Thesis (Ph. D.)--University of Adelaide, 1984. / Includes bibliographical references (leaves 133-148).

Thesis (M.S.)--University of Michigan, 1978.

Thesis (M.S.)--University of Michigan, 1978.

Thesis (Ph.D. 1979) from the Department of Biochemistry, University of Adelaide.

Abstract Dental caries is a common infectious disease affecting young children living in low-income families in the United States. Efficacious, safe, feasible and cost-effective caries prevention methods for these children are essential. Several studies have shown the efficacy of fluoride varnish and xylitol to improve the oral health of children. The efficiency of caries prevention programs including the use of fluoride varnish or xylitol chewing gum in early childhood has not been well documented in communities with private dental services. The purpose of this study was to determine the caries prevalence and distribution in the primary dentition, and to evaluate the effectiveness of two prevention programs, including applications of fluoride varnish and the use of xylitol chewing gum in randomized groups of preschool children attending Head Start school programs in Northern Florida. The caries preventive effect of fluoride varnish in the primary dentition was evaluated in a sample of 4–6 year-old Head Start schoolchildren in Alachua, Florida (n = 142). Caries progression after nine months was analyzed using dmf(s/t) and ds values. A modified caries scoring system, which differentiates between active and inactive carious lesions, was used to evaluate the effect of fluoride on early noncavitated enamel lesions. The effect of xylitol gum was evaluated by measuring the levels of salivary mutans streptococci before and after a three week chewing period in 3–5 year-old children attending the Head Start school in Starke, Florida (n = 61). This study is in line with earlier reports that caries prevalence is high in Head Start preschool children. This study showed that active noncavitated enamel lesions were common in the primary dentition and that applications of fluoride varnish may offer an effective means of arresting these early enamel lesions. Chewing the xylitol gum reduced the levels of salivary mutans streptococci, thereby possibly reducing the risk for dental caries in these children. While the detection and monitoring of early enamel lesions is critical in determining effectiveness of prevention therapy, this study suggests that fluoride varnish applications may offer an efficient, non-surgical treatment for decay in children. Also, the prevention program with xylitol may provide an additional method to be used in situations where other prevention methods are difficult to implement.

Xylitol is a high value polyalcohol being used in pharmaceutical, hygiene, and food products due to its functional properties such as anticariogenic, antibacterial as well as low calorie and low glycemic properties. An alternative route for xylitol production is the biotechnological method in which microorganisms or enzymes are involved as catalysts to convert xylose into xylitol under mild conditions of pressure and temperature. This method is unlike the conventional chemical method that requires high pressure and temperature and results in low product yield. The goal of this research is to employ an integrated process using all fractions of an agro-industrial biomass (oat hull) for xylitol bioproduction, preferably in a repeated batch bioconversion process, with C. guilliermondii as the biocatalyst. Processes including hydrolysis, biomass delignification, hydrolysate detoxification using adsorption process, and finally free- and immobilized-cell bioconversions were employed in this study. The kinetics of acid-catalyzed hydrolysis of hemicellulose was investigated under mild conditions (temperature: 110ºC to 130ºC and catalyst (H2SO4) concentrations from 0.1 to 0.55 N) to determine the kinetic mechanism and generation of monosaccharides (xylose, glucose, and arabinose) as well as the microbial inhibitors consisting of acetic acid, furfural, and hydroxymethylfurfural (HMF) in the hydrolysate. A maximum recovery of 80% was attained for xylose as the main monosaccharide and the substrate for xylitol; its generation in the hydrolysate followed a single-phase 2-step kinetic mechanism similar to that of the HMF. However, a single-phase mechanism with no decomposition could describe the formation of arabinose, acetic acid, and furfural. Glucose generation followed a biphasic mechanism (fast and slow releasing) apparently with no decomposition. In the alkaline delignification of the hydrolysis byproduct (solid fraction) and the intact (crude) biomass, kinetic models based on biphasic mechanism consisting of bulk and terminal phases gave the best results and fit to the experimental data. In the bulk phase, where the temperature ranged from 30ºC to 100ºC, the reaction rate constant varied from 0.15 to 0.19 1/min for the intact biomass and from 0.25 to 0.55 1/min for the hydrolysis byproduct. According to the models, accelerated lignin removal with the increased operating temperature could be due to the shift of the process from the terminal phase to the bulk phase. The values obtained for the activation energies herein ( 33 kJ/mol) were less than the values reported in the literature for other lignocellulosic materials. The removal or reduction of the microbial inhibitors in the medium was carried out by activated carbon (adsorptive detoxification). According to the results using the Langmuir model with the activated carbon as the adsorbent, the maximum monolayer capacities of 341, 211, and 46 mg/g were obtained, respectively, for phenol, furfural, and acetic acid. Thermodynamic analyses indicated that the adsorption of the three abovementioned chemicals by the activated carbon was exothermic (enthalpy: H0), spontaneous (free energy: G0), and based on the affinity of the solute toward the adsorbent (entropy: S0). In the concentrated hydrolysate, the removal of phenols, as the main inhibitor, was very successful such that by activated carbon doses of 1.25%, 2.5%, and 5% (w/v) they could be reduced to 34%, 13%, and 3% of the initial concentration (8.7 g/l), respectively. During xylitol bioproduction process in the repeated batch mode using C. guilliermondii, variables of pH control, medium supplementation, and cell recycling proved to be more important than medium detoxification. Processes involving pH-controlled condition combined with nitrogen supplementation and a mild detoxification performed very well with consistent conversion parameters in the successive batches; values of over 0.8 g/g, 0.55 g/l/h, and 53 g/l were obtained respectively for xylitol yield, volumetric productivity, and final concentration. On the other hand, in a single-batch bioconversion, there was no need for supplementing the medium with the nitrogen source. Kinetic modeling of the process showed that substrate (xylose) as well as co-substrate (glucose) consumption, product (xylitol) formation, and cell regeneration could be predicted by a diauxic model. In the aerated free-cell and immobilized-cell systems, aeration rates of 1.25 vvm and 1.25-1.5 vvm were required for free-cell and immobilized-cell systems, respectively, to reach the maximum bioconversion performance. In the immobilized-cell system, cell support also played an important role in this biotransformation. Application of the support based on the delignified hydrolysis byproduct resulted in high and consistent bioconversion parameters in all batches comparable to the ones in the free-cell system. However, bioconversions using the lignin-rich material (hydrolysis byproduct) resulted in a lower efficiency in the first batch which could be partly improved in the second batch and almost fully increased in the third batch to nearly reach performance parameters comparable to the ones obtained in the free-cell system. Overall, the integrated process employed in this investigation helps fill in the knowledge gaps existing on the lignocellulosic biomass application for xylitol bioproduction and biorefinery industries.

