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Avian Community Response To Fire In A Gambel Oak Woodland, Andreas Leidolf
Avian Community Response To Fire In A Gambel Oak Woodland, Andreas Leidolf
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
I assessed avian communities of Gam bel oak (Quercus gambelii) woodland and surrounding habitats at Camp W. G. Williams State Military Reservation , Utah, during summer of 1993-1998. I used point counts and incidental observations to compile an avian checklist. I observed 100 species, accounting for one third of all birds known from Utah. Overlap in species composition among habitats was considerable, yet each habitat supported a distinct complement of common species.
I compared bird species composition, abundance, richness, and diversity before and after fire in burned and unburned Gam bel oak woodland using point counts. I also investigated how …
The Effects Of Salmon Availability, Social Dynamics, And People On Black Bear (Ursus Americanus) Fishing Behavior On An Alaskan Salmon Stream, Danielle K. Chi
The Effects Of Salmon Availability, Social Dynamics, And People On Black Bear (Ursus Americanus) Fishing Behavior On An Alaskan Salmon Stream, Danielle K. Chi
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The primary goals of this research were to investigate 3 ecological factors influencing black bear (Ursus americanus) foraging behavior on an Alaskan salmon (Oncorhynchus spp.) stream: fish availability, social dynamics, and human activity. Over 900 observation hours were logged at 2 falls from July 1-September 1 1993-1995; the lower falls were open to public for wildlife viewing, but the upper falls were restricted to research personnel.
In general, black bears responded to differences in fish accessibility on both spatial and temporal scales. All years of the study, 3 indices of bear activity (bear minutes, bear numbers, bout …
The Role Of Iron And Reactive Oxygen Species In Particulate Air Pollution-Dependent Biochemical And Biological Activities, Kevin Richard Smith
The Role Of Iron And Reactive Oxygen Species In Particulate Air Pollution-Dependent Biochemical And Biological Activities, Kevin Richard Smith
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Particulate air pollution is known to exacerbate respiratory diseases, such as asthma and chronic obstructive pulmonary disease, in humans. It has been proposed that transition meta ls from inhaled particles may play a role in this exacerbation by generating radical species leading to damage in the lungs.
The aim of this research was to determine the role that iron from particulate air pollution played in the generation of reactive oxygen species and subsequently the induction of inflammatory mediators in cells in culture. The production of reactive oxygen species by particulate air pollution was found to be dependent on the mobilization …
Nest Success Of Dabbling Ducks In A Human-Modified Prairie: Effects Of Predation And Habitat Variables At Different Spatial Scales, Jaime E. Jimenez
Nest Success Of Dabbling Ducks In A Human-Modified Prairie: Effects Of Predation And Habitat Variables At Different Spatial Scales, Jaime E. Jimenez
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Nest success of dabbling ducks in the Prairie Pothole region of North America has been declining for the past 40 years in parallel with declines in duck populations. Low nest success seems to result from the combination of an extremely fragmented breeding ground in a human-dominated landscape with an abundant and expanding community of generalist nest predators. Studies that examined variables associated with nest vulnerability to predation have produced contradictory results, likely because of simplistic approaches, lack of spatio-temporal replication, use of artificial nests, and the effect of confounding variables. I attempted to clarify the equivocal findings of previous studies …
Influence Of Grazing, Fire, And Rainfall Regime On Plant Species Dynamics In An Ethiopian Perennial Grassland, Michael J. Jacobs
Influence Of Grazing, Fire, And Rainfall Regime On Plant Species Dynamics In An Ethiopian Perennial Grassland, Michael J. Jacobs
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The dominant habitat-type of Omo National Park (ONP), Ethiopia, is grassland. This grassland supports a variety of wild herbivores and indigenous people; the latter hunt large herbivores for subsistence or graze their domestic livestock in the Park. Therefore, an understanding of grassland dynamics is a high priority for ONP management. Grazing and fire are major factors influencing species composition and vegetation change in East African grasslands. Rainfall regime, in turn, can influence both grassland response to grazing and fire. The ONP grasslands occur along a rainfall gradient ranging from subhumid to semiarid. Research objectives were to: (1) test the Milchunas, …
Protein Production In The Milk Of Genetically Engineered Animals, Katherine M. Bates
Protein Production In The Milk Of Genetically Engineered Animals, Katherine M. Bates
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
