Microbial cross-contamination remains an on-going challenge in the food sector despite implemented sanitation programs. Antimicrobial coatings with inherent self-sanitizing properties have been explored to enhance current cleaning practice and support food safety. Prior work has demonstrated successful incorporation of dual antimicrobial characters, cationic polymers and N-halamines, into one coating system. In addition to the rechargeable nature of N-halamines, the coating was reported to exhibit biocidal effects due to the inherently antimicrobial cationic moieties and the chlorinated N-halamines. However, while these polymer coatings were able to retain antimicrobial activity after repeated chlorination, signs of hydrolysis was observed for the N-halamine bonds, indicating potential issues for long-term usage. Herein, we introduced varied molecular weight cross-linkers in an adaption of the established fabrication method to evaluate cross-linker molecular weight (styrene maleic anhydride (SMA) of 6, 8, 120, 250 kDa) influence on surface properties of the coating. All antimicrobial polymer coatings exhibited similar FTIR spectra, with a prominent absorption band at ~1650 cm-1 suggesting successful cross-link of the polyethyleneimine and SMA. Surface concentration of primary amines ranged from 350-900 nmol/cm2, and N-halamines from 90-130 nmol/cm2. Surface energy decreased with increasing molecular weight of SMA, but were not statistically different from one another. In the end, optimal cross-linker molecular weight was determined based on antimicrobial performance, where the coated PPs with 6 kDa SMAs demonstrated enhanced biocidal effects against E. coli O157:H7 in its chlorinated form. Further, the antimicrobial coating demonstrated efficacy of ~3 to >5 log reductions of microbial load in its unchlorinated and chlorinated form against E. coli O157:H7, L. monocytogenes, and P. fluorescens. Storage studies support the stability of the chlorinated halamines, with full retention of chlorinated N-halamines over a 24 h study (representative of time between sanitation cycles). These results support the potential application of this antimicrobial polymer coating in food processing and handling operations, in support of reducing cross-contamination of spoilage and pathogenic microorganisms.

Seafood products are a common consumer choice and a variety of cooking methods are used in seafood preparation. Although often cooked, products such as shrimp and salmon remain some of the most common carriers of foodborne disease. Cooking these products at elevated temperatures efficiently reduces foodborne disease causing pathogens to a safe level, but applying too much heat to seafood products can produce an overcooked, low quality food. It is necessary to investigate the cooking processes used in seafood preparation and establish appropriate consumer cooking parameters that optimize both the quality and microbial safety of the products. To achieve these goals, this study develops mathematical models for the inactivation of Salmonella sp., change in quality attributes, and the product heating profiles during the cooking process for shrimp and Atlantic salmon. Studies were performed to monitor the product heating profile during the baking and boiling of shrimp and the baking and pan-frying of salmon. Product color, texture, moisture content, mass loss, and pressed juice were evaluated during the cooking processes as the products reached the internal temperature recommended by the FDA. Studies were also performed on the inactivation of Salmonella cocktails in homogenized and non-homogenized shrimp and salmon. To effectively predict inactivation during cooking, the Bigelow, Fermi distribution, and Weibull distribution models were applied to the homogenized data. Minimum cooking temperatures necessary to destroy Salmonella sp. in shrimp and salmon were also determined. The heating profiles of the two products were modeled using the finite difference method. Temperature data directly from the modeled heating profiles was then used in the kinetic modeling of quality change and Salmonella inactivation during cooking. It was concluded that consumers need to judge the doneness of both shrimp and Atlantic salmon by the lightness factor (CIE L*) of the core region of both products. The core region's lightness factor, which a consumer may consider as opaqueness, more accurately represented the thermal doneness than the external qualities. The FDA's current recommendations for a 3 log reduction for intact seafood products and