In the blue cheese Stilton the starter mould Penicillium roqueforti grows and sporulates during the ripening period and is considered to be responsible for the unique blue cheese aroma. However, the sporulation of the mould, which results in the formation of blue veins, takes place in a fraction of the Stilton matrix which overall is very heterogeneous. Most blue cheeses develop a secondary microflora of yeasts which may affect their aroma. The aim of this study was to investigate the yeast flora of Stilton, the aroma profile of the cheese and the role of the yeasts in the aroma production. The approach in this work was to study individually the different sections of Stilton (the blue veins, the white core and the outer crust) as previous studies have demonstrated each section has a differing bacterial flora. In addition to the classical microbiology, a series of molecular techniques (Denaturing Gradient Gel Electrophoresis, Restriction Fragment Length Polymorphism and Terminal RFLP) were compared and applied for the screening of the local fungal communities in the cheese. The results showed that the two approaches were complementary. It was concluded that the structure of the fungal community was different for each section of the cheese. The aroma profiles of the three different sections of Stilton were studied using solvent extraction Gas Chromatography-Mass Spectrometry (GC-MS), a headspace GC-MS technique (SPME GC-MS) and direct headspace analysis (Atmospheric Pressure Chemical Ionisation [APCI]-MS). The different sections of Stilton presented different aroma profiles. Overall, the blue and the outer crust had similar profiles. These two sections contained higher amount of ketones while the white contained higher amounts of alcohols and aldehydes. Yeast isolates and the starter Penicillium roqueforti were cultivated alone and in combination in a cheese model and the aroma production was studied with SPME GC-MS analysis. The co-culture of the starter Penicillium roqueforti and individual yeast isolates resulted in aroma profiles different from those that were produced by the mould or the yeasts individually. The model of Penicillium roqueforti with Yarrowia lipolytica resulted in an aroma more similar to blue cheese than produced by the mould alone. Sensory analysis (Flash profile technique) was used in order to compare the aroma of this model with the aroma of blue cheeses and the perception of the combined culture was found to be similar to Stilton cheese, whereas that of the mould alone was not. Yeasts are a significant part of the microflora of Stilton and they are able to affect the aroma production. Selected isolates of Yarrowia lipolytica could be used in combination with Penicillium roqueforti for the production of blue cheese aroma e.g. as a starter culture.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:523085 |
| Date | January 2010 |
| Creators | Gkatzionis, Konstantinos |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/11395/ |
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