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- Title
- EFFICACY OF PULSED LIGHT TECHNOLOGY FOR THE INACTIVATION OF SALMONELLA ENTERITIDIS PT 30 ON ALMOND KERNEL SURFACE
- Creator
- Harguindeguy, Maite
- Date
- 2016, 2016-05
- Description
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Almond surfaces can be contaminated with pathogens such as Salmonella. Traditional thermal processing technologies used for inactivation of...
Show moreAlmond surfaces can be contaminated with pathogens such as Salmonella. Traditional thermal processing technologies used for inactivation of Salmonella on almonds can adversely impact the quality. Therefore, there is a need to investigate the efficacy of alternative technologies for inactivation of Salmonella on almonds without adversely affecting the quality. Pulsed light, a novel technology, can potentially be used to achieve this. Therefore, this study evaluated the efficacy of three pulsed light systems (operating at 1.8, 3, or 100 Hz) under various electrical input powers (1000, 1250 and 1500 W) and treatment times for inactivation of Salmonella Enteritidis PT 30 on almond surfaces. More than 4-log reduction was achieved at different treatment conditions for each of the control units. For instance, a 160 s treatment at 1500 W (100 Hz system) resulted in a 4.3 log CFU/almond reduction. Whereas, similar reductions were achieved in a shorter time with the lower frequency systems (1.8 or 3 Hz). Reductions of 4.6 and 5.9 log CFU/almond were achieved after 80 and 100 s treatment, respectively with the 1.8 Hz system (1250 W). Similarly, a 100 s treatment with the 3 Hz system (1000 W) resulted in a reduction of 4.7 log CFU/almond. Statistical analysis showed that the effect of equipment, treatment time, and electrical power input were significant (p<0.05). The D-values of 1.8, 3, and 100 Hz systems were 0.24, 0.53 and 0.73 min, respectively at 1500 W. In general, lower frequencies resulted in increased inactivation in shorter time. This can be attributed to the higher instantaneous power at lower frequencies. Similar trends were observed at other electrical input powers. The D-values found using pulsed light treatment are lower than the conventional dry heat treatment ones. Also, minimal color change was observed for treated almonds. These results indicate that pulsed light is efficacious for decontaminating almond surfaces within a relatively short time.
M.S. in Food Process Engineering, May 2016
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- Title
- ELECTROCHEMICAL AND TERMAL MECHANISTIC STUDY OF BEYOND LITHIUM ION SYSTEMS: LITHIUM SULFUR AND LITHIUM OXYGEN CELLS
- Creator
- Seo, Jeongwook
- Date
- 2016, 2016-05
- Description
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Electrochemical and Thermal Mechanistic Study of Lithium Sulfur Cell. The thermal behavior of Li/S cells was studied using IMC in terms of...
Show moreElectrochemical and Thermal Mechanistic Study of Lithium Sulfur Cell. The thermal behavior of Li/S cells was studied using IMC in terms of reversible and irreversible heat generation. The heat generation profile was compared with the voltage profile during discharge of the cell and it was found that the trend of heat generation rate shows excellent correlation with the evolution of reaction voltage, which demonstrates that the IMC technique can be used as an useful tool to study the elementary reactions of the Li/S cell. A simple heat generation model provides reasonable agreement with the measured trends in the heat release. The resistive heat evolution that is calculated by over voltage has the largest portion of total cell heat generation (85%) after the IMC heat evolution model analysis. The qualitative agreement between the aforementioned experimental results and heat generation model yields a comprehensive picture of the elementary reaction steps in Li/S cell. The increase of cell conductivity can be expected to bring about low heat evolution during cell cycling by reducing resistive heat. Doped Sulfur as a conductive cathode is a good suggestion to improve cell heat behavior. Furthermore, better cell cycle capability is expected by using lithium metal oxide cathode composites. The thermal behavior of three cathode materials for lithium/sulfur (Li/S) cell, namely - sulfur, sulfur-LiFePO4 (S-LFP) composite and sulfur-LiV3O8 (S-LVO) composite were comparatively studied using Isothermal Micro-Calorimetry (IMC) at various rates of discharge current. A continuum model was used to calculate the reversible entropic heat