Graduation date: 1981

Call number: LD2668 .T4 1965 T772 / Master of Science

Call number: LD2668 .T4 1952 W4 / Master of Science

Call number: LD2668 .T4 1952 C3 / Master of Science

No description available.

Single-strain cultures of Streptococcus cremoris, Streptococcus lactis, Streptococcus diacetilactis, and Leuconostoc citrovorum produced little or no acetone and no dimethyl sulfide when grown in milk culture. These organisms had little or no ability to decarboxylate antexogenous source of acetoacetic acid nor were they capable of producing dimethyl sulfide from methyl methionine sulfonium chloride. The dimethyl sulfide content of milk was increased by heating which indicated that a heat labile dimethyl sulfide precursor was present in milk. The precursor remained in the skimmilk fraction and was dialyzable. The precursor was identified as a methyl methionine sulfonium salt on the basis of its thin-layer chromatographic mobility and the heat instability of the compound. Heating of samples caused the disappearance of the precursor compound with a subsequent increase in the content of homoserine and dimethyl sulfide. Single strain cultures of Pseudomonas fragi, Pseudomonas fluorescens, Pseudomonas putrefaciens, and two marine Pseudomonas species reduced acetaldehyde, propionaldehyde, and butyraldehyde to the corresponding alcohols at 21°C. All species studied reduced propionaldehyde at 6°C. P. fragi and the marine species reducted butanone and/or acetone at both 6 and 21°C. Under aerobic conditions a strain of P. fragi quantitatively reduced added propionaldehyde to n-propanol. The quantities of acetaldehyde and ethanol produced by single-strain cultures of Lactobacillus brevis, Lactobacillus casei, Lactolactis, and Lactobacillus plantarum differed significantly both between species and between strains of a species on incubation at both their optimum growth temperature and 8°C. Growth and production of these Compounds were very slow at 8°C. All organisms studied were capable of reducing acetaldehyde and propionaldehyde to the corresponding alcohol. L. brevis strains alone reduced added butanone to 2-butanol. A strain of L. brevis produced n-propanol as a normal metabolite when grown in milk culture. Single-strain cultures of L. casei and L. plantarum accumulated diacetyl when grown in milk culture at both 8 and 30°C, but strains of L. lactis and L. brevis did not. Diacetyl reductase activity was demonstrated in single-strain cultures of L. casei, L. brevis, and L. lactis. Diacetyl reductase could be induced in L. plantarum by growth in the presence of citrate. Growth in milk medium supplemented with citrate resulted in a stimulation of diacetyl reductase activity with L. casei. / Graduation date: 1968

Graduation date: 1963

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

The traditional way of processing milk is the application of heat to destroy undesirable microorganisms. Though heat is an effective means of doing the job, it is associated with several limitations. High pressure (HP) processing has the potential for eliminating microorganisms without affecting the natural quality of the raw material. As a result, it has become a promising technique in recent years. Many factors are reported to influence HP destruction of microorganisms, the most important ones include food composition (i.e., lipid, carbohydrate and protein contents), water activity, process temperature, and mode of pressure treatment. Therefore, the objectives of this research were to: (a) evaluate the effect of milk composition on destruction of E. coli by HP, (b) evaluate kinetic models for spoilage and pathogenic microorganism in milk and the effect of different pressure mode (pulse and static) on the destruction rates; and (c) to evaluate the effect of milk type (UHT and raw milk) and temperate on destruction of microorganism.

No description available.