R. A. Mustapha and G.A. Ogundahunsi
Department of Nutrition and Dietetics
T. A. Ibrahim
Department of Food Science Technology, Rufus Giwa Polytechnic, Owo


The effects of cooking utensils (Clay pot, Iron pot, and Stainless steel pot) on the iron contents of four common staple foods in Nigeria were investigated. Chemical and instrumental methods to test the amount and the effect of cooking utensils on iron content of these four food groups of Cereal (Zea mays:maize),Tuber(Dioscorea sagittifolia:yam), Legume(Vigna unguiculata:cowpea) and Fruit(Musa paradisiacal:plantain) was carried out using Atomic Absorption Spectrophotometer (AAS).Result shows that the cooking utensils reduced or increased the level of iron in some of the food samples. Iron in Zea mays and Vigna unguiculata increased by 0.04 +0.01 and 0.05+0.01mg/100g of food sample cooked in cast iron pot respectively. There was reduction of iron content ranging from 0.01- 0.77mg/100g of the sample of all staple foods cooked in clay and stainless steel pot .Good cooking utensils will go a long way to conserve iron loss during cooking and improve iron intake from the staples, thereby reducing iron deficiency aneamia among the various vulnerable groups in the population. Women of reproductive age
need to be educated on cooking practices that affect micronutrients loss and should be encourage on the importance of regular intake of iron supplements.

Keywords: Cooking utensils, staple foods, iron, iron deficiency anaemia


Globally over 600 million people particularly in developing countries were affected by iron deficiency. Iron deficiency is the most common cause of aneamia and insufficient dietary iron intake are the most common causes of iron deficiency. However, infants, children and women of reproductive age were the most vulnerable to this disease (Kennedy et al, 2003; UNSCN, 2004).

Iron deficiency aneamia among women is associated with an estimated 111,000 maternal death worldwide yearly. The prevalence among this group in Nigeria ranges between 24 to 48 %( FMH, 2005; FAO, 2003). The deficiency is usually not due to the absolute lack of iron in there staple food or diets but rather to the processing methods adopted and or poor bioavailability of iron in these staple foods (Latunde-Dada, 1993). Even food staples that have adequate amount of this nutrient were either affected by losses during processing or increment from processing surfaces. Thus predisposing individual to unhealthy risk factors to disease conditions from iron deficiency or iron overdose (Wardlaw and Hampl, 2007; Chalton et al, 1973).

The majority of the population of most developing countries such as Nigeria relies on plant foods to provide their nutrients need. Staple cereals such as maize, millet, and sorghum supply an average 60% of dietary iron while staple roots and tubers only supply 24%.However, the availability of iron from these plant staples is very low (Hallberg,1981; Lee and Clydesdale, 1981). Other studies had shown that traditional processing procedures affect the availability of iron, sensory properties and consumer acceptance of wide range of foods prepared in iron cookware (Park and Brittin, 2000; Lee and Clydesdale, 1981).
Recently, a significant result was obtained from the study of Geerling et al (2003).Iron and aluminium cooking pots were used in cooking foods to determine their effect on consumers hemoglobin status of rural adults Malawian with malaria infection. Results shows that mean heamoglobin change was significantly increased after six weeks of consumption of foods from the iron pots. In Nigeria clay pots, stainless steel pots, aluminium pots and iron cooking pots were the most widely used utensils both in urban and rural communities. Information on the effect of iron content on foods cooked in some of these utensils are minimal and inadequate. Therefore this study is designed to investigate the effect of cooking utensils on the iron contents of maize (Zea mays), yam (Dioscorea sagittifolia), cowpea (Vigna unguiculata) and plantain (Musa paradisiacal) which are common staples in Nigeria.

Materials and methods

Sources and treatment of raw materials
Samples of four food staples were selected from food group comprising white yam (Dioscorea sagittifolia) from tubers, maize (Zea mays) from cereal, cowpea (Vigna unguiculata) from legumes and plantain (Musa paradisiacal) from fruits. Two of the food samples (Maize and cowpea) were bought in dry form while the yam and unripe plantain were purchased fresh in early November, 2007 from open market in Owo, Ondo State.

After washing to remove foreign and extraneous materials, one medium size yam and two medium size plantain were peeled and sliced to equal sizes. Four cups each of maize grains and cowpea were cleaned to removed stones and dirt. The cleaned maize grain and cowpea were washed. All samples were divided into four portions each. One portion of each food samples were cooked in cast iron pot, stainless pot and clay pot. They were cooked at temperature of 100 ºC for 1hr until soft for human consumption. Samples were drained for ashing. The remaining raw portions from each food sample were coded for analysis                                                                                                                         
Chemical and instrumental analysis
 The ash content of samples was determined by using Association of Analytical Chemist method (AOAC, 1995). Ash was estimated by weighing 3g of each sample into tarred porcelain crucibles. It was incinerated at 600 ºC for 6hr in ashing muffle furnace.

Iron estimation was carried out using wet digestion of the ashes of samples with nitric acid and perchloric acid. Iron was determined spectrophotometrically (Essien et al, 1992) by using Buck 200 atomic absorption spectrophotometer (Buck scientific Norwalk).The result obtained was compared with absorption standards of this mineral. All analyses were performed in triplicates.