homogenized seafood products were each analyzed. Results were in agreement with the recommended 68°C plus 15 seconds for homogenized products. For intact products, shrimp inactivation results were in agreement with the recommended 63°C plus 15 seconds, but intact salmon achieved only a 2 log reduction by the temperature-time combination. It was also found that predictive models can effectively describe the survival data for two Salmonella cocktails. The Weibull distribution model, which takes into account any tailing effect in survival data, fit the survival data of Salmonella in shrimp acceptably. The Fermi distribution model, which incorporates any shouldering effect in data, was an acceptable fit for the inactivation data for salmon. Using three-dimensional slab geometry for salmon fillets and two-dimensional frustum cone geometry for shrimp resulted in acceptable model predictions of thermal distributions for the cooking methods studied. The temperature data attained directly from the modeled heating profiles was effectively used in the predictive quality and inactivation models. Agreeable first-order kinetic models were formulated for Î L and Î C color parameters in shrimp and salmon. Other kinetic models formulated were for texture change in salmon and pressed juice in both salmon and shrimp. Using a fixed inactivation level of 3 logs and a fixed quality of 95% best quality, optimal cooking conditions were determined that both provide a high quality product and assure microbial safety. Based on the specific cooking methods in this study, the optimal boiling times for extra jumbo and colossal sized shrimp were 100 seconds and 159 seconds, respectfully. The optimal oven baking times were 233 seconds for extra jumbo shrimp and 378 seconds for colossal shrimp. For Atlantic salmon, the optimal oven baking time was 1132 seconds and the optimal pan frying time was 399 seconds. / Master of Science

No description available.

In this study conducted at Food Science Australia (FSA) and Berlin University of Technology (BUT), the effects of pulsed electric field (PEF) treatment, a novel non-thermal processing technology on bovine milk microflora and native enzymes and on the rheological and textural properties of rennet-induced milk gels was investigated. The PEF treatments were conducted at field intensities of 25-37 kV cm-1 (up to 50 kV cm-1)and temperature range of 30°C to 75ºC. Native milk enzymes selected for the study included alkaline phosphatase, lipase, xanthine oxidase and plasminand microbiological study included determining Total Plate Count (TPC) and Pseudomonas and Enterobacteriaceae counts in skim milk. At 30ºC PEF treatment at maximum field intensity inactivated AlP by 42% while at 60oC inactivation was higher (67%). Under these treatment conditions less than1 log reduction in TPC and Pseudomonas count and 2.1 logs reduction in the Enterobacteriaceae count was achieved at 30oC while at 60ºC TPC dropped by 2.4 logs and Pseudomonas and Enterobacteriaceae counts were reduced by 5.9 and 2.1 logs, respectively to below the detection limit of 1 CFU mL-1. Combining PEF treatment with heat increased the inactivation level of all enzymes which showed an increasing trend with increasing field intensity and temperature. Treatment time (4.8, 9.6, 19.2, 28.8 and 38.4 µs) was controlled by either changing the pulse frequencies (100-400 Hz) or product flow rate (30-240 mL min-1) at a constant field intensity of 31 kV cm-1 and it was found that changing the flow rate was a more effective way of enzyme inactivation than changing the frequency due to longer exposure time of enzymes to heat and field intensity. The size of casein micelles and fat globules was not affected by PEF treatment while severe heating of milk at 97oC for 10 min decreased both micelle and fat globule sizes marginally. The coagulation time of rennet-induced gels made from PEF-treated (35 to 50 kV cm-1) milks (whole and skim) increased as the treatment intensity increased, but remained shorter than gels made from pasteurised milk. The PEF treatment of milk at various field intensities and temperatures adversely affected the G′, G′′ and firmness of gels, but the effects were less pronounced than in gels made from pasteurised milks. This study concludes that for successful application in milk processing the PEF treatment needs to be combined with mild heat treatment. This approach could achieve safer milk with less damage to milk functionality. However, the quest for a suitable quality assurance indicator enzyme will need more extensive studies.