and irreversible resistive heat generated over the discharge process and the model data was compared to the experimental data to elucidate these contributions to the overall heat generated. The S-LVO composite cathode was found to show the least heat generation during discharge. Further, Accelerating Rate Calorimetry (ARC) was used to study the thermal safety of these three cells. The cell with the S-LVO composite cathode was found to have the highest onset temperature for thermal runaway and also the lowest maximum self-heat rate. The combination of high capacity, long cycle life and thermal stability makes the S-LVO composite cathode a very promising material for Li/S cells Oxygen Reduction Reaction Studies using Rotating Ring Disk Electrode for Li-Air battery. The oxygen reduction reaction (ORR) studies in aqueous electrolytes have reported the following reaction mechanisms: (i) four electron reaction, (ii) two electron reaction and (iii) one electron chemical reaction. On the other hand, the aprotic ORR literature has no reports of four electrons and two electrons transfer reaction. The kinetics of ORR on the cathode was carried out using rotating ring disk electrode (RRDE) technique. The first step of ORR which produces the superoxide radical was investigated on glassy carbon (GC) disk in 0.1 M tetrabutylammonium bis-(trifluoromethane)imide (TBATFSI)/dimethoxyethane (DME). One-electron reduction to the superoxide radical was founded in the linear sweep voltammetry (LSV) analysis. Further, ORR to produce LiO2 and Li2O2 was carried in bis(trifluoromethane)sulfonimide-lithium(LITFSI)/DME on porous carbon coated glassy carbon electrode disk. The reaction kinetic rate on the porous carbon was calculated using the Li-O2 ORR mechanism model. The kinetic rate was compared with the kinetic rate of glassy carbon electrode. The non-aqueous system has several advantages compared to the aqueous system such as high operation voltage and non-reactive electrolyte with Li+. However this system has some critical problems such as low solubility of Li2O2 and High charge over potential. One attempted solution for these disadvantages of the non-aqueous system was to carry out water addition into the solvent which was expected to produce highly soluble LiOH with lower overpotential. Small amount of Water, 0.5 wt% added into 0.1 M LiTFSI/DME and 1 wt% added in the 0.2 M TBATFSI/DME electrolyte, showed great electrochemical performance with lower onset potential and overvoltage. The kinetics of ORR study for the non-aqueous and aqueous hybrid system was carried out using RRDE technique. Koutecky-Levich plot and Tafel slope analysis indicated two electron transfer reaction on the hydrated 0.1 M LiTFSI/DME. This hydrated system can be expected to double energy storage by two electron transfer ORR for Li-O2 Cell.
Ph.D. in Chemical Engineeering, May 2016
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- Title
- INACTIVATION OF MURINE NOROVIRUS ON STRAWBERRIES USING PULSED LIGHT
- Creator
- Chen, Dongjie
- Date
- 2016, 2016-12
- Description
-
Norovirus have become the predominant viral causes of foodborne illnesses worldwide, the foodborne happened mainly in schools and childcare...
Show moreNorovirus have become the predominant viral causes of foodborne illnesses worldwide, the foodborne happened mainly in schools and childcare facilities, strawberries were identified as the most likely vehicle according to the analytical epidemiological studies. So this study evaluated the efficacy of pulsed light (PL) treatments to inactivate murine norovirus (MNV-1), a human norovirus surrogate, inoculated onto strawberries. Two different PL treatments were evaluated - 3 Hz and 100 Hz PL treatments. PL treatments inactivated 1.5-3 log PFU/g MNV-1 on strawberry in a time-dependent manner of 30-120 s at both 3 and 100 Hz. The inactivation efficacy of PL is dependent on the pulsed frequency received with both PL treatment parameters. It can achieve 1.7 log PFU/g reduction after 120 s 3 Hz PL treatment at the distance of 8.3 cm from the quartz window, on the other hand, MNV-1 was inactivated by 3.2 log PFU/g after 120 s exposure to 100 Hz PL treatment at the distance of 8.3 cm from the quartz window. These results demonstrated that higher inactivation effect of MNV-1 on strawberry was associated with higher frequency of PL treatment. Therefore, this technology could be used to improve the microbial safety of fresh strawberries.
M.S. in Food Process Engineering, December 2016
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