-Addition of CaCl 2 to skim milk, from 0 to 13.5 mmol·kg -1 , leads to significant physicochemical changes in milk salts equilibrium. Indeed, acidification, insolubilizations of calcium, inorganic phosphate and citrate are observed. Calculation of ion equilibria in the resulting milk ultrafiltrates indicates that the observed ion migrations, controlled by solubilities of calciumphosphate and calcium-citrate, do not cause change in ion activity products of dicalcium-phosphate (calculated as CaHPO 4 ·2H 2 O and Ca(HPO 4 ) 0.7 (PO 4 ) 0.2 ). In the same way, the acidification of calcium-supplemented milks in the range of pH 6.7-3.5 shows a solubilization of calciumphosphate similar to non-enriched milk. So whatever the added calcium concentration, the behaviour of colloidal calcium-phosphate seems to be unchanged. However, at room temperature, addition of calcium to milk originates a decrease in soluble casein concentration and tightly bound water of ultracentrifuged pellets. The consequences are (i) an increase in milk protein hydrophobicity; (ii) a decrease in zeta potential of casein micelles, without modification of their hydrodynamic diameter; and (iii) an increase in milk lightness and turbidity. Furthermore, calcium supplementation of milk seems to lead to a proteinic reorganization of micellar casein, responsible for an increase in micellar density. Milk / calcium / physicochemical characterization / calcium phosphate / acidification / supplementationRésumé -Caractérisation physicochimique d'un lait écrémé enrichi en calcium. L'addition de CaCl 2 à du lait écrémé, pour des concentrations allant de 0 à 13,5 mmol·kg -1 , induit d'importants changements physicochimiques du lait. En effet, une acidification, une insolubilisation du calcium, du phosphate inorganique et du citrate sont observées. Le calcul des équilibres ioniques dans les ultrafiltrats des différents laits montre que les flux ioniques observés, contrôlés principalement par les solubilités du phosphate et du citrate de calcium, ne modifient pas les produits d'activité ionique du phosphate dicalcique (calculés pour CaHPO 4 ,2H 2 O et Ca(HPO 4 ) 0,7 (PO 4 ) 0,2 ). De la même manière, l'acidification de ces laits supplémentés en calcium entre pH 6,7 et 3,5 montre une solubilisation du phosphate de calcium similaire à celle d'un lait non enrichi. Quelle que soit la concentration en calcium ajouté, le comportement du phosphate de calcium colloïdal semble donc inchangé. Par ailleurs, l'addition de calcium à du lait écrémé est responsable, à température ambiante, d'une diminution de la concentration en caséines ultracentrifugeables et de l'eau

Small peptides (MW Ͻ Ͻ Ͻ Ͻ Ͻ 1000 g/mol) and volatile fatty acids of goat cheese were studied for their favorite properties. The threshold values of 4-methyl-and 4-ethyl-octanoic acids-responsible for the typical goat note were evaluated at pH 5 for orthonasal aroma in a citrate buffer and for retronasal aroma after incorporation in a cheese model. Though the concentration of the 4-ethyl-was lower than the concentration of the 4-methyl-octanoic acid in goat cheese, its relative impact on the typical goat flavor appeared more important because of its much lower threshold value. The small peptides, isolated by nanofiltration of the ultrafiltered water-soluble extract at pH 5, were incorporated in the cheese model. Sensory evaluations with omission tests did not allow us to find any taste activity for this peptidic fraction.

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The aim of this study was to evaluate the impact of the components of a goat cheese water-soluble extract (WSE) on its flavor by both physicochemical and sensory techniques with special emphasis on taste. After characterization of the organoleptic properties of the cheese, the WSE was extracted with pure water and submitted to successive tangential ultrafiltrations and nanofiltration. The physicochemical assessment of these fractions led to the constitution of a model mixture (MWSE) compared by sensory evaluation to the crude WSE, using a panel of 16 trained members. The results of both sensory profile and triangular tests indicate no significant difference, therefore proving that the reconstitution of the WSE was correct, thereby showing the sensory neutrality of lipids and peptides smaller than 500 Da, which had not been included in the MWSE. Moreover, the cheese gustatory characteristics are comparable to those of the WSE despite weaker levels of sharpness and astringency in the extract, the respective origins of which are discussed.

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