The PEF treatments were conducted at field intensities of 25-37 kV cm-1 (up to 50 kV cm-1)and temperature range of 30°C to 75ºC. Native milk enzymes selected for the study included alkaline phosphatase, lipase, xanthine oxidase and plasminand microbiological study included determining Total Plate Count (TPC) and Pseudomonas and Enterobacteriaceae counts in skim milk. At 30ºC PEF treatment at maximum field intensity inactivated AlP by 42% while at 60oC inactivation was higher (67%). Under these treatment conditions less than1 log reduction in TPC and Pseudomonas count and 2.1 logs reduction in the Enterobacteriaceae count was achieved at 30oC while at 60ºC TPC dropped by 2.4 logs and Pseudomonas and Enterobacteriaceae counts were reduced by 5.9 and 2.1 logs, respectively to below the detection limit of 1 CFU mL-1. Combining PEF treatment with heat increased the inactivation level of all enzymes which showed an increasing trend with increasing field intensity and temperature. Treatment time (4.8, 9.6, 19.2, 28.8 and 38.4 µs) was controlled by either changing the pulse frequencies (100-400 Hz) or product flow rate (30-240 mL min-1) at a constant field intensity of 31 kV cm-1 and it was found that changing the flow rate was a more effective way of enzyme inactivation than changing the frequency due to longer exposure time of enzymes to heat and field intensity. The size of casein micelles and fat globules was not affected by PEF treatment while severe heating of milk at 97oC for 10 min decreased both micelle and fat globule sizes marginally. The coagulation time of rennet-induced gels made from PEF-treated (35 to 50 kV cm-1) milks (whole and skim) increased as the treatment intensity increased, but remained shorter than gels made from pasteurised milk. The PEF treatment of milk at various field intensities and temperatures adversely affected the G′, G′′ and firmness of gels, but the effects were less pronounced than in gels made from pasteurised milks. This study concludes that for successful application in milk processing the PEF treatment needs to be combined with mild heat treatment. This approach could achieve safer milk with less damage to milk functionality. However, the quest for a suitable quality assurance indicator enzyme will need more extensive studies.

Increasing consumer demand for new products with high nutritional qualities has spurred a search for new alternatives to food preservation. Pulsed electric field (PEF) is an emerging technology for non thermal food pasteurisation. Using this technology, enzymes, pathogenic and spoilage microorganisms can be inactivated without affecting the colour, flavour, and nutrients of the food. PEF treatment may be provided by applying pulsed electric field to a food product in a treatment zone between two electrodes at ambient , or slightly above ambient temperature. Exposure of microbial cells to the electric field induces a transmembrane potential in the cell membrane, which results in electroporation (the permeabilization of the membranes of cells and organelles) and/or electrofusion (the connection of two separate membranes into one) of the cells. An innovative pulsed electric field (PEF) unit was designed and constructed in the University of Auckland using modern IGBT technology. The system consists of main equipments, the high voltage pulse generator and the treatment chambers. The main focus of this work was to design an innovative PEF treatment chamber that provide uniform distribution of electric field, minimum increase in liquid temperature, minimum fouling of electrodes and an energy efficient system. Four multi pass treatment chambers were designed consisting of two stainless steel mesh electrodes in each chamber, with the treated fluid flowing through the openings of the mesh electrodes. The two electrodes are electrically isolated from each other by an insulator element designed to form a small orifice where most of the electric field is concentrated. Dielectric breakdown inside the chambers was prevented by removing the electrodes far from the narrow gap. The effect of the chambers different geometries on the PEF process in terms of electric parameters and microbial inactivation were investigated. Electric field intensity in the range of (17-43 kV/cm) was applied with square bipolar pulses of 1.7 µs duration. The effect of PEF treatment on the inactivation of gram-negative Escherichia coli ATCC 25922 suspended in simulated milk ultra-filtrate (SMUF) of 100%, 66.67% and 50% concentration was investigated. Treatments with the same electrical power input but higher electric field strengths provided larger degree of killing. The inactivation rate of E coli was significantly increased with increasing the electric field strength, treatment time and processing temperature. Morphological changes on E coli as a result of PEF treatment were studied under