Phage-insensitive Streptococcus cremoris starter strains were
selected by assaying cheese whey against potential starter
strains. Six strains were selected and characterized for continual
use in cheesemaking. Upon phage-infection, strains were removed
from the blend. Cheesemaking continued with remaining strains. A
phage-insensitive, fast-acid-producing mutant of the infected
strain was isolated and characterized. This mutant, similar to the
parent, was returned to the strain mixture. Multiple-blend
starters were also used in cottage cheese and cultured buttermilk
manufacture.
Individual strains were used as antigens for a rapid detection
test for lactic-streptococcal agglutinins in cheese milk. When
sedimentation was encountered, agglutinin-sensitive strains were
identified and replaced instead of an entire culture blend.
Phage-insensitive mutants were compared to their respective
parent strains. Traits examined included acid-producing activity,
optimum temperature, generation time, proteolysis, phosphate and
NaCl tolerance, phage adsorption, agglutination, morphology, and
induction. Mutant strains showed variations in individual characteristics,
but no general pattern of variation was observed.
Bulk starters, prepared by growing then freezing individual
strains in a commercial internal-pH-control medium (PHASE 4), were
stored for 3 mo with and without glycerol. Strains varied in
storage survival at -20 C. Glycerol enhanced cell viability and
activity at -20 C. Storage in PHASE 4 at -40 C and -80 C preserved
activity and viability without glycerol. Unfrozen PHASE 4 cultures
retained original activity and viability after 1 mo refrigerated
storage. Frozen and refrigerated PHASE 4 starters have been used
in Cheddar and cottage cheese manufacture for more than 1 yr.
Exclusive use of defined-strain cultures resulted in significant
manufacturing and economic improvements including elimination
of culture rotations and starter failure from phage infection, no
ripening period, greater cheese uniformity, predictable starter
activity, standardized manufacture, and improved cheese quality.
Grade-A cheese production was increased by almost 10%. This
technology enabled some factories to increase cheese yields by
adding whey cream to cheese milk. The combined improvements, based
on defined-strain technology, have enabled factories to increase
production—some by nearly 50%. To date, more than 150 million lb
of Cheddar cheese have been manufactured with defined-strain
cultures. / Graduation date: 1983
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27458 |
| Date | 04 November 1982 |
| Creators | Thunell, Randall Kirk |
| Contributors | Bodyfelt, F. W. (Floyd W.), 1937- |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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