Browsing by Subject "irradiation"
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Item Effect of electron beam irradiation on quality and shelf-life of Tommy Atkins mango (Mangifera indica l.) and blueberry (Vaccinium corymbsum l.)(Texas A&M University, 2007-04-25) Moreno Tinjaca, Maria AlexandraThe main goal of this research was to determine the feasibility of using electron beam irradiation as an alternative disinfestation technology while preserving the overall quality of mangoes, and to verify its suitability for the preservation shelf life of blueberries. Physicochemical and sensory characteristics of the fruits were evaluated. Mangoes were irradiated at 1.0, 1.5 and 3.1 kGy using a 10MeV (10 kW) linear accelerator (LINAC) with double beam fixture. Samples were stored at 12????C and 62.7% RH for 21 days. Blueberries packed in plastic clamshell containers were irradiated at 1.1, 1.6 and 3.2 kGy doses using the same linear accelerator with a single beam. The shelf life of the berries stored at 5????C and 70.4% RH was evaluated for 14 days. The firmness of mangoes irradiated at 1.5 and 3.1 kGy significantly (p > 0.05) decreased during storage. There was a reduction of total sugars (8.1% and 14.1%) in samples irradiated at 1.0 kGy and 1.5 kGy, respectively. All irradiated mangoes had significantly lower (50- 70 %) ascorbic acid content throughout storage. The phenolic compounds increased in samples irradiated at 1.5 kGy (27.4%) and 3.1 kGy) (18.3%). Sensory evaluation of the fruits irradiated with 3.1 kGy showed significantly less acceptability for overall quality, color, texture and aroma. Irradiation of blueberries at 1.1 kGy had no significant (p > 0.05) effect on the fruits' physicochemical characteristics with the exception of ascorbic acid which decreased by 17% after 14 days. A significant decrease in texture (firmness) of irradiated berries was observed during storage time. Total sugars decreased in all irradiated fruits while total phenolics and tannins increased (10 -20%). Sensory attributes of samples irradiated with 1.1 kGy and 1.6 kGy were found acceptable by the panelists. The high dose-treated fruits were considered unacceptable. The results from this research suggest that a 1.5 kGy is the best treatment to maintain the quality attributes of mangoes and increase the shelf life by three days. The electron beam irradiation of packed blueberries at doses of 1.1 and 1.6 kGy ensures and enhances the quality and the shelf life of blueberries up to 14 days.Item Improving the microbiological quality and safety of fresh-cut tomatoes by low dose electron beam irradiation(Texas A&M University, 2005-11-01) Schmidt, Heather MartinThe effect of electron beam irradiation upon microbiological quality and safety of fresh-cut tomatoes was studied. Preliminary studies were conducted to ensure reliability of the rifampicin-resistant strain versus the parent strain of Salmonella serovar Montevideo for use in this study. Growth curve, heat tolerance and lactic acid resistance studies were performed, all of which showed no differences in behavior between the organisms. Fresh tomatoes were obtained from a local supplier and then cut into cubes with stem scars being separated. Both cubes and stem scars were inoculated with a rifampicin- resistant strain of either Salmonella Montevideo or Salmonella Agona, separated into treatment groups and treated by electron beam irradiation at 0.0 kGy (control), 0.7 kGy or 0.95 kGy. The effect of electron beam irradiation was determined for Salmonella, yeast, mold, and lactic acid bacteria (LAB) populations as well as pH on tomato cubes and stem scars over a 15-day storage period at 4??C. Results indicated that while irradiation treatment significantly reduced most microbial populations on tomato samples, there were no differences in the microbial populations between treatments of 0.7 kGy or 0.95 kGy. Irradiation at either dose resulted in a significant reduction of Salmonella Montevideo when compared to the control, with an initial reduction of 1.8 and 2.2 log10 CFU/g on tomatoes for 0.7 kGy and 0.95 kGy, respectively. LAB, yeasts and molds were more resistant to the treatment than Salmonella. Populations present on stem scars and tomato cubes did experience some differences in log reductions, possibly due to the protective effect of the stem scar on microorganisms. However, no differences were detected between the two Salmonella serotypes in response to irradiation treatment. This study indicates that doses of irradiation greater than 1 kGy should be used in fresh-cut tomatoes to eliminate significant populations of pathogens, as well as to ensure the microbial quality of the product. Additional studies also need to be conducted to examine the effects of higher irradiation doses on the sensory qualities of fresh-cut tomatoes.Item Irradiation Stability of Carbon