EFFECT OF DRYING METHODS ON THE NUTRIENT AND PHYTOCHEMICAL PROPERTIES OF SOME CULTIVATED AND WILD LEAFY VEGETABLES.

ABSTRACT

The aim of this study was to determine the nutrient and phytochemical composition of fresh, sun and shade dried okra, bitter, scent, G. latifolium and roselle leaves. The vegetables were purchased from two markets. Okra, bitter, scent and G.latifolium leaves were purchased from Nsukka and roselle leaves were bought from Jos market. All the vegetables were washed, weighed and divided into two equal parts. Each part was sun, or shade dried, pulverized, packed and stored. The fresh samples for each of the vegetables served as control. The fresh, sun and shade dried samples of all the vegetables were separately analyzed for various nutrient and phytochemicals on dry weight basis using standard assay techniques. Data generated were statistically analyzed. The means were separated and compared. All the fresh samples had high moisture values(Okra leaf; 62.22%, bitter leaf; 62.32%, scent leaf; 62.46%, G.latifolium; 61.44% and roselle leaf; 85.53%) . The moisture content of the sun and the shade dried samples differed (P<0.05). The exception was that of roselle whose sun and shade dried values were comparable (6.36 and 6.38%) (P>0.05). Fresh samples of all the vegetables had lower protein. The processed okra, bitter, scent and roselle leaves had comparable values (P>0.05). Moisture lost due to drying increased nutrient density of the vegetables, especially the roselle leaves. The phytochemicals (Tannins, phytate, saponins and flavonoid) of the fresh samples were higher than those of the sun and the shade dried samples. This showed that fresh vegetables are better sources of phytochemicals as against the sun and the shade dried samples. The shade dried samples had lower tannins except for the bitter leaf and the sundried samples had lower phytate except the G. latifolium. The sun and the shade dried samples had comparable saponins and flavonoids content (P<0.05). As judged by the results, domestic food processing techniques improved the nutrient content of these vegetables and decreased some of the food toxicants and antinutrients.

CHAPTER ONE

1.   INTRODUCTION

Man must eat to survive for the continuity of the human race. The foods for human consumption are of both plant and animal origin. Cereals, legumes, roots, tubers, suckers, oils, nuts, fruits and vegetables are plant foods. Meat, milk, eggs and oils are animal products. Both plant and animal foods contain nutrients. Oxford Medical Dictionary (2003) defines nutrients as substances that must be consumed as part of the diet to provide energy, protein for growth or substances that regulate growth or energy production. Carbohydrate, proteins, fats, vitamins, minerals and water are the existing six nutrients.

It is known that too much or too little of these nutrients have adverse effects on health. The source of these nutrients equally determines how healthy one is. A typical example is in the case of fats. Animal fat contains about 40-60% of fat as saturated fatty acids. Plant oils contain mostly unsaturated fatty acids ranging from 73 to 94% of total fat (Wardlaw & Kessel, 2002). Plant oil is the most beneficial to health. Current studies showed that plant nutrients are not inferior to animal nutrients as it was earlier thought. In addition, plants contain other non-nutritive dietary components that are beneficial to health. These components are called phytochemicals. “Phyto” because they are only found in plant based foods (Pamplona-Roger, 2005). The present study  concentrated on nutrient and phytochemical levels of five cultivated and wild vegetables.

Vegetables are generally herbaceous (non-woody) plants that are cultivated in farms, collected from forest trees, market and home gardens as well as kitchen gardens for home use. Usually, all the botanical parts of the plants (leaves, buds or flowers, calyxes, fruits, stalk, roots are consumed) (Pamplona-Roger, 2005). This study laid emphasis on green leafy vegetables.

History shows that vegetables were used for a number of purposes. Many in the past consumed these vegetables without knowing all they contain. Scent leaf was used and is still being used to stop diarrhoea. How and what stops diarrhoea in scent leaf is still a puzzle to many. The foods our ancestors consumed consisted of carbohydrates, starchy vegetables, leafy vegetables and little or no animal products. There were not much occurrences of various chronic diseases such as morbid obesity, cancer, heart and renal failure three to four decades ago as they are now. The juvenile and paediatric cases of these diseases are on the increase. The cause of their increase is due to migration/changes in lifestyle and food habits (Ene-Obong, 2008). The very sharp shift from traditional diets as well as the advent of exotic diseases appears to suggest a serious warning. These warnings call for urgent increases in consumption of preventive and curative substances inherent in plant based food, especially vegetables.

