Selenium (Se) is an essential micronutrient, being a component of more than twenty seleno-proteins in humans. Previous studies suggested that increased intake of Se may reduce the risk of degenerative diseases including cancer; however, excessive intake can be toxic. Wheat is one of the major dietary sources of Se in humans, mainly in the form of L-selenomethionine (Se-met) but the impact of this source of Se on human health at the genome level was previously unexplored. This PhD project aimed to (a) determine the safe dose-range and bio-efficacy of Se-met in vitro; (b) identify the optimal concentration of Se-met for reduction of genome damage in vitro; (c) investigate the optimal concentration of Se-met for improving resistance to gamma radiation or hydrogen peroxide induced genome damage in vitro; d) determine the bioavailability and bioefficacy of Se in vivo, in the form of either Semet or wheat biofortified with Se; e) identify the nutrients and food groups that are correlated with Se intake/status and f) identify the nutrients, food groups and plasma mineral concentrations that are correlated to baseline lymphocyte DNA damage. The in vitro study was performed on the peripheral blood lymphocytes isolated from six males and cultured with media supplemented with Se-met in a series of Se concentrations from 3 to 3850 μg Se/l while keeping the total methionine (i.e. Se-met + L-methionine) concentration constant. Baseline genome stability of lymphocytes and the extent of DNA damage induced by 1.5 Gy γ-ray or 7.5 μM hydrogen peroxide (H₂O₂) were investigated using the Cytokinesis-block Micronucleus Cytome (CBMNCyt) assay and the alkaline Comet assay with and without glycosylase (Fpg or Endo III) treatment after 9 days of culture. Results showed that high Se concentrations (≥1880 μg Se/l) caused strong inhibition of cell division, extensive DNA damage and increased cell death indicating cytotoxicity and genotoxicity. Baseline frequency of nucleoplasmic bridges (NPBs) and nuclear buds (NBud) declined significantly as Se concentration increased from 3 μg Se/l to 430 μg Se/l (P trend = 0.03 and 0.008, respectively); however, a significant trend of increase in Comet DNA damage was also observed (P trend <0.05) in lymphocytes. Selenium concentration (≤ 430 μg Se/l) had no significant effect on baseline frequency of micronuclei (MN) or DNA oxidation and had no protective effect against γ-ray-induced or H₂O₂-induced genome damage in lymphocytes. A randomised double-blind placebo-controlled intervention trial was conducted on healthy South Australian males (n = 62, age (mean ± SD) 56 ± 7.0 years) with Se dosage increased every 8 weeks for a total duration of 24 weeks. This study compared the bioavailability, by using plasma Se concentration as the biomarker, and bioefficacy of Se, by using platelet glutathione peroxidase (GPx) activity and lymphocyte DNA damage as biomarkers, from wheat process-fortified with Se-met (PROFORT) and high-Se wheat biofortified with Se (BIOFORT) compared to non-fortified normal (CONTROL) wheat. It was found that increased Se intake from BIOFORT wheat increased plasma Se concentration effectively in a dose-response manner from a baseline of 122 μg/l up to 190 μg/l (P<0.001). Increased Se intake from PROFORT wheat also increased plasma Se with a plateau at 140 μg/l, being therefore less effective than BIOFORT wheat (P<0.001). There was no significant change in Se status in the CONTROL group. Improved plasma Se concentrations had no effect on platelet GPx activity or lymphocyte DNA damage in either of the intervention groups. Results from the food frequency questionnaire (FFQ) survey (n = 173) and plasma Se concentration survey (n = 179) suggested that the study population screened for participation in the in vivo trial described above had a mean plasma Se concentration (± SD) of 102 (± 12) μg/l and a mean (± SD) estimated Se intake of 165 (± 68) μg/d. This is a higher estimated Se intake than found in previous Australian studies. The major dietary sources of Se were found to be bread/cereals, fish/seafood and meat. However, increased intake of nuts/seeds, which are rich in Se, may have undesirable effects on lymphocyte DNA oxidation in this Se-replete population. In conclusion, the in vitro studies suggest that (1) Se-met at higher concentrations at greater or equal to 1880 μg Se/l is cytotoxic; (2) Se-met may improve specific genome stability biomarkers such as nucleoplasmic bridge and nuclear bud at concentrations up to 430 μg Se/l, but further studies are needed to verify this effect. The in vivo studies in older men showed that Se from BIOFORT wheat is more effective in raising plasma Se concentration than Se from wheat process-fortified by the addition of Se-met, when both wheat products were subjected to strong heat. However, the platelet GPx activity and lymphocyte DNA damage appeared not to be modified by improved Se status. This work contains two publications: 1) "The effect of selenium, as selenomethionine, on genome stability and cytotoxicity in human lymphocytes as measured by the cytokinesis-block micronucleus cytome assay". Mutagenesis 2009 May;24(3):225-32. 2) "Increased consumption of wheat biofortified with selenium does not modify biomarkers of cancer risk, oxidative stress or immune function in Australian males" Environmental Molecular Mutagenesis. 2009 July; 50 (6):489-501 The latter one was not able to be published in a journal of higher impact factor due to part of the data had been published elsewhere. Both articles are attached in Appendix. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1523459 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2010