There are numerous proteins that have potential uses in commercial and scientific applications that are not utilized to their full potential. this is partly because it is not economically feasible to isolate some of these proteins from their natural sources or to produce them using bacterial fermentation methods. The purpose of this research was to target recombinant protein expression to the mammary glands of genetically engineered or transgenic animals. Foreign protein expression has been achieved in the mammary glands of rabbits, sheep, cows, and swine. By using a strong mammary gland promoter and signal peptide fused to the protein, it …
Limitations On Canada Goose Production At Fish Springs National Wildlife Refuge, Utah, Dorie S. Stolley
Limitations On Canada Goose Production At Fish Springs National Wildlife Refuge, Utah, Dorie S. Stolley
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Canada geese (Branta canadensis) recently have become management problems in some areas due to overpopulation. At Fish Springs National Wildlife Refuge (NWR), managers are concerned with the opposite situation. Despite attempts to boost production, only 18 to 34 goslings of the western Canada goose (B. c. moffitti) were produced per year, from 1989 to 1993. I studied the breeding population from March to July in 1996 and 1997. Results suggest that production is limited in 3 ways: low gosling survival, low nesting success for ground nests, and low number of breeding pairs.
Gosling survival to fledging …
Identification Of Non-Nuclear Receptors For 1,25-Dihydroxyvitamin D3 In Chick Kidney And Brain, Zhiheng Jia
Identification Of Non-Nuclear Receptors For 1,25-Dihydroxyvitamin D3 In Chick Kidney And Brain, Zhiheng Jia
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
1,25-dihydroxyvitamin D3 (1,25(OH)2D3) has been shown to mediate the rapid, non-nuclear stimulation of calcium and phosphate transport in chick intestine through binding to a receptor localized in the basal lateral membrane. By using an antibody to the N-terminus of the membrane receptor, studies were undertaken to determine whether a comparable protein exists in kidney and brain, and whether it is present in a particular subcellular fraction.
The first step was to establish fractionation protocols to separate subcellular organelles as judged by marker enzyme analyses. Differential centrifugation and Percoll gradient fractions were prepared from chick kidney …
Antioxidant Activity Of Carnosine And Phytate: Application As Meat Preservatives, Beom Jun Lee
Antioxidant Activity Of Carnosine And Phytate: Application As Meat Preservatives, Beom Jun Lee
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The antioxidant activity of carnosine and phytic acid was investigated using several model systems. Carnosine and phytic acid alone inhibited metal ion-catalyzed deoxyribose degradation. Carnosine strongly inhibited metal ion-catalyzed lipid peroxidation in liposomes and in ground beef homogenates. Phytic acid facilitated oxidation of Fe (II) to Fe (III), and it inhibited hemeprotein + H2O2-catalyzed lipid peroxidation in linoleic acid micelles.
Antioxidant and color stabilizing effects of carnosine and phytate were investigated in a beef model system. Both compounds increased the rate of pH decline in pre-rigor beef muscle and stabilized fresh meat color by inhibiting metmyoglobin …
"Halfway Between Nobody Knows Where And Somebody's Starting Point": A History Of The West End Of Montrose County, Colorado, John A. Hardcastle
"Halfway Between Nobody Knows Where And Somebody's Starting Point": A History Of The West End Of Montrose County, Colorado, John A. Hardcastle
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The thesis contains interesting and relevant information concerning the impact of the mining and milling industry on communities located within a geographically, socially, politically, and economically defined area in southwestern Colorado. This area supplied a tremendous amount of radium, vanadium, and uranium in successive eras. The author focuses primarily on Uravan, and examines the town's role in the uranium procurement program during World War II. The study of Uravan also provides information on the social structure of a company-owned community. Also examined are the ways in which government policies affected these small communities, and the impacts of the mining and …
Clinician Perceptions Of Media Use By Male Sex-Offending, Conduct-Disordered, And Normal Youth, Melissa A. Vogel
Clinician Perceptions Of Media Use By Male Sex-Offending, Conduct-Disordered, And Normal Youth, Melissa A. Vogel
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Sexual offenses by youth have been increasing. The literature recognizes media as a socializer, yet few studies examine nonpornographic media and youthful sex-offending. The purpose of this research was to survey the perceptions of clinicians as to the use of media type and content for male sex-offending, conduct-disordered, and normal youth. The questionnaire was completed by 78 American clinicians from 30 states specializing in the treatment of youthful sex offenders.