Nanotubes and Related Materials(2012-09-28) Aitkaliyeva, Assel 1985-Application of carbon nanotubes (CNTs) in various fields demands a thorough investigation of their stability under irradiation. Open structure, ability to reorganize and heal defects, and large surface-to-volume ratio of carbon nanotubes affect materials' radiation response so that it differs from their bulk counterparts. Despite the work conducted to this date, radiation damage and mechanisms governing the evolution of CNTs under irradiation are still deficient in fundamental understanding. This dissertation is aimed to comprehend and characterize radiation response and crystalline-to-amorphous transition in ion and electron irradiated carbon nanotubes using various techniques, including but not limited to, transmission electron microscopy (TEM) and Raman spectroscopy. It shows that ion irradiation can be used to engineer properties of nanotubes in a controllable manner and significantly improve thermal diffusivity and conductivity of the material. This work also establishes the role of nuclear and electronic stopping powers in thermal diffusivity enhancement: thermal properties of irradiated CNTs are governed by nuclear stopping power of bombarding species. The change of thermal properties with irradiation is driven by two competing mechanisms: inter-tube displacement-mediated phonon transport and defect-induced phonon scattering. In addition to experiments, molecular dynamic simulations are used to confirm validity of the obtained results. Radiation damage in CNTs at various temperatures as a function of ion energy, flux and fluence is examined. Mechanisms governing crystalline-to-amorphous transition under electron and ion irradiations are explored, applicability of previously suggested models discussed, and new models introduced. The results show enhanced defect annealing at elevated irradiation temperatures, which delays the formation of amorphous regions. Investigation of nanotube stability after various processing techniques and irradiation indicated that radiation response of CNTs in a composite is similar to that of individual nanotubes.Item Postharvest irradiation treatment effect on grapefruit functional components and their role in prevention of colon cancer(Texas A&M University, 2005-11-01) Vanamala, Jairam Krishna PrasadThis dissertation examines the effects of postharvest treatment and processing on biologically active compounds of orange juice, and ??Rio Red?? grapefruit and their ability to prevent chemically induced colon cancer in rat model. The first study evaluated the differences in flavonoid content of commercial ??made from concentrate?? (MFC) orange juices and ??not from concentrate?? (NFC) orange and grapefruit juices. Total flavonoid content of MFC orange juices (53 mg/100 mL; n = 12) was significantly (P ≤ 0.05) higher than NFC orange juices (36.5 mg/100 mL; n = 14). The second study investigated the ionizing radiation and storage effects on bioactive compounds and quality of ??Rio Red?? grapefruit. Results showed that storage and irradiation significantly (P ≤ 0.05) affected the bioactive compounds in grapefruit, however, the effect of storage was prominent. The third study examined the influence of irradiation and freeze drying on bioactive compounds of grapefruit. Irradiation of grapefruit prior to freeze drying resulted in enhanced (P ≤ 0.05) flavonoid content (naringin and narirutin). Freeze drying markedly reduced (P ≤ 0.05) lycopene content. Freeze drying and irradiation reduced (P ≤ 0.05) volatile compounds (d-limonene and myrcene), with the exception of ethanol. In the fourth study suppression of colon cancer development in Sprague Dawley rats by natural and irradiated grapefruits and their functional compounds, naringin and limonin, were evaluated.The total number of aberrant crypts (AC; P = 0.02), number of high multiplicity AC foci (ACF; P = 0.01), and proliferative index (P = 0.02) were lower and apoptosis (P = 0.02) was higher in azoxymethane (AOM) injected rats on experimental diets. However, only natural grapefruit and limonin only suppressed AOM induced expansion (P = 0.008) of proliferative zone and also enhanced apoptosis more effectively than other experimental diets indicating that natural grapefruit and limonin may serve as better chemopreventive agents compared to IGFPP and naringin. The present study indicates that postharvest quarantine doses of irradiation slightly alter composition of bioactive compounds and in turn marginally reduce the chemopreventive ability of grapefruit against the promotion stage of colon cancer. These results warrant the necessity of testing the impact of post harvest treatments on fruits and vegetables chemopreventive ability.Item Safety Assurance of Pecans by Irradiation without a Detrimental Effect on Quality(2012-08-28) Karagoz, Isin 1983-Pecan nuts