- Top of page
- Experimental methods
Objectives To investigate the effect of cooking with an iron ingot on the iron content of several water and Cambodian food preparations.
Methods Various food and water samples were prepared, in replicate, in glass and aluminium pots with and without an iron ingot. The samples were subjected to iron content analysis using standard ICP–OES procedures.
Results Prepared with an ingot, the iron content was 76.3 μg iron/g higher in lemon water, 32.6 μg iron/g higher in pork soup and 3.3 μg iron/g higher in fish soup, than in the same foods prepared without an ingot. Acidity of the food samples was positively associated with iron leaching.
Conclusions Even when taking into account the low bioavailability of contaminant iron, approximately 75% of the daily iron requirement can be met by consuming 1L of lemon water prepared with an iron ingot. Its use may be a cheap and sustainable means of improving iron intake for those with iron-deficient diets.
Objectifs: Investiguer l’effet d’un morceau de fer dans la casserole pendant la cuisson sur la teneur en fer de l’eau simple et des préparations alimentaires cambodgiennes.
Méthodes: Différents échantillons d’aliments et d’eau ont été préparés en réplicas, dans des casseroles en verre et en aluminium avec et sans morceau de fer. Les échantillons ont été soumis à l’analyse de la teneur en fer en utilisant les procédures de la norme ICP-OES.
Résultats: Préparé avec un morceau de fer, la teneur en fer était de 76,3 μg/g plus élevée dans l’eau citronnée, 32,6 μg/g plus élevée dans la soupe de porc et 3,3 μg/g plus élevée dans la soupe de poisson, que dans les mêmes aliments préparés sans morceau de fer. L’acidité des échantillons d’aliments était positivement associée à la solubilisation du fer.
Conclusion: Même en tenant compte de la faible biodisponibilité du fer contaminant, environ 75% des besoins quotidiens en fer peuvent être atteints par la consommation de 1L d’eau citronnée préparée avec un morceau de fer. Son utilisation peut être un moyen bon marché et durable pour l’amélioration de l’apport en fer chez les personnes ayant une alimentation pauvre en fer.
Objetivos: Investigar el efecto de un lingote de hierro en la olla durante la cocción sobre el contenido de hierro del agua y de la comida preparada en Cambodia.
Métodos: Varias muestras de comida y agua se prepararon, en réplica, en ollas de vidrio y aluminio, con y sin un lingote de hierro. Las muestras fueron sujetas a un análisis de contenido de hierro utilizando los procedimientos estándares de espectroscopia de emisión óptica de plasma acoplado inductivamente (ICP-OES).
Resultados: Al prepararse con un lingote, el contenido de hierro era de 76.3 μg hierro/g mayor en agua con limón, 32.6 μg hierro/g mayor en sopa de cerdo, y 3.3 μg hierro/g mayor en sopa de pescado, que en las mismas comidas preparadas sin un lingote. La acidez de las muestras de comida estaban asociadas de forma positiva con la filtración de hierro.
Conclusiones: Aún teniendo en cuenta la baja biodisponibilidad del hierro contaminante, aproximadamente un 75% del requerimiento diario de hierro puede alcanzarse consumiendo 1L de agua con limón preparada con un lingote de hierro. Su uso puede ser una forma barata y sostenible de mejorar la ingesta de hierro entre aquellos con dietas deficientes en hierro.
- Top of page
- Experimental methods
Iron deficiency (ID) that causes iron deficiency anaemia (IDA) is the most common micronutrient deficiency. Globally, ID affects more than 3.5 billion people, the vast majority of whom live in the developing world where access to conventional medicine is limited and costly, and plant food is the staple (Hurrell 1997). Women and children are particularly burdened by the disorder: According to WHO, anaemia affects 66.4% of pregnant and 57.3% of non-pregnant women of reproductive age (McLean et al. 2008). Because the health and economic effects of anaemia can be severe and often irreversible, there is a great need for a cost-effective prevention and control strategy (McLean et al. 2008).
