CHAPTER ONE 1.1 Introduction Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, including the flowers, fruits, stems, leaves, roots, and seeds. An alternate definition of the term is applied somewhat arbitrarily, often by culinary and cultural tradition. It may exclude foods derived from some plants that are fruits, flowers, nuts, and cereal grains, but include savoury fruits such as tomatoes and courgettes, flowers such as broccoli, and seeds such as pulses. Originally, vegetables were collected from the wild by hunter-gatherers and entered cultivation in several parts of the world, probably during the period 10,000 BC to 7,000 BC, when a new agricultural way of life developed. At first, plants which grew locally would have been cultivated, but as time went on, trade brought exotic crops from elsewhere to add to domestic types. Nowadays, most vegetables are grown all over the world as climate permits, and crops may be cultivated in protected environments in less suitable locations. China is the largest producer of vegetables, and global trade in agricultural products allows consumers to purchase vegetables grown in faraway countries. The scale of production varies from subsistence farmers supplying the needs of their family for food, to agribusinesses with vast acreages of single-product crops. Depending on the type of vegetable concerned, harvesting the crop is followed by grading, storing, processing, and marketing. Vegetables can be eaten either raw or cooked and play an important role in human nutrition, being mostly low in fat and carbohydrates, but high in vitamins, minerals and dietary fiber. Many nutritionists encourage people to consume plenty of fruit and vegetables, five or more portions a day often being recommended. Vegetables are herbaceous plants whose parts are consumed in diets as supporting food or main dishes and may be aromatic, bitter or tasteless (Rahal and Kumar, 2009). Parts of vegetables usually consumed include but not limited to leaves, stem barks, roots, tubers, flowers, seeds and bulbs. They are cheap sources of important classes of food necessary for proper growth and development. Indigenous vegetables are plant species that are important for sustainability of economies, human nutrition and health, and social systems but are yet to attain global recognition as major vegetable commodities (Keatinge et al., 2015). Guarino, (1997) also defined indigenous leafy vegetables as vegetables of a locality which originated from an area and may or may not be confined to that particular region. Vegetables have proven nutritive value in terms of having high carbohydrate, protein, vitamins and minerals in comparison to that of exotic vegetables (Rahal et al., 2014). It is therefore important to note the importance of these ready food sources in daily diets especially in poverty stricken countries of the world. Several studies have emphasized that approximately half of the leafy vegetables consumed are from wild plants constituting significant micronutrient sources especially in times of drought and famine (Grivetti and Ogle, 2000; Lockett et al., 2000) and this is prevalent among the low income rural dwellers. 1.2 History of Vegetable Before the advent of agriculture, humans were hunter-gatherers. They foraged for edible fruit, nuts, stems, leaves, corms, and tubers, scavenged for dead animals and hunted living ones for food. Forest gardening in a tropical jungle clearing is thought to be the first example of agriculture; useful plant species were identified and encouraged to grow while undesirable species were removed. Plant breeding through the selection of strains with desirable traits such as large fruit and vigorous growth soon followed. While the first evidence for the domestication of grasses such as wheat and barley has been found in the Fertile Crescent in the Middle East, it is likely that various peoples around the world started growing crops in the period 10,000 BC to 7,000 BC. Subsistence agriculture continues to this day, with many rural farmers in Africa, Asia, South America, and elsewhere using their plots of land to produce enough food for their families, while any surplus produce is used for exchange for other goods. Throughout recorded history, the rich have been able to afford a varied diet including meat, vegetables and fruit, but for poor people, meat was a luxury and the food they ate was very dull, typically comprising mainly some staple product made from rice, rye, barley, wheat, millet or maize. The addition of vegetable matter provided some variety to the diet. The staple diet of the Aztecs in Central America was maize and they cultivated tomatoes, avocados, beans, peppers, pumpkins, squashes, peanuts, and amaranth seeds to supplement their tortillas and porridge. In Peru, the Incas subsisted on maize in the lowlands and potatoes at higher altitudes. They also used seeds from quinoa, supplementing their diet with peppers, tomatoes, and avocados. In Ancient China, rice was the staple crop in the south and wheat in the north, the latter made into dumplings, noodles, and pancakes. Vegetables used to accompany these included yams, soybeans, broad beans, turnips, spring onions, and garlic. The diet of the ancient Egyptians was based on bread, often contaminated with sand which wore away their teeth. Meat was a luxury but fish was more plentiful. These were accompanied by a range of vegetables including marrows, broad beans, lentils, onions, leeks, garlic, radishes, and lettuces. The mainstay of the Ancient Greek diet was bread, and this was accompanied by goat's cheese, olives, figs, fish, and occasionally meat. The vegetables grown included onions, garlic, cabbages, melons, and lentils. In Ancient Rome, a thick porridge was made of emmer wheat or beans, accompanied by green vegetables but little meat, and fish was not esteemed. The Romans grew broad beans, peas, onions and turnips and ate the leaves of beets rather than their roots. 