Chemically, green leafy vegetables are composed of water; 90 to 95%, minerals e.g. phosphorus, potassium, calcium, iron, vitamins, fibre, proteins, chlorophyll and most recently discovered- phytochemicals (Pamplona-Roger, 2005). Indigenous traditional foods are on the verge of extinction. The younger generation is ignorant of them as such; consume less of these vegetables (Ene-Obong, 2008). As most of these traditional foods are on the verge of extinction, so are the vegetables, condiments and spices used in their preparation. Some of the wild forest vegetables might have been used by a particular community in the past. Based on these serious observations associated with less consumption of indigenous foods and increases in many chronic ailments, it is imperative to study the nutrient and phytochemical potentials of some cultivated and wild vegetables.

1.1       Statement of problem

            The increase in the consumption of western diets and neglect of our traditional foods has precipitated a corresponding increase in ill-health due to diet related non-communicable diseases. These diseases are of various forms; cancer, kidney and liver diseases, diabetes and many more. Prevention of these diseases based on new incidences of these diseases is imperative. This is because these diseases are of increasing public health concern. Extensive studies are ongoing to address these public health threats both for the cure of already existing cases and prevention of new cases. One hopes that the results of these studies will provide baseline information as to their causes and treatment.   

However, some of the information based on the results of recent studies point to the type of foods consumed by people. Currently, nutrients from plant based foods have promising solution (Ene-Obong, 2008). Vegetable based foods are advocated because of their high content of non-nutritive dietary components that are safer and more beneficial to man. Some of these vegetables contain antioxidants and phytochemicals. Sadly, in Nigeria, little attention is paid to fruits and vegetables. Statistics from World Bank (1991) showed that at the National level, an average household expenditure on household staples was highest on fish (N140.84) followed by meat products (N81.54). The least weekly expenditure was on fruits (N13.12) followed by weekly expenditure on green leafy vegetables (N20.88).

Vegetables are the most affordable dietary sources of vitamins, trace elements and other bioactive compounds that offer the only practical and sustainable way to ensure that micronutrients are supplied through the diet (Odo, 2007). It is imperative to study more vegetables for their nutrient and photochemical potentials. The investigation of these vegetables would be of immense benefit to the society.

1.2       Objective of the study

            The general objective of the study were to determine the effect of drying methods on the nutrient and phytochemical properties of some cultivated and wild leafy vegetables.

The specific objectives of the study are to;     

1. determine nutrient, and phytochemical content of these vegetables
2. sun, shade dry and pulverize these vegetables to determine the nutrient content of their flours.  
3. determine the nutrient and phytochemical potentials of these vegetables on dry weight basis.

1.       Significance of the study

The results of this study would be a promising and useful tool to home makers on the increasing need to produce both cultivated and wild forest vegetable and consume them, especially the children and younger adults. Increase consumption of these vegetables might be the solution to the cases of micronutrient deficiencies world wide and some chronic and deadly diseases such as cancers and other diseases and their complications, particularly in developing countries, Nigeria inclusive.

CHAPTER TWO

•      LITERATURE REVIEW

In 2000, the member states of the United Nations committed themselves, to creating a “more peaceful, prosperous and just world” to “freeing our follow men, women and children from the abject and dehumanizing conditions of extreme poverty” to making “the right to development a reality for every one” and to ridding “the entire human race from want” (Von Braun, Swaminthan & Harlow, 2004). This declaration needed an enforcement which was the Millennium Development Goals (MDGs). The MDGs are specific and should be met by 2015. The MDGs cannot be achieved without a direct focus on nutrition because each of the eight goals is directly or indirectly linked to it.

Nutrition as defined by the council of Food and Nutrition of the American Medical Association is the “Science of food, the nutrients and the substances therein, their action, interaction and balance in relation to health and diseases, the process by which the organism ingests, digests, absorbs, transports, utilizes and excretes food substances (Wardlaw & Kessel, 2002). Nutrients are classified into micro and macro nutrients. The macro nutrients being proteins, carbohydrates and fats, and the micro are vitamins and minerals. Malnutrition is a condition of impaired development and function caused by either long term deficiency or an excess in energy and/or nutrient intake (Wardlaw & Kessel, 2002). The former, representing the nutritional state in Nigeria. The focus here was on micronutrient malnutrition which is of global public health importance.

