-Quantitative isolation of lactic acid bacteria exopolysaccharides (EPS) from dairy products is an important step to determine small amounts of EPS (between 25 and 890 mg·L -1 ) in a medium that contains 30 to 50 g·L -1 of lactose. Kefir grains CIDCA AGK1 are able to produce an exopolysaccharide commonly known as kefiran when grown in milk and deproteinised whey. Different methodologies were compared for kefiran isolation from milk and whey fermented for 96 h at 20°C with 100 g·L -1 of kefir grains. Methods that included one or two steps of ethanol precipitation, one step of ethanol precipitation followed by dialysis, direct dialysis with membranes of different cut-off (1 000, 6 000, 12 000), and a TCA precipitation step were evaluated. The effect of a heat treatment of the milk on EPS recovery was also studied. The highest recovery of EPS was obtained when samples were heated as a first step of isolation. Methods that contained two steps of ethanol precipitation, one step of ethanol precipitation followed by dialysis or direct dialysis (molecular weight cut-off lower than 6 000 to 8 000) gave the highest values of polysaccharide concentration (218 mg·L -1 of fermented milk and 247 mg·L -1 of fermented whey). One step of ethanol precipitation did not completely eliminate residual lactose. EPS was partially lost when dialysis was carried out with membranes of cut-off of 12 000. About 50% of EPS was lost when the method included a step of TCA precipitation. We conclude that polysaccharide quantified in milk and deproteinised whey fermented with kefir grains strongly depends on the isolation methodology used. Exopolysaccharide / EPS isolation / fermented milk / fermented whey / kefirRésumé -Étude comparative de différentes méthodologies pour déterminer la quantité d'exopolysaccharide produit par les grains de kefir dans le lait et le lactosérum. L'isolement quantitatif des exopolysaccharides (EPS) de bactéries lactiques à partir des produits laitiers est une étape importante pour déterminer de petites quantités d'EPS (entre 25 et 890 mg·L -1 ) dans un milieu contenant entre 30 et 50 g·L -1 de lactose. Quand les grains de kefir AGK1 croissent dans le lait et dans le lactosérum deprotéiné, ils sont capables de produire un EPS généralement connu comme kefiran. Dans ce travail, nous avons comparé différentes méthodologies pour isoler le kefiran dans du lait et du lactosérum fermentés. Pour réaliser ces essais le lait et le lactoserum ont été fermentés pendant 96 h 20°C avec 100 g·L -1 de grains de kefir. Les différentes méthodologies pour déterminer l'EPS sont: la précipitation à l'ethanol, la précipitation à l'ethanol suivie d'une dialyse, une dialyse directe

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S. Fermentation of deproteinised whey with kefir grains CIDCA AGK1 was studied focusing on polysaccharide production from lactose. Kefir grains were able to acidify whey at different rates depending on the grain\whey ratio. During fermentation, kefir grains increased their weight and a water-soluble polysaccharide was released to the media. Exopolysaccharide concentration increased with fermentation time, reaching values of 57n2 and 103n4 mg\l after 5 days of fermentation in cultures with 10 and 100 g kefir grains\l, respectively. The polysaccharide fraction quantified after fermentation corresponded to the soluble fraction, because part of the polysaccharide became a component of the grain. Weight of kefir grains varied depending on the time of fermentation. Polysaccharide production was affected by temperature. Although the highest concentration of polysaccharide in the media was observed at 43 mC at both grain\whey ratios, the weight of the grains decreased in these conditions. In conclusion, kefir grains were able to acidify deproteinised whey, reducing lactose concentration, increasing their weight and producing a soluble polysaccharide.