Evidence for proteolytic activity and biogenic amines production in Lactobacillus curvatus and L-homohiochii

After screening 372 strains of Lactobacillus spp. isolated from a Portugues e traditional dry fermented sausage, two Lactobacillus strains, a Lactobaci llus homohiochii and a L. curvatus were selected, because they were positiv e for tyrosine and ornithine decarboxylase activities. Evidence for extrace llular proteolytic activity was also demonstrated for the two Lactobacillus strains, with some strain variation in terms of specific activities toward s different substrates. Proteolytic activity was shown to be maximal in the early exponential growt h. This proteolytic activity was higher when cells were grown in a peptide- rich medium such as MRS, when compared to skim milk. A study using several protease inhibitors showed that this activity is asso ciated with metalloproteases in the case of the L. curvatus strain, but for L. homohiochii besides metalloproteases, serine-type proteases are also in volved. In proteinaceous substrates, like dry fermented sausages, the formation of the biogenic amines putrescine and tyramine cannot be excluded when ongoing proteolysis leads to their precursors, as it is the case in the presence o f these proteolytic Lactobacillus strains. Their ability to produce biogeni c amines may be used as an index of microbial quality of the fermented meat product. (C) 2001 Elsevier Science B.V. All rights reserved.