1.0 Introduction And Literature Review
1.1 Introduction
Vernonia amygdalina, a member of the Asteraceae family, is a widely used local vegetable in Nigeria, Uganda and other African countries. It grows in a range of ecological zones in Africa and the Arabian Peninsula (Bonsi et al., 1995). The leaf is commonly called “bitter leaf” in English, “Olubu or Onugbo” in Igbo, “Ityuna” in Tiv, “Oriwo” in Edo, “Ewuro” in Yoruba, “Chusar-doki” in Hausa, “Etidot” in Efik, “Omubirizi” or “Omululuza” in West and Central Uganda; “Olusia” in Luo, Kenya. It is used in various food preparations and in ethnomedicine for the treatment of malaria and gastrointestinal infections. It is a shrub of 2-5 m tall with petiolate leaves of about 6.0mm wide (Ojiako and Nwanjo, 2006). It is up to 20 cm long and its bark is rough. The bitter taste of the leaf has been attributed to the presence of anti-nutritive principles like saponins, alkaloids, tannins and glycosides (Buttler and Bailey, 1973). There have been several reports on its antimicrobial, antiplasmodial, antitumor, antioxidant and antihelminthic properties (Jisaka et al., 1993; Izevbigie, 2003; Farombi, 2003; Ehiagbonare, 2007). Aqueous leaf extracts of V. amygdalina have been previously reported to have prebiotic properties (Ukwah and Ezeonu, 2008; Ezeonu and Ukwah, 2009; Ezeonu et al., 2012).
For many years, medicine depended exclusively on leaves, flowers and barks of plants, until the 1970s when synthetic drugs came into use (Conway, 1973). In orthodox medicine, a plant may be subjected to several chemical processes before its active ingredients are extracted, while in traditional medicine, a plant is simply eaten raw, cooked or infused in water or native wine or even prepared as food (Sofowora, 1992; Jones, 1996; Reynolds, 1996). Plant extracts are potential sources of novel antimicrobial compounds (Lis-Balchin and Deans, 1997) especially against bacterial pathogens, but it is necessary to investigate those plants scientifically which have been used in traditional medicine to improve the quality of healthcare. Plants extracts are usually composed of many phytochemical constituents.
Prebiotics are non-digestible substances that when consumed provide a beneficial physiological effect on the host, by selectively stimulating the favourable growth or activity of a limited number of indigenous bacteria (Roberfroid, 2007; Mitchell, 2010). These prebiotic substances survive digestion in the stomach and reach the colon where they are metabolized by the bacteria, thereby directly providing the host with energy and metabolic substrates (Wang and Gibson, 1993; Cummings et al., 2001). Efficient prebiotics usually have a specific fermentation in the colon and have the ability to alter the faecal microflora composition towards a more beneficial community structure (Kolida et al., 2002; Chakraborti, 2011). Thus, prebiotics exert their beneficial effects on the host indirectly; by stimulating functions of the intestinal microflora. These include regulation of bowel function, modulation of gut immunity, inhibition of pathogens and anticarcinogenic properties.
In addition to these, prebiotics also have the advantage of relative ease of manufacture because they can be either directly extracted from natural sources or be produced by partial acid or enzymatic hydrolysis of polysaccharides or by transglycosylation reactions (Macfarlane et al., 2006; Falcao-e- Cunha et al., 2007).
The role of prebiotics in modulation of bowel function has been widely studied and reported (Gibson and Roberfroid, 1995; Hamilton-Miller, 2004; Lomax and Calder, 2009), but more recent studies have focused on their protective role against infections and diseases (Lomax and Calder, 2009; Chakraborti, 2011; Licht et al., 2011). The most widely studied prebiotics are inulin and non-digestible oligosaccharides such as oligofructose (Watzl et al., 2005; Leenen and Dieleman, 2007; Guarner, 2007; Lomax and Calder, 2009). These complex carbohydrates are non- digestible by the gastric juice, pancreatic and brush border enzymes and selectively stimulate the growth of intestinal microflora. These carbohydrates are commonly found in fruits, vegetables and plant products (Menne et al., 2000; Rastall et al., 2005).
In the large intestine, prebiotics, in addition to their selective effects on intestinal bacteria, influence many aspects of bowel function through fermentation (Cummings et al., 2001). These substances are fermented by bacteria such as Bifidobacteria and Lactobacilli in the colon, to produce short chain fatty acids (SCFA) such as propionic, lactic, acetic, folic, and butyric acids. Hydrogen gas (H2) and Carbon dioxide (CO2) are also major products of prebiotic metabolism (Wang and Gibson, 1993; Cummings et al., 2001; De Vuyst et al., 2005; Saulnier et al., 2007). Besides the stimulation of intestinal bacteria, fermentability is an important property for evaluating or screening potential prebiotics, according to Cummings et al (Cummings et al., 2001). However, recent studies show that there may be other candidate-prebiotics such as xylitol, sorbitol, mannitol and lactulose (Chakraborti, 2011).
Pharmaceutical and nutritional industries are exploring more natural treatments for health conscious consumers as natural treatments have been effective since immemorial and are staging a comeback and natural ‘renaissance’ is happening all over the globe. The emerging area of prebiotics points towards the holistic role of nature in the health and nutrition of human beings.
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