Despite this advantage, iron cooking equipment is generally not well accepted because it is prone to rusting, heavier, more difficult to clean and of poorer manufacturing quality than other pots and food left in the pot overnight is perceived to change in taste and appearance (Geerligs et al. 2003). Aluminium pots are perceived as easier to clean and less expensive than iron pots; thus, they are more common in many countries, including Cambodia.
Previously, we conducted a community trial to determine the long-term effectiveness of cooking with an iron ingot. Study participants were instructed to place an ingot in the daily cooking pot when preparing soup and/or when boiling drinking water to which citrus juice was added (Charles et al. 2011). Participants who cooked with an iron ingot had a lower prevalence of anaemia 3 months after the start of the trial than women who cooked without the ingot (Charles et al. 2011).
Although field research is needed to assess the value of an intervention under different settings, laboratory studies are also required to see whether, and to what extent, iron is leached from the ingot. The aim of the current study was to determine the iron content of several water/food preparations, including two commonly consumed Cambodian soups, when prepared in glass and aluminium pots that contained an iron ingot during the cooking process. The meals were selected after qualitative field work that identified commonly used recipes.
- Top of page
- Experimental methods
The iron content of five water or food preparations, cooked in two types of pots either with or without an iron ingot, was determined. Three batches of water or food were prepared for each pot type and ingot combination, from which three samples from each batch were taken for iron content analysis. All samples were prepared on the same day, and the same ingot was used for each replicate batch. The pH of each sample was recorded prior to iron content analysis (Accumet Basic AB15, Fisher Scientific Intl., Hampton, NH, USA).
The iron ingots were designed and produced using readily available scrap iron at a factory in Kandal Province, Cambodia. To enhance compliance to the treatment regime at the household level, the ingots were designed to resemble a local fish species that is considered lucky in village folklore (Figure 1). This design with its relatively flat profile also combined maximal surface area (142.5 cm2) with light weight (177.5 g). To ensure safety of use, quality assurance tests using acidified water (HCl to pH≈2) were conducted to determine the presence of metal contaminants. A random sub-sample of the ingot batch was boiled in varying aliquots of distilled water (from 0.5l to 3l) over varying time periods (from 10 min to 2 h). These samples were then analysed appropriately for manganese, arsenic, nickel, mercury, copper, zinc, lead, iron and magnesium. All samples met WHO drinking water quality standards (Gorchev & Ozolins 1984).
Figure 1. Iron ingot designed to resemble a species of Cambodian fish for use during preparation of water and food samples (surface area, 142.5 cm2; mass, 177.5 grams).
Download figure to PowerPoint
Aluminium pots are most commonly used throughout Cambodia and were therefore selected for this study (Thermalloy Aluminium®, Browne Halco Inc., Union, NJ, USA). However, metal contaminants may be leached from the metal pot; therefore, we also used a glass pot for comparison (CorningWare®, World Kitchens Inc., Reston, VA, USA). Both pot types had 1.5l capacity, were uninsulated, flat-bottomed and had one side handle and a lid. Two identical, unused glass pots and two identical, unused aluminium pots were used. One glass pot and one aluminium pot were chosen for use with the iron ingot, resulting in four experimental set-ups: (i) glass pot (control), (ii) glass pot with iron fish, (iii) aluminium pot (control) and (iv) aluminium pot with iron ingot.
Five food preparations were used in the experiment: distilled water, weakly acidic water (lemon water), saline water and two commonly consumed Khmer soups (Table 1) prepared according to recipes from a rural Cambodian village (personal observation, CVC). The first soup was lemon fish soup (sngor chuok trey), and the second was sweet and sour pineapple and pork soup (salor machu manor nung s’ung chrouk). All foods were prepared using non-metal utensils. Where possible, fresh, authentic ingredients from a large Asian market in Toronto were used. After weighing out the correct portions of each ingredient, a 1000-ml sample was prepared in each pot. The ingredients for the meals were purchased at the same time, and all experiments were performed within 48 h of purchasing the ingredients.
