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

After screening 372 strains of Lactobacillus spp. isolated from a Portuguese traditional dry fermented sausage, two Lactobacillus strains, a Lactobacillus homohiochii and a L. curvatus were selected, because they were positive for tyrosine and ornithine decarboxylase activities. Evidence for extracellular proteolytic activity was also demonstrated for the two Lactobacillus strains, with some strain variation in terms of specific activities towards different substrates. lytic activity was shown to be maximal in the early exponential growth. This proteolytic activity was higher when cells were grown in a peptide-rich medium such as MRS, when compared to skim milk. y using several protease inhibitors showed that this activity is associated with metalloproteases in the case of the L. curvatus strain, but for L. homohiochii besides metalloproteases, serine-type proteases are also involved. teinaceous 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 of these proteolytic Lactobacillus strains. Their ability to produce biogenic amines may be used as an index of microbial quality of the fermented meat product.