Milk is a complex emulsion, and understanding the adsorption of the various surface-active macromolecules onto the fat/water interface newly formed during homogenization is critical for optimizing dairy processing. This study investigates the adsorption dynamics using a commercial whey protein ingredient and melted anhydrous milk fat (50 degrees C). By employing drop surface tension measurements, interfacial dilatational rheology and a comprehensive modelling approach, we explore the adsorption process under realistic conditions. We propose a model describing diffusion, progressive saturation of the surface and reorganisation of proteins. For reorganisation, the proposed model introduces three parameters: the maximum loads of the interface without (Gamma min) and with (Gamma max) reorganisation and a characteristic time of reorganisation (tau reorg). The kinetic properties of whey proteins have been characterised by adjusting the parameters of the model. In addition, interfacial rheology and macroscopic observations of the droplets revealed regime changes in the organisation of the interface, confirming our hypothesis about the reorganisation built into the model. This study opens the way to the construction of a model for predicting the composition of the interface after homogenization at high pressure (HPH), taking account of competition between macromolecules (casein, phospholipids etc.).

An exhaustive analysis was performed on more than 2000 microbiotas from French Protected Designation of Origin (PDO) cheeses, covering most cheese families produced throughout the world. Thanks to a complete and accurate set of associated metadata, we have carried out a deep analysis of the ecological drivers of microbial communities in milk and "terroir" cheeses. We show that bacterial and fungal microbiota from milk differed significantly across dairy species while sharing a core microbiome consisting of four microbial species. By contrast, no microbial species were detected in all ripened cheese samples. Our network analysis suggested that the cheese microbiota was organized into independent network modules. These network modules comprised mainly species with an overall relative abundance lower than 1%, showing that the most abundant species were not those with the most interactions. Species assemblages differed depending on human drivers, dairy species, and geographical area, thus demonstrating the contribution of regional know-how to shaping the cheese microbiota. Finally, an extensive analysis at the milk-to-cheese batch level showed that a high proportion of cheese taxa were derived from milk under the influence of the dairy species and protected designation of origin.

Bisifusarium domesticum is among the main molds used during cheese-making for its "anticollanti" property that prevents the sticky smear defect of some cheeses. Previously, numerous cheese rinds were sampled to create a working collection and not only did we isolate B. domesticum but we observed a completely unexpected diversity of "Fusarium-like" fungi belonging to the Nectriaceae family. Four novel cheese-associated species belonging to two genera were described: Bisifusarium allantoides, Bisifusarium penicilloides, Longinectria lagenoides, and Long-inectria verticilliformis. In this study, we thus aimed at determining their potential functional impact during cheese-making by evaluating their lipolytic and proteolytic activities as well as their capacity to produce volatile (HS-Trap GC-MS) and non-volatile secondary metabolites (HPLC & LC-Q-TOF). While all isolates were proteo-lytic and lipolytic, higher activities were observed at 12 degrees C for several B. domesticum, B. penicilloides and L. lagenoides isolates, which is in agreement with typical cheese ripening conditions. Using volatilomics, we identified multiple cheese-related compounds, especially ketones and alcohols. B. domesticum and B. penicilloides isolates showed higher aromatic potential although compounds of interest were also produced by B. allantoides and L. lagenoides. These species were also lipid producers. Finally, an untargeted extrolite analysis suggested a safety status of these strains as no known mycotoxins were produced and revealed the production of potential novel secondary metabolites. Biopreservation tests performed with B. domesticum suggested that it may be an interesting candidate for biopreservation applications in the cheese industry in the future.

The most abundant minerals in milk are calcium, potassium, chloride, phosphorus, sodium and magnesium. This article first discusses the composition and distribution of these elements and citrate between the soluble (serum) and micellar (casein micelle) phases of milk. Then, it describes how this distribution, named the salt equilibria, is affected by the main physico-chemical treatments applied to milk in dairy processing (heating, cooling, pH variation, milk concentration, calcium salt and calcium chelator additions). Finally, sample preparation and some analytical methods to determine the mineral and citrate content and distribution in dairy liquids are described.