Table 1. Required ingredients and sources for 3 different water preparations and 2 different Khmer soups
|Ingredient||Fish Soup||Pork Soup||Distilled Water||Lemon Water||Saline Solution||Source|
|Distilled water||1000 ml||1000 ml||1000 ml||1000 ml||1000 ml||Canadian Springs, Toronto, Canada|
|Lemon juice concentrate||–||–||–||5 ml||–||No Name Brand®, Loblaws Inc., Toronto, Canada|
|Non–iodized, coarse salt||–||2.5 ml||–||–||5 mg||Sifto Canada Corporation, Mississauga, Canada|
|Catfish||680 g||–||–||–||–|| |
|Pork riblets||–||455 g||–||–||–|| |
|Jasmine Rice||30 ml||–||–||–||–|| |
|Fresh pineapple||–||355 ml||–||–||–|| |
|Green onion||2 stalks||–||–||–||–|| |
|Bean sprouts||–||475 ml||–||–||–|| |
|Tomato||–||240 ml||–||–||–|| |
|Sweet basil||120 ml||–||–||–||–|| |
|Asian coriander||120 ml||–||–||–||–|| |
|Fish sauce||15 ml||30 ml||–||–||–||Squid Brand, Thai Fishsauce Factory Co. Ltd., Bangkok, Thailand|
|Fresh tamarind paste||–||15 ml||–||–||–|| |
|Lemon grass||1 stalk||–||–||–||–|| |
|Garlic||–||2 cloves||–||–||–|| |
|Fresh lemon||Juice of 1||–||–||–||–|| |
|Black pepper||1.25 ml||1.25 ml||–||–||–||Kirkland Signature, Costco Wholesale Canada Ltd., Ottawa, Canada|
|Sugar||7.5 ml||30 ml||–||–||–||Red Path Sugar Ltd., Toronto, Canada|
|Fresh chilli pepper||1 small||2 small||–||–||–|| |
After preparing each sample batch, the cooking pots were cleaned with water and a plastic scouring pad and dried with a paper towel. The pots were then rinsed with distilled water and left to air-dry. All samples were cooked on identical, previously unused electric burners (Better Chef Better Results®, Vernon, CA, USA).The water samples and soups were each cooked on the maximum setting of the burner (120 °C) for 20 min. The cooking time mimicked conditions in the community as determined in consultation with residents of a rural Cambodian village. In the pilot study, we had instructed participants to use the iron ingot when cooking for at least 10 min (Charles et al. 2011); but we later observed that participants typically cooked fish for 20 min or longer (personal observation, CVC).
For analysis, 15-ml samples of the boiled waters and the liquid portion of each soup were extracted from the pot using a glass eye dropper fitted with a paper filter to prevent sampling of food particles. To account for potential bias from extraction of only the liquid portion of the soup, three replicates from each batch were collected, weighed and analysed; there were no significant differences in the weight of the samples, suggesting that they were comparable.
Inductively coupled plasma optical emission spectroscopy (ICP–OES) was used for analysis of total iron content of each prepared sample. All samples first underwent microwave-assisted digestion. Next, they were brought to volume using Nanopure water, and then, the clear extract supernatant was removed and analysed in duplicate without further processing. Blanks, consisting of deionized water, reagents and SRM 8435, were subjected to similar sample preparation and analytical procedure for quality control. The Division of Laboratory Services at the University of Guelph performed all elemental analyses.
The iron content of the water and food preparations was averaged over the replicate samples to determine the mean and standard deviation of the iron content for each. The lower detection limit for the method of analysis was <0.40 μg iron/g. Observations with a result of <0.40 μg iron/g were replaced by 0.20 μg iron/g for statistical analysis. Total iron content in each sample was regressed on the putative factors using linear regression. The factors examined comprised of the use of the iron ingot; pot type; inclusion of an acidifying agent (for the water samples); fish soup vs. pork soup. For the purposes of this experiment, control samples are defined as those which were prepared without an iron ingot present during the cooking process.
