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University of Canberra (2020)

Compositional Analysis of Prickly Pear (Opuntia spp.) Fruit and its Physiological Effects upon Consumption in Humans

Gouws Caroline

Titre : Compositional Analysis of Prickly Pear (Opuntia spp.) Fruit and its Physiological Effects upon Consumption in Humans

Auteur : Gouws Caroline

Université de soutenance : University of Canberra

Grade : Doctor of Philosophy (PhD) 2020

Résumé
The Opuntia spp. cactus is grown for its juicy and sweet ‘Prickly Pear’ (PP) fruit and edible leaves. Internationally, the cactus is enjoyed as food, used in various traditional and complementary medicines, employed in the dye industry (cochineal beetle ; food, clothing) or used as a fencing material in rural communities. The situation regarding the Australian PP differs substantially from the international landscape, in that the Australian cactus and its fruit are often wasted, if not salvaged as livestock feed. Consumption of the PP in Australia is limited due to i) social misconceptions, the confusion with a different (nationally banned) invasive weed, ii) ‘farm-to-plate’ agricultural distribution challenges, such as the short harvest season and high seasonal yield, and iii) the physical characteristics of the fruit (i.e. the spines). Internationally, the PP is associated with numerous health claims, including anti-atherosclerotic and anti-hyperglycaemic effects, attributed to the fruit’s composition. The PP fruit is known for its high fibre and phytochemical (antioxidant and bioactive) content, which is demonstrated to vary with geographical location and harvest conditions. Preliminary investigations prove the fruit composition to also be sensitive to food processing techniques. Together, the mentioned challenges have contributed to the food waste experienced in Australia, whereby applications of the crop, such as a source of food or a potential medicinal agent, have been almost neglected. Therefore, this thesis aims to ; i) determine the compositional characteristics of the Australian PP fruit, ii) evaluate the methods of processing and storage ; and iii) investigate its consumption-associated effects on risk factors of chronic diseases such as cardiovascular disease (CVD) and associated comorbidities. In doing so, this research highlights the versatility of the hardy and drought-resistant crop as a source of food, nutrition, and as a potential medicinal agent, while creating a preliminary basis to consider greater global impacts. Presented as a ‘thesis containing published works’, the thesis chapters are either peer-reviewed publications or unpublished manuscripts. The chapters range in the style of investigation from a narrative review (Chapter 2) to systematic reviews (Chapters 5 and 6), to food-science based papers (Chapters 3 and 4), and lastly, a clinical trial in humans (Chapter 7). Chapters 2 and 3 investigate the composition of the fruit, Chapters 3 and 4 examine the effects of juice processing and cold storage techniques on the preservation of the fruit’s phytochemical content, and Chapters 5 through to 7 explore the consumption-associated effects of the PP fruit. Throughout this doctoral research, the techniques investigated were designed to be mindful and practical for current Australian stakeholders’ and their constraints, such as the use of affordable technologies for ‘on-site’ processing. Within this thesis, the cactus (crop) is introduced to have the potential to assist in addressing sustainable development goals, through applications in improving food insecurity, dietary quality, and to have the potential to assist in reducing the risk of chronic diseases. The potential of the Opuntia ficus indica crop is proposed to have its most significant impacts in marginal regions facing environmental or climatic adversities. The findings of this thesis confirms that the PP is a good source of soluble-fibres and that the Australian PP fruit has a high phytochemical content. PP is proposed to be a suitable dietary addition to fruit consumption, particularly in environments where common household fruits are less likely to thrive. The effects of juice processing and cold storage on the preservation of the fruit’s phytochemical content largely depend on the specific phytochemical investigated. The PP’s antioxidant and bioactive characteristics were demonstrated to fluctuate over time, when stored in freezer conditions, ultimately clarifying conflicting literature.

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