Diversity and activities of yeasts from different parts of a Stilton cheese

Blue cheeses are very complex food matrices presenting significant spatial differentiation between sections and the Stilton variety also has a hard brown crust making its matrix even more complex. The mycobiota communities in the three sections (blue veins, white core and outer crust) of a Stilton blue cheese were studied by employing culture-independent (TRFLP, DGGE) and culture-dependent analyses. Yeasts isolated from the cheese were studied for aroma production in a dairy model system with and without the starter Lactococcus lactis and filamentous fungus Penicillium roqueforti using SPME GC–MS. Significant qualitative and quantitative differences were observed in the yeast communities between the cheese sections with all the techniques. Yarrowia lipolytica presented strong synergistic activity with P. roqueforti enhancing the production of ketone aroma compounds, characteristic of blue cheeses. Culture techniques allowed the observation of the presence and uneven distribution of two different morphological groups of Debaryomyces hansenii in the different sections and of Trichosporon ovoides but failed to isolate Candida catenulata which dominated some parts of the cheese in the culture-independent analysis. This suggests that this species may be an important early coloniser but fails to survive into the final cheese. The study indicated that the yeast flora in the cheese sections differ including isolates that could affect their aroma profiles.