Dynamics and characterization of yeasts during ripening of typical Italian dry-cured ham.

The evolution of the yeast population during manufacturing and ripening of dry-cured Parma ham was investigated. Contamination levels ranged from 10(5) to 10(7) cfu/g on muscle surface, 10(4) to 10(6) cfu/g on covering fat and exceeded 10(7) cfu/g on spreadable fat mince ("sugna"). Two hundred and sixty one yeast isolates underwent identification test, showing that the predominant species of yeast population during the whole maturing process were Debaryomyces hansenii, Candida zeylanoides, Debaryomyces maramus, and to a lesser extent, Candida famata and Hyphopichia burtonii. The species Candida catenulata, Candida guilliermondii, Candida edax and other genera like Cryptococcus and Wingea were occasionally found. The yeast counts and species distribution changed according to the stage of processing and to the ham sampling location. At the end of the cold phase, the washing procedure was effective in lowering the yeast count in muscle and fat surface layers, but during the next ageing stages, yeast colonization of unskinned ham muscle increased again, though species distribution changed if compared to previous manufacturing phases. The ripening steps taken into account from the end of the cold phase to the final outcome, were always characterized by more than one yeast species, suggesting that yeasts other than Debaryomyces spp. could play a remarkable role on the sensory and safety properties of typical Italian dry-cured ham.