1.3 Etymology of vegetable The word vegetable was first recorded in English in the early 15th century. It comes from Old French, and was originally applied to all plants; the word is still used in this sense in biological contexts. It derives from Medieval Latin vegetabilis "growing, flourishing" (i.e. of a plant), a semantic change from a Late Latin meaning "to be enlivening, quickening". The meaning of "vegetable" as a "plant grown for food" was not established until the 18th century. In 1767, the word was specifically used to mean a "plant cultivated for food, an edible herb or root". The year 1955 saw the first use of the shortened, slang term "veggie". As an adjective, the word vegetable is used in scientific and technical contexts with a different and much broader meaning, namely of "related to plants" in general, edible or not as in vegetable matter, vegetable kingdom, vegetable origin, etc. The exact definition of "vegetable" may vary simply because of the many parts of a plant consumed as food worldwide roots, stems, leaves, flowers, fruits, and seeds. The broadest definition is the word's use adjectivally to mean "matter of plant origin". More specifically, a vegetable may be defined as "any plant, part of which is used for food", a secondary meaning then being "the edible part of such a plant". A more precise definition is "any plant part consumed for food that is not a fruit or seed, but including mature fruits that are eaten as part of a main meal". Falling outside these definitions are edible fungi (such as edible mushrooms) and edible seaweed which, although not parts of plants, are often treated as vegetables. In the latter-mentioned definition of "vegetable", which is used in everyday language, the words "fruit" and "vegetable" are mutually exclusive. "Fruit" has a precise botanical meaning, being a part that developed from the ovary of a flowering plant. This is considerably different from the word's culinary meaning. While peaches, plums, and oranges are "fruit" in both senses, many items commonly called "vegetables", such as eggplants, bell peppers, and tomatoes, are botanically fruits. The question of whether the tomato is a fruit or a vegetable found its way into the United States Supreme Court in 1893. The court ruled unanimously in Nix v. Hedden that a tomato is correctly identified as, and thus taxed as, a vegetable, for the purposes of the Tariff of 1883 on imported produce. The court did acknowledge, however, that, botanically speaking, a tomato is a fruit. 1.4 Nutrition and health of Vegetable Vegetables play an important role in human nutrition. Most are low in fat and calories but are bulky and filling. They supply dietary fiber and are important sources of essential vitamins, minerals, and trace elements. Particularly important are the antioxidant vitamins A, C, and E. When vegetables are included in the diet, there is found to be a reduction in the incidence of cancer, stroke, cardiovascular disease, and other chronic ailments.[19][20][21] Research has shown that, compared with individuals who eat less than three servings of fruits and vegetables each day, those that eat more than five servings have an approximately twenty percent lower risk of developing coronary heart disease or stroke. The nutritional content of vegetables varies considerably; some contain useful amounts of protein though generally they contain little fat,[23] and varying proportions of vitamins such as vitamin A, vitamin K, and vitamin B6; provitamins; dietary minerals; and carbohydrates. However, vegetables often also contain toxins and antinutrients which interfere with the absorption of nutrients. These include α-solanine, α-chaconine,[24] enzyme inhibitors (of cholinesterase, protease, amylase, etc.), cyanide and cyanide precursors, oxalic acid, tannins and others. These toxins are natural defenses, used to ward off the insects, predators and fungi that might attack the plant. Some beans contain phytohaemagglutinin, and cassava roots contain cyanogenic glycoside as do bamboo shoots. These toxins can be deactivated by adequate cooking. Green potatoes contain glycoalkaloids and should be avoided. Fruit and vegetables, particularly leafy vegetables, have been implicated in nearly half the gastrointestinal infections caused by norovirus in the United States. These foods are commonly eaten raw and may become contaminated during their preparation by an infected food handler. Hygiene is important when handling foods to be eaten raw, and such products need to be properly cleaned, handled, and stored to limit contamination. CHAPTER TWO 2.1 INDIGENOUS VEGETABLES OF NIGERIA Indigenous vegetables are available in wild and cultivated forms. Over 40 indigenous leafy vegetables are eaten in Nigeria, with the south-western part accounting for 24 of them (Adebooye et al., 2003). Amongst the Tiv community in Benue state, North Central, Nigeria, a total of 42 wild plants species in 27 families have been identified as edible plants utilized by the local people and ruminants (Shomkegh et al., 2013). Edwin-Wosu et al, (2012) carried out an ethnobotanical survey of indigenous