Milk containing Enterococcus

The test strain used for the preparation of the batch of reference material is Enterococcus faecium, which has been isolated from water. The idendification was based on (1) biochemical identification, (2) identification with the API-20-STREP method, and (3) serological testing for group D antigen, which confirmed the strain of Enterococcus faecium. These methods are described in details elsewhere [38]. 

Commercial sterile evaporated milk was used for the preparation of the reference material, with a dry mass concentration of 200-300 g L and a fat mass concentration of 40 g L . Pink gelatin capsules were used, gamma irradiated with a dose of 10 kGy prior to use. A test strain Enterococcus faecium was cultured in 100 mL THE at 37 C for 48 h, while shaking at 100 rpm. Next the culture was centrifuged for 20 min at 2000 

The variation in the number content of colony-forming particles between samples in one reconstituted capsule (Tj) and between samples of different capsules of one batch (T2) were tested separately. Although the T,-value exceeded the critical values twice, the batch was still considered as being of good quality because the deviations of the critical value were small and considered to be of random nature. An additional homogeneity verification was performed using two alternative methods as described in the certification report [38]. 

For the certification of the Salmonella reference material, two different procedures were used. The first procedure determined the number of colony forming particles in one capsule whereas the second procedure determined the presence or absence of Salmonella in one capsule. Both procedures were carried out according to a detailed protocol and Standard Operating Procedures described elsewhere [37]. 

For the enumeration procedure, each laboratory received 60 capsules and a maximum number of 50 enumerations was requested. The extra capsules were supplied to replace the capsules that were not acceptably dissolved. The capsules were dissolved in 2 rounds each of 30 capsules. For each series also a control was tested, consisting of a Petri-dish containing peptone saline to which no capsule was added. The procedure can be summarised as follows (1) dissolution of a capsule in 5 mL peptone saline solution in a Petri-dish for (45 5) min in an incubator at (38.0 0.5)°C while shaking at ca. 100 rpm (2) repair of Salmonella in Plate Count Agar (incubation time (4 1) h at (37  

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Dairy starter cultures have been used traditionally in the production of a variety of fermented milk products. These cultures consist mainly of several members of the LAB and have been involved in the production of numerous fermented foods, such as yogurts, sour cream, buttermilk, acidophilus milk, kumiss, kefir, and approximately 2,000 different cheeses (O Sullivan 2005). LAB are the backbone of the dairy industry and the main dairy industry starters are contained in five genera Lac-tococcus lactis. Enterococcus faecalis and faeciunr, Lactobacillus bul-garicus, L. casei, L. brevis, L. helveticus, L. rhamnosus, L. fermentum, L. curvatus, L. johnsonii, and L. gasseri (O Sullivan 2005). 

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