Abstract
Streptococcus thermophilus is a thermophilic lactic acid bacterium used as starter culture for the manufacture of fermented dairy products. For the production of Crescenza and other soft cheeses, Sacco has developed and provides dairies with three different defined blends of S. thermophilus strains. Each blend contains two different S. thermophilus strains. The strains were selected based on their unique technological properties as well as different phage profiles. Analysis of 133 whey samples collected in 2009–2010 from Italian dairies showed a high prevalence (about 50%) of bacteriophage attacks on the blend ST020. More specifically, the strain S. thermophilus ST1A was found to be the preferred target of the bacteriophages. A bacteriophage insensitive mutant (BIM5) of the phage-sensitive strain ST1A was successfully developed and used to substitute strain ST1A in the Crescenza starter culture ST020. The strain BIM5 showed identical technological and industrial traits as those of the phage-sensitive strain ST1A. The improved resistance of the modified Crescenza starter culture ST020R was confirmed at Italian dairies, and its effectiveness monitored on 122 whey samples collected in 2011–2012. Compared to the previous values (2009–2010), the use of the phage-hardened blend ST020R allowed reducing of frequency of phage attacks from about 50 to less than 5% of the whey samples investigated.
Highlights
Streptococcus thermophilus is the second most important industrial species after Lactococcus lactis (Fox and Cogan, 1993; Hols et al, 2005) and it is used in the manufacture of yogurt as well as many traditional Italian cheeses such as Mozzarella and Crescenza
The Bacteriophage-Insensitive Mutants (BIMs) more similar to the strain ST1A were selected for pilot scale production, blended at 50% ratio with the strain ST1B, and the acidification performance of the resulting starter culture ST020R was compared to that of ST020 using the Cinac4 as described above
TECHNOLOGICAL TEST OF THE NEW BLEND To verify if the blend ST020R containing the BIM of ST1A was suitable for the production of high quality Crescenza, at a pilot plant of a local dairy two Crescenza productions were performed, one with ST020 and one with ST020R
Summary
Streptococcus thermophilus is the second most important industrial species after Lactococcus lactis (Fox and Cogan, 1993; Hols et al, 2005) and it is used in the manufacture of yogurt as well as many traditional Italian cheeses such as Mozzarella and Crescenza. The manufacture of Crescenza – and of cheese in general – requires the inoculation of milk with carefully selected bacterial strains blends, known as starter cultures, allowing the control of fermentation and production of high-quality fermented products. For the production of Crescenza, Sacco provides three blends of starter cultures each composed by two strains of S. thermophilus. Because significant amounts of bacterial cells are cultivated in the fermentation vats, most cheese industries have experienced problems with phage contaminations (Emond and Moineau, 2007). The generation of Bacteriophage-Insensitive Mutants (BIMs), described by Mills et al (2007), has received particular attention by starter culture manufacturers. BIMs are useful to fermentation-based industries; it is possible to introduce them in the starter culture instead of the strains, which www.frontiersin.org
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