Means, standard deviations, and percentages were calculated, which provided descriptive data. Male sex-offending and conduct-disordered youth are believed by clinicians to be more frequent consumers of aggressive, explicit, and sexually …
Effects Of Infant Massage On Aspects Of The Parent-Child Relationship: An Experimental Manipulation, Vonda K. Jump
Effects Of Infant Massage On Aspects Of The Parent-Child Relationship: An Experimental Manipulation, Vonda K. Jump
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Benefits of attachment security have been demonstrated in the realm of socioemotional development. Studies have investigated some of the antecedents associated with the development of secure attachments. This study looked uniquely at the impact of touch, and more specifically, infant massage, on the development of attachment security in infants.
Fifty-seven mother-infant dyads were randomly assigned to either a treatment or control group. Infants were less than 8 months of age at the time of recruitment. The treatment group received training in infant massage as well as education about infant development. The control group received similar education about infant development. Mothers …
The Role Of An Invasive Exotic Plant On The Structure Of Aquatic Invertebrate Assemblages: Tamarix In The Southwest United States, Bert Lewis
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Over the past 100 years, riparian vegetation communities throughout the Southwest United States have been extensively invaded by Tamarix spp. (saltcedar). Saltcedar derives its common name from its physiological adaptation to excrete salts. The production of Tamarix detritus with associated secondary chemicals may affect the quality of aquatic invertebrate food and habitat resources. An alteration in food and habitat quality may affect the composition and structure of aquatic invertebrate assemblages.
A series of experiments was conducted contrasting aquatic invertebrate assemblage densities, colonization rates, and growth rates associated with Tamarix versus native vegetation, Populus fremontii (cottonwood) and Salix exigua (willow), to …
Influence Of Boat Density Levels On Boaters' Satisfaction At Hyrum Lake, Utah, Floyd Alma Powell
Influence Of Boat Density Levels On Boaters' Satisfaction At Hyrum Lake, Utah, Floyd Alma Powell
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The purpose of this study was to evaluate the effects of boat density on boaters' satisfaction at Hyrum Lake State Park, Utah. The study evaluated relationships between boaters' satisfaction with their Hyrum Lake experience and density of boats at different locations on the lake and among participants in different boating activities.
The participants in this study were boaters who used Hyrum Lake between May and September of 1996. An oral, on-site interview survey was randomly given to 282 boaters as they left the lake for the day. The surveys were conducted on high-density days (weekends) and low-density days (weekdays), which …
Management Of Microbial Nitrate Production In Agricultural Soils, Wei Shi
Management Of Microbial Nitrate Production In Agricultural Soils, Wei Shi
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Nitrate (NO3-) is of central importance in the internal soil nitrogen (N) cycle. While animal wastes and nitrification inhibitors have been used in modern agriculture for decades, their effects on soil NO3- concentrations in relation to microbial NO3- production have not been well characterized. The objective of this research was to determine microbial NO3- production in relation to ammonium (NH4+) availability and nitrifier population activity in agricultural soils receiving animal wastes or nitrification inhibitors.
Several laboratory and field studies assessed the impacts of variously treated dairy wastes and …
The Role Of Ammonia In Reproductive Inefficiency In High-Producing Dairy Cows Fed Excess Rumen Degraded Protein, Douglas Scott Hammon
The Role Of Ammonia In Reproductive Inefficiency In High-Producing Dairy Cows Fed Excess Rumen Degraded Protein, Douglas Scott Hammon
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The role of ammonia in reproductive inefficiency in early lactation dairy cows was studied in a series of experiments designed to determine the concentrations of ammonia in normal bovine follicular fluid (bFF), to determine the effects of ammonia on the bovine embryo during specific stages of development, and to test the hypothesis that elevated plasma urea nitrogen concentration is associated with elevated ammonia and urea nitrogen concentrations in the reproductive fluids.
