration device based on a spinning cone evaporator has been specifically designed to process viscous products at low evaporation temperatures. Its effectiveness was evaluated for the concentration of skim milk and a whey protein concentrate with 80% (w/w) protein on a dry-matter basis (WPC80). The concentrates were dried and the powders were compared to standard products obtained with conventional technology. WPC80 at 259.1 g kg−1 total solids (TS) and preconcentrated skim milk at 404.9 g kg−1 TS were concentrated up to 425.4 and 570.5 g kg−1 TS, respectively. No noticeable protein denaturation was evidenced on either concentrate. Particle size and bulk density were higher in the WPC80 powder than a standard product. Although the skim milk concentrate was highly viscous, drying was possible by applying a higher pressure at the inlet of the dryer. The resulting powder had physical properties (density, particle size, solubility) comparable to those of a standard product.

Digestion of proteins leads to the release of numerous peptides in the gastrointestinal tract, among them several bioactive peptides. This review compiles, organises and critically analyses the information available on bioactive peptides present in vivo in the digestive tract of adult humans and animals. It focuses on milk proteins, which are recognised as one of the main sources of bioactive peptides with different biological functions. To date, few studies have been performed on the presence of milk-derived peptides in the intestinal tract in vivo. The diversity of these studies is remarkable in terms of the milk products that have been tested, the animal models selected and the segment of the digestive tract considered. Altogether, 69 bioactive peptides identified in vivo are reviewed. Most of them are released from casein, and especially from β-casein, to which 38 bioactive peptides are attributed. These sequences can be classified mainly as angiotensin-converting enzyme (ACE) inhibitors, opioids and antimicrobial peptides. Particular attention is paid to β-casomorphins and caseinomacropeptide-derived peptides. The function of caseinophosphopeptides as a mineral carrier is also discussed. Few bioactive peptides derive from whey proteins., The authors are involved in the Food and Agriculture COST (European Cooperation in Science and Technology) Action FA1005 “Improving health properties of food by sharing our knowledge on the digestive process” (INFOGEST)

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.

Camel milk and colostrum are known to be a rich source of bioactive proteins. Camel milk, colostrum and colostral whey proteins were successively hydrolysed by pepsin and pancreatin using an in vitro protocol mimicking gastro-intestinal digestion. The degradation of proteins was characterised by electrophoresis and reversed-phase ultra-high performance liquid chromatography. Two whey proteins, α-lactalbumin and immunoglobulins G, were more resistant to the digestive proteolytic enzymes than other camel milk and colostrum proteins. Undigested and digested samples were assayed for their antioxidant, angiotensin I-converting enzyme inhibitory and antimicrobial properties. Camel colostrum, colostral whey and milk proteins had unveiled angiotensin I-converting enzyme (ACE) inhibitory activity following in vitro enzymatic digestion and a higher free radical scavenging activity than before their digestion. Moreover, Escherichia coli XL1 blue and Listeria innocua LRGIA01 cells growth were both inhibited by undigested and digested samples, suggesting that antimicrobial proteins resisted to the action of digestive enzymes or that antimicrobial fragments of camel milk and colostrum proteins were released or both. After pepsin and pancreatin hydrolysis, camel milk and colostrum proteins digests still had an antibacterial activity and their antioxidative and ACE-inhibitory activity even increased, suggesting that bioactive fragments of camel milk and colostrum proteins such as antioxidative and ACE-inhibitory peptides were released. Among 181 peptides identified by tandem mass spectrometry, 25 were homologous to known bioactive peptides, particularly with ACE inhibitors and free radical scavengers.

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.

Under denaturing conditions, copper was shown to induce dimerization of bovine β-lactoglobulin (β-Lg). The occurrence of this chemical reaction and the characterization of the species formed were investigated under various experimental conditions. When β-Lg solution was heated or treated with a denaturant in the presence of copper, covalent dimerization through oxidation of SH groups was observed. The rate of dimer formation increased with increased concentration of both copper and denaturant. The copper-dependent conversion rate of native protein into the covalently- linked dimer was found to be seven to ten-fold faster for variant B than for variant A. The functional and biological implications of the copper-modified β-Lg are discussed., En conditions dénaturantes, nous avons observé que la présence du cuivre conduit à la formation de dimères de β-lactoglobuline (β-Lg) bovine. Nous avons étudié cette réaction chimique et caractérisé l’espèce moléculaire formée dans différentes conditions expérimentales. En présence d’un agent dénaturant ou après traitement thermique, la réaction de dimérisation a lieu par oxydation des groupements thiols de la protéine. La cinétique de dimérisation augmente avec les concentrations du cuivre et de l’agent dénaturant. Cette cinétique est par ailleurs sept à dix fois plus rapide pour le variant B de la β-Lg par rapport à celle du variant A. L’implication biologique éventuelle de cette réaction, favorisée par les atomes de cuivre, est présentée.

