Date of Award:

1979

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Advisor/Chair:

Gary H. Richardson

Abstract

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.

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