- Top of page
- Experimental methods
Iron deficiency and IDA pose a severe public health problem in Cambodia (McLean et al. 2008). The most recent estimates suggest that 61.9% of pre-school-aged children, 44.3% of non-pregnant women and non-lactating women, 53.6% of lactating women and 57.1% of pregnant and lactating women are anaemic (McLean et al. 2008). This study demonstrates that cooking with an iron ingot, regardless of cooking vessel, increases the iron content of water and food preparations. Lemon water and two varieties of soup cooked with an iron ingot contained more iron than ingot-free preparations (P-values < 0.001). In distilled water and saline, the iron ingot made no difference, highlighting the importance of acidity in iron leaching. Our previous research showed that the iron ingot is an acceptable and at least partially effective treatment (Charles et al. 2011). This study confirms the potential impact of iron ingots as an adventitious iron source.
Studies on the influence of iron pots and utensils on iron content in a variety of foods have consistently shown that foods cooked in iron pots and/or with iron utensils have significantly higher iron content than foods cooked with non-iron equipment (Brittin & Nossaman 1986; Cheng & Brittin 1991). Both crude and available iron content appear to be positively influenced by iron cooking equipment: Foods cooked in iron pots had around twice as much crude iron and five times more available iron in meat and vegetable preparations than controls (Adish et al. 1999). Liu et al. (1990) reported an estimated increase in iron intake of about 14.5 mg for adults and 7.4 mg for children when iron pots were used. Continuous use of adventitious iron utensils has negligible effect (P < 0.05) (Cheng & Brittin 1991). The effect of life usage of the ingot has not been determined but should be investigated in a field trial over several years.
Iron requirements vary according to age, gender, menstrual status and pregnancy status (Table 3) (Herbert 1987). Because iron bioavailability is dependent on a number of factors, most guidelines for dietary iron are based on an estimate of 10% absorption from total dietary iron (Borigato & Martinez 1998; Herbert 1987). Based on the estimated bioavailability, greater percentages of daily iron requirements are met by drinking water and soup samples prepared with the iron ingot. Importantly, based on a daily water intake of 1.0 l, approximately 76.5% of the iron requirements are met in children, adult males and post-menopausal women. Although the approximate iron contribution of the Khmer soup appears low (Table 3), the soup is only one meal per day, and together with the iron contribution from lemon water, daily iron requirements could easily be met. Water and soup intake may vary among individuals, and in particular, children may consume less than adults; thus, the overall benefit may vary accordingly.
Table 3. Iron requirements and iron intake when preparing water and food samples with an iron ingot
|Group||Iron Requirements (mg per day)||Lemon Water (1.0 l per day)||Khmer Fish Soup (0.5 l per day)||Khmer Pork Soup (0.5 l per day)|
|Fe||Daily %*||Fe||Daily %*||Fe||Daily %*|
|Children (1.0–9.9 years)||10||76.5||76.5||1.7||1.7||17.3||17.3|
|Males (10.0–17.9 years)||12||76.5||63.8||1.7||1.4||17.3||14.4|
|Males (18.0 + years)||10||76.5||76.5||1.7||1.7||17.3||17.3|
|Females (10.0–49.9 years)||15||76.5||51.0||1.7||1.2||17.3||11.5|
|Females (50.0 + years)||10||76.5||76.5||1.7||1.7||17.3||17.3|
Iron overload owing to increased dietary iron has only been recognized in some areas of sub-Saharan Africa; therefore, the risk of overload resulting from the use of the iron ingot is limited (Gordeuk et al. 1992). However, the long-term effect of the use of the iron ingot or other iron utensils should be assessed.
The effectiveness of this supplementation technique depends on two factors: the amount of iron that is leached during cooking and the amount of leached iron that is absorbed. Both factors are, in turn, influenced by a number sub-factors (Figure 2). Iron that is leached from both the iron ingot and iron cooking equipment is referred to as contaminant iron (Harvey et al. 2000). Contaminant iron sources are non-haem in nature and are typically in either the ferrous (Fe+2) or ferric (Fe+3) form as these are the only oxidation states that are stable in an aqueous medium (Hurrell 1984). In the presence of oxygen, ferrous iron is rapidly oxidized to the ferric form. Thus, the form of iron presented to the body depends on both the iron source(s) and the degree of oxidation during cooking and/or storing the food. We do not know what type of iron the ingot adds, which makes it difficult to determine how the leached iron varies in solubility and affinity for reaction with other compounds, specifically the enhancers and inhibitors of iron absorption.