International audience; The pH-induced physico chemical changes in a reconstituted heated (90 °C - 10 min) skim milk were studied during fermentation by lactic acid bacteria at two temperatures (30 °C and 42 °C). Different variables were examined during acidification: the water content of ultracentrifugation pellets (150 000 g for 70 min at 30 or 42 °C), the partition of proteins into pelleted and unpelleted fractions (analysed by RP-HPLC on supernatants) and the dissociation of colloidal salts (determined by atomic absorption spectrophotometry on the ultrafiltrates). The proportion of unpelleted protein was found to be pH-dependent with a gradual linear decrease during acidification. All the caseins pelleted below pH 5.5. As the pH was reduced, calcium was progressively released from the micelles. In contradiction with a number of previous findings, fermentation induced a shift toward acid pH values of the salt dissociation compared with a glucono-delta-lactone acidification. The partition of casein between the pellet and the supernatant due to acidification by fermentation was temperature-dependent, as was the solvation of the pellet. Both were greater at 30 °C compared with 42 °C. The temperature had no effect on the salt distribution. The results are discussed in terms of transfer phenomena between the colloidal and the solvent fractions and diffusion-limited processes.; Fermentation du lait reconstitué traité thermiquement par des bactéries lactiques à deux températures. I - Protéines et minéraux. L'effet du pH sur les évolutions physico-chimiques de lait écrémé reconstitué et traité thermiquement à 90 °C, 10 min a été étudié au cours d'une acidification par fermentation lactique à deux températures (30 °C et 42 °C). La quantité d'eau a été évaluée par séchage des culots d'ultracentrifugation (150 000 g pendant 70 min à 30 ou 42 °C). La distribution des protéines entre le culot et le surnageant a été analysée par chromatographie RP-HPLC sur les surnageants avec ou sans dithiothreitol. La dissociation des sels colloïdaux a été déterminée par spectrométrie d'absorption atomique dans les ultrafiltrats de lait. La proportion de protéines dans le surnageant était dépendante du pH avec une diminution graduelle au cours de l'acidification. La majorité des caséines était culottée vers pH 5,5. Au cours de l'acidification, il y a une dissociation progressive du calcium colloïdal. La température est sans effet sur les équilibres minéraux. Comparée à l'acidification par la glucono-delta-lactone, la fermentation induit un décalage vers des pH plus acides de la dissociation des sels colloïdaux. La répartition de la caséine entre le culot et le surnageant, tout comme la teneur en eau des culots, est fonction de la température de fermentation et augmente à 30 °C par rapport à 42 °C. La baisse de la température accroît les concentrations de caséines non centrifugées, particulièrement autour de pH 6,0. Ces résultats sont discutés en terme de phénomènes de transfert entre le solvant et la fraction colloïdale et de limitation par la diffusion.

Gelation of heat-treated milk protein solutions by acid fermentation was performed using a model system of micellar casein alone (systR), micellar casein and β -lactoglobulin (systB) or micellar casein and egg ovalbumin (systO) dissolved in a milk ultrafiltrate and heat-treated at 90°C for 24 min. Solubility of globular proteins at given pH values and their interactions with casein were determined. Particle size and ζ -potential of the protein systems were measured before and after heat treatment. Acid gelation of the heated systems was monitored using dynamic low-amplitude strain oscillation. Ovalbumin alone or with casein produced larger particles than casein alone or with β -lactoglobulin upon heat treatment. The systems gelled at different pH values, i.e. 4.88, 5.47 and 5.88 in systR, systB and systO, respectively. The latter two pH values were clearly related to the pH of the loss of solubility of the heated globular proteins. While the gelation pattern for systR resembled unheated milk, the pattern for systB and systO showed the usual maximum for tan δ of heated milk.