Caseins are recognized as safe for consumption, abundant, renewable and have high nutritional value. Casein molecules are found in different aggregation states and their multiple binding sites offer the potential for delivering biomolecules with nutritional and/or health benefits, such as vitamins, phytochemicals, fibers, lipids, minerals, proteins, peptides, and pharmaceutical compounds. In the present review, we highlight the interactions between caseins and food-derived bioactive molecules, with a special focus on the aggregation states of caseins and the techniques used to produce and study the particles used for delivering. Research on interactions between caseins-minerals and casein-pharmaceutical molecules are not included here. This review aims to support the development of new and innovative functional foods in which caseins can be used as designed delivery systems.

This study investigated the effect of pH on the denaturation extent, the surface chemical composition, the water sorption isotherm and the glass transition temperature of camel and bovine whey protein's powders. The LC-MS analysis indicated that the β-Lactoglobulin was the most denatured protein in bovine whey powders regardless the pH value, while this protein was totally absent in camel whey. The α-Lactalbumin was relatively heat stable after drying and predominated the powder surface (X-ray photoelectron spectroscopy results) in both camel and bovine whey powders regardless the pH (neutral (6.7) or acidic (4.3 and 4.6)). Analysis of the water sorption isotherms indicated that decreasing the pH induced the increase of the water activity of lactose crystallization for camel and bovine whey powders. Finally, decreasing the pH led to the decrease of the glass transition temperature of camel and bovine whey powder (at 0.13, 0.23, and 0.33 of water activity).

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.

Lactococcus lactis group (composed of the lactis and cremoris subspecies, recently reassigned as two distinct species) plays a major role in dairy fermentations. Usually present in starter cultures, the two species enable efficient acidification and improve the organoleptic qualities of the final product. Biovar diacetylactis strains produce diacetyl and acetoin, aromas from the citrate metabolization. As these populations have distinct genomic and phenotypic characteristics, the proportions of each other will affect the final product. Today, there is no quantitative test able to distinguish between the two species and the biovar in dairy ecosystems. In this study, we developed a specific, reliable, and accurate strategy to quantify these populations using, species-, and diacetylactis-specific fluorescent probes in digital droplet PCR assays (ddPCR). Species were distinguished based on three single nucleotide polymorphisms in the glutamate decarboxylase gadB gene, and the citD gene involved in citrate metabolism was used to target the biovar. Used in duplex or singleplex, these probes made it possible to measure the proportion of each population. At 59°C, the probes showed target specificity and responded negatively to the non-target species usually found in dairy environments. Depending on the probe, limit of detection values in milk matrix ranged from 3.6 × 103 to 1.8 × 104 copies/ml. The test was applied to quantify sub-populations in the L. lactis group during milk fermentation with a commercial starter. The effect of temperature and pH on the balance of the different populations was pointed out. At the initial state, lactis and cremoris species represent, respectively, 75% and 28% of the total L. lactis group and biovar diacetylactis strains represent 21% of the lactis species strains. These ratios varied as a function of temperature (22°C or 35°C) and acidity (pH 4.5 or 4.3) with cremoris species promoted at 22°C and pH4.5 compared to at 35°C. The biovar diacetylactis strains were less sensitive to acid stress at 35°C. This methodology proved to be useful for quantifying lactis and cremoris species and biovar diacetylactis, and could complete 16S metagenomics studies for the deeply description of L. lactis group in complex ecosystems.