vegetable species in Cross River State which revealed about 34 species which are part of their staple diet. In addition, 30 traditional leafy vegetables and spices were listed in a survey carried out in Ebonyi State, Southeast, Nigeria (Oselebe et. al., 2013). Indigenous vegetables have played a significant role as food supplements during the times of drought and to fortify diets especially in hunter gatherer societies. Vegetables together with other wild plant foods are often referred to as the ‘hidden harvest’ (Harvest, 2011) since they are simply collected from the wild such as agricultural fields and swampy areas and require little or no cultivation. Table 1 shows a list of the indigenous vegetables cited in literatures from different parts of Nigeria. Table 1: Some Indigenous Vegetables of Nigeria Scientific name Common name Local Parts used name Geograp Referen hical ce zone Araceae family Xanthosoma sagittfolium Cocoyam Koko Leaves SS 1 Opoto, Leaves, roots SE 5, 6 (L.)Schott Colocasia esculentus L. Taro Nkashi Amaranthaceae family Amaranthus hybridus L. African spinach Alefu Leaves, stem SS, SE, 4, 5 Amaranthus viridis L. Green amaranth NA Leaves, stem SS, SE 1, 5 Amaranthus spinosus L. Spiny amaranth Inene Leaves SS, SE 5, 6 Celosia argentea L. Quail tail Idodo Leaves SS, SE, 1, 4, 5 NC Asclepiadacaeae family Gongronema latifolium Benth Amaranth globe Utazi Leaves SE, SS 4, 7 Olubu, Ewuro Leaves, stem SE, 3, 4, 5, SW,SS 6, 7 Aninge Leaves, NC 2 Asteraceae family Vernonia amygdalina L. Bitter Leaf Emilia coccinea Cass. Tassel flower Flowers Solanecio biafrae (Olive NA Worowo Leaves SW 3 Ebolo Leaves SW 3 NA Leaves SW 3 Leaves SW 3 Leaves, stem SE, SW 1, 3 Leaves SE, SS 4, 6 Leaves SE 6 Leaves, fruits SE, SW 3, 5, 6 Leaves, seeds SE, SW 1, 3, 4, 6 Leaves, fruit SS, SW 1, 3 Leaves, fruit SW 3 Leaves NC 2 &Heirne) C. Jeffry Crasscocephalum crepidoides Parsley leaf (Olive & Herine) S. Moore Crasscocephalum togoense L. NA Launea taraxacifolia (Willd.) African lettuce NA Basellaceae family Basella rubra L. Indian Spinach Laali Bombacaceae family Bombax buonopozense L. White silk cotton Gaertn. Apkuto Bignoniaceae family Newbouldia laevis (P.Beauv) Boundary Tree Omirima Cucurbitaceae family Cucurbita pepo L. Pumpkin Ugbara Telfaria occidentalis Hook F. Fluted pumpkin Momordica charantia L. Bitter gourd Ugwu NA Trichosanthes cucumerina . Snake Tomato L. Tomati elejo Caelsapinioideae family Daniella oliverii NA Chiha Convolvoluceae family Ipomoea batata L. Sweet potato Ekwuoku Leaves SE 6 Leaves SS 1 Leaves SS 1 Leaves SS 4 Fruits SW 3 Leaves SS 1 Leaves SS 1, 4 Leaves SS 4 Leaves SS, SE 4, 7 Leaves NC, SS, 2, 3, 4 Euphorbiaceae family NA Euphorbia hirta L. NA Manihot esculentum Krantz Cassava Uapaca heudoloti Baill NA Tetracarpidium conophorum NA NA NA Catholic vegetable NA NA (Muell. Arg.) Hutch. & Dalziel Jatropha tanjorensis L. Fabaceae family Albizia zygia WestAfrican Siri NA Oko albizia Erythrina senegalensis DC Coral tree Pterocarpus soyauxii Taub. African padauk Pterocarpus santalinoides L’ NA Okazi Herit ex. DC SE Gnetaceae family Gnetum africana Welw. African joint fir Leaves SS 4 Fruit SW 3 Leaves SW, SE, 1, 4, 6, 7 Irvingiaceae family Irvingia gabonensis Aubry- NA Oro LeComte ex O'Rorke) Baill Laminaceae family Occimum grattissimum L. Scent leaf Ahunji SS Okazzi Occimum basilicum L. Sweet basil Leaves SE, SS 1, 4 Leaves, fruit SW, SE, 1, 3, 6 Malvaceae family Abelmoschus esculentus Okra, Ladies finger Moench. Ila, Ophfuru SS Moraceae family Ficus glumosa Del. Fig tree NA Ekwuakp uru Leaves, fruit SS 4 Ficus capensis Thunb. Fig Moringaceae family Moringa oleifera Lam Drumstick plant Fruit Ekwuesis a SE 6 Leaves, seed, SE 6 stem, flower Passifloraceae family Adenia Planch Isororo cissampeliodes Zepernick Leaves SE 6 Leaves, SW 3 Leaves, seed SE, SS 1, 4, 6 Leaves SE 5 Root NC 2 Leaves SS, SE 1, 4, 5, 6 Leaves SE 5 Leaves SS 4 Leaves SE 6, 7 Leaves SE 6 False sesame Pedaliaceae family NA Cerathotheca sesamoides E. West African black Mey pepper flower Uzuza Piperaceae family Piper guineense Schum and Elephant grass Thonn. Eru Poaceae family Pennisetum purpureum Cogon grass Hila Schumach Imperata cylindrica Water leaf Ngbolodi Portulacaceae family Talinium triangulare (Jack.) Purslane WIld. NA Portulaca oleracea L. Bush apple NA Rubiaceae family Heinsia crinita (Afzel.) G. NA Tayl. Nkaa Rutaceae family Zanthoxylum zanthoxyloides NA Lam. Ukpuocha Sapindaceae family Lecaniodiscus cupanioides NA NA Sapotaceae family Chrysophyllum albidium G. African star apple NA Fruit SW 3 Fruit SW 3 Don Synsephalum dulcificum (Schumacher & NA Thonn.) Daniell Odu, Anara Solanaceae family Solanum nigrum L. Glossy night shade Igbagba Leaves, seed, SW, SE 3, 6, 7 flower Solanum macroacarpon L. Solanum aethiopicum L. Africa egg plant Gilo Akpoko Leaves, fruit SW 3 Leaves, Fruit SW, SE, 4, 5 SS Capiscum frutescens L. African pepper Ewedu, Anra Leaves SE 6 Leaves SW, SE, 1, 3, 4, Tiliaceae family Corchorus olitorius L. Jute mallow Uchakuru SS 5,6 SE, SS 4, 5, 6, 7 Verbanaceae family Vitex doniana 2.2 Black plum Leaves THE ROLE OF VEGETABLES IN ECONOMIC GROWTH A positive correlation between vegetable commercialization and household income has been recognized over the years and the economic value of vegetables have confirmed by various researchers. For example, (Muriithi and Matz, 2015) found a positive welfare effect for vegetable producers in Kenya where fruit and vegetable crops generate more income for farmers compared to traditional staple crops in the region. In addition, they generate