vi, 90 leaves : tables, graphs ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1979) from the Dept. of Biochemistry, University of Adelaide

Type 2 diabetes is a devastating disease that has been rising in prevalence in the United States over the last 70 years, a rise which has paralleled the obesity epidemic and use of artificial sweeteners. This is especially concerning due to the many detrimental comorbid complications stemming from this potentially longstanding disease, including retinopathy, nephropathy, and neuropathy. Xylitol is an alternative sweetener that has been gaining popularity due to its intense sweetening power, as well as reported antidiabetic effects. Studies on rats induced with type 2 diabetes have found that xylitol helps in reducing blood glucose and insulin secretion, as well as increase protein and fat metabolism, post prandial satiety, and oxygen free radical destruction. These promising results have provided ample evidence to test the effects of xylitol on humans. The proposed study will examine the results of daily xylitol intake (0%, 2.5%, 5%, and 10%) on blood sugar levels over 1 year in newly diagnosed type 2 diabetics. Plasma samples will be taken 3 times during the study period to examine HbA1c, fasting blood glucose, Glucagon-Like Peptide 1, Cholecystokinin, and Superoxide Dismutase. At the end of 1 year of treatment, patient samples will be averaged into 6 month and 12 month results for each parameter and compared using ANOVA and student T-tests. We will test whether the results of this study mirror those seen in previous research on rats, that the antidiabetic effects of xylitol increase relative to concentration. This study hopes to provide further evidence on the need for xylitol supplementation in the diet of type 2 diabetics, either independently or to augment medical treatment, in helping to prevent progression of disease and reduce comorbid complications.

No description available.

In spite of the vast research on polymer-based tissue regeneration, extensive studies to develop an elastic and cell-promoting polymer biomaterial are still ongoing. However, using a renewable resource and a simple, environment-friendly synthesis route to synthesize an elastic polymer has not been successfully achieved yet. The objective of this work was to develop an elastic polymer for tissue engineering and drug delivery applications by using non-toxic, inexpensive and renewable monomers. A new nature-derived renewable material, xylitol, was used to synthesize an elastic polymer with the presence of a crosslinking agent, dodecanedioic acid. Here a simple melt condensation polymerization method was used to synthesize the poly(xylitoldodecanedioic acid)(PXDDA). The physicochemical and biological properties of the new PXDDA polymer were characterized. Fourier transform infrared (FTIR) confirmed the formation of ester bonding in the polymer structure, and thermal analysis demonstrated that the polymer was completely amorphous. The polymer shows high elasticity. Increasing the molar ratio of dodecanedioic acid resulted in higher hydrophobicity and lower glass transition temperature. Further, the polymer degradation and in vitro dye release studies revealed that the degradation and dye release from the polymer became slower when the amount of dodecanedioic acid in the composite increased. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection