Microbiological and physico-chemical characterisation of deep spoilage in Spanish dry-cured hams and characterisation of isolated Enterobacteriaceae with regard to salt and temperature tolerance

The microbiological and physico-chemical characteristics of dry-cured Spanish "serrano" hams with deep spoilage were compared to unspoiled hams, and the evolution of similar characteristics was studied during the early curing stages of previously refrigerated or frozen hams. The results suggest a relationship between deep spoilage and the presence of Enterobacteriaceae, caused by insufficient NaCl concentrations during curing. Strains of Serratia liquefaciens, Enterobacter cloacae and Proteus vulgaris, which comprised the most frequently isolated species of enterobacteria from spoiled hams, were therefore characterised in a model system in order to examine their ability to grow in different NaCl concentrations at different temperatures. Strains isolated from normal hams during early curing stages and from the production environment were included for comparison. The results showed that all strains were able to grow in 7% NaCl at 5 degrees C, and that strains isolated from spoiled hams did not differ from those isolated from normal hams and from the environment. The NaCl tolerance of strains isolated from spoiled hams was closely linked to incubation temperature, and a reduction in temperature from 5 degrees C to 2 degrees C reduced the tolerance significantly.