CHAPTER ONE
INTRODUCTION
Reactive oxygen species (ROS) and reactive nitrogen species (RON) are free radicals, which derived either from normal metabolic processes or from external sources (Magalhaes, 2006). These species are essential to energy supply, detoxification, chemical signalling and immune function (Dimitrios, 2006). However, overproduction of these free radical may lead to damage to valuable biomolecules such as DNA, lipids and proteins.
These free radicals are often associated with the oxidation in food and biological systems which will cause oxidative rancidity in foods and the development of several human diseases such as neurological degeneration, diabetes and certain types of cancer (Magalhaes, 2006).
An antioxidant is any substance which is capable of delaying, preventing the oxidative damage of lipids, protein and nucleic acids by reactive oxygen species, which include reactive free radicals such as superoxide, hydroxyl, peroxyl, alkoxyl and non-radicals such as hydrogen peroxide and hypochlorous (Lim et al., 2007).
Thus, antioxidants have gained numerous attention in the past few years, especially within the food, biological and agrochemical fields. There is increasing evidence that the consumption of vegetables and fruits is associated with a reduced risk of degenerative disease such as cancer, cardiovascular disease and cataracts (Chinnici et al., 2004). This association is often attributed to the natural antioxidant present in fruits and vegetables, such as vitamin C and E, carotenoids, phenolic acids and flavonoids, which prevent free radical damage (Silva et al., 2004).
Epidemiological studies have established a positive correlation between the intake of fruits and vegetables and prevention of diseases like atherosclerosis, cancer, diabetes, arthritis and also ageing (Kaur and Kapoor, 2001).
Annona muricata L. (A. muricata) is one of the tropical fruits that demonstrate antioxidant properties. This plant contains annonaceous acetogenins in the twigs, unripe fruit, seeds, roots, and bark tissues, which display antitumor, pesticidal, antimalarial, anthelmintic, piscicidal, antiviral, and antimicrobial effects, thus suggesting many potentially useful applications. Ripe A. muricata pulp extract contains three prominent acetogenins: asimicin, bullatacin, and bullatalicin.
Previous research on A. muricata was focused on the leaves, seeds and roots for pharmaceutical purposes (Gleeve et al., 1997; Jaramillo et al., 2000; Onimawo, 2002). Little attention has been paid to the study of the pulp and peel of A. muricata fruit. This study was therefore conducted to compare the antioxidant properties, phyto-constituents, proximate and mineral compositions of the peel and pulp of A. muricata.
Persea americana Mill (Luraceae) is one of the 150 varieties of avocado pear. The tree is widely cultivated in tropical and subtropical areas (Lu et al., 2005). The seed of P. americana (avocado seed) has diverse application in ethno–medicine, ranging from treatment for diarrhea, dysentery, toothache, intestinal parasites, skin treatment and beautification.
The avocado seed oil has several health benefit e.g. for controlling human weight (especially used for obese for weight loss) (Lopez et al., 1996; Roger, 1999). P. americana leaves have been reported to have or possess anti-inflammatory and analgesic activities (Adeyemi et al., 2002). The edible part (fruit) is very popular in vegetarian cuisine, making a substitute for meat in sandwiches and salads, because of its high fat content and high in valuable, health-promoting fats (Lu et al., 2005) . The fruit is not sweet but fatty, almost distinctly, yet subtly flavoured, and of smooth, almost creamy texture. Avocado fruits in many countries such as Mexico, Brazil, South Africa and India are frequently used for milkshakes and occasionally added to ice-cream (Zeldes, 2010).
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