Formation of amino acid (L-leucine, L-phenylalanine) derived volatile flavour compounds by Moraxella phenylpyruvica and Staphylococcus xylosus in cured meat model systems.

A bacterial strain isolated from Danish immersion curing brine, Moraxella phenylpyruvica 0100, and a commercial meat starter culture, Staphylococcus xylosus DD34, were tested for their ability to form characteristic volatile compounds in minimal medium with the added amino acid L-leucine or L-phenylalanine under different environmental conditions (pH 5.5 and 6.0; 0 and 210 ppm nitrate; pre-incubation with and without agitation) and compared with respect to their ability to form volatile compounds in cured meat extracts and vacuum-packed cured meat cuts. The characteristic cured meat aroma precursors/compounds 3-methylbutanal and 3-methylbutanol were found to be formed in cured meat extracts and vacuum-packed cured meat cuts inoculated with M. phenylpyruvica. These volatiles are most probably formed by metabolic conversion of the amino acid L-leucine by M. phenylpyruvica, as they were also produced in minimal media with added L-leucine inoculated with this organism. The characteristic L-phenylalanine derived compound, benzaldehyde, formed by M. phenylpyruvica in minimal medium in the presence of nitrate (210 ppm), was not produced in any noticeable amount in cured meat extracts or vacuum-packed cured meat inoculated with M. phenylpyruvica. In contrast, benzacetaldehyde, which has been described as a possible metabolic product of the microbial conversion of L-phenylalanine, was found to be a characteristic volatile compound formed in cured meat extracts and vacuum-packed cured meat inoculated with M. phenylpyruvica, indicating an alternative metabolic pathway for L-phenylalanine by this organism in a cured meat environment. Even though S. xylosus was able to form volatile compounds characteristic of cured meats (3-methylbutanal, 3-methylbutanol) in minimal media with added L-leucine, this bacterial strain seemed not to be able to produce these characteristic volatiles in the studied cured meat systems. The present data imply that M. phenylpyruvica, in particular, is a potential meat starter for ensuring superior flavour development in cured meat.

Proteolytic and lipolytic activities of Micrococcus roseus (65), Halomonas elongata (16) and Vibrio sp. (168) isolated from Danish bacon curing brines.

Viable cells, cell free extracts and extracellular concentrates of Micrococcus roseus (65), Halomonas elongata (16) and Vibrio sp. (168) isolated from Danish bacon curing brines were examined for lipase, esterase, proteinase and aminopeptidase activities on natural and synthetic substrates. Micrococcus roseus (65) produced one intracellular esterase with affinity for short chain esters, and two intracellular aminopeptidases with affinity for nonpolar amino acids and L-arginine, respectively. One extracellular aminopeptidase with affinity for L-proline was also observed. Three intracellular esterases with affinity for short chain esters and a membrane bound esterase with affinity for butyric to capric esters were found in Halomonas elongata (16), but almost no aminopeptidase activity was found. Vibrio sp. (168) had four intracellular esterases with affinity for short chain esters and one esterase with affinity for all tested esters. Furthermore, an enzyme, which did not migrate on electrophoretic gels, had activity on all examined esters and tributyrin. Small intracellular activity on L-alanine was observed for this bacterial strain. There was no proteinase activities in the tested bacteria.