dc.contributor.author | Gebreselassie, Hailay Kidanu | |
dc.date.accessioned | 2014-08-07T10:39:17Z | |
dc.date.available | 2014-08-07T10:39:17Z | |
dc.date.copyright | 2014 | |
dc.date.issued | 2014-08-07 | |
dc.identifier.uri | http://hdl.handle.net/11250/216859 | |
dc.description.abstract | A study on diversity of bacterial strains and bacteriophages in Norwegian cheese production
was assessed on samples from TINE`s cheese production. Samples were obtained from a dairy
plant in Nærbø that was experienced fermentation problems. 96 bacterial strains were also
isolated from another TINE's dairy plant in Storsteinnes which was producing quality cheese.
Both dairies were using the same commercial starter cultures. For phage isolation bulk starter
and whey samples were used to infect 96 bacterial strains. Forty phages were isolated from
specific indicator strains. Using the isolated phages, phage typing of all the 96 strains was
performed, and plaque formation was obtained on 80 strains. The sensitivity of bacterial
strains was highly variable and isolated phages had a broad host range infecting between 4%
(Ф837) and 44% (Ф878) of the strains. In addition, (GTG)5-PCR enabling the differentiation of
all the bacterial strains in to 8 clusters. Furthermore, cell wall polysaccharide genes typing of
bacterial strains were also carried out and 91 strains were found to have genes encoding
different CWPS types, while five strains were suggested to have another type of cell surface.
Our results showed that Lactococcus lactis of CWPS group B were the predominant starter
culture used in the Norwegian cheese production. Finally, the effect of the isolated phages in
fermentation activity of mixed starter cultures was also assessed and results showed a change
in pH during milk fermentation. Though, pooled phage isolates caused inhibition in acid
production, our phage isolates alone were not shown to cause a severe effect in the activities
of the commercial starter culture. Therefore, further studies using single starter culture are
recommended to reveal the actual impact of the isolated phages on dairy fermentation
processes. | nb_NO |
dc.language.iso | eng | nb_NO |
dc.publisher | Norwegian University of Life Sciences, Ås | |
dc.subject | VDP::Matematikk og Naturvitenskap: 400::Basale biofag: 470::Generell mikrobiologi: 472 | nb_NO |
dc.subject | VDP::Teknologi: 500::Næringsmiddelteknologi: 600 | nb_NO |
dc.title | Diversity of bacterial strains and bacteriophages in Norwegian cheese production | nb_NO |
dc.type | Master thesis | nb_NO |
dc.source.pagenumber | 55 | nb_NO |
dc.description.localcode | M-MB | nb_NO |