might become contaminated with foodborne pathogens, such as Salmonella and E. coli., through birds and other potential sources of contamination that can lead to serious illness or even death, as well as financial losses. For example, the outbreak of Salmonella in pecan products in Texas caused major product recalls in 2010. Irradiation with electron beams could be an effective method of preventing potential outbreaks without changing the pecans' taste, color and flavor and without causing any risk of recontamination before the product reaches the consumer. However, when irradiation is applied alone, the shelf life of the product is decelerated because of the detrimental effect of lipid oxidation. Therefore, to extend the shelf of the pecans while assuring their safety, irradiation of pecans under modified atmosphere packing (MAP) conditions could be a viable option. This research showed that when treated with electron beams, surrogates of Escherichia coli (a cocktail of BAA-1427, BAA-1428, and BAA-1430), and Salmonella (S. Typhimurium LT2) were more resistant to ionizing radiation (higher D10 values) when packed under vacuum (VP) than under air or other MAP conditions. This research also showed that lipid oxidation in pecans (due to exposure to ionizing radiation) shows a lag phase, probably due to the antioxidants present in pecan nuts. The lag phase represents a delay period before the pecan nuts start to get rancid (increase in PV formation), and it is best described by a modified Gompertz model. Kinetic evaluation of the lipid oxidation reaction suggests that the dose level has a more drastic effect in PV formation than the type of package used during the irradiation treatment, e.g., vacuum packed versus nitrogen-packed. Moreover, accelerated shelf life studies (4 weeks at 48.9oC) showed that vacuum-packed (VP) pecans can be stored at -25 degrees C up to three years, while irradiated (at 3.0 kGy) VP pecans can be stored only for eight months, without the detrimental effects of lipid oxidation. Therefore, irradiation of pecans under air at 3.0 kGy reduces the shelf life of the nuts in terms of rancidity, but vacuum-packaging can be used to extend their shelf-life. Irradiation in oxygen packaging increases rancidity and the oxidation reaction rate accelerates with increasing dose. Irradiation under nitrogen packaging requires lower doses to achieve the almost same number of log reductions in microbial population. The use of nitrogen packaging also inhibits the oxidative reaction leading to rancidity in pecans. Although there are some drawbacks to the application of nitrogen packaging in an irradiation plant (special machinery and packaging films (permeability specifications for N2 gas)), the savings induced by avoiding recalls may make this technology worthy of consideration.Item Symmetric and asymmetric hybridization in citrus spp.(2009-05-15) Bona, Claudine M.The United States is the second largest producer of oranges and grapefruit. However, the US citrus industry experiences constraints in production due to pests, diseases and environmental concerns. Furthermore, due to the low diversity in current commercial scion cultivars any exotic diseases, if introduced into any of the producing states could be devastating. To maintain the US industry competitiveness it is necessary to improve cold, pest and disease resistance to allow expansion of citrus production areas in the US, and to improve fruit quality characteristics such as sweetness, vitamins and phytochemical contents and seedlessness. Sexual hybridization in most Citrus species is complicated because they are highly apomictic. Polyembryony makes it difficult to create large segregating populations for selection. Somatic hybridization by protoplast fusion circumvents sexual incompatibilities and is a powerful tool in genetic improvement. Symmetric and asymmetric hybdridization (gamma irradiation plus iodoacetamide) via protoplast fusion were performed with the objective of producing somatic hybrids of Citrus paradisi with C. sinensis and C. reticulata with C. sinensis. These hybrids could be used for grapefruit improvement and to create genetic diversity. Furthermore, irradiated Swinglea glutinosa microprotoplasts were fused with ?Ruby Red? grapefruit and ?Mucott? tangor to assess the possibility of introgression of pieces of S. glutinosa chromosomes into the recipient protoplasts, a possible first step for radiation hybrid mapping. Double-inactivated fusions (irradiation + iodoacetamide) produced tetraploid and aneuploid plants, and hybridity was confirmed by amplified fragment length polymorphism (AFLP) analysis. This is the first report of obtaining rooted Citrus asymmetric hybrid plants, produced by irradiation plus iodoacetamide. AFLP confirmed presence of S. glutinosa into the receptor genomes, showing a possible donor introgression.