Résumé : Yeasts are commonly detected in cheese. Two yeast species, Kluyveromyces lactis and Pichia fermentans, were isolated at high populations from raw-milk Cantal cheese, a French Protected Denomination of Origin hardcheese. To investigate the interest of these 2 species as adjunct cultures to promote...Yeasts are commonly detected in cheese. Two yeast species, Kluyveromyces lactis and Pichia fermentans, were isolated at high populations from raw-milk Cantal cheese, a French Protected Denomination of Origin hardcheese. To investigate the interest of these 2 species as adjunct cultures to promote flavor development of Cantalet cheese, they were added at 105 cfu/mL to microfilteredmilk. The global microbiological, biochemical, and flavor changes induced by the presence of the yeasts in cheese were determined. Adjunct yeasts were presentat 106 cfu/g in curd, declined to 104 to 105 cfu/g in cheese, and did not influence gross composition, content of free amino acids, or content of free fatty acids. By using 8-way gas chromatography-olfactometry in parallel with gas chromatography-mass spectrometry, 30 odorous compounds of Cantalet cheese were identified. The olfactory profiles of K. lactis cheeses contained significantly greater levels of 8 odorous compounds (ethanol, ethylhexanoate, 4 aldehydes, and 2 branched-chain acids)compared with the control and P. fermentans cheeses.Sensory analysis of cheeses flavor discriminated K. lactischeeses on only 2 attributes (acetaldehyde and alcohol odors). This study shows that yeast contribution is species-specific and that K. lactis, at a population of 106viable cells/g, can influence Cantalet cheese flavor
Résumé : Abstract # Cantal is the third French Protected Denomination of Origin cheese. The Cantal cheesemaking process is similar to Cheddar cheese. Both processes involve a milling and a dry salting step which results in a homogeneous salted curd. In order to determine the key parameters of...Abstract # Cantal is the third French Protected Denomination of Origin cheese. The Cantal cheesemaking process is similar to Cheddar cheese. Both processes involve a milling and a dry salting step which results in a homogeneous salted curd. In order to determine the key parameters of themanufacturing process acting on the specific characteristics of this cheese variety, an extensive and kinetic study repeated three times was carried out at nine stages from the raw milk to 120 d ripened cheese. The microbial ecosystem was explored by numeration and by direct extraction of DNA and PCR-Temporal Temperature Gradient Electrophoresis. Lysis of the lactic acid bacteria was checked by quantification of the intracellular lactate dehydrogenase activity. Carbon sources changes, solubilisationof minerals, proteolysis, lipolysis, and formation of neutral volatile compounds were alsoassessed. Cheese microstructure modifications and bacterial localisation were determined by confocal scanning laser microscopy. The controlled manufacturing conditions and the use of a complex mixture of starters led to very similar ripened cheeses. The compositional attributes (in particulartotal solids, fat, nitrogen forms), the lipolysis (0.7 ± 0.2% fat) and proteolysis final extent (34.4 g·kg#1 free amino acids in juice) were similar as well as major neutral volatiles compounds (2-butanone, ethanol and 2-butanol). Nevertheless, lactose and citrate metabolisms differed between the three trials and some free amino acids (Arg, Pro, Ser, Cit, Homocys) concentrations varied drastically during the ripening time course. CLSM micrographs showed that fat globuleswere disrupted during pressing and bacteria were preferentially localised at the fat/protein interface.As the lactic starter species were the same in the three trials and predominant during the cheese manufacture, the observed differences could result of one or several of the followings: (i) the raw milk microflora which showed to be different leading to growth or metabolism activity of particularsubdominant populations during the process and the ripening
Résumé : n spite of its high production (18000 T yearly), very few studies have been devoted to Cantal, a French AOC (Appellation d'Origine Contrôlée) cheese variety whose making process is close to that of Cheddar. To improve the knowledge of this type of cheese, two ripened Cantal cheeses issued from...n spite of its high production (18000 T yearly), very few studies have been devoted to Cantal, a French AOC (Appellation d'Origine Contrôlée) cheese variety whose making process is close to that of Cheddar. To improve the knowledge of this type of cheese, two ripened Cantal cheeses issued from raw milk and two different industrial processes were biochemically, physicochemically, structurally and microbiologically characterised through the analysis of both cheese sectors and juices extracted by pressure. The results obtained were compared with Cheddar and Emmental cheeses. The main differences between Cheddar and Cantal cheeses of the same age were a higher rate of proteolysis for Cantal cheese shown by both the total nitrogen content and the TCA soluble nitrogen in the respective cheese juices, and higher CaT content as well as an increased molar CaT/PT ratio in the Cantal cheese. Free amino contents in the cheese aqueous phase were similar but individual variations suggested an effect of the secondary ripening microflora provided by the raw milk used. Microbial counts done on different media showed a dominant mesophilic and thermophilic lactic acid bacteria flora, a subdominant flora composed of various ripening bacteria and yeasts and a very low level of some coliforms and of Pseudomonas. An amount of 44 neutral volatile compounds were identified but 3 of them determined by GC-MS (ethanol, 2-butanone and 2-butanol) represented more than 95% of the total peak area. Some variations in these main compounds as well as in minor ones confirmed a difference in the native microflora in the two studied Cantal cheeses. Nevertheless, these data appeared in the range of those reported for Cheddar. The microstructure of fat determined by confocal laser scanning micrography showed that little is present in Cantal cheese as intact fat globules. Most of this component appeared as free fat included in the casein matrix with a high ability to oil off, especially the part which is near the crust. As well as offering a precise characterisation of many compositional aspects of ripened Cantal cheese, this study opens the way for further works on the process kinetics carried out in the making processes and for a better knowledge of the ecosystem metabolism.