The surface flora of bacterial smear-ripened cheeses from cow's and goat's milk

Abstract

Debaryomyces hansenii was found to be the predominant yeast in all stages of ripening in several studies on semi-hard Tilsit cheese, soft Chaumes cheese and semi-hard goat's cheese. 75–95% of the bacterial flora was made up of coryneform bacteria. Brevibacterium linens was found at 0–15%. Yellow pigmented coryneform isolates (1–30%) belonged to Arthrobacter nicotianae. Non pathogenic staphylococci (mainly Staphylococcus equorum) were found at 5–15% of the total flora. Model systems were used to study the microbial interactions for growth, colour and aroma development within the surface flora to be able to formulate a defined starter culture. Commercially available surface starters do not reflect the microbial composition of the cheese surface. Too much emphasis is put on B. linens because of the orange pigmentation. New results showed that the red–brown or orange pigments are most likely due to the yellow pigmented Arthrobacter sp. in the surface flora. The mechanisms of developing the different shades of red are not yet understood. B. linens may be more important for aroma development, due to a highly efficient sulfur metabolism which also affects colour development. The importance of commercial S. xylosus is not clear since S. equorum was predominant instead, on all cheese varieties analysed. Brines were determined to be a natural reservoir for salt-tolerant S. equorum. The successful use of a defined 5-strain starter (D. hansenii, B. linens, A. nicotianae, Corynebacterium ammoniagenes and S. sciuri) for Tilsit cheese ripening was demonstrated on a 10 kg scale. Further improvement is currently being tested within an EU funded project.