Thesis (Ph. D.)--University of Wisconsin--Madison, 1948. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Bibliography: leaves [76]-77.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 82-84). Also available via the Internet.

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Quality Control (QC) reference materials are widely used in microbiology to demonstrate the efficacy of testing methods and culture media. The current method for preparation of QC materials is by serial dilution of a microbial broth culture to obtain a suspension that contains an estimated number of colony forming units (cfu). Commercial reference material products are available with dried microbial cells, however, the numbers of cells are variable between batches as the production processes are reliant on cell suspensions of estimated cell number. This study developed a method to produce precise microbial reference materials with a accurate number of viable cells. Flow cytometry was used to count and dispense precise numbers of cells into a single droplet of fluid. The droplets were then mixed with a lyoprotectant solution and subjected to freeze-drying. The resultant freeze-dried pellets showed consistent average cfu counts between 28-33 cfu with a standard deviation < 3 cfu. The freeze-drying methodology and developed conditions of cell growth enabled > 90% of the cells to survive freeze-drying and remain viable for one year at a storage temperature below -18??C. The methodology for the production of freeze-dried pellet was applied to a range of genera including, different E. coli strains, Gram positive bacteria such as Listeria and Staphylococcus, the yeast Candida albicans and a spore-producing Bacillus cereus. The precision of cell numbers was comparable between different microbial genera and strains and a consistent standard deviation below 3 cfu was achieved. The same freeze-dried pellet method was used for the different micro-organisms, except for changes to preparation of cell suspensions. Different methods of broth culture were developed to ensure freeze-dried cell survival. A measurement of method reproducibility was obtained when 99 batches of pellets were produced, and within batch and between batch variation was determined.

Quality Control (QC) reference materials are widely used in microbiology to demonstrate the efficacy of testing methods and culture media. The current method for preparation of QC materials is by serial dilution of a microbial broth culture to obtain a suspension that contains an estimated number of colony forming units (cfu). Commercial reference material products are available with dried microbial cells, however, the numbers of cells are variable between batches as the production processes are reliant on cell suspensions of estimated cell number. This study developed a method to produce precise microbial reference materials with a accurate number of viable cells. Flow cytometry was used to count and dispense precise numbers of cells into a single droplet of fluid. The droplets were then mixed with a lyoprotectant solution and subjected to freeze-drying. The resultant freeze-dried pellets showed consistent average cfu counts between 28-33 cfu with a standard deviation < 3 cfu. The freeze-drying methodology and developed conditions of cell growth enabled > 90% of the cells to survive freeze-drying and remain viable for one year at a storage temperature below -18??C. The methodology for the production of freeze-dried pellet was applied to a range of genera including, different E. coli strains, Gram positive bacteria such as Listeria and Staphylococcus, the yeast Candida albicans and a spore-producing Bacillus cereus. The precision of cell numbers was comparable between different microbial genera and strains and a consistent standard deviation below 3 cfu was achieved. The same freeze-dried pellet method was used for the different micro-organisms, except for changes to preparation of cell suspensions. Different methods of broth culture were developed to ensure freeze-dried cell survival. A measurement of method reproducibility was obtained when 99 batches of pellets were produced, and within batch and between batch variation was determined.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2009. / Includes bibliographical references. Also available on the World Wide Web.

Proefschrift Uppsala, Swedish University of Agricultural Sciences. / Includes bibliographical references.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 161-179). Also available in electronic version.

The influence of freezing rate, rate of heat input and drying chamber pressure on freeze-drying rate was studied to determine the thermal and physical properties of MacIntosh apple and Netted Gem potato tissue. The samples were frozen either by immersion in dry ice and ethanol (fast frozen) or by placement in a refrigerated cabinet maintained at a temperature between -10° and +5° F (slow frozen). The samples were suspended in a chamber maintained at a pressure of 550 or 1400 microns of mercury and surrounded by a constant temperature water bath which provided a radiant heat source of 86° or 104°F. The weight, and the surface and centre temperature of the sample were recorded continuously during freeze-drying. Vapor diffusion was the rate limiting factor for fast frozen samples while heat transfer was rate limiting for slow frozen samples. Chamber pressure had little influence on the freeze-drying rate of slow frozen samples. Potato tissue thermal conductivity varied from 0.66x10⁻² BTU/Hr.°F Ft. at a pressure of 550 microns to 0.78x10⁻² at 1400 microns. The thermal conductivity of apple tissue was 1.0 x 10⁻² BTU/Hr.°F Ft. at both pressures. The eutectic temperature of apple and potato tissue was found to be -10°F and -1°0F. respectively. / Land and Food Systems, Faculty of / Graduate