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Energy expenditure on traditional activities by Nigerian women, monitored by Oxylog

E. C. Okeke. E. N. Etta. and D. O. Nnanyelugo

Abstract

This study was undertaken to evaluate the energy expended by Nigerian women in preparing two traditional foods from cowpeas, akara (fried paste) and moimoi (steamed paste), both by traditonal methods and using processed pea flour. Data were collected using a questionnaire, and energy expenditure was monitored with an Oxylog apparatus.

In making akara by the traditional method, a mean of 44.4 ± 1.5 kcal (185.5 ± 74 kJ) of energy was spent per kilogram of peas processed, as against 25.7 ± 0.6 kcal (1074 ± 2.8 kJ)/kg using pea flour. For moimoi, 276 ± 0.8 kcal (115.6 ± 3.3 kJ)/kg was spent by the traditional method, against 14.6 ± 1.5 kcal (61.2 ± 6.3 kJ)/kg using flour. While the overall energy cost of the methods using pea flour was significantly lower than the traditional methods, the energy cost of aerating the paste for making akara was almost 2.5 times as high as in the traditional method. This higher energy internsity is due to the slower solubilization of proteins in flour required to form and sustain foam. Longer soaking of the flour paste could reduce the energy required for aeration.

Introduction

Nutritionists as well as physiologists have studied the energy expenditure and intake of individuals involved in different work activities, particularly in men [1]. Data are lacking or limited, however, on the energy expenditure of women in different occupations and activities in Nigeria. In a project being conducted in collaboration with the University of Georgia in the United States, one mandate is to monitor the energy expended by women while making cowpea preparations.

Nigeria is the greatest consumer of cowpeas (Vigna unguiculata) in the world [2]. The bulk of the peas are cultivated as a pulse for human consumption. The seeds are a valuable and most prominent source of plant proteins in the diet of Nigerians. The peas are prepared and eaten in various forms: they can be boiled, dehulled or in the hull, and cooked into pottage, and can be eaten alone or with other foods such as rice, yams, corn, or gari. They can also be milled into flour or paste and used for delicacies such as akara (fried paste) or moimoi (steamed paste).

Traditionally, cowpea paste is prepared in households by the combined processes of wet dehulling, soaking, and wet milling. These processes are tedious, time-consuming, and labour-intensive. However, with improved technology, the paste can now be prepared from processed pea flour. The suitability of this flour as a starting ingredient in the paste is a subject of increasing scientific interest. During the preparation of akara, the paste is whipped to incorporate enough air to form a stable foam, which is a gas-in-liquid dispersion, ready for frying. The consistency and frying characteristics of the paste reconstituted from pea flour and the quality of the resulting akara balls are influenced by the processing techniques, the variety of pea, and the particle size distribution and hydration pattern of the flour [3].

In this pilot study we monitored the energy expended by women while preparing akara and moimoi by the traditional methods and using a pea flour developed under the Collaborative Research Support Program.

Materials and methods

Data collection and sample population

A validated structured questionnaire was administered by interview to 200 women selected randomly from the community of Nsukka for background data on their general food-consumption patterns. Twenty-five per cent of the women were in the age range 20-29 years, 63% 30-39 years, and the remaining 12% 40-49 years; 75% had elementary-school education and 25% had none.

A subsample of eight of the women participated in a study of their energy expenditure while preparing akara and moimoi. Their physical characteristics were measured by standard anthropometric methods. The sample was small because the study required the subjects to wear an Oxylog apparatus, as described below, throughout the process.

Nsukka lies at approximately 6°50' north latitude and 7°30' east longitude. The study was carried out in January and February, when the weather was hot and humid. The temperature ranges from 32.2°C maximum to 21°C minimum in these months, with an average daily relative humidity of 81.3% and an average daily sunshine duration of 6.1 hours. Mean rainfall for January and February is 15.5 mm. Rainfall determines the timing of the cultivation, planting, and harvesting of crops and controls the application of fertilizers and the selection of crop varieties. It also controls residents' occupations; for example, some people are migrant farmers in one season and traders in another.

The Oxylog apparatus

The Oxylog (P. K. Morgan, Kent, UK) is a portable instrument that measures pulmonary ventilation and oxygen consumption in humans [4]. It weighs 2.6 kg, measures 19 x 8 x 22 cm, and can be worn by a subject without restricting physical activity (figs. 1 and 2). The subject breathes in atmospheric air through a small turbine flowmeter that contains a thermistor. One cm³ of expired air per breath is pumped into a mixing chamber by an integral pump triggered by a fall in the inspiratory flow rate at the end of each inhalation. At the same time a similar-size sample of atmospheric air is drawn into a second mixing chamber.

