Composition of raw cow milk and artisanal yoghurt collected in Maroua (Cameroon)

The composition of milk is of most importance to the dairy industry and human health. This study was conducted to provide data on the composition of raw cow milk and artisanal yoghurt collected in Maroua (Cameroon). Milk and yoghurt samples were collected from 11 breeding sites and 12 producers in the city of Maroua, respectively. The following parameters were determined: pH, dry matter, ash, fat, lactose, total protein, non-casein nitrogen (NCN), non-protein nitrogen (NPN), true protein, whey protein, casein, amino acid composition, α-lactalbumin, β-lactoglobulin, αS1-casein, αS2-casein, β- casein, κ-casein and mineral composition. The results showed that, the composition of the milk and yoghurt varied from one sample to another. The chemical composition of some of the milk and yoghurt studied differed from the corresponding samples in previous studies. For example the mean pH of the raw cow milk (6.25) and artisanal yoghurt (3.84) were lower. The mean NPN levels of the cow milk and yoghurt (0.21g/100g) were higher. The mean fat content of milk (4.48 g/100 g) was higher. The protein fraction was lower in yoghurt while Fe, Cu and Mn levels were lower in both cow milk and yoghurt. The data reported in this paper would be helpful in dairy technology and public health.Key words: Composition, cow milk, artisanal yoghurt, Maroua, Cameroon

Stability of casein micelles cross-linked with genipin: a physicochemical study as a function of pH

Chemical or enzymatic cross-linking of casein micelles (CMs) increases their stability against dissociating agents. In this paper, a comparative study of stability between native CMs and CMs cross-linked with genipin (CMs-GP) as a function of pH is described. Stability to temperature and ethanol were investigated in the pH range 2.0-7.0. The size and the charge ($\zeta$-potential) of the particles were determined by dynamic light scattering. Native CMs precipitated below pH 5.5, CMs-GP precipitated from pH 3.5 to 4.5, whereas no precipitation was observed at pH 2.0-3.0 or pH 4.5-7.0. The isoelectric point of CMs-GP was determined to be pH 3.7. Highest stability against heat and ethanol was observed for CMs-GP at pH 2, where visible coagulation was determined only after 800 s at 140 $^\circ$C or 87.5% (v/v) of ethanol. These results confirmed the hypothesis that cross-linking by GP increased the stability of CMs.Comment: 5 pages, 2 figures, International Dairy Journal, 201

The surface properties of milk fat globules govern their interactions with the caseins: Role of homogenization and pH probed by AFM force spectroscopy

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

Gradual disaggregation of the casein micelle improves its emulsifying capacity and decreases the stability of dairy emulsions

The casein micelle is a highly aggregated colloid consisting of phosphoproteins and minerals, in particular calcium and phosphate. Its properties are affected by physico-chemical changes which provide possibilities for the development of new casein aggregates (CAs) with novel functionalities. The aim of this study was to investigate the emulsifying and emulsion-stabilizing capacity of gradually demineralized CAs in model dairy emulsions. Tri sodium citrate (TSC) was used to remove calcium and inorganic phosphate from pure casein micelles in order to produce four suspensions of differently demineralized CAs. Two types of milkfat-in-suspension (30:70 v/v) emulsions were then prepared to study the emulsifying and emulsion-stabilizing capacity of these CAs separately. Casein micelles were progressively demineralized (from 24 to 81% calcium reduction) and dissociated with the increase in TSC concentration. Three distinct populations of particles (micelle-like aggregates, sodium caseinate-like aggregates and casein monomers) were present in every suspension in different proportions. The smaller CAs had better emulsifying capacity and similar surface activity according to interfacial studies. The state of aggregation of the CAs was thus the main factor that controlled their emulsifying capacity. However, the emulsions formed with these smaller aggregates were less stable against creaming and flocculation, but still resisted coalescence under our storage conditions (21 days at 50 °C). The properties of the interfacial casein layers did not depend on the aggregation state of the CAs used to form the emulsions. The differences in instability were attributed to the nature of the non-adsorbed CAs and storage conditions

Different Types of French Cheeses: Scientific and Technological Aspects

Cheese is probably one of the most ancestral conservation form of major milk components (protein and lipid). It is also a universal food consumed in various parts of the world. Thanks to the knowledge acquired on the composition of milks and development of different dairy technologies performed at artisanal or industrial scale, the Human created a large variety of cheeses. This variety is extraordinary especially in France, with more than 400 different types of cheeses. This diversity is obtained thanks to different practices (milk preparation, curd fabrication, salting and ripening conditions) used during the cheese making. Cheeses can be classified in different ways (origin of milk, heat treatment of milk before its transformation, type of microorganisms used, types of coagulation, level of salt added, conditions of ripening, etc). However, the most common criterion used to classify them is the texture (in relation with the dry matter). Thus we find, on the market, - acid fresh cheeses (Cream cheese, faisselle,…)- soft cheeses (Camembert, Brie, Munster, Epoisses, ...)- semi-hard cheeses (Edam, St Paulin, …)- hard cheeses (Emmental, Comté, Beaufort, ...)- whey cheeses (Brocciu, …)- processed cheeses (Vache qui rit,…). All these cheeses differ also by their biochemical and microbiological compositions, nutritional properties, tastes, odours, forms, weights, time of conservation

The minerals of milk

The salt of milk constitutes a small part of milk (8–9 g·L–1); this fraction contains calcium, magnesium, sodium and potassium for the main cations and inorganic phosphate, citrate and chloride for the main anions. In milk, these ions are more or less associated between themselves and with proteins. Depending on the type of ion, they are diffusible (cases of sodium, potassium and chloride) or partially associated with casein molecules (cases of calcium, magnesium, phosphate and citrate), to form large colloidal particles called casein micelles. Today, our knowledge and understanding concerning this fraction is relatively complete. In this review, the different models explaining (i) the nature and distribution of these minerals (especially calcium phosphate) in both fractions of milk and (ii) their behaviour in different physico-chemical conditions, are discussed

Les impacts de la qualité du lait sur ses aptitudes à sa transformation : cas des fromages et des laits UHT

Pour répondre à ses objectifs, l’industriel laitier doit impérativement utiliser des laits crus qui doivent être de qualité en termes microbiologique et biochimique de façon à ce qu’ils soient transformés selon un cahier des charges bien précis. Le produit final doit être celui attendu par le transformateur et consommé sans aucun risque sanitaire. Il s’avère que dans certains cas le lait cru soit d’une qualité non maitrisée avec comme conséquence une mauvaise transformation et un produit final de mauvaise qualité. Deux exemples reliant qualité des laits crus et transformation (fromages et en lait UHT) sont présentés

Determination of calcium-binding constants of caseins, phosphoserine, citrate and pyrophosphate: A modelling approach using free calcium measurement

Determination of calcium-binding constants of caseins, phosphoserine, citrate and pyrophosphate: A modelling approach using free calcium measuremen