DOCTOR OF PHILOSOPHY Rice preparation for cadmium and arsenic reduction while maintaining a healthy microbial load Pogoson, Esesua Ebahi Award date: 2021 Awarding institution: Queen's University Belfast Link to publication Terms of use All those accessing thesis content in Queen’s University Belfast Research Portal are subject to the following terms and conditions of use • Copyright is subject to the Copyright, Designs and Patent Act 1988, or as modified by any successor legislation • Copyright and moral rights for thesis content are retained by the author and/or other copyright owners • A copy of a thesis may be downloaded for personal non-commercial research/study without the need for permission or charge • Distribution or reproduction of thesis content in any format is not permitted without the permission of the copyright holder • When citing this work, full bibliographic details should be supplied, including the author, title, awarding institution and date of thesis Take down policy A thesis can be removed from the Research Portal if there has been a breach of copyright, or a similarly robust reason. 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Pogoson, Esesua Ebahi Award date: 2021 Awarding institution: Queen's University Belfast Link to publication Terms of use All those accessing thesis content in Queen’s University Belfast Research Portal are subject to the following terms and conditions of use • Copyright is subject to the Copyright, Designs and Patent Act 1988, or as modified by any successor legislation • Copyright and moral rights for thesis content are retained by the author and/or other copyright owners • A copy of a thesis may be downloaded for personal non-commercial research/study without the need for permission or charge • Distribution or reproduction of thesis content in any format is not permitted without the permission of the copyright holder • When citing this work, full bibliographic details should be supplied, including the author, title, awarding institution and date of thesis Take down policy A thesis can be removed from the Research Portal if there has been a breach of copyright, or a similarly robust reason. If you believe this document breaches copyright, or there is sufficient cause to take down, please contact us, citing details. Email: [email protected] Supplementary materials Where possible, we endeavour to provide supplementary materials to theses. This may include video, audio and other types of files. We endeavour to capture all content and upload as part of the Pure record for each thesis. Note, it may not be possible in all instances to convert analogue formats to usable digital formats for some supplementary materials. We exercise best efforts on our behalf and, in such instances, encourage the individual to consult the physical thesis for further information. Download date: 12. Mar. 2021 RICE PREPARATION FOR CADMIUM AND ARSENIC REDUCTION WHILE MAINTAINING A HEALTHY MICROBIAL LOAD. A thesis submitted to the School of Biological Sciences, Queen’s University Belfast For the degree of DOCTOR OF PHILOSOPHY By ESESUA POGOSON (MSc) MARCH, 2021 Queen’s University Belfast Acknowledgements I would like to thank my supervisors Prof. Andy Meharg and Dr. Caroline Meharg. I honestly could not have done any of this without you both and for this I am deeply grateful. I thank you for all the support, care, advice and expert tutelage that you both constantly offered. I am grateful that you pushed me to do my best and encouraged me at my low moments. Thank you so very much. I would also like to thank Dr. Manus Carey for all his technical expertise, friendship and encouragement throughout the course of the project, as well as Jayani, my friend. To my parents, Prof. & Prof. (Mrs) O.I Pogoson, I thank you. I am honored to be following in your footsteps and I am eternally grateful for the immense support you both offered me since the beginning of my program and even until now. I appreciate you greatly. To my husband, Sowunmi, thank you for all the love and support. Thank you for waiting for me and for being a source of strength throughout. Also, to my sisters, Iwaoya and Ozien, thank you for everything. You both are my rock. To my nephew and nieces, Runu, Chimamanda, Mega and Ziora, this is also for you. I would also like to acknowledge Queens University Belfast for the sponsorship offered throughout the course of my degree. Finally, and most importantly I acknowledge God Almighty, the reason for my existence and my absolute cornerstone through it all. This is dedicated to You. i Abstract Cadmium is a class one carcinogen and long-term exposure to cadmium can cause damage to the lungs and kidneys. The main route of exposure to the human body is