The structure development of a soft cheese curd model has been studied in relationship to its rheological properties and its biochemical characteristics (pH, amount and partition of minerals, casein proteolysis) at different technical steps including cutting, drawing, three turns and demoulding. Scanning electron microscopy was used to observe structural changes during the drainage of a fat-free soft cheese. The micrographs provided visual evidence of changes in the casein matrix from casein particles aggregated in clusters to uniform strands observed at the demoulding. The initial increase of loss tangent and of the exponent of the power law between G′ and G′′ and frequency (that were maximal at the second turn) was related to the solubilization of micellar calcium phosphate, while intact caseins and large casein fragments accumulated in the curd. After the second turn, the strength, Youngs' and loss moduli of the curd increased greatly. The hydrolysis of αs1-casein into αs1-I-CN f(24–199) may facilitate the rearrangement of casein particles within the curd. The pH-induced solubilization of calcium phosphate continued throughout the manufacture process but was unexpectedly incomplete at the end of the drainage. Combination of electron microscopic observations with dynamic rheological measurements and chemical and biochemical assessments provided increased knowledge about the structure of soft cheese during drainage, an important but poorly understood cheese making stage.

International audience; Soft cheeses were prepared from milk modified by membrane technologies to modify the casein level (CN, 27-37 g$\cdot$kg$^{-1}$) and the whey protein to casein ratio (WP/CN, 0.12-0.24). Characterisation of milk coagulation, of whey drainage kinetics and of the drained curd was performed to quantify the effect of the parameters on the process. Moreover, the effect of pasteurisation was tested at 2 casein levels. No effect of WP/CN was observed on coagulation nor drainage. Pasteurisation induced a decrease in the drainage rate at the beginning of the process finally resulting in the same amount of whey expelled. CN had an effect on coagulation, on drainage and on drained curd composition.; Étude de l'égouttage et caractérisation du caillé égoutté en fromagerie à pâte molle, en relation avec la composition du lait (teneur en caséine et proportion protéines solubles/caséine) et la pasteurisation. Un lait de fromagerie a été traité par des technologies à membranes afin de modifier la teneur en caséine (CN, 27-37 g$\cdot$kg$^{-1}$) et le rapport de la teneur en protéines solubles à la caséine (WP/CN : 0,12-0,24). Par ailleurs, l'effet de la pasteurisation a été testé aux 2 teneurs en caséine. Des fromages de type pâte molle ont été préparés et les paramètres de coagulation et d'égouttage ainsi que les propriétés du caillé égoutté (composition et rhéologie) ont été déterminés. Aucun effet de WP/CN n'a été observé sur l'égouttage. Par contre la pasteurisation entraîne un retard de l'égouttage. Moins de sérum est recueilli au début de l'égouttage bien que la quantité de sérum total soit la même en fin d'égouttage. La teneur en caséine du lait a un effet sur la coagulation, sur la quantité de sérum obtenue, sur la cinétique de l'égouttage et sur la composition du caillé égoutté.

We have studied the effect of ionic strength from about 0 to 0.12 M on physicochemical characteristics of micelles and on gelation by rennet. Native phosphocaseinate powder was used as it exhibits attractive technological properties. The powder was dissolved at 25 g l(-1) casein concentration with 0.2 g l(-1) sodium azide into deionised water, NaCl or CaCl(2) solutions, at ionic strength from 0 to 0.12 M. The pH of micelle suspensions was corrected to pH 6.6 and, after overnight equilibration at 20 degrees C, pH values were checked and eventually corrected. After re-equilibration, calcium and phosphorus partition, micelle size, centrifuged pellet hydration were determined and kappa-casein hydrolysis and gelation of the suspensions were followed after rennet addition. The increase in NaCl concentration of casein micelle suspensions resulted in calcium and phosphorus solubilisation from micelles, and increase in pellet hydration. In the same way, the first-order rate constant of the kappa-casein hydrolysis with rennet was reduced, while CMP at the clotting time determined by Formagraph was unchanged. Rennet gelation was consequently retarded by NaCl increase. Suspensions of casein micelles into CaCl(2) solutions did not exhibit calcium binding onto the micelles, as in milk, but a small reduction of diffusible phosphorus from 1.55 to 0.24 mM was shown. Pellet hydrations were unchanged. The increase in ionic strength with CaCl(2) retarded kappa-casein hydrolysis, with an enhanced effect compared to NaCl study. As the CMP at the rennet clotting time was strongly reduced by CaCl(2) addition, the effect of CaCl(2) increase is typically biphasic, with an initial decrease and a following increase in rennet clotting times. From a technological point of view, reduction of ionic strength of milk led to reduced rennet clotting time. Results are discussed in terms of physicochemical modifications of milk micelles and the effect of ionic strength on enzymic reaction.