Table 1.
Conditions for the enumeration of the considered bacterial populations present in bovine raw milk samples (M1, M2 and M3) during cold storage for up to 7 days at 6°C.
| Bacterial types | Media | Supplier | Incubation conditions | Notes |
|---|---|---|---|---|
| “Total counts” (TM) | Plate Count Agar (PCA) | Lab M, Ltd., Lancashire, United Kingdom | 30°C/3d | All distinct colonies were enumerated |
| Gram-negative bacteria (G-) | Mac Conkey Agar | ” | 30°C/3d | All distinct colonies were enumerated |
| Spores | PCA | ” | 30°C/3d | Milk samples were heated for 12 min at 80°C prior to the analyses |
| Protease producers (Pr+) | Skim milk-enriched agar1 | – | 30°C/3d | A clear zone surrounding a colony is indicative of protease activity |
| Lipase producers (Li+) | Tributyrin + Victoria Blue agar2 | – | 30°C/3d | A dark “blue” zone or a contrasted area that surrounds a colony corresponds to lipase activity |
| Phospholipase C producers (PLa+) | PCA supplemented with egg yolk2,3 | – | 30°C/3d | A colony surrounded by an opaque ring was considered as producing phospholipase C |
| Psychrotrophs (Psy) | PCA | Lab M, Ltd., Lancashire, United Kingdom | 7°C/10d | All distinct colonies were enumerated |
| Haemolytic colonies (Hem+) | Blood Agar + 6% sheep blood | bioTrading, Benelux B.V., Mijdrecht, Netherlands) | 30°C/3d | Colonies that showed either α or ß-haemolytic activities were recorded4 |
1Modified from Harper et al., 1978; 2Dogan and Boor, 2003; 3Chrisope et al., 1976;4Alexander and Strete, 2001.