One-hundred Streptococcus thermophilus strains isolated from atypical Italian semi-hard cheese were tested for their acidification activity and growth kinetics in milk incubated at 42 degreesC. The pH was measured at 5-min intervals during 24 h of incubation. Indirect impedance technique was used to monitor growth kinetics. At the end of fermentation time several kinetic parameters were evaluated, which were elaborated using cluster analysis in order to classify the cultures into defined categories with similar acidification and growth performances. Analysis of acidification kinetics evidenced the presence of an urease activity in most of strains, activity that can be evidenced by two peaks of acidification rates during fermentation time. Clustering of acidification and growth parameters grouped the cultures in 3 clusters, well correlated with bad, medium and good performances. This grouping procedure may be recommended as a valuable tool for selecting starters for specific purposes.
ACIDIFICATION AND GROWTH KINETICS IN STREPTOCOCCUS THERMOPHILUS STRAINS: CLASSIFICATION OF CULTURES BASED ON CLUSTER ANALYSIS
MARINO, Marilena;MAIFRENI, Michela;RONDININI, Gabriella
2004-01-01
Abstract
One-hundred Streptococcus thermophilus strains isolated from atypical Italian semi-hard cheese were tested for their acidification activity and growth kinetics in milk incubated at 42 degreesC. The pH was measured at 5-min intervals during 24 h of incubation. Indirect impedance technique was used to monitor growth kinetics. At the end of fermentation time several kinetic parameters were evaluated, which were elaborated using cluster analysis in order to classify the cultures into defined categories with similar acidification and growth performances. Analysis of acidification kinetics evidenced the presence of an urease activity in most of strains, activity that can be evidenced by two peaks of acidification rates during fermentation time. Clustering of acidification and growth parameters grouped the cultures in 3 clusters, well correlated with bad, medium and good performances. This grouping procedure may be recommended as a valuable tool for selecting starters for specific purposes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
