The influence of yeasts on the aroma of Stilton cheese

Blue cheeses comprise secondary microbial flora which is not controlled during production. The secondary flora of Stilton comprises distinct yeast communities in each section of the cheese (blue veins, white core, outer crust). Previous work has identified yeasts species-specific effects on aroma development. However, large variation between replicates was observed and this emulates the problem faced by the industry in achieving product consistency. Stilton shows variation in aroma between and within batches produced. In the present study factors influencing yeasts' impact on aroma variation were investigated by incubating Stilton yeast isolates in milk-based models, with and without the mould Penicillium roqueforti, which is the major contributor to blue cheese aroma development. Resultant aroma profiles of models were analysed via Solid-Phase Microextraction Gas Chromatography-Mass Spectrometry (SPME GC-MS) and Principal Component Analysis (PCA). Sensory studies (Flash Profile, Napping®, Triangle, Paired Comparison and Constant Reference ranking tests) were conducted to determine whether findings were perceivable by humans. The concentration of yeasts and growth conditions of the models influenced aroma generation. The production of ketones, major contributors to blue cheese aroma, increased as the concentration of Yarrowia lipolytica, inoculated into models containing P. rouqeforti, increased. Variation in the aroma profiles of replicate samples decreased as the concentration of Kluyveromyces lactis, inoculated into models containing P. roqueforti, decreased. Sensory analysis indicated the effects of Y. lipoltyica and K. lactis on aroma profiles observed instrumentally may not be perceivable by humans. The results of this study suggest that yeasts could be used as adjuncts in Stilton production to manipulate the production of aroma compounds and limit variation in aroma profiles.