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

Sterile fish muscle homogenate was prepared from the individually line caught black rockfish (Sebastes melanops) and inoculated with the pure culture of Pseudomonas putrefaciens strain 17. The inoculated homogenate was incubated at 5°C and the growth and production of volatile sulfur compounds determined by a combined gas-liquid chromatography and mass spectrometry. A column containing 90-100 mesh diatomaceous earth coated with 10% Carbowax 20M was developed and tested for the quantitative determination of dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS). The DMDS levels in fish homogenate closely paralleled that of P. putrefaciens growth. The maximum DMDS level of 2.00 μg per 100 g fish homogenate was obtained after 10 days at 5°C in samples treated with 1.5% NaCl. NaCl was not required by P. putrefaciens but both the growth and DMDS production were stimulated by 1-2% of NaCl. The DMDS production and the growth of P. putrefaciens were reduced when the homogenate was treated with sodium benzoate (SB) or ethylenediaminetetraacetic acid (EDTA). The maximum levels of DMDS in 0.05% SB treated fish were 0.75 μg per 100 g and 0.85 μg for 0.05% EDTA treatment, respectively. The SB inhibited the growth rate as well as the maximum growth of P. putrefaciens, while EDTA had no effect on the maximum growth but extended the lag period and reduced the rate of growth. Potassium sorbate (PS) had little effect on DMDS production or the growth of P. putrefaciens. The maximum level of DMDS in fish homogenate, treated with 0.1% PS, was 1.80 μg per 100 g and the growth curve was similar to that of the control. / Graduation date: 1974

In order to determine the source of bacteria in Tillamook Bay, Oregon, water samples were collected monthly for six months during the rainy season from October 1975 through March 1976 from the bay and its tributaries, the Kilchis, Trask, Tillamook, and Wilson Rivers. Fecal coliform levels of these samples were determined and the 1,917 bacteria isolated were tested for their resistance patterns to chloramphenicol (Cm), streptomycin (Sm), ampicillin (Am), tetracycline (Tc), chlortetracycline (Ct), oxytetracycline (Ot), neomycin (Nm), nitrofurazone (Ni), nalidixic acid (Na), sulfathiazole (Su), kanamycin (Km), and procaine penicillin G (Pe). The fecal coliform count per 100 ml of bay water ranged from 3.6 to 42.0. The counts for Tillamook River ranged from 13.5 to 112.0, Trask River from 0.0 to 132.0, Wilson River from 8.5 to 105.0, and Kilchis River from 0.5 to 13.9. The rise and fall of fecal coliform levels were characteristic of the sampling date and each sampling station showed its characteristic maximum and minimum levels. The 1,917 fecal coliform isolates showed 176 different resistance patterns to the 12 antibiotics tested. None of the patterns, however, was characteristic of any specific sampling site. The fecal coliform counts of the bay were statistically compared to 135 independent variables that included the fecal coliform counts of tributaries, temperature, river flow data, tide information, antibiotic use data, and the antibiotic resistance patterns. Bay fecal coliform levels were highly correlated with the fecal coliform counts of tributaries especially those of the Trask and Wilson Rivers, degree of resistance to antibiotics, recreational activities, and precipitation. Negative correlation existed between bay fecal coliform count and the ambient temperature. two potentially useful linear regression models to predict bay fecal coliform level were developed using a computerized stepwise multiple linear regression program. / Graduation date: 1977

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