Browsing by Subject "encapsulation"
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Item Antimicrobial Efficacy of Liposome Encapsulated Nisin and Nisin's Inhibition Against Listeria monocytogenes in Fluid Milk at Different Storage Temperatures(2010-10-12) Schmidt, Shannon E.Nisin is a naturally occurring food antimicrobial that inhibits many Grampositive pathogens, including Listeria monocytogenes, a bacterial pathogen responsible for ~500 deaths in the U.S. annually. Factors known to counteract the nisin activity in a food matrix include: antimicrobial interaction with food components, insolubility, protease inactivation, and target cell-driven envelope modifications. Encapsulating nisin in liposomes can help protect nisin functionality by regulating its introduction to the external environment. The objectives of this study were to determine the encapsulation efficiency (%EE) of nisin within liposomes as a function of encapsulation method and the capacity of liposomal nisin to inhibit L. monocytogenes in fluid milk. Phosphatidylcholine (PC) and phosphotidyl-DL-glycerol (PG) were used to prepare three lipid molar formulations: PC, PC/PG 7:3, and PC/PG 6:4 (mol.%). Liposomes were formulated to entrap the self-quenching fluorophore calcein and nisin. Unencapsulated analyte was removed via size-exclusion chromatography, and percent EE was determined. To determine antilisterial activity of liposomes, fluid milk samples containing L. monocytogenes (4 log10 CFU/mL) in combination with liposomal or unencapsulated nisin at 50 IU/mL were mixed and aerobically stored at 5 degrees C and 20 degrees C. Surviving L. monocytogenes were enumerated via plating on a non-selective microbiological medium after 0, 1, 3, 6, 12, 24, 48, and 72 hours of incubation. Encapsulation of nisin via extrusion resulted in a mean EE% of 84.20%, 77.33% and 80.78% for PC, PC/PG 7:3, and PC/PG 6:4 liposomes, respectively. Freeze-thaw cycling formed liposomes without detectable fluorophore entrapment. L. monocytogenes populations grew to 5 log10 CFU/mL after 72 hours at 5 degrees C and 8 log10 CFU/mL at 20 degrees C after 48 hours. Unencapsulated nisin exerted statistically greater inhibition of Listeria in skim milk compared to liposomal nisin, regardless of incubation temperature. No statistically significant differences in Listeria populations exposed to free or encapsulated nisin in whole milk were observed at either incubation temperature. Results indicate storage temperature and presence of milk fat exert greater influence then nisin delivery (free vs. encapsulated) over Listeria inhibition. Further research is needed to confirm these findings and develop more effective means of liposome entrapment of nisin for the inhibition of foodborne bacterial pathogens.Item Application of Luminescent Materials to Optical Sensing(2014-09-05) Ritter, Sarah CDevelopment of sensors for detection of various chemical and biological species is an important and ever-growing field. In particular, optical-based sensors enable a remote, rapid method for continuous or on-demand monitoring. Monitoring humidity is important across many applications, such as humidity control within moisture-sensitive environments and in medical, semiconductor, and food science fields. Following a study of photobleaching, defect-related emission of zinc oxide nanoparticles was monitored as a function of relative humidity. An important next step is its application to monitoring toxic gases, as air pollution has been identified as a major health concern. Of importance for the biomedical field is monitoring key blood analytes for human health. Monitoring blood pH is critical for specific patient groups, such as those suffering from diabetic ketoacidosis and congenital lactic acidosis. A pH-sensitive fluorophore was loaded within red blood cells for use as a continuous blood analyte monitor. Future work will focus on glucose, as current estimates show that one out of every three children born in 2000 will develop diabetes in his or her lifetime ? thus, the global impact of this disease is immense. Results from ZnO studies indicate that photobleaching is related to the surface area to volume ratio. ZnO nanoparticles display a linear response to humidity with a sensitivity of 0.008417 RH^-1 and 0.01898 RH^-1 for nitrogen and air environments, respectively. Owing to reversibility and high sensitivity, ZnO nanoparticles have great potential as optical-based environmental sensors. Results from dye-loaded ghost studies indicate that fluorescence intensity of intracellular dyes report on extracellular pH. Resealed ghosts loaded with a fluorescein isothiocyanate-glycylglycine conjugate reversibly track pH with a resolution down to 0.014 pH unit. For use in vivo, the development of an NIR pH-sensitive dye was paramount. Unfortunately, all NIR dyes tested exhibited poor pH sensitivity while displaying sensitivity to external factors (e.g., temperature, concentration, proteins). However, circulation kinetics of resealed ghosts were easily monitored once injected in vivo with an optical fiber-based system. Although the cells were rapidly removed from circulation, the loaded ghosts resulted in higher signal than would be expected for free dye alone. Once optimized, the resealed ghosts could serve as a long-term, continuous, circulating biosensor for the management of diseases.Item Effects of amounts and types of sodium bicarbonate in wheat flour tortillas(Texas A&M University, 2007-04-25) Garza Casso, Jessica BeatrizThe effects of different types and amounts of sodium bicarbonate (NBC) were evaluated during the processing of flour tortillas. Fat encapsulated NBC, BS199, BS195, BS193, BS180, BS184, HM50 and HM70, and different particle-sized, non-encapsulated NBC, grade 1, grade 2, grade 3 and Tortilla Blend TM, were tested at different levels and combinations. Longer shelf stable tortillas with lower opacity were obtained when the level of NBC decreased. Tortillas with higher opacity, diameter and volume were obtained using the correct types of NBC. Increased tortilla opacity, thickness and shelf stability were obtained using 3 g encapsulated NBC/kg compared to non-encapsulated NBC. Encapsulation of NBC enables a temperature-triggered leavening reaction during baking of tortillas. Combinations of different levels and ratios of fast- and slow-release NBC did not yield significant improvements in tortilla properties. Tetrasodium pyrophosphate (TSPP, 0.15%) was added to modify protein functionality in tortilla dough containing less NBC. Tortillas with improved opacity, thickness and shelf stability resulted using TSPP with 3 g Grade 1 NBC/kg but similar improvements were not seen with encapsulated NBC. The effects of TSPP with low levels of NBC and slow reacting leavening acids were tested. Slight improvements in opacity were observed with sodium aluminum phosphate (SALP) compared to sodium aluminum sulfate (SAS) using encapsulated and non-encapsulated NBC. Tortillas produced with these formulations have longer shelf stabilities with similar properties. This benefits the consumers. The manufacturing costs for ingredients are 1.2% less using 0.15% TSPP with 3 g non-encapsulated NBC/kg flour. The manufacturer gains not only by the reduced cost of ingredients but also by the increased ease of attaining target diameter of tortillas. This could also be accomplished by using less dough to form the tortilla.