<p>Successful adoption of biofortified orange maize in developing countries requires careful consideration of factors across the chain from farm to fork. This includes consideration of post-harvest storage conditions optimal for the retention of both proviatamin A carotenoids and cooking quality critical to consumers. In these considerations, identification of economical storage methods is critical considering the limitations within specific countries that biofortified maize is being disseminated. To address these points, this dissertation research focused on evaluation of the utility of the Purdue Improved Crop Storage (PICS) bags as a post-harvest storage solution for biofortified maize. The specific focus of this research was to monitor retention of provitamin A and other carotenoids in two biofortified maize genotypes (OPVI and OPVII) as well as storage effect on flour functionality. Finally, a preliminary assessment of the impacts of storage on carotenoid bioaccessibility was completed to begin to translate findings to practice.</p><p>Maize grain from 2016 harvest was stored at ambient conditions for eight months in either PICS bags with or without an O₂ scavenger, (PICS-oxy) and (PICS-noxy), respectively and compared to storage in common polypropylene woven bags (control). After 4 months of storage carotenoid content was significantly higher (p<0.05) in PICS-oxy compared to PICS-noxy and woven bags demonstrating the importance of entrapped oxygen on maize carotenoid degradation. Furthermore, differences in carotenoid stability between maize genotypes were observed with OPVI having higher retention than OPVII. After 8 months, carotenoid retention remained dependent on storage bag and genotype with retention being greater in PICS-oxy and PICS-noxy compared to woven bags. However, final levels after 8 months were more similar between storage methods. Overall, oxygen content and genotype were found to be determining factors in the effectiveness of PICS to mitigate carotenoid degradation during post-harvest storage of maize.</p><p>While reducing the rate of carotenoid degradation during postharvest storage of biofortified maize is important, success of biofortified maize is also dependent on consumer adoption of these grains and their performance in traditional food preparation. Assessment of the rheological and functional properties of these two biofortified maize genotypes as a function of post-harvest storage was completed to assess the impact of post-harvest storage in PICS bags on flour functionality and rheological properties for the two biofortified orange maize genotypes and a control white maize genotype. Flour pasting profiles were assessed initially and at 4 and 8 months. After 8 month storage in woven and PICS bag, OPVI and OPVII produced porridges with similar viscosities to their initial viscosities regardless of postharvest storage type. White maize viscosities progressively decreased with storage and were significantly lower (p<0.05) in woven compared to PICS storage. Sequestration of oxygen (PICS-oxy) had modest but significant effects (p<0.05) on key pasting parameters including peak and final viscosities. These results suggest that oxygen sequestration has a critical effect on final flour functionality. DTT treatment partially restored flour pasting profiles suggesting disulfide linkages may modify pasting profiles of flour. There was also an increase in free ferrulic and <i>p</i>-coumaric acids during storage which may have contributed to observed decreases in porridge viscosities. Evidence of this was found through Raman spectroscopy with spectral intensity at both 478cm^-1 and 2911cm^-1 decreasing with storage suggesting the potential for structural changes induced by storage on starch polymer. While storage in PICS bags does not seem to adversely affect flour functionality it may provide some additional economic benefit resulting from requiring proportionally less flour to achieve similar final viscosities as flour from woven bag stored grains. </p><p>Finally, the effect of postharvest storage on bioaccessibility of carotenoids was explored using experimental wet cooked porridges made from ‘fresh’ and stored grains using an established three stage in-<i>vitro</i> digestion model. Relative carotenoid bioaccessibility (% micellarization) was generally higher in less viscous porridge made from grains stored in woven bags compared to porridge from initial or PICS bags stored grains suggesting that higher viscosity might partly explain lower relative bioaccessibility in porridge from grains stored in PICS bags. Absolute carotenoid bioaccessibility from experimental porridge was dependent on carotenoid species and storage system. Extrapolation of relative bioaccessibility (%) to absolute bioaccessibility (µg/g flour) suggests that fresh grains and their corresponding porridges would provide more absolute bioaccessible carotenoids compared to stored grains despite some improvement in relative accessibility. As such, storage losses remain the main factor impacting total available carotenoids and should continue to be an area of focus for future mitigation. With the potential to minimize post-harvest losses, improve carotenoid retention and provide a product with improved cooking performance, PICS bags do appear to offer a viable storage alternative to improve both food and nutrition security in developing countries.</p><p></p>