Iron leaching is dependent on the acidity, moisture content and cooking time of the food preparation. More acidic, moister foods and foods cooked longer have higher iron content than controls when cooked with an iron ingot or pot (Brittin & Nossaman 1986; Kollipara & Brittin 1996). Iron incorporation into food also depends on the frequency of use of an iron utensil or ingot (Brittin & Nossaman 1986). During the first use, more iron leaches than at later uses, so the iron ingot would be most effective during the first few uses. The effective lifespan of the ingot remains to be determined.
After consumption of dietary iron, an unknown percentage of the mineral joins the common pool of non-haem iron while the rest is not readily absorbed. In the end, only 1–25% of the iron from the non-haem iron pool is absorbed (Harvey et al. 2000). This percentage depends, among other factors, on meal constituents (presence/absence of iron absorption inhibitors and enhancers) and the size of the iron stores.
Our findings correlate well with the previous research on the iron content of foods prepared with iron pots: More acidic, moister foods cooked in iron vessels have a higher iron content than controls. Lower pH correlates well with higher iron content. Distilled water with a small amount of lemon juice had a pH of 3.20 and leached the most iron from the ingot. The two soup preparations were also acidic: the fish soup had a pH of 4.45 and the pork soup had a pH of 4.58. Both had significantly higher iron concentrations than controls. Pork soup contained significantly more iron than fish soup (Table 4), which may be accounted for by the higher iron content of pork meat (Kongkachuichai et al. 2002). Conversely, the least acidic preparations had the lowest iron concentrations, even when cooked with an iron ingot: Distilled water had a pH of 7.06, while saline had a pH of 5.80.
Table 4. Predicted increase of iron content after cooking soup, water or acidified water with an iron ingot
|Factor||Coefficient (β)||Standard Error of β||P-value|
|Glass pot vs.aluminium pot||2.8||6.43||0.67|
|Lemon water with ingot vs. lemon water||76.3||7.21||<0.0001|
|Fish soup with ingot vs.fish soup||3.3||0.94||0.006|
|Pork soup with ingot vs. pork soup||32.6||4.83||0.0001|
|Pork soup with ingot vs. fish soup with ingot||29.4||4.92||0.0001|
|Lemon water with ingot vs. distilled water with ingot||76.3||7.21||<0.0001|
|Lemon water with ingot vs. fish soup with ingot||73.0||7.27||<0.0001|
|Lemon water with ingot vs. pork soup with ingot||43.7||8.68||0.0005|
In the preliminary community trial, participants were encouraged to cook with the ingot for a minimum of 10 min per day, preferably when preparing soup (Charles et al. 2011); the use of the ingot when boiling water was given as an alternative only. In the current experiment, water with lemon juice was the most acidic preparation (pH = 3.20) and accordingly had the highest iron content when prepared with an ingot. Thus, instructions for use should be modified as it is now clear that benefit is maximized when using the iron ingot to prepare boiled drinking water with lemon, followed by preparation of acidified soups. Boiled drinking water would be consumed in greater quantities than soup; thus, an individual would benefit more using the ingot to prepare drinking water. Both boiled drinking water with citrus juice and soup are particularly advantageous for two reasons: the acidity of these preparations is important for maximizing iron leaching, and both are acidified with ascorbic acid, an enhancer of iron absorption (Hurrell & Egli 2010).
Iron deficiency and IDA in Cambodia constitute a severe public health problem requiring immediate attention from the government and organizations responsible for community health. The iron ingot and other interventions that utilize adventitious iron sources to improve iron intake may provide an alternative to the relatively costly and unsustainable supplementation programs currently in place. Importantly, the ingot was widely accepted by household members; it is cheap, lightweight and easy to use and therefore a good alternative to iron cooking pots (Charles et al. 2011). The ingot must undergo further testing in representative households and communities to determine both the efficacy and effectiveness of this possible preventive option.