transmission electron microscopy (TEM). Significant morphological changes on E coli after PEF treatment were observed. The TEM studies suggested that the microbial inactivation was a consequence of electroporation and electrofusion mechanisms. Kinetic analysis of microbial inactivation due to PEF and thermal treatment of E coli suspended in SUMF were also studied. Comparison between measured (experimental) and predicted (theoretical) variation of E coli concentration with time following the PEF treatment was discussed, taking into consideration the recirculation mode of the PEF treatment. The treated liquid was circulated more than once through the treatment chamber to provide higher microbial inactivation. Arrhenius constants and activation energies of E coli inactivation using combined PEF and thermal treatment were calculated and generalized correlation for the inactivation rate constant as a function of electric field intensity and treatment temperature was developed. / Fonterra Research Institute (NZ) and the Foundation for Research Science and Technology (NZ)

Increasing consumer demand for new products with high nutritional qualities has spurred a search for new alternatives to food preservation. Pulsed electric field (PEF) is an emerging technology for non thermal food pasteurisation. Using this technology, enzymes, pathogenic and spoilage microorganisms can be inactivated without affecting the colour, flavour, and nutrients of the food. PEF treatment may be provided by applying pulsed electric field to a food product in a treatment zone between two electrodes at ambient , or slightly above ambient temperature. Exposure of microbial cells to the electric field induces a transmembrane potential in the cell membrane, which results in electroporation (the permeabilization of the membranes of cells and organelles) and/or electrofusion (the connection of two separate membranes into one) of the cells. An innovative pulsed electric field (PEF) unit was designed and constructed in the University of Auckland using modern IGBT technology. The system consists of main equipments, the high voltage pulse generator and the treatment chambers. The main focus of this work was to design an innovative PEF treatment chamber that provide uniform distribution of electric field, minimum increase in liquid temperature, minimum fouling of electrodes and an energy efficient system. Four multi pass treatment chambers were designed consisting of two stainless steel mesh electrodes in each chamber, with the treated fluid flowing through the openings of the mesh electrodes. The two electrodes are electrically isolated from each other by an insulator element designed to form a small orifice where most of the electric field is concentrated. Dielectric breakdown inside the chambers was prevented by removing the electrodes far from the narrow gap. The effect of the chambers different geometries on the PEF process in terms of electric parameters and microbial inactivation were investigated. Electric field intensity in the range of (17-43 kV/cm) was applied with square bipolar pulses of 1.7 µs duration. The effect of PEF treatment on the inactivation of gram-negative Escherichia coli ATCC 25922 suspended in simulated milk ultra-filtrate (SMUF) of 100%, 66.67% and 50% concentration was investigated. Treatments with the same electrical power input but higher electric field strengths provided larger degree of killing. The inactivation rate of E coli was significantly increased with increasing the electric field strength, treatment time and processing temperature. Morphological changes on E coli as a result of PEF treatment were studied under transmission electron microscopy (TEM). Significant morphological changes on E coli after PEF treatment were observed. The TEM studies suggested that the microbial inactivation was a consequence of electroporation and electrofusion mechanisms. Kinetic analysis of microbial inactivation due to PEF and thermal treatment of E coli suspended in SUMF were also studied. Comparison between measured (experimental) and predicted (theoretical) variation of E coli concentration with time following the PEF treatment was discussed, taking into consideration the recirculation mode of the PEF treatment. The treated liquid was circulated more than once through the treatment chamber to provide higher microbial inactivation. Arrhenius constants and activation energies of E coli inactivation using combined PEF and thermal treatment were calculated and generalized correlation for the inactivation rate constant as a function of electric field intensity and treatment temperature was developed. / Fonterra Research Institute (NZ) and the Foundation for Research Science and Technology (NZ)

