No description available.

No description available.

Long-term administration of recombinant bovine somatotropin (rbST) significantly increased milk and 3.5% fat-corrected milk production without altering milk composition. These effects occurred regardless of breed, parity or drug delivery system (daily or sustained-release) utilized. Somatotropin did not affect apparent digestibility of rations, dry matter intake, crude protein intake, energy intake or energy balance. Body energy reserves, measured as body condition scores, decreased during rbST treatment resulting, together with the increase in milk yield, in an improvement of the efficiency of conversion of feed to milk for cows treated with rbST. Body condition was completely regained during the dry period. No effects of rbST on mastitis or metabolic diseases were observed. During lactation, injection of rbST produced elevated circulating concentrations of non-esterified fatty acids, glucose, insulin, bST and IGF-I but lipid composition of liver and ketogenic functions were not altered. These lipolytic and diabetogenic activities might contribute to the galactopoietic response elicited by rbST. Somatotropin did not modify the nutritional status of cows during pregnancy or the nutritional status and growth rate of their calves from birth to weaning. / With regard to reproduction, somatotropin augmented ovarian progesterone production during the first two estrous cycles post-injection and during gestation. These effects may have been mediated through increased ovarian IGF-I synthesis. Somatotropin enhanced the GnRH-induced LH response at 14 d postpartum. In spite of these positive observations, somatotropin treatment tended to produce longer calving to conception intervals. Nevertheless, the higher persistency of milk production by cows treated with rbST may compensate for this difference economically.

The development of synthetic culture flavors for use in dairy products such as sour cream, cottage cheese, butter, and buttermilk has created the need for a rapid quantitative analysis for the synthetic flavor concentrates. An internal standard gas chromatographic method has been developed which is capable of +10% accuracy for each flavor compound in single sample analyses. The separation of water, acetaldehyde, dimethyl sulfide, acetic acid, diacetyl, propylene glycol, and acetone (the internal standard) was performed with a column consisting of a 1/8 inch OD section of stainless steel tubing 10 feet in length packed with 120-150 mesh Porapak Q plus a stainless steel precolumn 1/8 inch OD and 10 inches in length packed with 120-150 mesh Porapak R. The column was operated isothermally at 155°C with a flow rate of 44 ml per min of nitrogen carrier gas. A flame ionization detector was used. In the course of the investigation, Porapak Q (available from Waters Associates Inc., Framingham, Mass.) was evaluated. The optimum mesh size under the conditions employed was the 120-150 mesh range. The efficiency of Porapak Q columns, as reflected by the number of theoretical plates per foot for n-propanol and the resolution of n-propanol and iso-propanol, was found to increase when the column diameter was increased from 1/16 inch OD to 1/8 inch OD to 1/4 inch OD. / Graduation date: 1967

Acetaldehyde is known to be responsible for the green or yogurt-like flavor defect of lactic cultures. This study was undertaken to extend the knowledge of acetaldehyde production and utilization by microorganisms normally found in mixed-strain butter cultures. It is anticipated that the resulting information will contribute to a more thorough understanding of the development of a green flavor defect; hence, to methods of avoiding and overcoming this defect. Acetaldehyde production by single-strain cultures of S. lactis, S. cremoris, and S. diacetilactis was found to parallel the increase in microbial population. S. lactis and S. cremoris were found to remove some of the acetaldehyde produced on continued incubation at 21°C. S. diacetilactis did not remove any of the acetaldehyde produced. The ratio of diacetyl to acetaldehyde in the strains of S. diacetilactis studied was found to be unfavorable for a good culture flavor at all times up to 22-24 hr incubation. All of the cultures studied produced a distinct green flavor when grown in milk media. All of the lactic streptococci studied produced both ethanol and acetone when grown in a boiled milk medium. No evidence of acetone utilization by S. diacetilactis was observed. A tentative mechanism for the formation of acetone from pyruvate via acetoacetate was proposed. Single-strain cultures of Leuconostoc dextranicum and Leuconostoc mesenteroides were shown to be capable of utilizing added acetaldehyde under a variety of culturing conditions. These two organisms, along with L. citrovorum were combined into two-strain mixtures with various lactic streptococci. The production and utilization of acetaldehyde varied widely among different two-strain mixtures. The ratio of different lactic organisms comprising the flora of a desirably flavored commercial mixed-strain butter culture was determined. The microbial shift occurring when this culture developed a green flavor defect was found to be an overgrowth of the homo-fermentative lactic streptococci by the S. diacetilactis population. It was found that the concentration of acetaldehyde in a ripened single-strain lactic culture could be significantly reduced by adding a large inoculum of a culture of L. citrovorum and continuing incubation at 21°C or by cooling and holding the culture at 5°C after the addition of L. citrovorum. / Graduation date: 1966

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: 1962

No description available.

Thesis (MScAgric)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet

Thesis (Ph. D.)--University of Chicago. / Includes bibliographical references. Also available on the Internet.