employment for the rural workers, and therefore improve access to food (Weinberger and Lumpkin, 2007). Vegetables constitute a source of cash income for the households and create opportunity to increase smallholder farmers’ participation in the market (Alemayehu et. al., 2010). Vegetables are harvested fresh, dried and sold during offseason to generate income in rural households in Nigeria. Through the Nigeria-Canada Indigenous Vegetable Project, previously marginalized rural women farmers in Nigeria now realize an average income of about US$3,376/year from the sale of indigenous vegetables compared to a pre-project income figure of US$1,994/year due to increased yield (NICANVEG 2013). Vegetables are also used as source of raw material for local processing industry. A large proportion of gross domestic product can be generated within the primary sector by smallholder farmers. Agricultural development has been shown to be up to four times more effective in reducing poverty relative to growth in other sectors, and growth in smallholder agricultural productivity has been shown to have a positive impact on both urban and rural populations in three key ways: 1. lower food prices for consumers; 2. higher incomes for producers and 3. growth multiplier effects through the rest of the economy as demand for other goods and services increases (Alston et. al., 2000). The market share of indigenous vegetables in Nairobi, Kenya has been going up recently, accounting for about 30% of overall vegetable sales (Vorley et. al., 2007). Likewise, the consumption of African leafy indigenous vegetables has been increasing in several countries in eastern Africa (Mwangi and Kimathi, 2006; Smith and Eyzaguirre, 2007; Chelang’a et. al., 2013) and Nigeria should therefore not be an exception. 2.3 Phytochemical Component of a Vegetable Phytochemicals/ phytonutrients/ phytonutriceuticals are organic compounds derived from plants that have health protective effects. Besides the common nutrients such as carbohydrates, amino acids and protein, there are certain non- nutrient phytochemicals in vegetables that have biological activity against chronic diseases. They are low in fat and like all plant products, contain no cholesterol. Most phytochemicals are found in relatively small quantities in vegetable crops. However, when consumed in sufficient quantities, phytochemicals contribute significantly towards protecting living cells against chronic diseases. Major phytochemicals have been classified in to ten different classes based on their biological activities including: (1) Carotenoids (α - and β - carotene, β - cryptoxanthin, lutein, lycopene, and zeaxanthin), (2) Glucosinolates (sulforaphane, indole-3 carbinol), (3) Phenols (flavanoids), (4) Cyclic phenolics (chlorogenic acid, ellagic acid, and coumarins) (5) Saponins, (6) Phytosterols (campestrol, β - sitsterol, and stigmasterol), (7), Sulfides and thiols (8) Phyto-estrogens (isotlavones, daidzenin, genistein, and lignans), (9) Protease inhibitors, and (10) Inositol phosphates (phytate, inositol tetra and penta phosphates). Vegetables have been shown to protect against specific types of cancer for example, the crucifers (Brassicaceae) including Broccoli, Brussels sprouts, Kale and Cabbage have been shown to protect against lung and chemically induced cancers. The alliums (Liliaceae), including garlic, chive, and onion have been shown to protect against stomach cancer, the solanaceous vegetables (Solanaceae) including tomatoes and pepper have been shown to protect against esophageal, gastric, and prostrate cancers. The chenopods (Chenopodiaceae) including spinach and chard have been shown to inhibit DNA synthesis in proliferating human gastric adenocarcinoma cells. There is increasing evidence for a link between antioxidant nutrients (e.g. vitamin C, vitamin E, β - carotene and selenium) in fruits and vegetables and lower risk of cardiovascular disease. Studies have found 35 per cent reduction in mortality due to cardiovascular disease among those who consumed vegetables rich in vitamin E and C. A 40-50 percent reduction in risk of colon cancer in populations with higher vegetable consumption, especially garlic and dietary fiber has also been reported. In addition to reducing cancer and cardiovascular diseases, a diet high in vegetables has also been linked to reducing rheumatoid arthritis, anemia, diabetes, macular degeneration and gastric ulcer. The carotenoids, Vitamin E, and Vitamin C arc now firmly established as protective dietary antioxidants with additional beneficial functions. Polyphenols and flavonoids are also gaining prominence and the protective role of folate is above dispute. All of these components are uniquely found in fresh and cooked vegetables, which underline the importance of vegetables in healthy diets. The exact mechanism by which vegetable consumption reduces human diseases have not yet been fully understood, however Research over the last 2 decades has provided a scientific basis to support the common wisdom that fruit and vegetable-rich diets are beneficial to health. The protective role of AO- rich diets in disease progression and ageing are beyond doubt, and advances in medicine over the past half century have resulted in a significant increase in lifespan in the developed world. 