2.1Micronutrient malnutrition in Nigeria

In 1990, the term hidden hunger was adapted to refer to micronutrient deficiency due to substances so small that one could not see them. One out of three people in the world are affected by one or multiple micronutrient deficiencies (WHO, 2006). Micronutrient deficiencies of international interest include vitamin A, iron, iodine and zinc. Their deficiencies among the Nigerian population have been documented (Ene-Obong, 2008). The Nigerian Food Consumption and Nutrition data showed that 29.5% of children had marginal vitamin A deficiency, and 13% of mothers and 19.2% of pregnant woman were at risk of vitamin A deficiency. The study also showed that 20% of the children were both iron and zinc deficient while 14.5%, 8% and 4% had mild, moderate and severe iodine deficiency (Maziya-Dixon et al., 2004). A study by Ene-Obong, Odoh and Ikwuagwu (2003) showed that despite adequate intakes of vitamin A, 40% of male and 32% of female adolescents had low plasma concentration of vitamin A (< 20 ug /dl). The  first, fourth, fifth and sixth MDGs (which are to; Eradicate extreme poverty and hunger, reduce child mortality, improve maternal health and combat HIV/AIDS, malaria and other diseases) are directly linked to micronutrient malnutrition. To combat micronutrient deficiency, food and nutrition security is paramount and this cannot be achieved if agriculture and nutrition are not given top priority.

Sadly, indigenous food crops are no longer given the top priority they deserve (Okafor, 1975). They and are at the point of extinction (Okeke, Ene-Obong, Uzuegbunan, Ozioko & Kuhnlein, 2008). The younger generations do not even know them, like them, let alone consume them (Ene-Obong, 2008). Some food items such as African yam bean and pigeon pea are now rarely consumed by urban dwellers. This is because of the length of time they take to cook and amount of fuel they consume, despite the fact that they are highly nutritious (Okigbo, 1980). They equally contain both micro and macro nutrients in appreciable amounts. The above scenario shows that there is need for advocacy and sensitization on the importance of indigenous food crops and vegetables. The focus here is on vegetables, nutrients and phytochemicals content.

2.2 Vegetables

The term vegetable usually refers to the fresh edible portion of a herbaceous plant -root, stem, leaves, flower or fruits (Encarta, 2008). Vegetable are naturally low in fat and calories. None have cholesterol and many are good sources of fibre. They are rich in minerals and vitamins (Iloveindia, 2004). Until most recently, a group of chemicals known as phytochemicals were discovered. They are found only in plant based food in very small amount. They perform numerous preventive and healing functions within the body (Pamplona-Roger, 2005).

Vegetables equally contain carbohydrates, proteins, and fat. They can be categorized according to their type and taste e.g.

 Bulb vegetables e.g. onions, garlic and shallots.

 Fruit vegetables e.g.  avocadoes, cucumbers, okra, tomatoes, pepper and   eggplant.

Inflorescent vegetables e.g. broccolis and artichokes.

Leafy vegetables e.g. bitter leaf, scent leaf, lettuce, spinach and cabbage.

Root vegetables e.g. carrots, beets, radishes and turnips.

Stalk vegetables e.g. asparagus, bamboo and celery.

Tuber vegetables e.g. cassava, yam, sweet potato, and taro.

Source: Iloveindia (2004).

• Roselle (Hibiscus sabdariffa)

Roselle is a native of the old world tropics and a species of hibiscus. It is an annual, erect, bushy herbaceous subshrub that grows up to 2.4m tall. The leaves are alternate 7.5-12.5cm long, the flowers borne singly in the leaf axils, are up to 12.5cm wide yellow or buff with a rose or maroon eye and turn pink as they wither at the end of the day. The typically red calyx consists of 5 large sepals with a collar (epicarlyx) of 8 to 12 slim pointed bracts around the base (Morton, 1987). It is known as roselle in Australia, meshta in the Indian subcontinent, bissap in Senegal, Mali, Burkina Faso, Benin and Niger, rozelle, sorrel or red sorrel in English speaking regions, rosella in Indonesia and zobo in Nigeria (Wikipedia-Roselle, 2009).