Saturday, 6 August 2011

Adding Value to Orange Fleshed Sweet Potatoes: Fighting Vitamin A Deficiency!


The this brief  is about the formulation of ready to use foods using orange fleshed sweet potatoes as the base and other locally available food materials to increase the farmers value for sweet potatoes while combat malnutrition especially vitamin A deficiency  in Uganda. The brief aims at formulating numerous nutri dense foods including flours, porridges, biscuits and cakes. The raw materials have to be readily available and the products have to be affordable by the population. The technologies used include milling, mixing, baking; which are easily adapted by the community. At the end of reading this brief, one must able to apply the acquired knowledge from this writing and take on the technologies as a business.

Food materials that can be used

 The locally available raw materials include among others; Soy beans, wheat, rice, Orange fleshed sweet potatoes and maize.

Orange fleshed sweet potatoes (OFSP)

Reasons for choosing OFSP
Sweet potato is grown as a food crop in many Sub-Saharan Africa countries and covers an estimated 2.1 million hectares with annual estimated production of 9.9 million tones of roots. It is the third most important food crop in East Africa and ranked seventh among the food crops produced in the world and has an annual production of 138 million metric tons (Edison, 2000).

Uganda is the world’s second largest producer of sweetpotato and first in Africa. Sweetpotato plays a primary role in food security in Uganda especially in the eastern region where two crops per year are grown for both home consumption and to supplement household income by sale to local markets and urban centres.

In spite of the increasing popularity of sweetpotato in both rural and urban food systems, most local varieties grown throughout the region have white or cream-coloured flesh, and supply little or no pro vitamin A in the body (Draft Sweetpotato Technical manual, 2003). Vitamin A deficiency is one of the major health problems which most developing countries currently face. This micronutrient is critically deficient in the diets of the majority of people in the East African
region especially in rural areas, particularly for young children. Severe deficiency leads to
night blindness, while less severe forms reduce a person’s general health and capacity to fight off malaria, measles, diarrhea, AIDS associated illnesses, pneumonia and other diseases. Vitamin A deficiency has been identified as the leading cause of early childhood death and a major risk factor for pregnant and lactating mothers in East Africa (FAO/WHO, 1992). Whereas Food and Agriculture Organization’s (FAO) food balance sheet indicates an improving trend of Vitamin A in the diets for most developing countries in the last 20 years, in East Africa the overall vitamin A supply is actually decreasing (United Nations, 1992). According to International Food Policy Research Institute (IFPRI) projections 2000, the number of the malnourished children will continue to increase from 33 million in 1997 to somewhere between 39 and 49 million in 2020.

Prevalence of Vitamin A Deficiency in Children and Women
In Uganda, 20 percent of children 6-59 months and 19 percent of women of childbearing age were vitamin A deficient in 2006 (UDHS 2006). According to UBOS 2001, the prevalence of Vitamin A deficiency (VAD) was estimated at 28% for children aged 6-59 months and 52% for women aged 15-49 years.
 Vitamin A deficiency levels among children and women are similar within Ugandan regions. The prevalence of VAD among children and women was highest in East Central Uganda (32 and 31 percent, respectively) followed by East and Central Uganda. The lowest levels of VAD were reported among IDP populations (9 and 12 percent of children and women, respectively) and in Karamoja (6 and 7 percent, respectively). Boys were more likely to have VAD than girls (22 percent and 19 percent, respectively). The risk of VAD was higher among children under 18 months (18 percent) than older ones (22 percent). WHO classifies Uganda as having a moderate public health problem with VAD. (FANTA 2010)
According to FAO/WHO report (1992) vitamin A intake is often inadequate because of the seasonality of food sources, the early abandonment of exclusive breast feeding, high morbidity levels, and practice of not giving vitamin A-rich food to young children. Dependence on capsules donations from UNICEF and use of fortified foods is quite costly and not implemented widely. The best sources of beta-carotene are liver and fish liver oils, which are very expensive for the rural poor. The best plant sources of beta-carotene, which the body turns into vitamin A as needed, are carrots, green vegetables and orange-fleshed sweetpotato (OFSP). Whereas most rural people especially in Eastern Uganda associate carrots with rich families and greens are regarded as inferior vegetables to be used during periods of scarcity, sweetpotato is traditionally regarded a famine crop that can substitute for cassava and fits in many food mixtures (blends) and forms.
During bumper harvests, farmers often sell sweet potatoes at throw-away prices. Losses after harvesting are high due to their perishable nature. In some communities in Eastern Africa, sweet potatoes are preserved for the dry season by sun-drying to make dried sweet potato chips. The dried chips are boiled and mashed with beans, milled or pounded to make flour, which can be mixed with either millet or cassava flours to make stiff porridge.

