Biomedical subjects

Maria Emanuela Fornasari

Publications and source records attributed to Maria Emanuela Fornasari.

4 recordsLinked to original sources

PubMed2006

Cultivability of Streptococcus thermophilus in Grana Padano cheese whey starters.

The application of a culture-independent approach, that of reverse transcriptase-length heterogeneity-PCR coupled with epifluorescence microscopy, allowed us to observe that Streptococcus thermophilus is metabolically active, but only partially cultivable in Grana Padano cheese whey starters. A short preincubation of the starters in sterile skimmed whey was followed by cultivation in sterile skimmed whey-enriched M17. This procedure restored the cultivability of S. thermophilus and enabled us to detect S. thermophilus at ranges (10(7)-10(8) CFU mL(-1)) which have rarely been reported in these cultures. The use of cheese whey as a cultivation-revitalization substrate can be useful to obtain an unbiased picture of the microbial composition of whey starters for Grana Padano cheese, thus avoiding an underestimation of S. thermophilus in these cultures.

Bacteriological Techniques↗

PubMed2005

Heterogeneity of putative surface layer proteins in Lactobacillus helveticus.

The S-layer-encoding genes of 21 Lactobacillus helveticus strains were characterized. Phylogenetic analysis based on the identified S-layer genes revealed two main clusters, one which includes a sequence similar to that of the slpH1 gene of L. helveticus CNRZ 892 and a second cluster which includes genes similar to that of prtY. These results were further confirmed by Southern blot hybridization. This study demonstrates S-layer gene variability in the species L. helveticus.

Amino Acid Sequence↗

PubMed2003

Yeasts associated with Manteca.

Manteca is a traditional milk product of southern Italy produced from whey deriving from Caciocavallo Podolico cheese-making. This study was undertaken to obtain more information about the microbiological properties of this product and particularly about the presence, metabolic activities, and technological significance of the different yeast species naturally occurring in Manteca. High numbers of yeasts were counted after 7 days ripening (10(4)-10(5) cfu g(-1)) and then decreased to 10(2) at the end. A total of 179 isolates were identified and studied for their phenotypic and genotypic characteristics. The most frequently encountered species were Trichosporon asahii (45), Candida parapsilosis (33), Rhodotorula mucilaginosa (32), Candida inconspicua (29). Some of these yeasts showed lipolytic activity (32 strains) and proteolytic activity (29 strains), NaCl resistance up to 10% and growth up to 45 degrees C (42 strains). Biogenic amines were formed by proteolytic strains, in particular phenylethylamine, putrescine and spermidine. Spermidine was produced by all the yeasts tested in this work, but only Trichosporon produced a great quantity of this compound. Histamine was not detectable. Caseinolytic activity was common to almost all strains, corresponding to the ability to efficiently split off amino-terminal amino acids. The highest and most constant activity expressed by all species was X-prolyl-dipeptidyl aminopeptidase. The findings suggest that the presence of yeasts may play a significant role in justifying interactions with lactic acid bacteria, and consequently with their metabolic activity in the definition of the peculiar characteristics of Manteca cheese.

Aminopeptidases↗

PubMed2003

Synthetic peptides as substrate for assaying the proteolytic activity of Lactobacillus helveticus.

Four Lactobacillus helveticus strains were studied for proteolytic capacity and general aminopeptidase (AP) and X-Pro dipeptidyl aminopeptidase (DAP) activity. The rate of hydrolysis and the activity against synthetic substrates with N-terminal residues of Arg, Lys, Leu, Glu or Pro, varied markedly among the strains. The X-Pro DAP activity was consistently high. The crude cell-wall and cytoplasm extracts from strain Lb. helveticus ISLC59 were analysed thoroughly for their proteolysis ability by using four synthetic peptide substrates, including alpha(s)1-CN(f1-23). Peptides formed during in vitro hydrolysis of the synthetic substrates by cell wall and cytoplasm preparations were identified by LC-ESI/MS. In doing so, it was possible to infer a prevalent endopeptidase activity splitting Lys7-His8 and Gln13-Glu14 bonds in the cytoplasm, and to deduce a secondary activity, which hydrolysed Glu14-Val15, Leu16-Asn17, Glu18-Asn19 and Lys3-His4 bonds lacking in the cell-wall. The presence of exopeptidases, as mainly AP, DAP, and carboxypeptidase (CPase) was deduced from the formation of several N- and C-terminally truncated peptides sets. The AP activity was higher in the cell-wall layer, where CPase activity was absent. The in vitro assays with cell extracts of the Lb. helveticus ISLC59 strain revealed extensive exopeptidase and endopeptidase activities. In several cases, the hydrolytic system of Lb. helveticus that splits in vitro alpha(s)1-CN(f1-23) peptide bonds was similar to that of Lactococcus lactis. The effects were also compared with those occurring in vivo in hard cheese such as Grana Padano.

Amino Acids↗