2.4 Glucosinolates and Chemoprevention of Cancer Glucosinolates or β-D-thioglucosides are a diverse class of S- and N-containing secondary metabolites that are mainly found in members of the Brassicaceae (Cruciferae) and in 15 other families of dicotyledonous angiosperms. Glucosinolates molecule comprises of a skeletal βthioglucose moiety, a sulfonated oxime moiety (glucone), and a variable aglucone R-group that defines the structure of each glucosinolate. The biosynthetic origin of glucosinolates is derived frorn a number of common amino acids. In crucifers, the dominant glucosinolates are derived from methionine, phenylalanine,tryptophan, valine and tyrosine. About 120 different glucosinolates have been identified so far, but only about 20 have been detected in vegetable crops. Based on their R-group structure, glucosinolates have been classified into aliphatic, aromatic and indolyl. Crucifer vegetables viz., Broccoli, Brussels sprouts, kale, Chinese cabbage, Red cabbage, Savoy cabbage are the main source of glucosinolates. Broccoli has the maximum content of glucosinolate, in which it constitutes about 0.05-0.2% of the fresh weight of broccoli (0.05 to 1.0g/kg). Several studies have suggested that intact glucosinolates have no biological activity against cancer, however the breakdown products have been shown to stimulate mixed function oxidases involved in the detoxification .of carcinogens. Upon tissue disruption, glucosinolates are rapidly hydrolyzed by myrosinase (thioglucoside glucohydrolase; EC 3.2.3.1) to unstable intermediates that, as dictated by chemical conditions, spontaneously rearrange to isothiocyanates, thiocyanates, or nitriles. Although the primary biological function of glucosinolates in plants is unknown, glucosinolate breakdown products are proposed to act as allelo-chemicals and to play a role in plant defenses against herbivores, pests, and pathogens. Furthermore, indolyl glucosinolates can be converted into indoleacetic acid and may thus contribute to active auxin levels in cruciferous plants. As components of food for humans and feed for livestock, the biological activities of glucosinolate hydrolysis products have generated considerable toxicological and pharmocological interest. Depending on glucosinoiate composition and on the prevalence of hydrolysis products, consumption of glucosinolates by mammals has been linked with goitrogen ic effects (thiocyanates) or with a reduced risk of developing cancer (isothiocyanates) in experimental animals. Studies have shown that rat fed on a diet containing intact glucosinolates from broccoli had no effect on the metabolism of the carcinogens viz., antipyrine and metronidazole, however, glucosinolate hydrolyzed by myrosinase prior to feeding, enhanced the detoxification of the two carcinogens by 67 and 200 percent respectively, suggesting, that glucosinolate breakdown product and not intact glucosinolate are biologically active against chemical toxicants. Sulforaphane (4methylsulfinylbutyl isothiocyanate) and indole-3-carbinol are the two most widely studied glucosinolate breakdown products exhibiting anti-carcinogenic properties. Sulforaphane is the breakdown product of the aliphatic glucosinolate glucoraphanin, while indole-3-carbinol is the breakdown products of indolyl glucosinolate glucobrassicin. Other breakdown products of glucosinolates that have been shown to protect human and animal cells against carcinogenesis are phenyl isothiocynate, 1-cyano-2- hydroxy-3-butene and breakdown products from sinigrin and glucoiberin that have yet to be characterized. Studies on laboratory animals and human subjects have shown that induction of detoxification enzymes (phase II enzymes) and inhibition of activation enzymes (phase I enzymes) are two major mechanism of cancer prevention by glucosinolate breakdown products. The exact mechanism has not yet been fully characterized, but it has been suggested that Phase II enzymes are capable of conjugating with activated carcinogens and converting them into inactive water- oluble compounds that can be easily cleared by the kidney. Mechanistic studies have shown that isothiocynates such as sulforaphane, indole-3-carbinol and phenylethylisothiocynates target mammalian Phase II drug-metabolizing enzymes, resulting in increased carcinogenic detoxifycation. For example, the methionine derived isothiocynate sulforaphone, have been shown to be potent inducers of the phase II enzymes glutathione-stransferase, quinone reductase, NADPH reductase and glucouronyl transferase in hepatoma cells. Sulforaphane is the most powerful natural inducer of chemo protective enzymes thus far reported and has become a metabolic target of breeding strategies to enhance the anti carcinogenic potency of cruciferous vegetables. A second mechanism for the glucosinolate breakdown products involves inhibition of enzymes involved in the induction of cancer. Chemical carcinogens generally require metabolic activation in order to be able to bind to DNA and contribute to cancer development. Phase I enzymes are responsible for in vivo and in vitro metabolic activation of most carcinogens in human and animal cells. Studies have shown that, under certain conditions, the products of Phase I enzymes serve as substrates for Phase II enzymes, which convert them into electrophilic carcinogens that can easily be excreted through the urine. There is also ample evidence that some glucosinolate breakdown products inhibit the catalytic activity of PhaseI enzymes (Cytochrome P450 enzymes). Cytochrome P450 enzymes are a battery of Phase I enzymes that have been shown to metabolically activate chemical carcinogens such as nitrosamines and aflatoxins. The glucosinolate break down products can be mono-or-bifunctional inducers based on their effect on Phase