Time-related changes in nitrogen fractions and free amino acids of lean tissue of frech dry-cured ham.

The 80 hams of 40 pig carcasses from one slaughter batch were taken on the day after slaughter. The 40 left hams were dry-cured. Groups of 10 hams were taken for analysis at 74 days (end of rest), 81 days (end of heating), 179 days (mid-seasoning) and 273 days (end of seasoning) after the beginning of processing. A slice of about 150 g was taken in the middle of the Biceps femoris and used for analysis of nitrogen fractions and free amino acids by HPLC. Levels of insoluble nitrogen compounds did not vary significantly, while levels of soluble protein nitrogen decreased strongly from 26 to 16% of total nitrogen, with the fastest decrease observed between days 179 and 273. Levels of non-protein nitrogen increased regularly during the processing from 12 to 23% of total nitrogen. Nitrogen of free amino acids ranged from 3·6% in fresh muscle to 16·6% of total nitrogen at day 179, then decreased to 4·4% of the total nitrogen at the end of the processing. The HPLC method allowed the identification of 29 compounds, among which 27 were amino acids and 2 were dipeptides. The average levels of free amino acids of non-protein origin tended to decrease before day 74, then to increase until day 179 and to decrease again. The levels of compounds of protein origin increased or tended to increase from the beginning until day 179, then decreased.