Vitamin A deficiency has been recorganised as a widespread problem affecting about 750 million people, mostly in developing countries. Mortality due to vitamin A deficiency can be reduced by as much as 23% with improved vitamin A status. Vitamin A’s immune-enhancing aspects strengthen the body’s defence system against infections such as measles, malaria and diarrhea thus preventing death.
Orange fleshed sweet potato (OFSP) has emerged as a promising plant source with a high beta-carotene content that can make a significant contribution to the vitamin A intake of individuals at risk of Vitamin A deficiency.             

Raw materials;
Ø  Orange fleshed sweet potatoes, Wheat flour, soy beans, maize, baking fat, eggs, sugar, cooking oil and other baking materials.
Requirements used for making sweet potato chips and flour
·         Mature sweet potato roots.
·         A clean area ideally raised working surfaces.
·         Large plastic containers, preferably 10- to 20-litre buckets with lids
·         Supply of clean water
·         Knives for peeling and chipping
·         A convenient solar drier

Procedure used in the making sweet potato chips and flour

Step 1: Choosing the roots
The roots are purchased, sorted to use the undamaged and mature – three to four months for the early maturing varieties and five to six months for the late maturing varieties

Step 2: Washing
·         The potatoes are washed in clean water in large buckets, changing water as frequently as required.

Step 3: Draining
·         After washing, the potatoes are drained by placing them on nylon sacks.

Step 4: Chipping or slicing
·         The washed potatoes are peeled and chipped to uniform size (3-6 mm thick) manually with sharp knives.

Step 5: Drying
·         Sweet potato chips are spread evenly on trays and loaded into a solar drier (can also be sun dried but the quality will lower than that of a solar drier), dried for about eight hours until brittle according to the sun’s intensity.
·         The dried chips are packed in polyethene bags and stored  in buckets until further  processing to flour
Step 6: Milling
·         The potatoes are milled using a hammer mill (village “posho” mill) into flour.

Step 7: Packaging and labeling
  • The flour is packed in strong (thick gauge) black polyethylene bags, Labeled to state source, date of manufacture and expiry date (after six months).
·         The bags are placed into buckets to protect the flour from light.
If OFSP is sliced and subjected to four different treatments;
  1. Slicing while leaving the potatoes in open air
  2. Slicing and immersing the chips in water
  3. Slicing and immersing the chips in water mixed with sodium meta bisulphite
  4. Un- peeling the roots followed by slicing
  5. Steaming the potatoes for 25 minutes before slicing and drying
Treatment i, the chips will brown even before putting them in the drier, the flour made from the dried chips subjected to this treatment will be discolored due to oxidation. The orange color will not be pronounced and the flour will have a brown coloration.

Treatment ii, the orange colour leaches into the water and the flour made from these chips is nearing to white; the smell of the OFSP will though still pronounced. However the vitamin A is fat soluble and will not be lost in the soaking water

Treatment iii; chips immersed in water with Meta bisulphite will retain the orange color. The flour made from these chips will be most attractive.

Treatment IV; the peel of OFSP is proved to be rich in nutrients, however on drying the peel will tend to blacken and the black substances will also be manifested in the flour which  will makes the flour unattractive.

Treatment v; Steaming the potatoes for 25 minutes before slicing and drying will retain more orange color and hence the carotenoids as compared to slicing and drying without steaming. Slicing the potatoes and drying the potatoes immediately will retain as much carotenoids as pre-steaming. Therefore we prefer slicing and drying without steaming because it saves energy and it’s convenient in terms of labor. The flour will also keep better than the fresh potatoes.

Potential Products that Can Be Made From OFSP Flour

The products that can be made from this OFSP flour included; cakes, biscuits, composite flour, buns, cookies and doughnuts.
1.      Biscuits
·         125g   Orange fleshed sweet potato flour
·         125g     Wheat flour
·         3.75g   Baking powder
·         50g   sugar
·         80g   margarine
·         1 egg
·         100ml water
Procedure to flow
a)      Sieve the dry ingredients in a bowl to trap air and to ensure uniform mixing i.e. wheat flour, OFSP flour, baking powder and sugar.
b)      To the mixture of dry ingredients above, rub in the margarine until crispy.
c)      Add water a little at a time only to ensure that all the dry ingredients are lightly soaked.
d)     Knead the dough until its smooth and non sticky.
e)      Roll the dough on a floured flat surface to a thickness of 0.5cm thickness.
f)       Cut the dough into shapes using biscuit cutters.
g)      Put the cut biscuits on a well greased tray and bake in an oven pre-heated at 1500c. Bake for 20 minutes.
h)      Remove from the oven if the biscuits turn lightly brown and leave to cool before packaging.

