Thesis (Ph. D.)--University of Wisconsin--Madison, 1960. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 92-96).

München, Techn. University, Diss., 2002.

Thesis (doctoral)--Lund University, 1997. / In the title, [beta] is represented by the Greek letter.

Thesis (doctoral)--Lund University, 1997. / In the title, [beta] is represented by the Greek letter.

Graduation date: 2004

Strains of Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris with potential use in the food industry which had been previously isolated from nature using 16S rRNA probes were characterized for unique identifying traits and for attributes important for potential use in cheese manufacture. Strains of Lc. cremoris which showed desirable characteristics for cheesemaking were selected for Cheddar cheese making trials where they were used first as single strains then in combination. Biochemical testing included lithium chloride sensitivity using Alsan medium. Strains of Lc. cremoris showed greater sensitivity to lithium chloride than Lc. lactis. strains. however sensitivity was generally indicated by reduced colony size rather than absence of growth as predicted for Lc. cremoris. strains. Strains of both Lc. lactis and Lc. cremoris produced blue colonies on Alsan medium indicating citrate utilization. Citrate utilization could not be confirmed by other traditional methods. Carbohydrate utilization using API 50 test kits revealed no pattern which could definitively differentiate strains of Lc. lactis from Lc. cremoris. It was found that all strains fermented galactose, D-glucose. D-fructose. D-mannose. N-acetyl glucosamine and lactose. Regardless of genotype. strains which were shown to be phenotypically Lc. lactis generally fermented additional carbohydrates. whereas Lc. cremoris phenotype strains did not. Only one probe-isolated strain of Lc. lactis fermented D-xylose. Tests to identify potential Cheddar cheese starter strains were performed on all environmental isolates. All strains which were phenotypically identified as Lc. lactis were rejected as potential starters because they railed to coagulate milk after 15 to 18 hours or they developed undesirable flavors in milk. Nine of twenty strains that were both phenotypically and genotypically Lc. cremoris were identified as having good potential for use as Cheddar cheese starter cultures. Four strains (MS-9, MS-23, MS-24, MS-51) were selected for Cheddar cheesemaking trials. Twenty small vats of cheese were made using each of the four strains individually then in every possible combination. In each case the experimental strains showed good functional characteristics with no sensitivity to bacteriophage present in the manufacturing environment. Five commercial scale cheese trials (53,500 lbs of milk) with automated equipment were also undertaken. Each strain was used first individually then in combination. Starter activity in the automated system using the experimental strains was sufficient to allow a 14% reduction in starter usage and still obtain good acid development. Flavor development of the cheese was monitored for one year of aging. Single strains varied in flavor development, with bitter notes being the most prominent off flavor detected. For some strains the bitter flavor was transitory and varied in intensity. Cheese produced from the four combined strains never developed the bitter defect, indicating that proteolysis of the combined strains was sufficient to degrade the bitter peptides as they were produced. / Graduation date: 1999

Thèse de doctorat : Procédés biotechnologiques et alimentaires : INPL : 2007. / Titre provenant de l'écran-titre.

The inoculation of Aspergillus flavus spores into a culture of Streptococcus lactis in LTB medium resulted in none or little aflatoxin production even though growth of the fungus was not hindered. The drop in pH and reduced nutrients in the medium as the result of S. lactis growth were not the cause of the observed inhibition. The inhibition was not eliminated by the addition of carbohydrate equal to the amount utilized by the bacterium prior to the inoculation with the fungus. Aflatoxin production was also inhibited when S. lactis was inoculated after A. flavus had grown. In addition to inhibiting the synthesis of aflatoxin, S. lactis also degraded pre-formed toxin. Aflatoxin, on the other hand, not only reduced the growth of S. lactis but also affected the morphology of the bacterial cell--the cells became elongated and formed long chains. / S. lactis produced and excreted the inhibitor into the medium during the early stage of growth (4 h). The inhibitor was a heat stable low molecular weight compound (MW (LESSTHEQ) 500). Neither volatile (acetic) nor non-volatile (succinic and lactic) acids which were detected in extracts containing the inhibitor were responsible for this inhibition. Lactic acid was found in larger quantities in mixed cultures and its addition to mono fungus culture was found to stimulate aflatoxin production. Chloroform: methanol extraction of the S. lactis culture filtrate removed all the activity to the organic phase. Further, the active compound was insoluble in hexane, not extracted by sodium bicarbonate and was soluble in acetone, indicating a polar lipid. Autoradiographic studies showed that the inhibitor was a product of glucose metabolism. Further characterization indicated that the inhibitor was a phosphoglycolipid containing an aromatic ring structure. / Filtrate extracts of A. flavus grown in presence of S. lactis were toxic to Bacillus megaterium but did not exhibit mutagenic or carcinogenic activity in the Salmonella/Mammalian microsome mutagenicity test.

The malty flavor defect produced by Streptococcus lactis var. maltigenes has been the cause of considerable economic distress to various segments of the dairy industry. This study was conducted in order to develop a more thorough understanding of the chemical nature of this defect, and to formulate a synthetic malty flavor preparation. An 18 hour malty culture and an acidified heated skim milk control were steam distilled using a specially designed, low temperature, reduced pressure glass apparatus fitted with ground glass ball or standard taper joints. After subsequent ethyl ether extractions, the aqueous distillates yielded flavor concentrates which were suitable for gas-liquid chromatographic (GLC) and mass spectrometric analysis. Flavor component identifications were made on both a tentative and positive basis. Tentative identifications were made using the technique of GLC relative retention times. Identifications were considered positive when GLC retention data could be coupled with mass spectral data. Compounds positively identified as being present in the malty culture included acetaldehyde, 3-methylbutanal, phenylacetaldehyde, ethanol, butanol, 2-methylpropanol, 3-methylbutanol, 2-furfurol, phenethyl alcohol, acetone, butanone, 2-pentanone, 2-heptanone, 2-nonanone, ethyl formate, ethyl acetate, ethyl butyrate, ethyl isovalerate, ethyl octanoate, isoamyl acetate and toluene. Compounds tentatively identified included 2-methylpropanal, pentanal, benzaldehyde, 2-furfural, 2-undecanone, 2-tridecanone, ethyl hexanoate, ethyl decanoate, methyl acetate, γ-octalactone, δ-octalactone, formic acid and acetic acid. In the heated skim milk control, acetaldehyde, benzaldehyde, 2-furfural, 2-furfurol, 2-pentanone, 2-heptanone, 2-nonanone, 2-undecanone, 2-tridecanone, ethyl acetate and methyl chloride were positively identified while pentanal, hexanal, octanal, nonanal, 2-hexanone, 2-octanone, ethyl formate, ethyl octanoate, methyl acetate, γ-octalactone and δ-octalactone remained as tentative identifications. Quantitative evaluations of the volatile constituents present in each of four strains of the malty culture were conducted using a gas entrainment, on-column trapping, GLC technique. From the quantitative data obtained from a 24 hour S. lactis var. maltigenes L/M-20 culture, a synthetic malty flavor preparation, suitable for use in baked foods, was developed. This investigation used biscuits as a model system for the baking studies. The biscuits were prepared using the General Mills' Bisquick mix and a malty milk preparation replaced the normal milk requirement. The milk contained 1.70 p.p.m. acetaldehyde, 34.20 p.p.m. 3-methylbutanal, 17.90 p.p.m. 2-methylpropanolr 90.10 p.p.m. 3-methylbutanol and 10.00 p.p.m. diacetyl. / Graduation date: 1968

Graduation date: 1994