-This paper deals with the most recent developments of cross flow microfiltration (CFMF), some of them just patented, in the dairy industry. Combination of the use of uniform transmembrane hydraulic pressure concept (UTP) with its different ways of carrying out microfiltrate recirculation, longitudinal porosity gradient and of new ceramic membrane materials allows nowadays to get a differential separation of each category of milk particles. Pretreatment by CFMF of incoming milk is used for the production of low heated fluid milks having a flavor similar to that of raw milk and a shelf life 3 to 5 times longer than that of classical products. Results observed in the retention by the MF membrane of pathogenic bacterial species allow it to be said that the hygienic safety of cheeses made from raw MF milk is, at least, equal or even higher than that of cheeses made from pasteurized milk. Numerous other applications of CFMF are under development such as removal of residual fat from whey or the clarification and the removal of bacteria from cheese brine but the most promising are undoubtedly the differential separation of micellar casein and of small milk fat globules. With the products obtained on both sides of the MF membrane, dairy technology will have the possibility not only to improve yield and quality of many dairy products but also to create a diversified range of new textures. microfiltration / membrane / liquid milk / native casein / brine / whey / cheese Résumé -Développements actuels de la technologie de microfiltration dans l'industrie laitière. Cet article traite des développements les plus récents, certains tout juste brevetés, de la microfiltration tangentielle dans l'industrie laitière. La combinaison de l'utilisation du concept de pression transmembranaire uniforme, avec ses différentes possibilités de mise en oeuvre : recirculation du microfiltrat, gradient de porosité longitudinal, et de nouveaux matériaux membranaires céramiques Lait 80 (2000) 541-553 541

(Reçu le 5 mai 1994; accepté le 30 juin 1994) Résumé -La microfiltration tangentielle sur membrane 0,14 um de lait épuré par le procédé Bactocatch suivie d'une diafiltration, préalablement à sa déshydratation par atomisation, permet l'obtention d'une poudre de phosphocaséinate natif à haute teneur en matière azotée totale (90,2 g pour 100 g de matière sèche) et de bonne qualité bactériologique (population bactérienne < 5 000 ufclg). La réalisation d'un concentré enrichi en caséine micellaire entraîne des modifications profondes des caractéristiques physiques des poudres de phosphocaséinate natif. L'indice de solubilité est de 73,7% à 24°C, diminuant ainsi la qualité intrinsèque de ces poudres. Dans la présente étude, nous avons essayé de comprendre au mieux la cause de cette formation d'insoluble. Des modifications biochimiques des concentrés (diminution du pH, augmentation de la force ionique, ajout de lactose) et physiques des poudres (diminution de la taille des grains) ont permis d'améliorer sensiblement J'indice de solubilité jusqu'à 92,6% à 24°C. L'insoluble observé lors de la reconstitution de concentré à partir de poudre de phosphocaséinate natif ne serait pas lié à une dénaturation thermique, mais à une diminution de la vitesse de transfert de J'eau de reconstitution. L'ajout de lactose ou "augmentation de la surface de contact entre le grain et l'eau de reconstitution a permis d'augmenter cette vitesse de transfert en améliorant ainsi l'indice de solubilité des poudres de phosphocaséinate natif.

We present an extensive description and analysis of a microfiltration process patented in our laboratory to separate different fractions of the initial milk fat globule population according to the size of the native milk fat globules (MFG). We used nominal membrane pore sizes of 2 to 12 microm and a specially designed pilot rig. Using this process with whole milk [whose MFG have a volume mean diameter (d43) = 4.2 +/- 0.2 microm] and appropriate membrane pore size and hydrodynamic conditions, we collected 2 extremes of the initial milk fat globule distribution consisting of 1) a retentate containing large MFG of d43 = 5 to 7.5 microm (with up to 250 g/kg of fat, up to 35% of initial milk fat, and up to 10% of initial milk volume), and 2) a permeate containing small MFG of d43 = 0.9 to 3.3 microm (with up to 16 g/kg of fat, up to 30% of initial milk fat, and up to 83% of initial milk volume and devoid of somatic cells). We checked that the process did not mechanically damage the MFG by measuring their zeta-potential. This new microfiltration process, avoiding milk aging, appears to be more efficient than gravity separation in selecting native MFG of different sizes. As we summarize from previous and new results showing that the physico-chemical and technological properties of native milk fat globules vary according to their size, the use of different fat globule fractions appears to be advantageous regarding the quality of cheeses and can lead to new dairy products with adapted properties (sensory, functional, and perhaps nutritional).

-EGF, BTC, IGF-I, IGF-II, TGF-β1, TGF-β2, FGF1 and 2, and PDGF are the main growth factors present in bovine milk and colostrum. All of these growth factors are also found in human milk but at a lower concentration. The various compositional data reported in the literature vary greatly but it is evidenced that the day of lactation has the most important effect. Milk growth factors are characterized by a neutral to alkaline isoelectric point (pI) and a molecular mass between 6400 g·mol -1 and 30000 g·mol -1 . However, many of the growth factors are in a latent form, bound to high-molecular-mass proteins. Milk growth factors are resistant generally to pasteurization but disulfide reducing agents have been found to inactivate some species such as TGF-β's. The published data on bioavailability of milk growth factors are somewhat contradictory but it is generally accepted that they are resistant to gastric digestion and they can exert local and systemic effects on the gastrointestinal tract. Cation-exchange chromatography has been widely used for the extraction of milk growth factors because of the basic nature of these molecules. Membrane separations such as microfiltration (MF) have also been used successfully for the extraction of immunoglobulins and of some growth factors from colostrum, while ultrafiltration (UF) was successful only at separating IGF-I and IGF-II in whey. Milk growth factor extracts have been developed for various applications such as treatment of gastrointestinal disorders and skin diseases, wound healing, and induction of oral tolerance.

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