Antioxidants in fruit and vegetables

Degeneve, Alexandra (2004) Antioxidants in fruit and vegetables. MSc(R) thesis, University of Glasgow.

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Abstract

Diets rich in fruits and vegetables are associated with a reduced risk of cardiovascular disease and some cancers. It has been more difficult for researchers to identify the specific component(s) of these diets responsible for the "protective" effects. Attention has recently been focused on phenolic and polyhenolic components, which may have biological activity in humans, by acting as antioxidants. Levels of such compounds in individual fruits and vegetables are affected by soil, climatic conditions, physiological stress under which they are grown or even agricultural methods. In particular, organic products are thought to be healthier than their conventional equivalents. To date, few studies have investigated the impact of various agricultural practices on the level of phenolic compounds present in the crops. In this study, the total phenolic content, as well as the antioxidant activity and the vitamin C content of different fruits and vegetables were measured in both organically or conventionally grown crops, available from a local market. The present study also compared the effect of the consumption of conventionally and organically produced kiwi fruits on the plasma antioxidant activity of humans. Despite the interest of consumers in organic products, the findings from this project did not show any consistent differences in antioxidant capacity, vitamin C or phenolic content between conventional and organic crops, available to consumers at local supermarkets. The number of natural polyphenols has been estimated to be several thousands, as they occur in plants as conjugates. In the present study, we tried to determine, which of these compounds contributed to the antioxidant capacity in a range of 17 commonly consumed fruits and vegetables, which may be the basis for the beneficial effect of these foods. By combining three different techniques - HPLC, MS and on-line measurement of antioxidant activity - we could identify and quantify the bioactive compounds (vitamin C, polyphenols) present in a range of fruits and vegetables and determine their individual contribution to the total antioxidant activity. Results showed that the nature and the occurrence of antioxidants vary markedly among plant species; the total antioxidant activity is due to the cumulative effects of different compounds rather than any individual compound. Identification of polyphenols in fruits and vegetables is important in regard to their potential health effects. However, it is also necessary to determine if they are absorbed, metabolized in human body, and whether the dietary components and their metabolites provide any benefit within the gastrointestinal tract. In the present study, we investigated the absorption and excretion of anthocyanins and proanthocyanidins: a healthy subject with an ileostomy was fed 200 g of redcurrants and then provided plasma, urine and ileostomy fluid for analysis. This allowed an excretion profile to be obtained, giving a time span for the absorption of redcurrant polyphenols. Following the consumption of redcurrants, we could see that prodelphinidins were poorly absorbed (as 86% were recovered in the ileal fluid), and their potential action was, thus, restricted to the intestine, where they could act as antioxidants. Quantitative analysis of anthocyanins in urine collected over a 24 h period after ingestion of redcurrants accounted for only 0.02% of the amount ingested. No anthocyanins were detected in plasma. However, only 35 % of the ingested dose of anthocyanins was recovered in the ileal fluid, suggesting 65 % of the anthocyanins were transformed and/or absorbed. Further work would be required to identify the "missing" anthocyanins and determine their fate and their potential health effects within the body.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Keywords: Food science, Nutrition
Date of Award: 2004
Depositing User: Enlighten Team
Unique ID: glathesis:2004-71893
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 09:31
Last Modified: 17 May 2019 09:31
URI: http://theses.gla.ac.uk/id/eprint/71893

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