In the first study, ammonia concentration in different size follicles and the effect of ammonia during in vitro maturation on embryo development were determined. Ammonia concentration in the bFF …
The Effects Of Retinoic Acids On The Angiogenic Growth Factors Produced By Solid Tumors, Lynn C. Burgess
The Effects Of Retinoic Acids On The Angiogenic Growth Factors Produced By Solid Tumors, Lynn C. Burgess
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
These studies investigated the effects of retinoic acid (RA) on angiogenesis. Three human, neoplastic cell lines were used to examine angiogenic promotion and/or inhibition. The cell lines, U-373MG glioblastoma, DU-145 prostate carcinoma, and TCCSUP bladder transitional cell carcinoma, were treated with the following: all-trans, 9-cis, or 13-cis RA, at doses from 0.0001 to 100 μM. Hypoxia was used to assist the expression of the angiogenic phenotype. Conditioned media (CM) were prepared by growing the tumor cells in the presence of RA and hypoxia for 24 hours, and then the CM was transferred to bovine, capillary endothelial …
Rangeland Dynamics And Pastoral Development In The High Andes: The Camelid Herders Of Cosapa, Bolivia, Lita P. Buttolph
Rangeland Dynamics And Pastoral Development In The High Andes: The Camelid Herders Of Cosapa, Bolivia, Lita P. Buttolph
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Current models of rangeland system dynamics were evaluated in Cosapa, a pastoral community on the Bolivian altiplano. Two specific models were tested: the "equilibrium" model, which assumes biotic interactions dominate rangeland dynamics and lead to system stability, and the "nonequilibrium" model, in which stochastic, abiotic factors control systems such that equilibrium is never attained. A livestock development project (called "Project Alpaca") working in the community was then assessed in terms of how its assumptions of system dynamics compared with empirical findings. The goal of Project Alpaca was to increase incomes for camelid (i.e., llama and alpaca) herders on the …
Assessing Mental Health Of Native American Children: Relationship Of Acculturation With Social, Emotional, And Behavioral Functioning, Christopher H. Morris
Assessing Mental Health Of Native American Children: Relationship Of Acculturation With Social, Emotional, And Behavioral Functioning, Christopher H. Morris
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The literature indicates that, in comparison to children of other ethnic minority groups, Native American children may be at greater risk for a variety of emotional and behavioral Ill disorders and negative psychosocial conditions. Many may also struggle to resolve issues related to cultural identity. Understanding how Native American children and families relate to the cultures within which they live is a critical aspect of preventing and treating childhood mental disorders. Although Native children and families face persistent social pressure to adapt to a multicultural world, no systematic research exists examining the relationship between families' experience of acculturation and their …
Physically And Sexually Violent Juvenile Offenders: A Comparative Study Of Victimization History Variables, Monique R. Frazier
Physically And Sexually Violent Juvenile Offenders: A Comparative Study Of Victimization History Variables, Monique R. Frazier
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The primary purpose of this study was to examine and compare physically and sexually violent juvenile offenders (PVJOs and SVJOs) to determine whether specific factors in their abuse histories, if present, tend to be associated with-the type of violent offense pattern they exhibit. The Youth Experiences and Behaviors Structured Interview (YEBSI)--an instrument which assesses for primary (victimization), secondary (witnessing), and perpetrated abuse of an emotional, physical, and sexual nature, by and/or toward family members, acquaintances, strangers, and animals--was developed by the primary researcher for use in this study. Thirty-six PVJOs and 30 SVJOs were interviewed. Results indicated that the YEBSI …
A Descriptive Study Of The Relation Between Domestic Violence And Pet Abuse, Claudia V. Weber
A Descriptive Study Of The Relation Between Domestic Violence And Pet Abuse, Claudia V. Weber
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
This was a descriptive study that examined the relation between domestic violence and pct abuse. Participants were questioned about their styles of conflict resolution with partners and how pets were treated in the home. Information was gathered using the Conflict Tactics Scale, and three surveys were developed for this study: the Battered Partner Shelter Survey, Families and Pets Survey, and the Child 's Observations and Experience with Pets. Four groups were recruited: (a) women in crisis shelters who chose to include one of their children in the study (n = 39), (b) women in crisis shelters who did not …
The Nonuse Of Figurative Language In Conduct Disordered Adolescents, Mike Berger
The Nonuse Of Figurative Language In Conduct Disordered Adolescents, Mike Berger
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The relationship between the literal language and conduct problems among conduct disordered adolescents was examined in 109 subjects. The inability to use figurative language was found to be positively related to ratings of conduct problems. Both the parents' discipline style and nonuse of figurative language were related to conduct problems in conduct disordered adolescents. The possible role of other variables, for example, age, sex, and IQ, was examined. Possible mechanisms that could relate the lack of figurative competence and conduct problems were explored.
