Characterisation of Egyptian Ras cheese. 2. Flavour formation

Thirteen samples of commercial Ras cheese made from raw milk at different ripening-times were collected to evaluate the sensory properties and to identify the typical flavour compounds. Cheeses were assessed by sensory evaluation and the rheological properties were determined using a texture analyser. The flavour volatile compounds were identified by the purge-and-trap, thermal desorption cold-trap (TDCT), and gas chromatography mass spectrometry (GC-MS). The sensory results indicated that nine samples were typical Ras cheeses and four samples were not typical. Typical Ras cheeses are tasty, piquant and sharp in flavour, not too hard and not soft in texture and the body includes some mechanical opening and gassy opening and the colour is regular. A good correlation was found between the rheological measurements calculated by machine and the texture score evaluated by panellists. GC-MS analysis revealed that, sixty-eight volatile compounds were detected in Ras cheese samples, including 13 alcohols, 11 aldehydes, 17 ketones, 25 esters and four other compounds, which are responsible for the cheese flavour. There were differences in the concentrations of these aroma-compounds, corresponding with the age of the cheeses. GC-MS data showed a good correlation with the organoleptic descriptions.