Fractionation of globular milk fat by membrane microfiltration

Separation of milk fat in small globules (SG) (diameter lower than 2 μm) and in large globules (LG) (diameter higher than 2 μm) was realized by a patented process using special ceramic microfiltration membranes. Transformations in drinking milks, yoghourts, sour cream, camembert, Swiss cheese and butters were realized from milks of which the fat content was adjusted either by reference cream or by creams issued from the SG or the LG fractions. Significant differences in texture and organoleptic properties were found in the manufactured products. Except for butter, use of milks containing small fat globules led to more onctuous products and more finer textural characteristics versus products made with reference creams or with mainly large fat globules. Fat globule membrane appeared to have a high ability to bind water in cheese and so, to allow a significant increase in cheese yield. microfiltration / fat globule size / texture / dairy product Lait 80 (2000) 93–98 93 © INRA, EDP Sciences * Correspondence and reprints. maubois@labtechno.roazhon.inra.fr H. Goudédranche et al. 94 glycosylated [6]. At least 25 different enzymatic activities have been found to be associated with MFGM [6]. According to Walstra [10], the MFGM average thickness would be 15 nm and would represent 0.4 g.L–1 of milk. On the other hand, the complex material of MFGM leads to a zeta potential of –12 mV and an isoelectric pH of the washed milk fat globules of 3.7. It is well known that a strong increase of the fat globule number by homogenization modifies the mouth feeling of a liquid milk. For the same fat content, homogenized milk appears sweeter and has more body than the reference milk [1]. Moreover, it can be supposed that a large part of the microstructure and consistency of dairy products such as cheeses is largely affected by interactions between the casein matrix and fat globule membranes. Consequently, a possible way to increase or to decrease these interactions could be to modify, in the milk to be processed, the number of fat globules, for a given fat content. Moreover, it could also be considered that an increase of the fat globule number i.e. to prepare a milk with small fat globules, would have other effects due to the ability of the MFGM to bind water [4] and the difference in fatty acid composition between large and small fat globules [8]. Such an adjustment of fat globule number could not be done by homogenization because this mechanical treatment disrupts the MFGM integrity and often leads to detrimental consequences such as accelerated lipolysis. Among the separation technologies known for not damaging MFGM and which could allow separation of fat globules according to their size, centrifugation [8] and membrane microfiltration (MF) are conceivable; the latter was preferred since we thought that fat globule size could be a much better separation criterion between small and large globules than fat globule density. Consequently, a patented process [5] was developed to fractionate milk fat globules from whole milk and creams by MF with special ceramic membranes. This paper reports the preliminary results observed on dairy products made from milks of which the fat portion was composed either by large globules (LG) (diameter higher than 2 μm) or by small globules (SG) (diameter lower than 2 μm). 2. MATERIALS AND METHODS