Characteristics Of Internalizing Social-Emotional Behaviors Of Southwestern Native American Children, Carolyn Thomas Morris
Characteristics Of Internalizing Social-Emotional Behaviors Of Southwestern Native American Children, Carolyn Thomas Morris
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The knowledge base targeting internalizing symptomatology in Native American children is surprisingly limited. As yet, it is not clear if the process and symptoms of internalizing disorders are the same across cultures. The need for further investigation is heightened by the fact that, compared to the majority population, Native Americans are believed to be at greater risk for psychological problems because of impoverished conditions, high unemployment, and high numbers of traumatic events on the reservations. Additionally, the losses of traditional culture and language are considered risk factors for greater psychopathology. The negative ramifications of internalizing disorders (e.g., depression and anxiety) …
Kokanee Fry Recruitment And Early Life History In The Lake Tahoe Basin, Christine K. Gemperle
Kokanee Fry Recruitment And Early Life History In The Lake Tahoe Basin, Christine K. Gemperle
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Lake Tahoe kokanee salmon have experienced decreasing mean adult size and fluctuating populations since 1970. We proposed to determine whether fish production was limited by spawning and incubation processes in Taylor Creek, or by growth constraints, or by mortality in the lake by studying egg-to-fry survival rates and early life history. Estimated egg-to-fry survival was 15. 9% for the 1994 brood year and 1.5% for the 1995 brood year. Egg-to-adult survival was 3.5% for the 1991 brood year and 5.9% for the 1992 brood year. Of the 35 possible survival scenarios, egg-to-fry survival was 7.5-20% and fry-to-adult survival (inlake phase) …
Influence Of Streptococcus Thermophilus Mr-1c Capsular Exopolysaccharide On Cheese Moisture Level, Deborah Low
Influence Of Streptococcus Thermophilus Mr-1c Capsular Exopolysaccharide On Cheese Moisture Level, Deborah Low
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
This study investigated the role of exopolysaccharide (EPS) in cheese moisture retention. Analysis of low-fat Mozzarella cheese made with different combinations of EPS-producing (Streptococcus thermophilus MR-1C and Lactobacillus delbrueckii ssp. bulgaricus MR-lR) and non-EPS-producing (S. thermophilus TA061 and L. helveticus LH100) starters showed significantly higher moisture levels in cheese made with S. thermophilus MR-1C. To determine if the S. thermophilus MR-1C EPS was responsible for increased moisture retention, gene replacement was used to inactivate the epsE gene in this bacterium. Low-fat Mozzarella cheese made with L. helveticus LH100 plus the EPS-negative mutant, S. thermophilus DM1O, had significantly lower …
Diet, Health Practices, And Variables Associated With Breastfeeding In Caucasian And Asian Participants In The Special Supplemental Food Program For Women, Infants, And Children: A Comparative Study, Rebecca E. Blaine
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The United States Department of Health and Human Services wrote Healthy People 2000 National Health Promotion and Disease Prevention Objectives. One major goal is to reduce the mortality rate for infants by reducing low birthweight. The disparities have been great when goals and objectives are applied to poor and minority populations.
Objectives have been set to reduce risk factors associated with low infant birthweight. These include addressing inappropriate health practices, and appropriate nutrition for mother and infant.
