Seven strains of Streptococcus cremoris and Streptococcus lactis were tested for temperature sensitivity on a temperature gradient bar. A temperature of 37 C was the optimum for differentiating between temperature-sensitive and insensitive strains. Temperature-insensitive strains produced cell masses with absorbance values of 0.1 or higher and activity levels of 1.0 (expressed as a decrease in pH) or above at 37 C. Temperature-sensitive strains failed to produce these cell masses and activity levels, Strain selection and resistant- mutant isolation made it possible to identify ten strains of Streptococci sufficiently free of phage sensitivity for use in a cheese plant rotation program. These resistant mutants failed after being successfully used in mixed cultures for a short period of time, They became either slow acid producers or were again attacked by new bacteriophages. More work is needed to successfully isolate phage-resistant mutants suitable for cheese starters.
| Identifer | oai:union.ndltd.org:UTAHS/oai:digitalcommons.usu.edu:etd-6252 |
| Date | 01 May 1979 |
| Creators | Jeng, Luna Ying-Chung |
| Publisher | DigitalCommons@USU |
| Source Sets | Utah State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | All Graduate Theses and Dissertations |
| Rights | Copyright for this work is held by the author. Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user. For more information contact digitalcommons@usu.edu. |
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