Growth and aroma production by Staphylococcus xylosus, S. carnosus and S. equorum--a comparative study in model systems.

A laboratory medium inoculated with 20 different Staphylococcus strains was prepared in accordance with a full factorial experimental design investigating the effect of temperature, pH, NaCl and glucose on growth. The 12 strains most suited to growth in a fermented meat environment were inoculated in sausage minces together with Pediococcus pentosaceus, incubated at 25 degrees C for 1 week and the produced aroma compounds collected. The data were analysed by multiple linear regression and partial least squares regression analysis. The results showed that increasing pH and temperature from 4.6 to 6.0 and 10 to 26 degrees C, respectively, increased growth of all strains with strong synergy between temperature and pH. Increasing salt concentration from 5% to 15% w/v decreased growth of most strains, but the effect of pH and temperature was much stronger than the effect of salt. Strains of S. carnosus were more salt tolerant than strains of S. equorum and S. xylosus, especially at high pH and temperature. Addition of glucose up to 0.5% w/v had no significant influence on growth of any of the strains. With regard to aroma production, species characteristics were detected. S. carnosus and S. xylosus were quite different regarding the overall aroma profiles, whereas the profiles of S. equorum lied somewhere in-between. Contrary to S. carnosus, S. xylosus and S. equorum did not produce 2-methyl-1-butanol. On the other hand, in particular, S. xylosus produced more 3-methyl-1-butanol. Except for one of the strains of S. equorum, S. xylosus and S. equorum formed more diacetyl, 2-butanone and acetoin and also more of the methyl-branched ketones arising from degradation of leucine, isoleucine and valine. S. carnosus produced more methyl-branched aldehydes, acids and corresponding esters from leucine, isoleucine and valine compounds that have been correlated with fermented sausage maturity in former studies. S. equorum produced the least of the methyl-branched aldehydes.