This study aimed at investigating the chemical composition and microstructure of spray dried camel and cow milk powders' surfaces with two different milk-fat contents (1 and 20g 100 g(-1)). The SEM (Scanning Electron Microscopy) micrographs showed that spherical particles with a 'brain'-type surface for both milk powders were produced. The surface roughness (Ra) of whole (WDMP) and skimmed (SDMP) camel milk powders (Ra = 7.6 +/- 0.4 nm and 5.6 +/- 0.7 nm, respectively) were significantly lower as compared with the partially skimmed (PSCMP) and skimmed (SCMP) cow milk powders. The XPS (X-ray Photoelectron Spectroscopy) analysis highlighted that the surface of skimmed camel milk powders contained twice the lactose amount (17.7 +/- 0.8%) as compared to cow milk powders (8.7 +/- 0.4%). Furthermore, both milk powders showed the overexposure of proteins and fats at their surfaces regardless of the fat content. The CLSM (Confocal Laser Scattering Microscopy) micrographs highlighted that most of the camel milk fat globules were encapsulated by the proteins near the powder surface. Camel milk fat behavior during particle formation was attributed to their lower size distribution and their higher crystallization temperature.

This study aimed at investigating the changes in skim camel milk (SCMP) and skim bovine milk (SBMP) powders produced by spray-drying. The physical (sorption isotherms at 25 degrees C and the glass transition temperature T-g at 0.13, 0.23 and 0.33 of water activities (a(w))) and the biochemical (LC-MS, before and after drying) properties were assessed. Compared to SBMP, the results for SCMP indicated lower protein denaturation extent, lower critical a(w) for lactose crystallization (a(w) = 0.60 instead of 0.70), and lower T-g at 0.13 of a w (54.6 +/- 1.4 degrees C instead of 57.8 +/- 0.4 degrees C). Fitted to Guggenheim, Anderson and De Boer (GAB) model, the water sorption isotherms showed that both powders exhibited the same monolayer moisture content (X-m = 2.0 g 100 g(-1), p > 0.05). These findings were linked to the absence of beta-lactoglobulin, the high surface lactose content, the high initial lactose crystallization and the low size distribution (d(50) < 10 mu m) of SCMP.

The properties of casein micelles are known to be affected by modifications to the environment, such as variations in pH or the addition of salts, yet the scientific literature typically considers the effects of one factor at a time, while in industrial processes, several modifications are performed simultaneously. The aim of this study was to assess the impact of multifactorial environmental modifications on the colloidal, structural and rennet coagulation properties of casein micelles in a simplified model system. A key finding was that dense regions (similar to 20 nm in size) could be released from the casein micelle. The addition of NaCl and CaCl2 had opposing effects, i.e. enhancing or limiting this micellar disruption, respectively. A decrease in pH had the strongest impact on the mineral balance, causing the colloidal CaP to solubilize and the micelle to swell. The rennet clotting time was impacted by variations in pH and NaCl content. Interestingly, a consideration of all three levels of casein micelle structure and their interactions was needed to explain variations in the firmness of rennet gels. This study illustrates the complex interplay of factors affecting micellar structure and improves our understanding of how micelles can be manipulated to control their properties.

The surface of milk fat globules consists of a biological membrane rich in polar lipids and glycoproteins. However, high shear stress applied upon homogenization disrupts the membrane and leads to the adsorption of casein micelles, as the major protein fraction of milk. These changes in the interface properties could affect the interactions between native or homogenized milk fat globules and the surrounding protein matrix, at neutral pH and upon acidification. In this study, macroscale rheometry, microscopic observations, nanoscale AFM-based force spectroscopy and physico-chemical analysis were combined to examine the interfacial composition and structure of milk fat globules and to evaluate their interactions with casein micelles. We showed that the surface properties of milk fat globules (biological membrane vs. caseins) and pH govern their interactions with casein micelles. The adhesion between individual fat globules and casein micelles was higher upon homogenization, especially at acid pH where the work of adhesion increased from 3.3 x 10-18 to 14 x 10-18 J for native and homogenized fat globules, respectively. Consequently, casein-coated homogenized fat globules yield stiffer milk acid gels. These findings cast light on the importance of colloidal particle's surface properties and pH on their connectivity with the surrounding matrix, which modulates the bulk microstructure and rheological properties with potential functional consequences, such as milk lipid digestion.