Increasing consumer demand for new products with high nutritional qualities has spurred a search for new alternatives to food preservation. Pulsed electric field (PEF) is an emerging technology for non thermal food pasteurisation. Using this technology, enzymes, pathogenic and spoilage microorganisms can be inactivated without affecting the colour, flavour, and nutrients of the food. PEF treatment may be provided by applying pulsed electric field to a food product in a treatment zone between two electrodes at ambient , or slightly above ambient temperature. Exposure of microbial cells to the electric field induces a transmembrane potential in the cell membrane, which results in electroporation (the permeabilization of the membranes of cells and organelles) and/or electrofusion (the connection of two separate membranes into one) of the cells. An innovative pulsed electric field (PEF) unit was designed and constructed in the University of Auckland using modern IGBT technology. The system consists of main equipments, the high voltage pulse generator and the treatment chambers. The main focus of this work was to design an innovative PEF treatment chamber that provide uniform distribution of electric field, minimum increase in liquid temperature, minimum fouling of electrodes and an energy efficient system. Four multi pass treatment chambers were designed consisting of two stainless steel mesh electrodes in each chamber, with the treated fluid flowing through the openings of the mesh electrodes. The two electrodes are electrically isolated from each other by an insulator element designed to form a small orifice where most of the electric field is concentrated. Dielectric breakdown inside the chambers was prevented by removing the electrodes far from the narrow gap. The effect of the chambers different geometries on the PEF process in terms of electric parameters and microbial inactivation were investigated. Electric field intensity in the range of (17-43 kV/cm) was applied with square bipolar pulses of 1.7 µs duration. The effect of PEF treatment on the inactivation of gram-negative Escherichia coli ATCC 25922 suspended in simulated milk ultra-filtrate (SMUF) of 100%, 66.67% and 50% concentration was investigated. Treatments with the same electrical power input but higher electric field strengths provided larger degree of killing. The inactivation rate of E coli was significantly increased with increasing the electric field strength, treatment time and processing temperature. Morphological changes on E coli as a result of PEF treatment were studied under transmission electron microscopy (TEM). Significant morphological changes on E coli after PEF treatment were observed. The TEM studies suggested that the microbial inactivation was a consequence of electroporation and electrofusion mechanisms. Kinetic analysis of microbial inactivation due to PEF and thermal treatment of E coli suspended in SUMF were also studied. Comparison between measured (experimental) and predicted (theoretical) variation of E coli concentration with time following the PEF treatment was discussed, taking into consideration the recirculation mode of the PEF treatment. The treated liquid was circulated more than once through the treatment chamber to provide higher microbial inactivation. Arrhenius constants and activation energies of E coli inactivation using combined PEF and thermal treatment were calculated and generalized correlation for the inactivation rate constant as a function of electric field intensity and treatment temperature was developed. / Fonterra Research Institute (NZ) and the Foundation for Research Science and Technology (NZ)

Increasing consumer demand for new products with high nutritional qualities has spurred a search for new alternatives to food preservation. Pulsed electric field (PEF) is an emerging technology for non thermal food pasteurisation. Using this technology, enzymes, pathogenic and spoilage microorganisms can be inactivated without affecting the colour, flavour, and nutrients of the food. PEF treatment may be provided by applying pulsed electric field to a food product in a treatment zone between two electrodes at ambient , or slightly above ambient temperature. Exposure of microbial cells to the electric field induces a transmembrane potential in the cell membrane, which results in electroporation (the permeabilization of the membranes of cells and organelles) and/or electrofusion (the connection of two separate membranes into one) of the cells. An innovative pulsed electric field (PEF) unit was designed and constructed in the University of Auckland using modern IGBT technology. The system consists of main equipments, the high voltage pulse generator and the treatment chambers. The main focus of this work was to design an innovative PEF treatment chamber that provide uniform distribution of electric field, minimum increase in liquid temperature, minimum fouling of electrodes and an energy efficient system. Four multi pass treatment chambers were