Nutrition & Food Science
Permanent URI for this communityhttp://hdl.handle.net/1903/2267
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Item Novel Antimicrobial Treatments Based on the Interaction of Gallic Acid and UV Light: Characterization, Investigation of Antimicrobial Mechanism, and Application on Fresh Produce(2018) Wang, Qingyang; Tikekar, Rohan V; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Produce safety continues to be a challenge because produce undergoes minimal processing prior to consumption and existing sanitizers are not effective in inactivating pathogens. Novel decontamination technologies for produce are required as alternatives to traditional methods. In this project, two non-thermal process techniques were developed based on the interaction of UV light and gallic acid (GA) to enhance the safety of fresh produce. The first technique is the simultaneous application of UV-A light and GA (UVA+GA). UVA+GA treatment was effective against E. coli O157:H7, and the mechanism behind the synergistic antimicrobial effect was associated with the cellular uptake of GA, generation of reactive oxidative species (ROS), inactivation of enzymes superoxide dismutase, and damage to the bacterial membrane. In the second technique, the antimicrobial activity of GA was enhanced by its prior UV-C exposure (UVC-GA) against E. coli O157:H7 and was persistent for at least 4 weeks. The antimicrobial activity was affected by solution pH and the wavelength of UV-C exposure. The generation of ROS during UV light exposure and photo-oxidized compounds of GA such as quinone contributed to the antimicrobial activity of the UVC-GA solution. Both UVA+GA and UVC-GA treatments can enhance the inactivation of inoculated E. coli O157:H7 on produce such as spinach leaves and tomatoes without affecting the color and firmness. Common environmental stresses could confer complex cross-stress response in E. coli O157:H7 towards UVA+GA and UVC-GA treatments in that both resistance and sensitization can be induced depending on the stress applied and the technology studied. Repeated exposure to moderate UVA+GA or UVC-GA treatment can also select for sub-population that demonstrates higher resistance towards these treatments as well as cross-resistance to other lethal stress such as heat and acid. ROS scavenging enzymes and alternative sigma factor RpoS are highly likely to be associated with the adaptive response process. In conclusion, both UVA+GA and UVC-GA treatments are promising novel non-thermal techniques that are potential alternative methods for fresh produce disinfection. For future work, a better understanding of the inactivation mechanisms, optimizing of processing parameters, and the development of adaptive response associated with the two treatments need to be explored.Item Development of Encapsulation Systems from Zein and Metal-Organic Frameworks (MOFs) for Improved Functional Properties of Essential Oils(2013) Wu, Yunpeng; Wang, Qin; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Essential oils (EOs), which are derived from plants, have antifungal, insecticidal and antimicrobial activities, but they are slightly soluble in water and impart to the water their odor and taste, which limit their applications in food area. Zein, a prolamin from corn, is able to form nanoparticles by liquid-liquid dispersion process. These nanoparticles are well dispersed in water and stable, which can be further applied to encapsulate functional materials that are insoluble in water. We have developed zein nanoparticles to encapsulate thymol and carvacrol in order to improve their solubility. The DLS (dynamic light scattering) and SEM (scanning electron microscopy) proved that zein nanoparticles encapsulated with EO were formed. The particles size was between 200~300nm before lyophilizing. 65-75% EOs have been encapsulated in the nano-sized particles. DPPH assay results proved good antioxidant property of the product. For the Ferric-ion spectrophotometric assay, hydroxyl free radicals had been cleared by 60~90% in overall. In the antimicrobial experiment, the nanoparticles encapsulating EOs reduced 0.8-1.8 log units of E. coli after 48h incubation. Furthermore, we have applied Metal-Organic Frameworks (MOFs) to encapsulate thymol. Metal-Organic Frameworks (MOFs) or porous coordination polymers (PCPs) is a new class of hybrid materials, which are formed by the self-assembly of metal-connecting points and polydentate bridging ligands. MOFs in this study was synthetized by Zinc nitrate hexahydrate and 2-aminoterephthalic acid in N, N-dimethylformamide (DMF). Thymol was then loaded inside the MOFs at the loading rate of 3.95%. The structure of porous crystal MOFs was confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Inhibition to E. coli O157:H7 was measured both in TSB medium and on TSA agar. An E. coli O157:H7 reduction of 4.4 log CFU/mL have been achieved at a thymol to broth ratio of 0.04g/100g. An inhibition area of 223.73 mm2 was observed after 12h incubation. With the two methods (zein nano-particles and MOFs), EOs can be encapsulated and well dispersed in water solution. The enhanced antioxidant activity and antimicrobial ability of the encapsulated EOs promise their further applications in food industries.Item Intervention Strategies for Escherichia coli O157:H7 and Salmonella in Organic Soil and on Fresh Produce(2012) Nguekam Yossa, Irene Nadine; Lo, Martin; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently, foodborne diseases caused by Escherichia coli O157:H7 and Salmonella have been increasingly associated with the consumption of fresh produce. Consumers' demand for safe, natural products has led to research on natural antimicrobials for effective control of foodborne pathogens on fresh produce, which can be inadvertently contaminated by soil. Therefore, there is a need to control microbial loads in soil to minimize contamination. The objectives of this study were to evaluate the antimicrobial activity of cinnamaldehyde, Ecotrol®, eugenol, Sporan® and acetic acid against E. coli O157:H7 and Salmonella in organic soil, and to evaluate the antimicrobial effects of cinnamaldehyde and Sporan® alone, or in combination with acetic acid against E. coli O157:H7, Salmonella, and the native microflora of iceberg, romaine and spinach leaves. The quality parameters of the treated fresh produce were monitored, whereas the modes of action of cinnamaldehyde and Sporan® were investigated. The results showed that cinnamaldehyde had the highest bactericidal activity against E. coli O157:H7 and Salmonella in organic soil. Increases in oil concentration resulted in further reduction of both microorganisms. Up to 5 and 6 log CFU/g of E. coli O157:H7 and Salmonella, respectively, were reduced with 2% Sporan® and acetic acid after 24 h. Sporan® in combination with acetic acid (1000SV) and 800 ppm cinnamaldehyde-Tween reduced significantly E. coli O157:H7 (~3 log CFU/g) on iceberg and spinach leaves following treatment at day 0. Likewise, 1000SV treatment reduced Salmonella ~ 2.5 log CFU/g at day 0. E. coli O157:H7 and Salmonella populations in treated iceberg, spinach and romaine leaves were reduced during storage at 4°C. The native microflora of untreated and treated spinach and lettuce leaves increased during the storage time. The texture and the color of iceberg, romaine and spinach leaves treated with essential oils were not significantly different from the control lettuce after 14 days. The scanning and transmission electron microscopy of oil-treated bacterial cells indicated possible cell structural damage and leakage of cellular content. This study shows the potential use of essential oils to effectively reduce E. coli O157:H7 and Salmonella populations in soil and on fresh produce without adversely affecting leaf color and texture.