A GNA feature by Audrey Dekalu
The high value and significant source of dietary energy in Ghana makes yam a major stable food in most tropical countries.
wpid-Yams-at-the-Kokomba-market.jpgAcreage under yam cultivation in 2011 was estimated at 403,798Ha with corresponding production of approximately 5,855,138MT with 27,000 MT for export.
According to the Food Research Institute of the Council for Scientific and Industrial Research, (CSIR) per capita consumption of yam in Ghana is estimated at 42kg/annum making the country the third largest producer and consumption of the crop in the world, following Nigeria and Cote d’Ivoire.
Yam production in Ghana is concentrated largely in the Brong Ahafo, which makes up 37 per cent and the Northern, Upper East and Upper West regions constituting 34 per cent.
The crop is planted in February – April every year and harvested in August – November depending on the variety. Ideal rainfall condition for yam cultivation is about 1,000mm annually and spreads over five months.
However one of the major problems with yam is how to find simple methods to prolong the dormancy period of tubers after harvesting.
Low temperatures (15?C) together with fungicide treatment or ionizing radiation (0.08 – 0.12 KGy) have been reported to prolong the storage duration of yam.
Unfortunately there is lack of success in prolonging dormancy effectively by the application of sprout suppressant chemicals such as those widely used for potatoes.
A likely reason for this is that for yam, sprouts are not formed until a late stage of dormancy and they originate from beneath the periderm, thus protected from the effects of such treatment.
However under an EU funded project in collaboration with CSIR -Food Resources Institute (FRI) and Natural Resources Institute (NRI) of University of Greenwich UK, with focus on making gains from losses of roots and tubers like yam and cassava, a more promising approach to prolong dormancy and increase storage life has been introduced.
It is done through the application of plant growth regulators known as Gibberellic acid (GA3), which is well known to induce dormancy in the tubers.
The technologies were developed under work package two and disseminated under work package seven of the GRATITUDE project for agricultural institutions, agriculturist, agricultural professionals, agricultural students and agricultural research institutes is to enable further dissemination to yam and cassava farmers.
The project is being run in Ghana, UK, the Netherlands, Nigeria, Thailand and Vietnam.
The technology developed by researchers- Dr Charles Tortoe, Mr Solomon Dowuona and Dr Nanam Tay Dziedzoave of the CSIR-Food Research Institute select freshly harvested mature yam tubers and cleans the dirt.
Dr Tortoe, explained that the apical portion (head) of the clean tuber is then dipped in a preparation of 600ppm potash solution of burnt cocoa pod in one litre(1000ml) of water for two minutes after which it is removed and stored in improved yam barns.
This technology has addressed post-harvest problems with yam in two different ways as direct prevention of losses or modification of the storage environment.
Both ionization and cool storage reduce post-harvest losses to a negligible level, due to the almost complete inhibition of sprouting and a decrease in respiration.
However, the high cost of the techniques make them not feasible in West Africa due to high costs and the need for high-tech equipment.
Other methods have been direct prevention of losses by using pesticides and other pre-storage conditioning as in curing.
In view of the influence of sprouting on post-harvest losses, efforts have been made to prolong dormancy by applying sprout regulators such” as potash to nib the problem in the bud.?
Yam is a member of the Dioscoreae family. Depending upon the yam variety, of which there are about 200, its flesh may be of varying colours including white, ivory, yellow or purple while its thick skin may either be white, pink or brownish-black.
Its shape is long and cylindrical, oftentimes having offshoots referred to as “toes”. Its exterior texture is rough and scaly. Yam has a very starchy and slippery texture and when cooked, it will either be creamy or firm, depending upon the variety.
Its taste is earthy and hardy, with most varieties having minimal, if any, sweetness. Specific types of yam include Dioscorea alata (Hawaiian yam), Dioscorea batatas (Korean yam) and Dioscorea esculenta (sweet yam).
Yam is a good source of energy; 100 g provides 118 calories. Its crunchy edible part chiefly composed of complex carbohydrates and soluble dietary fiber.
Dietary fiber helps reduce constipation, decrease bad (LDL) cholesterol levels by binding to it in the intestines and lower colon cancer risk by preventing toxic compounds in the food from adhering to the colon mucosa.
Additionally, being a good source of complex carbohydrates, it regulates steady rise in blood sugar levels, and, for the same reason, recommended as low glycemic index healthy food.
The tuber is an excellent source of B-complex group of vitamins. It provides adequate daily requirements of pyridoxine (vitamin B6), thiamin (vitamin B1), riboflavin, folic acid, pantothenic acid and niacin. These vitamins mediate various metabolic functions in the body.
Its fresh root also contains good amounts of anti-oxidant vitamin; vitamin-C. It provides about 29 per cent of recommended levels per 100 g. Vitamin C has some important roles in anti-aging, immune function, wound healing, and bone growth.
Yam contains small amounts of vitamin-A, and beta-carotene levels. Carotenes convert to vitamin A in the body. Both these compounds are strong antioxidants. Vitamin A has many functions like maintaining healthy mucus membranes and skin, night vision, growth and protection from lung and oral cavity cancers.
Further, the tuber is one of the good sources of minerals such as copper, calcium, potassium, iron, manganese, and phosphorus. 100 g provides about 816 mg of Potassium.
Potassium is an important component of cell and body fluids, which helps control heart rate and blood pressure by countering hypertensive effects of sodium. Copper is required in the production of red blood cells. Manganese is used by the body as a co-factor for the antioxidant enzyme, superoxide dismutase. Iron is required for red blood cell formation.
According to the World Health Organisation ,under nutrition which includes foetal growth restriction, stunting, wasting and deficiencies of vitamin A and zinc, along with suboptimal breastfeeding; is the underlying cause of death in an estimated 45 per cent of all fatalities among children under five years.
The proportion of underweight children in developing countries has declined from 25 per cent to 15 per cent between 1990 and 2012.
This rate of progress is close to the rate required to meet the Millennium Development Goals (MDGs) target, however improvements have been unevenly distributed between and within different regions.
Stunting in children less than five years of age has decreased globally from 40 per cent to 25 per cent over the same period.
Eating more yam would surely promote the MDGs especially goal one of halving the proportion of people who suffer from hunger.



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