I and Phase II enzymes. Sulforaphane and phenylethyl isothiocyanates are mono-functional inducers that induce Phase II enzymes and either has no effect or inhibit phase I enzymes, while indol-3-carbinol and its parent glucosinolate glucobrasicin, and neoglucobrassicin are bifunctional inducers that induce both Phase I and Phase II enzymes. In addition to modulating the Phase I and Phase II enzymes, the glucosinolates and their breakdown products have also been shown to have a direct effect on the cancer development by suppressing the promotion phase of cancer cell formation and reducing invasion and metastasis. Recent evidences also suggest that isothiocyanates may regulate cancer cell development by promoting apoptosis. Apoptosis, or programmed cell death, is genetically encoded active cell destruction. Indol3-carbinol has been shown to promote apoptosis in rodent cell lines. Glucosinolate breakdown products have also been shown to prevent and/or suppress estrogen dependent cancers, such as cervical and breast by blocking the estrogen receptor function. The chemo-protective properties of natural isothiocyanates have renewed interest in glucosinolate biosynthesis. While significant progress has been made in understanding the biochemistry and enzymology of glucosinolate synthesis, little is known about the structural and regulatory genes involved. CHAPTER THREE 3.1 Nutritional and Medicinal Importance of Indigenous Vegetables Micronutrient deficiency is a universal problem, which presently affects over 2 billion people worldwide, resulting in poor health, low worker productivity, high rates of mortality and morbidity. Deficiency in micronutrients has led to increased rates of chronic diseases and permanent impairment of cognitive abilities in infants born to micronutrient deficient mothers (Flyman and Afolayan, 2006). Local vegetables are important contributors to rural and urban people's diets in Nigeria (Barminas et. al., 1998). They play an important role in traditionalfood culture and various ethnic groups consume varieties of different indigenous types of vegetables for different reasons (Mensah et. al., 2008). Approximately half of the leafy vegetables consumed in most Nigeria diets are from indigenous sources and they constitute significant micronutrients such as Vitamin C, Mg, Fe, Zn and Ca, proteins and fibre among other nutrients. (Lockett et al., 2000; Grivetti and Ogle, 2000). Vegetables serve as relish which is consumed alongside with main diets. They usually complement staple starchy diets which are made from cereals and tuber crops and they serve as substitutes for proteins in soups where they cannot be afforded. However, where alternative relish is available, they are referred to as supplements (Kepe, 2008). Indigenous vegetables have played significant roles as food supplements during times of drought and to fortify diets especially in hunter gatherer societies. Smith and Ezyaguirre, (2007) and Oniang’o et. al. (2003) stated that relish is an indispensable part of the African diet as the main staple cereal is not normally eaten in the absence of relish. Thus, the presence of relish directly impacts on the consumption of the bulk of the main staple even though the relish is required and consumed in smaller proportions relative to the staple. This relates so much to the importance of vegetable in enhancing satisfaction even at the household level. Dark green vegetables aid the maintenance of alkalinity and supply chemical compounds which are able to retard the spread of degenerative disease in the human body due to their high vitamin, dietary fiber and mineral contents and antioxidant activity. Vegetables provide nutrients vital for health and maintenance of the body. Eating green vegetables which are rich in fiber may help regulate the digestive system thereby aiding bowel health and lowering the risk of colon cancer (Asaolu et al., 2012). Foliate intake can also reduce the risk of heart related disease such as heart attack and stroke. Leafy vegetables intake contributes to the production of serotonin, which help ward off depression as well as improving mood. Riboflavin and niacin are B vitamins that help prevent cataracts, while vitamin C help slow bone loss and decrease the risk of fractures. It also allows the body to make collagen which is a major component of cartilage, which aids in joint support and flexibility. (Madisa et. al., 2010). Large consumption of vegetables treats hemorrhoids, gallstones, obesity and constipation. Green leafy vegetables used for soup preparation cut across different cultures within Nigeria and other parts of West Africa with similar cultural and socio economic background (Mensah et. al., 2008). Indigenous vegetables possess medicinal properties in that they contain antioxidants which protect against oxidative stress caused by free radicals and reactive oxygen species. They help in preventing major ailments such as cardiovascular diseases and certain cancers (FAO/WHO, 2005). Indigenous vegetables are therefore necessary for proper human growth and physiology and are much more nutritive than the conventional ones such as spinach, kale and cabbage (Flyman and Afolayan, 2008). Vegetables containing antioxdants when consumed in sufficient amount would contribute greatly towards meeting human nutritional requirement for normal growth and adequate protection against diseases arising from malnutrition (Asaolu et. al., 2012). Bitter gourd (Momordica charantia) fruits are a rich source of β-carotene, vitamin C, folic