No abstract

A specifically aimed SPME/GC-MS method has been assessed in order to describe the volatile fraction of intense flavoring cheeses like Fiore Sardo PDO, a prevalent lipolytic ripening sheep cheese from Sardinia, Italy. A DVB/ CAR/PDMS 50/30 µm fiber and a 3-min exposure time showed to be the best compromise between the possibility to extract compounds with a wide range of polarity and molecular mass and the need to avoid competition and displacement effects among analytes. The volatile compound profile of Fiore Sardo PDO sheep cheese was largely characterized by carboxylic acids (about 68% of the total area of recognized peaks), whereas esters (14%), ketones (9%), and alcohols (8%) represented other abundant classes of low molecular weight species. A number of low-smelling thresh-old trace compounds were also identified as likely contributors of aroma of the Fiore Sardo PDO cheese.

The contribution to flavor generation and secondary proteolysis of 2 strains of mesophilic lactobacilli isolated from cheese was studied. Miniature soft cheeses (200 g) were produced with or without the inclusion of a culture of Lactobacillus plantarum I91 or Lactobacillus casei I90 in the starter composed of Streptococcus thermophilus. During ripening, cheeses containing the added lactobacilli showed an increased content of total free amino acids, but this increase was only significant in cheeses with Lb. plantarum I91. In addition, free amino acid profiles were modified by selective increases of some amino acids, such as Asp, Ser, Arg, Leu, and Phe. Cheeses inoculated with Lb. plantarum I91 or Lb. casei I90 were also characterized by a significantly higher concentration of diacetyl, a key flavor compound, and an increased content of acetoin. Results suggest an increase in the catabolism of either citrate or aspartate, with the production of the derived aroma compounds. Overall, aspartate content increased in both lactobacilli-added cheeses, whereas citrate was more or less constant, suggesting that aspartate could be the source of increased diacetyl and acetoin. A triangle aroma test showed that the addition of the lactobacilli strains significantly changed the sensory attributes of cheeses. At least 11 of 12 panelists commented that the aroma of cheeses with adjuncts was more buttery than that of control cheeses, which is desirable in most soft cheeses. Both Lb. plantarum I91 and Lb. casei I90 performed well as adjunct cultures by influencing cheese aroma development and cheese proteolysis.