Heat resistant sporeforming psychrotrophic bacteria were
isolated from raw milk samples from 59 Grade A farms in Oregon.
Forty-nine of the 59 (83%) raw milk samples in this survey
contained sporeforming psychrotrophic bacteria; isolates from
twenty-four (40%) of the samples exhibited proteolytic properties. Populations of sporeforming psychrotrophic bacteria ranged
from <10 to >10,000 CFU/mL for all samples. One hundred-two
isolates were identified as Bacillus species. Twelve different
Bacillus species were identified with B. licheniformis being the
most predominate (18% of the samples) and B. laterosporus the
least frequently isolated species, (2%). Fifty-eight percent of
the bacilli isolates produced a bitter off-flavor and putrid
odor, while 42% produced a fruity and/or rancid off-flavor when
inoculated into sterile whole milk. Based on biochemical
activity tests, 83% of the thermoduric isolates hydrolysed
casein while 56% were proteolytic (in litmus milk), 57% demonstrated
lipolytic activity and 31% produced acid in litmus milk. Forty-eight isolates that tested positive for proteolysis were
evaluated quantitatively for activity, which ranged from 0.93 to
1.93 units (expressed as mM of alanine). Isolates of Bacillus
cereus var. mycoides demonstrated significantly higher
(p>0.05) proteolytic activity than other Bacillus species
isolated. / Graduation date: 1988
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27089 |
| Date | 07 August 1987 |
| Creators | Meer, Ralph R. |
| 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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