dietary and rice is the most implicated food product Since rice is consumed by half of the world’s population, this poses a food safety threat to consumers. In addition to cadmium, other impurities such as arsenic and its inorganic compounds which are similarly classified as class one non-threshold carcinogens are also present in rice in its organic form as dimethylarsinic acid (DMA) and inorganic species. Here, results from exploring two main techniques for cadmium, inorganic arsenic and DMA removal from rice grain are presented. The first technique involves the use of citric acid as a chelating agent for cadmium removal. Two chapters test the use of citric acid pre-soak for 12 hours, followed by another 12-hour neutralization using calcium carbonate on both white rice grain, and brown rice grain. For white rice, this resulted in removal rates of 79% for cadmium, 81% for inorganic arsenic and 66% for DMA while trace element content, particularly potassium, sulphur and zinc were severely reduced. For brown rice, this removal technique resulted in removal rates of about 62% for cadmium and 53% for inorganic arsenic, as well as 41% for DMA. Similarly, trace elements potassium, phosphorus, and zinc were severely reduced while calcium was fortified by 2-orders magnitude, as with white rice as well. This technique was also explored during the rice parboiling stage but conferred no effect on toxic metal removal, however, a considerable loss in cadmium and arsenic from the rice husk of about 63% and 67% reduction respectively was reported. The effect ii of this technique on rice grain quality was then explored with regards changes to grain structural morphology of which considerable changes were observed. In addition, slight changes to functional groups between each treatment were observed. As rice can be heavily laden with Bacillus cereus, a pathogenic microorganism, it was ensured that the proposed technique did not enhance proliferation of the pathogen. Results showed that there was 99% reduction in the bacterial population after soaking in citric acid and 96% reduction after soaking in calcium carbonate, which is an advantage for rice consumers. The second proposed technique involves the use of food waste citrus peel adsorbent for toxic metal removal from rice grain. Adsorbents were prepared from lemon and orange peels followed by a 12-hour pre-soak in each adsorbent and subsequent boiling. Processed peel resulted in removal of cadmium and arsenic, although to varying degrees, with lemon peel being responsible for an average of 60% cadmium removal at 5 g of adsorbent per 25 ml of distilled water and 5 g of rice. Arsenic species are also reduced by approximately 60% for inorganic arsenic and 25 % for DMA. A considerable loss of phosphorus and potassium from the rice grain was also reported. Overall, this thesis has identified two methods which can be translated into the rice and rice product manufacturing industry for the protection of the health of consumers especially those in areas where toxic metal load in rice grain is a major burden. iii Publications related to thesis Pogoson E., Carey M., Meharg C., Meharg A.A. Reducing the cadmium, inorganic arsenic and DMA content of rice through food-safe chemical cooking pre-treatment. Food Chemistry 338 (2021) 127842. DOI: https://doi.org/10.1016/j.foodchem.2020.127842 iv List of figures and tables Figure 1.1: A schematic of cadmium transport from the soil to grains in rice…………. 5 Table 1.1: Applications and uses of citric acid in industry with their related functions………………………………………………………………………………………………………………. 24 Figure 1.2: A thin-sectioned spore of B. cereus……………………………………………………… 34 Figure 1.3: Morphology of Gram- stained Bacillus cereus……………………………………… 34 Figure 1.4: Gram stain of haemorrhagic brain biopsy specimen with histological sections showing clusters of elongated bacillary forms…………………………………………. 35 Figure 1.5: Colonies of B. Cereus growing on 5% sheep blood agar, showing grey, opaque granular spreading colonies……………………………………………………………………... 36 Figure 1.6: Smooth colonies of B. cereus on 5% sheep blood agar…………………………. 37 Table 2.1: Recoveries of elements and arsenic species from CRM NIST 1568b, rice flour, along with limits of detection (LoD)……………………………………………………………… 55 Figure 2.1: The effect of 12 hour soaking in molar concentrations of citric and ascorbic acid and then subsequent cooking in pure water, on cadmium and arsenic content and pH of Arborio rice…………………………………………………………………………………………… 57 Figure 2.2: The effect of calcium carbonate, calcium chloride and calcium citrate on the arsenic, cadmium and pH levels of rice grain after pre-soaking with the calcium salts for 12 hours and subsequent boiling…………………………………………………………….