Microstructure, physicochemistry, microbial populations and aroma compounds of ripened Cantal cheeses

In spite of its high production ( 18000 T yearly), very few studies have been devoted to Cantal, a French AOC (" Appellation d'Origine Controlee") 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 Ca-T content as well as an increased molar Ca-T/P-T 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.