A composite face-centered experimental design was used to investigate the influence of spray drying conditions on the physicochemical characteristics of camel and cow milk powders. Response surface methodology (RSM) was deployed to appraise the effects of these processing parameters (the outlet drying temperature and the milk fat content) on water activity (a(w)), glass transition temperature (T-g), bulk density, and free fat quantity. According to RSM analysis, it was noticed that the a(w) and the T-g were primarily influenced by the outlet drying temperature instead of by milk fat content. Our results highlighted the negative effects of milk fat content and of the outlet drying temperature on the bulk density as well as on the free fat quantity of camel milk powder. Likewise, our findings underlined the negative effect of the outlet drying temperature on the bulk density of cow milk powder. However, the increase of fat content has led to the overexposure of fat at the free surface of the cow milk powder. Our results suggested a marked similarity of the overall thermodynamic behavior of both milks, during drying. Nevertheless, some differences were highlighted regarding the structuring of the particles of camel milk powder.

Resumo A importância primária das micelas de caseína reside no fato de que os processos empregados na transformação do leite em quaisquer de seus derivados dependem, direta ou indiretamente, de sua estabilidade ou de sua desestabilização controlada. Assim, o objetivo do presente trabalho é apresentar uma revisão atualizada sobre a organização estrutural das micelas de caseína. Em termos físico-químicos, as micelas de caseína podem ser definidas como agregados supramoleculares esféricos e porosos, altamente hidratados, carregados negativamente, com diâmetro médio de 200 nm, e que apresentam aproximadamente 104 cadeias polipeptídicas. Além de água, as micelas são constituídas por quatro tipos de caseínas, chamadas de αS1, αS2, β, e κ-caseínas, que estão unidas por meio de interações hidrofóbicas e eletrostáticas, e pela presença de minerais, sobretudo sais de fosfato de cálcio, os quais são os principais responsáveis pela manutenção da estrutura micelar. A estabilidade das micelas de caseína é atribuída à presença de uma camada externa difusa, formada basicamente por κ-caseína. Apesar de as propriedades coloidais das micelas de caseína serem conhecidas, ainda não há consenso sobre como as moléculas de caseína estão estruturadas em seu interior. Portanto, os principais modelos que descrevem a organização interna das micelas de caseína são apresentados na parte final do artigo.

Casein micelles (CMs) can be used as nanocarriers in food and pharmaceutical applications, but can be destructured by changes in the physicochemical environment. Enzymatic crosslinking with transglutaminase (Tgase) is a possibility to stabilize CMs. The objective of this paper was to evaluate the stability of native CMs and CMs cross-linked by Tgase (CMs-Tgase) as a function of pH, in the presence of following destabilizing agents: urea, sodium citrate, high temperature and ethanol. Suspensions of native and CMs-Tgase were prepared at 27.5 g/L in 25 mM HEPES buffer with 2 mM CaCl2 at pH 7.10 The CMs' size and zeta-potential were determined by dynamic light scattering. Native CMs precipitated below pH of 5.5. CMs-Tgase precipitated between pH 4.5 and pH 3.5 but was stable in the pH range of 7.0-4.5 and between pH 2.0 and 3.0. Isoelectric points of CMs and CMs-Tgase were determined as been 4.6 and 4.1, respectively. CMs-Tgase were stable at pH 2.0, in the presence of 100 mM of sodium citrate, 8 M urea, 99.5% (v/v) of ethanol and presented an heat coagulation time higher than 500 s at 140 degrees C. These results were interpreted as a consequence of the formation of internal covalent bounds between casein chains, and to a covalent attachment of the kappa-caseins onto the surface of the CMs. In light of these results, it is possible to investigate CMs-Tgase as stable food-grade nanocarriers, whose characteristics can be modulated according to the chemical nature of the target biomolecule.