acid, magnesium, phosphorus and potassium (Yuwai et. al., 1991). The fruits are often used in folk medicine to treat type II diabetes, a rapidly spreading non-communicable disease that afflicts millions of people living in lowand middle-income countries (WHO, 2012; IDF, 2013). Almost all parts of pumpkin (Curcubita spp.) – fruit, leaves, flowers, and seeds are edible and can be prepared in a variety of dishes, using the fruit in soup, baked, stuffed, stir-fried or as a sweet dessert. Tender leaves and shoots are also good sources of micronutrients including provitamin A and minerals such as calcium, iron, and zinc. Growing vegetables, in particular leafy nutrient-dense species, in home gardens is important for families to obtain daily access to safe and nutritious food (Keatinge et. al., 2012). This is very important for reducing vitamin A and iron deficiency in vulnerable groups such as elderly people and pregnant women, and in improving maternal health and the health of children under five (Lyimo et. al., 2003).Studies by Adebooye et. al. (2003) stated that plants are also sources of traditional medicine in southwest Nigeria and are used in treating various diseases and ailments. Many indigenous vegetables species in sub-Saharan Africa, species such as Moringa (Moringa oleifera), Amaranth (Amaranthus spp.), Sweet potato (Ipomoea batatas) leaves and Spider plant (Cleome gynandra) also have high levels of anti-inflammatory phytochemicals such as flavonoids and other antioxidants that are of value to human health (Yang et. al., 2013) in addition to their great nutritional value. 3.2 Bioavailability- The Challenge of Nutritional Capabilities in Indigenous Vegetables The food security concept of food utilization goes beyond food use and includes how a person is able to absorb essential nutrients from the consumed food (FAO, 2008) and this incorporates the concept of bioavailability. The bioavailability of nutrients is influenced by the presence in a meal of substances that either promote or inhibit absorption of nutrients by the gut (Lonnerdal 2003; Gupta et. al. 2006). These substances, which include phytate, oxalate and polyphenols are called anti-nutrients or anti-nutritional factors. They occur not only in indigenous and wild vegetables but also in cultivated vegetables and fruits (as oxalates), cereal and legume seeds (as phytates) and beverages such as tea and coffee (as polyphenols) (White and Broadly 2009). Some authors have expressed their concern as to the ability of vegetables to meet the nutritional requirements of man. This is attributed to the presence of the antinutrients such as Tannins, saponins, phytates, oxalates, phytic acid and alkaloids. In the human body, oxalate binds to calcium to form calcium oxalate crystals that prevent the absorption and utilisation of calcium leading to diseases such as rickets and osteomalacia (Ladeji et. al., 2004). Tannins have the ability to precipitate certain proteins by combining with digestive enzymes thereby making them unavailable for digestion (Abara, 2003). Phytic acid combines with some essential elements such as iron, zinc and phosphorus to form insoluble salts known as phytate. This prevents the absorption of these minerals by the body leading some mineral deficiency disorders. In Brazil, high levels of tannins were reported in the leaves of Talinum fruticosum (Leite et al., 2009). However, some of these antinutirents can be lost during processing such as boiling, lanching and drying (Lola, 2009; Mosha et. al., 1995a, b; Oboh, 2005; Yadav and Sehgal, 2003). Some common vegetables including Amaranthus, Solanum and Corchorus species have been found to contain very low levels of anti-nutrients (Agbaire, 2012). The subject of bioavailability therefore requires adequate research so as to understand the effects of antinutrients and phytochemicals in the human to ensure optimum use of these important nutrient sources. 3.3 Women and Institutional Roles in Vegetable Research and Future Development Global public spending on agricultural research and development reached US$ 31.7 billion in 2008 and has increased at an average annual rate of 2.4% since 2000, mostly driven by China, India and the United States (Beintema et. al., 2012). Although data are not disaggregated by crop, it would be safe to say that very little of this money is spent on research for fruit and vegetables, and virtually none of it goes into the improvement of indigenous vegetables (Keatinge et. al., 2015).In a country like Nigeria, these indigenous vegetable crops have been neglected by researchers, policy makers and funding agencies and are currently threatened with extinction, which would mean a substantive reduction in biodiversity (Adebooye and Opabode, 2004). Indigenous vegetables are currently underutilized, and have been neglected by researchers and policy makers. Lack of prioritization by African governments and other stakeholders in terms of research is the major reason for genetic erosion of this species (Shackleton, 2003; Adebooye and Opabode, 2004). Transdisciplinary (Td) studies among researchers which use different methods to generate information can be used to gather up- to- date knowledge on indigenous vegetables. It is generally agreed that the question of food security requires an interdisciplinary approach to solving, bringing the agriculturalists and nutritionists together (Aragrande et. al., Argenti, & Lewis, 2001; Global Food Security (GFS), 2013; Ingram, 2011; Maunder & Meaker, 2007; Rocha, 2007). Community seed production and storage