Forty-eight Asian and 50 Caucasian participants were compared for maternal diet, health practices, breastfeeding initiation and duration, and infant growth parameters. Data were …
Effect Of Aging On The Quality Of Beef Semitendinosus Muscle Treated With Ultra High Temperature Pasteurization, Habiba Ali Nur
Effect Of Aging On The Quality Of Beef Semitendinosus Muscle Treated With Ultra High Temperature Pasteurization, Habiba Ali Nur
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The objective of this study was to determine the effect of aging on the tenderness and palatability of beef from the semitendinosus muscle of the round. Tenderness may be affected by the length of the aging period and the aging temperature. Steaks from the semitendinosus muscle were stored for 0, 3, 6, 9, 12, and 24 hr at two temperatures, 43.3°C and 2.2°C. Ultra high temperature (UHT) pasteurization was accomplished by subjecting the meat to 1100°C for 20 seconds. UHT pasteurization denatures surface proteins, destroys vegetative pathogens, and eliminates some spoilage organisms from the surface of the meat. UHT -treated …
Tryptophan Catabolism By Lactobacillus Spp. : Biochemistry And Implications On Flavor Development In Reduced-Fat Cheddar Cheese, Sanjay Gummalla
Tryptophan Catabolism By Lactobacillus Spp. : Biochemistry And Implications On Flavor Development In Reduced-Fat Cheddar Cheese, Sanjay Gummalla
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Amino acids derived from the degradation of casein in cheese serve as precursors for the generation of key flavor compounds. Microbial degradation of tryptophan (Trp) is thought to promote formation of aromatic compounds that impart putrid fecal or unclean flavors in cheese, but pathways for their production have not been established. This study investigated tryptophan catabolism by Lactobacillus casei LC301 and LC202 and Lactobacillus helveticus CNRZ32 and LH212 cheese flavor adjuncts in carbohydrate starvation (pH 6.5, 30 or 37°C, no sugar) and cheese-like conditions (pH 5.2, 4% NaCl, 15°C, no sugar). Enzyme assays of cell-free extracts revealed both species of …
Establishing Threshold Levels Of Nitrite Causing Pinking Of Cooked Meat, Kevin M. Heaton
Establishing Threshold Levels Of Nitrite Causing Pinking Of Cooked Meat, Kevin M. Heaton
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
Sporadic problems with pink color defect, or pinking, has occurred in cooked meat products for decades. Pink color can be due to the presence of undenatured myoglobin, denatured globin hemochromes, or nitrosylhemochrome. This research documented the level of added nitrite that produced nitrosylhemochrome in processed meat rolls from fabricated beef round, pork shoulder, turkey breast, and chicken breast. For each meat type, preliminary studies were conducted to narrow the range at which added nitrite caused pinking. Subsequently, the nitrite levels were increased incrementally by 1-ppm, and pink color was measured by trained panelists and by a Hunter color meter. Nitrosylhemochrome …
Influence Of Stress Treatments On The Resistance Of Lactococcus Lactis To Freezing And Freeze-Drying, Chan Lin
Influence Of Stress Treatments On The Resistance Of Lactococcus Lactis To Freezing And Freeze-Drying, Chan Lin
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
This study investigated the effect of cold, heat, or osmotic shock treatment on the resistance of L. lactis subsp. cremoris MM160 and MM310 and Lactococcus lactis subsp. lactis MM210 and FG2 cheese starter bacteria to freezing and freeze-drying. The ability to withstand freezing at -60°C for 24 h was variable among lactococci, but resistance to this treatment was significantly improved (P < 0.05) in most strains by a 2-h cold shock at l0°C or a 25-min heat shock at 39°C (L. lactis subsp. cremoris) or 42°C (L. lactis subsp. lactis). Stress treatments that improved lactococcal freeze resistance were also found to significantly (P < 0.05) enhance the resistance of most strains to lyophilization. Increased resistance to freezing or lyophilization was not detected when stress treatments were performed in broth that contained erythromycin, which indicated stress-inducible proteins were involved in cell protection. Membrane fatty acid analysis of stress-treated cells suggested that enhanced resistance to freezing and lyophilization may be related to heat or cold shock-induced changes in cell membrane composition. Heat-shocked cells had a higher 19:0 cyclopropane fatty acid content than did control cells, and cold-shocked cells contained a lower ratio of saturated to unsaturated fatty acids. Other factors must also be involved in cell protection, however, because similar changes in membrane composition were also detected in strains whose resistance to freezing and lyophilization was not improved by heat or cold shock.