Statistical analysis
The procedures of Steel and Torrie (1991) were used to calculate the means and standard
deviation for all the values.


Table 1: Cooking Utensils and their effects on iron content (mg/100g) of staple foods.

                                                Iron Content (mg/100g Sample)

Parameters   Dioscorea Sagittifolia  Zea mays   Vigna unguiculata   Musa paradisiacal
                        (White yam)              (Maize)          (Cowpea)                 (Plantain)


Raw foods      0.46+0.01                    2.50+0.01        4.08+0.04                    3.14+0.06


Cooked in       0.41+0.02                    2.48+0.02        3.31+0.07                    2.60+0.01
Stainless pot

Cooked in       0.47+0.02                    2.54+0.00        4.13+0.02                    3.21+0.20
Cast iron pot

Cooked in       0.45+0.01                    2.45+0.01        3.54+0.03                    2.81+0.05
Clay pot
* Values are means of triplicate determinations + standard deviation (SD)


Table 2: Proximate Change in Iron content (mg/100g) of staple foods after cooking

                                                Change in Iron Content (mg/100g Sample)

Parameters   Dioscorea Sagittifolia Zea mays   Vigna unguiculata   Musa paradisiacal
                        (White yam)              (Maize)          (Cowpea)                 (Plantain)


Cooked in        ↓0.05+0.01                 ↓0.02+0.00      ↓0.77+0.04                  ↓0.54+0.01
Stainless pot

Cooked in       ↑0.01+0.00                  ↑0.04+0.01      ↑0.05+0.02                  ↑0.07+0.02
Cast iron pot

Cooked in       ↓0.01+0.00                  ↓0.05+0.02      ↓0.54+0.01                  ↓0.33+0.02
Clay pot
* Values are means of triplicate determinations + standard deviation (SD). ↓=decreased in iron content.↑=increase iron content.                          

Results and discussion                                                                                               
Presented in Table 1 above are the results of iron content of four staple foods cooked in stainless steel pot, cast iron pot, and clay pot. From the result, it was found that iron content of raw foods were 0.46mg(yam) 2.50mg (maize) 4.08mg(cowpea) and 3.14mg (plantain). Iron content of all these food varied from values obtained in food composition tables (Platt, 1975; FAO, 1968).This may probably be due to variety of the foods that were analyzed, soil conditions and maturity at harvest of the various food samples. The result also shows that cowpea has the highest amount of iron at raw and after cooking. Although appreciable amount was found in maize and plantain. This means that adequate intake of these three staples can supply over 40% RDA of the needed iron per day by an adult. However, irons from food of plant origin are less bioavailable to human nutrition compare to iron from animal food source. In table 2, result shows that quite appreciable quantity of iron were loss through cooking in clay and stainless steel pot which ranges between 0.01-0.77mg/100g of food samples cooked. Although normal recommended daily intake of iron for adult males and females were 8 and 18mg/day respectively. Cumulative loss of iron in utensil such as clay pot during the various daily cooking of foods can lower this value which can lead to iron deficiency for consumers of such foods. It shows that consumers of foods cooked in these types of utensils are likely to be prone to iron deficiency aneamia.                                             

However, a range of 0.01-0.07mg/100g of food samples cooked in cast iron was also discovered. This amount is appreciable enough to boost iron intake in addition to iron from other food sources, thereby making consumers of foods cooked in this utensil meeting the daily recommended intake. These findings are consistence with Cheng et al (1991) results.  It was found that processes like washing, dicing and peeling had less significant effect on iron content of edible portion of the staple foods cooked in the three utensils. However, it was reported by Latunde-Dada (1993) that significant losses of iron occur during the processes of blanching and squeeze washing of vegetables which are common among Nigeria household food handlers.      The iron losses during cooking of maize and cowpea were found to be minimal compared to other staple foods. This might be because the hull of these two staples conserved the leaching of iron into the cooking water. Therefore peeling and dehulling food staples may have a negative effect on iron and other micronutrients content during cooking.                                                                        
Conclusion and recommendations
It is shown from this study that some cooking pots contribute to iron content of staple foods cooked in this utensils. There is need for in-depth research to further probe into this area of study so as to throw more light this micronutrient which is of high importance to human health. Nigerian women at household level need to be encouraged using utensils that will promote adequate iron intake and not utensils that can course iron overload to the consumer of those food cooked in them. Food handlers also need education on the effect of various processing procedure employed in the preparation of food that will lead to losses or conservation of micronutrients. Rural peasant women should be educated on the use of cast range of iron cooking pots and avoid preparation practices that reduce iron and other micronutrients loss from foods.Moreso, awareness should be created on the need to biofortified some foods with micronutrients that can easily leached into water through utensil inner surface like clay pot during the cooking period. This fact should be of high priority for dissemination among the nutritionist extension agents that are responsible to pass this to peasant rural women and food handlers in Nigeria. Therefore, good cooking utensils will go a long way to conserve iron loss during cooking and improve iron intake from the staples, thereby reducing iron deficiency aneamia among the various vulnerable group in the population. Women of reproductive age need to be educated on cooking practices that affect micronutrients loss and should be encourage on the importance of regular intake of iron supplements. 


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