systems must be set up in villages, where growers can be trained to produce reasonably genetically pure seed to store in low relative humidity conditions after drying (Manzanilla et. al., 2011; Ebert et. al., 2013). Women and children are usually the predominant gatherers of these important plant species. For example, a study of 135 different societies with various subsistence bases estimated that women provided 79% of total vegetal food collected (Barry & Schlegel, 1982; Howard, 2003). In South Africa, the Agricultural Research Council (ARC) is one of the institutions that has been at the forefront of promoting wild vegetables for food security and nutrition through research. Nigerian scientific, agricultural and economic organizations and institutions can collaborate in carrying out problem solving research on her indigenous vegetables. Baseline surveys need to be conducted in Nigeria to ascertain market values of wild vegetables. To promote indigenous vegetables, several researches on water use efficiency, plant nutrition; cultivation practices (planting methodology, spacing and harvesting, allelopathic effects and agronomic traits) are required to ensure domestication. The Nigeria-Canada Indigenous Vegetable Project (NICANVEG, 2015) which was a collaboration between Obafemi Awolowo University, Ile Ife, Osun State University, Osogbo, University of Manitoba, Canada and Cape Breton University, Canada carried out researches on selection and improvement of genotypes, development of drought, pest and disease resistant varieties, and cultivation of wild vegetables under different conditions as well as the phytochemical and organoleptic studies of the vegetables. Studies on the nutritional composition of vegetables are required and controlled experiments on aspects such as effect of soil type, effect of fertilizer amount and type, and age of harvesting on the nutritional composition of vegetables need to be carried out. However, conservation of genetic diversity and seed supply systems to store and supply a wide variety of indigenous vegetable species are of utmost importance. Such partnerships as these partnerships will generate a wealth of knowledge on indigenous vegetables and most of the work has been published or presented in conferences and academic gatherings. The need for more in depth participatory studies on the indigenous knowledge systems about vegetable species as well as on their current importance in the household economy has been suggested by Mavengahama et. al. (2013). The abundance and diversity of these vegetables need to be determined. Diversity studies are especially important as a preliminary step in breeding of these species for desirable traits such as low anti-nutrients and low astringency, high micronutrient content as well as high yield of the edible parts. The potential of these vegetables to contribute to agro-biodiversity at farm and household level through intercropping them with other crops also needs to be explored. In addition, the possibility of commercializing indigenous vegetable production and making them available all year round needs to be researched. More empirical studies on the nutritional values of underutilized species and their subsequent domestication may be an important step towards alleviating nutritional deficiencies among marginal input communities of Nigeria. CHAPTER FOUR 4.1 Summary 4.2 Conclusion Vegetables have been part of human diet from time immemorial and as a result several measures should be put in place by all sectors so as to ensure their continuous availability. Perishability, seed viability and availability and pest and diseases are some of the factors necessary for consideration during domestication and commercial farming, Research on pest and diseases that affect productivity of indigenous vegetables is strongly encouraged. Appropriate post-harvest management and storage techniques are advised so as to reduce perishability of indigenous vegetables. It is recommended to place vegetable crops in a cool environment to prolong their shelf life. Sharing and disseminating information about the different indigenous vegetable types and species, their nutritional value for health, and how they can be Preservation of important character traits of indigenous vegetables can be properly achieved through molecular characterization so as to prevent genetic erosion by exotic species. Furthermore, researches on morpho-genetic characterization to enable selection of species with desirable traits, agronomic and chemical evaluation and the effects of cooking and processing on chemical composition and nutritional value of these species are needed to generate adequate information. Molecular markers could be used to aid in the selection for low antinutritional levels and other undesirable characteristics. In Nigeria, Policy makers should support the generation of persuasive research-based information, and initiate suitable national legislation and information campaigns especially among the malnourished fraction of the population. There is need to educate the populace especially the rural dwellers on the inherent potentials of the indigenous vegetables so as to make them an important part of their mainstream diet in order to enhance food security, prevent malnutrition and generate income through extension the activities of extension workers and the mass media. Promotion of the use of indigenous vegetables among urban dwellers is highly recommended so as to annul the notion that vegetables are diets for the poor and hungry people.