designed consisting of two stainless steel mesh electrodes in each chamber, with the treated fluid flowing through the openings of the mesh electrodes. The two electrodes are electrically isolated from each other by an insulator element designed to form a small orifice where most of the electric field is concentrated. Dielectric breakdown inside the chambers was prevented by removing the electrodes far from the narrow gap. The effect of the chambers different geometries on the PEF process in terms of electric parameters and microbial inactivation were investigated. Electric field intensity in the range of (17-43 kV/cm) was applied with square bipolar pulses of 1.7 µs duration. The effect of PEF treatment on the inactivation of gram-negative Escherichia coli ATCC 25922 suspended in simulated milk ultra-filtrate (SMUF) of 100%, 66.67% and 50% concentration was investigated. Treatments with the same electrical power input but higher electric field strengths provided larger degree of killing. The inactivation rate of E coli was significantly increased with increasing the electric field strength, treatment time and processing temperature. Morphological changes on E coli as a result of PEF treatment were studied under transmission electron microscopy (TEM). Significant morphological changes on E coli after PEF treatment were observed. The TEM studies suggested that the microbial inactivation was a consequence of electroporation and electrofusion mechanisms. Kinetic analysis of microbial inactivation due to PEF and thermal treatment of E coli suspended in SUMF were also studied. Comparison between measured (experimental) and predicted (theoretical) variation of E coli concentration with time following the PEF treatment was discussed, taking into consideration the recirculation mode of the PEF treatment. The treated liquid was circulated more than once through the treatment chamber to provide higher microbial inactivation. Arrhenius constants and activation energies of E coli inactivation using combined PEF and thermal treatment were calculated and generalized correlation for the inactivation rate constant as a function of electric field intensity and treatment temperature was developed. / Fonterra Research Institute (NZ) and the Foundation for Research Science and Technology (NZ)

This thesis discusses the development of an improved microbial inactivation model for analyzing continuous flow UV-LED air treatment systems and use of the model to evaluate the impact of several treatment system design parameters on inactivation. Model development includes three submodels: a radiation submodel, a fluid flow submodel, and an inactivation kinetics submodel. Radiation modeling defines the UV irradiance throughout the system. Fluid flow modeling provides the residence times that microbes spend exposed to the UV irradiation while passing through the system. Inactivation modeling combines irradiance and residence times with inactivation kinetics to calculate species-specific inactivation in a treatment system. The most significant development focuses on the radiation submodel as it is key to linking the UV intensity emissions to treatment system properties and inactivation rates. Various radiation transfer models previously developed by other researchers are evaluated for computational efficiency and effectiveness in modeling non-uniform LED emission and diffuse and specular wall reflections. The Discrete Ordinates Method (DOM) with Legendre-Chebyshev quadrature sets is selected for use in this research due to its ability to represent both non-uniform LED emission profiles and combined specular and diffuse surface reflection. The DOM and associated quadrature schemes are reviewed in detail and limitations in representing LED emissions discussed. Sensitivity to spatial and directional discretization is evaluated. The radiation submodel is combined with a well-accepted inactivation kinetics correlation and two simple fluid flow models: a uniform flow model and a fully-developed flow model. The use and validity of these submodels is explained and their limitations discussed. Predicted microbial inactivation from the overall model is shown to compare well with limited data from a test system. Model flexibility in evaluating several system operating and design parameters is illustrated. These analyses show that for a similar number of LEDs, highly reflective surfaces (diffuse or specular) produce higher inactivation. Other parameters are shown to impact inactivation but to a lesser degree. Square ducts result in higher inactivation than non-square ducts, a fully-developed flow profile slightly increases inactivation over a uniform flow profile, positioning LEDs on all four duct walls slightly increases inactivation when surfaces are non-reflective or diffuse, and positioning LEDs closer together results in slightly higher inactivation.