2.      Orange fleshed sweet potato cakes
·         700g wheat
·         300g OFSP flour
·         500g sugar
·         500g fat
·         8 eggs
·         100g baking powder.
·         500 ml milk
Procedure (makes 24 cakes)
a)      Cream the sugar with the margarine in a bowl until the mixture is fluffy with a creamy colour.
b)      Mix separately the dry ingredients i.e. OFSP flour, wheat flour, and baking powder.
c)      Beat eggs separately until fluffy
d)     Add the eggs a little a time while beating at a high speed to form a smooth un-broken mixture.
e)      Fold in the flour mixture using a ladle and add milk a little at a time until the mixture is smooth, and soft with a dropping consistency.
f)       Grease the baking tins.
g)      Put 1table spoonful into each of the greased tins.
h)      Bake the dough in a hot oven pre-heated at 180oc until golden brown. This will take about 30 minutes.
i)        Remove from the tins and place on a rack to cool.

Cost calculation for cakes




wheat flour

OFSP flour

baking powder





film paper


2 people

1 person



1 packet holds 2 cakes sold at 1800shs

24 cakes make 12 packets

12,824 makes 24 cakes i.e. 12 packets

1 packet costs 12,824/12 = 1068.67

profit per packet= 1800-1068.67 which is 731.33

Profit from 1 batch of production = 731.33 x 12 which is 8775.96

3.      Composite flour for Porridge
·         150g OFSP
·         350 soy flour
a)      Mix the OFSP flour with the soy flour and sieve to ensure uniform mixing.
b)      Pack in air tight polythene bags and protect against wetting

Cost calculations per pack
cost calculations for composite flour

OFSP flour
soy flour
Milling cost
primary package
secondary package





1 packet of flour costs 2800 shs

cost of production is 2300 per packet

profit per unit is 2800-2300 = 500Ugx

4.      Doughnuts
·         1.5g active dry yeast
·         25g lukewarm water
·         150mls lukewarm milk
·         50g white sugar
·         1g salt
·         1 egg
·         34g margarine
·         150g OFSP flour
·         350g wheat flour
a)      Sprinkle the yeast over the warm water, and let stand for 5minutes, or until foamy.
b)      In a large bowl, mix together the yeast, milk, sugar, salt, eggs, shortening, and half the flour cups of the flour. Stir with a wooden spoon. Beat in remaining flour, until the dough no longer sticks to the bowl. Knead for 5 minutes or until smooth and elastic. Place the dough into a greased bowl, and cover. Set in a warm place to rise until double. Dough is ready if you touch it, and the indention remains.
c)      Turn the dough out onto a floured surface, and gently roll out to 0.5 inch thickness. Cut with a floured doughnut cutter. Let doughnuts sit out to rise again until double. Cover loosely with a cloth.
d)     Heat oil in pan to 1750c. Slide doughnuts into the hot oil using a wide spatula. Turn the doughnuts over as they rise to the surface. Fry the doughnuts on each side until golden brown. Remove from hot oil, to drain on a tray lined with a paper.

5.      Buns
·         60g OFSP flour
·         200g Wheat flour
·         20g sugar
·         2.5g salt
·         1.875g active yeast
·         30g margarine
·         1ml cooking oil
·         Adequate warm water
a)      Mix the yeast and a little sugar in a little lukewarm water. Leave for 5 minutes to activate the yeasts until foamy.
b)      Mix the dry ingredients together in a bowl i.e. OFSP flour, sugar, salt and wheat flour.
c)      Add and rub margarine into the dough and then mix.
d)     Make a well in the dough mixture and add oil, then mix.
e)      Add the yeast solution to the mixture a little at a time.
f)       Add some warm water a little at a time, while mixing and kneading the dough until it is smooth, non sticky and elastic.
g)       Put the dough in greased plastic bag ad leave it to rise for one hour.
h)      Punch the dough down and knead the dough again to remove air.
i)        Divide the dough into small portions of the desired bun size.
j)        Mould the dough portions into small balls and put and put on a greased baking tray.
k)      Place the balls about 0.5cm apart on a greased baking tray.
l)        Cover the balls with plastic sheet and leave the balls to swell until they almost double their size for 1 hour.
m)    Bake the balls in a hot oven pre-heated at 1800c until the top turns light brown. This will take about 20minutes.
n)      Remove the burns from the sheet and brush the top with fat.
e)      Leave to cool on a wire and pack in air tight packages.


Edison, S, 2000. Role expectations for tropical tuber crops in the new millennium in India: Net working concept. In: Potential of root crops for food and industrial resources.
FAO/WHO (Food and Agriculture Organisation of the United Nations and the World Health Organisation). 1992. Major issues for nutrition strategies: Summary.  Presented at the International Conference on Nutrition, FAO, Rome, Italy.
Proceedings of the twelfth symposium of the International Society for Tropical Root crops (ISTRC) held on Sept. 10-16, 2000, Tsukuba, Japan. Nakatani and Katsumi Komaki (eds).
Third Draft Technical manual for Sweetpotato Integrated Pest and Production Management Farmer Field Schools in East Africa,, June 2003. NRI, CIP FAO and KAARI Farmer Field Technical Team (key eds).
United Nations. 1992. Micronutrients. In: ACC/SCN second report on the World nutrition situation 1992. Chapter 3. ACC/ SCN, Washington, D.C., USA.