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1.0     Introduction

Sweet potato (Ipomoea Batatas L.) belongs to the morning glory family       (Convolvulaceae), and both the storage roots and leaves are edible. It is thought to have originated in southern Central America. Early trading vessels disseminated sweet potato throughout the world. Sweet potato has long been an important food crop to many peoples, particularly to the poor, and is the 6th most important food crop in the world and 4th most important in the tropics       (FAOSTAT, 2010). Sweet potato has a starchy and sweet taste, with different varieties having their own unique flavour profiles. They are often grouped into 2 categories depending on texture; some are firm, dry, and mealy when cooked, while others are soft and moist when cooked.

World annual production was > 127 million metric tons in 2004, 98.5% of which was in developing countries (FAOSTAT, 2010). Asia accounts for the largest part of world sweet potato production, which amounted to 112.4 million tons annual production in 2003 (FAOSTAT, 2010). Production is greatest in China, accounting for 94% of the Asian sweet potato production.

In contrast, African farmers produced about 11.4 million metric tons of sweet potato in 2003 (FAOSTAT, 2010). These data need to be interpreted with caution because of the difficulties in estimating production for a crop produced by small farmers on non-contiguous plots, harvested several times a year, and neither sold through regulated domestic marketing channels nor traded internationally in appreciable quantities. In many developing countries in Africa, Asia, Latin America, and the Caribbean, the sweet potato is a secondary staple food or an important vegetable crop that is grown primarily by poor small farmers. Sweet potato is typically a small farmer crop and often grown on marginal soils with limited yields. For example, in Kenya the average plot size is < 0.2 hectares, and about half of the harvest is kept for home use. Because sweet potato is considered a “backyard crop,” there are no reliable data on the extent to which it contributes to local food supplies. Overall, average yield in developing countries is low, at 15 metric tons per hectare, and there is wide variation. For example, African yields are about one‐third that of Asian yields (CIP, 2013). However, the sweet potato is a reliable crop for small‐scale production, and because it can be left in the ground for extended periods and harvested when needed, sweet potato is especially appealing to small farmers (Qaim, 2016).

1.1     Background to the Study

Both the amount of sweet potato consumed and the manner in which it is consumed vary widely. Average annual per capita supply of fresh roots for 2003 was estimated as Africa, 112 kg; Asia, 16 kg; Oceania, 18 kg; North and South America, 2 kg; Europe < 0.5 kg (FAOSTAT, 2010). Sweet potato consumption also varies within countries, by regions, by time of year, and by income group. Green tips are used as a vegetable in some areas and can be an important source of protein and micronutrients.

Sweet potato is widely used by small farmers to sustain local livestock production systems. Almost everywhere that sweet potato is cultivated, some part of the plant, in some form, and is used in some type of animal production. Sweet potato roots and vines are being increasingly used in pig and other livestock systems in China, and FAO estimated that 50 million tons in 2002 was used as feed (FAO‐STAT, 2009). About 45% of Asia’s domestic sweet potato supply is used for animal feed, and nearly 50% is used for human consumption, either as fresh or processed products (CIP, 2013).

In contrast, 85% of Africa’s domestic sweet potato supply is for human consumption. For example, per capita sweet potato consumption in Rwanda is estimated as 147 kg/y; Burundi, 120 kg/y; and Uganda, 88 kg/y, and most of this occur in the drier seasons. Sweet potato can be used as a seasonal staple when there is a shortage of other foodstuffs (CIP, 2013). It is also an important crop in northern regions of South Africa. In Africa, commercial farmers use vines as fodder for livestock. Humans consume both the roots and young leaves and tips as green vegetables. Sweet potato root is generally consumed boiled (and mashed) or fried. It is also processed commercially or at home into flour that is then often mixed with other flours to make composite flour. These flours are used to make porridge, which is an important complementary food for breastfed children. Less commonly, the flour is used to make bread and pastries. Poor households tend to eat boiled or baked sweet potato roots. Fresh roots are also fried and the chips eaten as a snack food.

In China, humans mostly consume sweet potato as a vegetable or health food, not as a staple food, and the roots are typically boiled or baked. Sweet potato starch is used for making fresh or dry starch noodles and sheets, and for fresh starch cakes. Snacks of dry sweet potato slices and bars are also popular. In Japan, consumers use many of the deeply coloured root varieties and consume sweet potato mostly as processed snacks, noodles, and candies. Sweet potato is grown and the roots are consumed in the drier and poorer regions of India.

In Latin America, there is great diversity of varieties. Most sweet‐potato roots are again eaten boiled or baked. Use varies in the Caribbean region. Sweet potato is the main staple in some South Pacific islands, especially in Papua New Guinea highlands where many varieties are available, providing the dominant portion of the energy and protein requirements of the population ( Okuda and et al 2012; CIP, 2012 ). In Oceania, in 2008, it was the most important tuber and root crop after potato (FAOSTAT, 2010).

For long‐term storage, the roots are sliced into thin chips for food or strips for animal feed that are sun‐ (usual) or shade‐dried. Chips can be stored in the dried state, rehydrated, and then cooked. Alternatively, they can be ground into flour that can be mixed with wheat as composite flour; the proportions of wheat and sweet potato vary depending on taste. Pure or composite flour is used to make gruels, bread, donuts, cakes, and other products. Starch is extracted and used to make noodles, sheets, and cakes in China.

In some countries, processed products made from sweet potato, including starch, noodles, candy, desserts, and flour, are made by farm households to extend the availability, diversify the use of, and increase the value of the crop. In China, in particular, production of sweet potato starch in recent years has evolved into a cottage industry that uses millions of tons of roots per year as raw material inputs. The magnitude of these new uses is not easy to quantify in a systematic way; partly for that reason, the available statistics on processing do not always reflect their true level of importance (CIP, 2013).

Sweet potato is also consumed in Europe and the United States as a cooked vegetable. Sweet potato has a low glycaemia index, indicating low digestibility of the starch despite its high carbohydrate content.

1.2     Statement of the Problem

Lectin are carbohydrate binding protein present in most plants, especially seeds and tubers like cereals, potatoes and beans. It is well established that many lectin are toxic, inflammatory, and resistant to cooking and digestive enzymes and present in much of our food and sometimes cause “food
poisoning”. If the lectins in sweet potatoes are causative in initiating all these diseases, it should be possible to carryout an investigation on the best possible way of consumption.


1.3     Aim and Objective of the Study

The aim is to understudy the health implications of consuming sweet potatoes in its fresh, boiled and roasted states. The objective is to isolate, identify and quantify lectins present in fresh sweet, roasted sweet potatoes, and boiled.

1.4     Scope of the Study

This work is expected to cover;

  1. Practical examination of sweet potatoes in its fresh, boiled and roasted state.
  2. Extraction of the lectins component in all state. Quantification of lectins from the three states.


Nutrition wise, it has been established that sweet potatoes are a good source of some vitamins and minerals. They contain high level of potassium, which had been shown to decrease the risk of heart diseases. They are also a good source of vitamin C and folate. More so, the skins partly are high in antioxidants, such as chlorogenic acid. The compound has been associated with a reduced risk of heart disease and type 2 diseases. Potatoes have also been shown to be more satiating than many other common foods, which can aid weight loss. Giving the said benefits in consuming sweet potatoes, it is important to carryout an assessment of the level of lectins present in fresh sweet potatoes, boiled and roasted.


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