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Berry fruit anthocyanins in human nutrition : bioavailability and antioxidant effects : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Science at Massey University, Palmerston North, New Zealand
Anthocyanins (ACNs), which are responsible for the red and blue colours displayed by many vegetables and fruits (particularly berries), belong to secondary plant metabolites, and are a component of our daily diet. There is an increasing interest on their biological activities as they are claimed to enhance health by protecting against some chronic diseases. However, before ACNs can perform health-promoting effects in vivo, they must first be sufficiently absorbed, distributed within the human body, and reach target tissues in adequate concentrations. To date, all studies investigating ACN absorption and metabolism came to the conclusion that their bioavailability is extremely low. To benefit from the proposed health effects of ACNs, their bioavailability, including absorption, metabolism, and excretion must first be understood. The main objective of this thesis was to provide further knowledge on ACN absorption, including the absorption site and mechanism, and the influence of food and other flavonoids on ACN absorption, as well as the investigation of their antioxidant effects in vivo. In vitro experiments using Ussing chambers showed that a strong absorption of ACNs occurred from the jejunum in mice. This was supported with a further in vivo study, where the major absorption site for ACNs may be the jejunum in rats. The limitation of ACN absorption to mainly one part of the intestine suggested the participation of a particular transport mechanism. In a further Ussing chamber study it was shown that flavonols, another common flavonoid group present in many fruits and vegetables, strongly inhibit ACN absorption, indicating a specific transport mechanism, with preference for other flavonoid compounds. Further in vivo studies have shown that the simultaneous ingestion of food components, such as breakfast cereals, resulted in a delayed absorption profile in two animal species. However, the additional food did not influence the antioxidant effect of ACNs. During a human intervention study, several measures of oxidative stress improved, but this improvement occurred equally in the treatments and placebo control, and may have resulted from changes in lifestyle. The results of these studies aid to understand details of ACN absorption and help to formulate future recommendations for ACN intake with increased bioavailability in humans.