Small samples of the contents of the two mixing chambers are analysed by two compact polaro-graphic oxygen sensors. The difference in the partial pressure of oxygen between the two samples is used in conjunction with the inspiratory flow rate to calculate the oxygen consumption. A digital display gives instantaneous readouts of ventilatory volume and oxygen consumption in terms of both total volume and volume per minute in the preceding minute. The Oxylog operates on rechargeable batteries and is therefore particularly suitable for measuring energy expenditure in remote field conditions. The manufacturers suggest that estimates of oxygen consumption be converted to energy expenditure by multiplying by 5.0 kcal per cm³ of O₂.

Recording energy expenditure

Energy expenditure was monitored carefully. Once the Oxylog was strapped on, the subject was given some time to stabilize before starting actual monitoring since the equipment was unfamiliar and anxiety could alter the reading. Most measurements were made in the morning before breakfast.

Each activity was timed with a stop watch, and the reading of the Oxylog was recorded after five minutes of the activity. Activities longer than five minutes were allowed to continue until their end. After each activity, the Oxylog was reset for a new activity. The sensors were changed when spent. The recording and timing were continued until the entire preparation process was completed for example, from dehulling the cowpeas to frying.

These readings were converted to energy expended, in kilocalories per kilogram of peas, using the formula

where 5 is the constant of calorific value. Kilocalories are converted to kilojoules by multiplying by 4.18. The energy expended in each activity per unit of body weight was calculated as

Results

Half of the respondents were akara and moimoi vendors, and the rest used cowpeas at the household level. A 24hour recall indicated that on the previous day 63% ate peas plus other staples. Among the respondents 62% cooked the peas for 30 to 60 minutes without potash, and 38% cooked them for less than 30 minutes with potash. The vendors prepared akara and moimoi daily, whereas 12.5% of the householders prepared it daily, 37.5% two to three times a week, 25% once a week, and 25% once or twice a month.

The eight women in the energy study ranged in age from 25 to 45 years, with a normal body mass index (BMI) range of 19.1-26.5. Their mean weight was 55.4 ± 10 kg, mean height 157.7 ± 6.5 cm, and mean BMI 22.1 ± 2.4 (table 1).

Table 2 shows the activities carried out by the subjects and the mean energy expended.

In traditional moimoi preparation, dehulling the peas took 19.7 kcal per kilogram of peas processed. Milling was not actually done by the subjects but by a miller who was close to the vendors; what was measured was the energy expended while waiting for the miller to mill the dehulled peas into paste, 2.4 kcal/ kg. Mixing chopped onions and pepper into the paste expended a mean energy of 3.2 kcal/kg, and wrapping before steaming 2.3 kcal/kg. A mean total of 27.6 + 0.8 kcal of energy per kilogram of peas was expended for the entire process, which took 48 minutes.

Only three activities were involved in preparing moimoi using pea flour. Chopping onions and pepper took 3.2 kcal/kg; mixing the chopped onion and pepper, Maggi, crayfish, and salt into the flour with the addition of water took 7.9 kcal/kg; and wrapping for steaming took 3.5 kcal/kg. Thus a total of 14.6 ± 1.5 kcal/kg was expended for the entire preparation, lasting 27 minutes.

TABLE 1. Subjects' age, weight, height, and body mass index (BMI)

TABLE 2. Energy expended in preparation of moimoi and akara

TABLE 3. Comparative energy expenditure for two methods

For akara preparation by the traditional method, dehulling required 20.2 kcal of energy per kilogram of peas. Milling took 3.2 kcal/kg; chopping pepper and onions took 3.5 kcal/kg; aerating the paste, 4.9 kcal/kg; and frying, 12.5 kcal/kg. A mean total of 44.4 ± 1.5 kcal/kg was expended, with all activities lasting 63 minutes.

Using pea flour to prepare akara also involved several activities. Adding water and aerating in a mortar took 12.1 kcal/kg; grinding onions and pepper and mixing them in used 2.9 kcal/kg; and frying used 10.7 kcal/kg. A total of 25.7 ± 0.6 kcal/kg was expended for the activities, which took 42 minutes.

The difference between the mean total energy used in making akara as against that in making moimoi by the traditional processes (44.4 and 27.6 kcal/ kg respectively; table 3) is significant (t = 7.75, p < .05). Likewise, the difference between the two products made from flour (25.7 and 14.6 kcal/kg respectively) is significant (t = 7.9; p < .05).

Discussion

A majority of the subjects used potash to cook the peas without considering the fact that it destroys nutrients, especially the B-complex vitamins.

Most of the rural women (90%) prepared akara and moimoi from pea flour because the paste made by the wet-dehulled method spoils very rapidly. The urban vendors, however, preferred the wet paste because consumers complained that akara from flour paste was heavy and dense rather than light and fluffy. This confirms a similar finding by others [5].

Although the total energy spent in preparing akara and moimoi from pea flour was only between half and two-thirds of that required by the traditional wet-pasting process, the energy cost of the aeration step in making akara was almost 2.5 times as high in the flour method (12.1 kcal kg) as in the traditional method (4.9 kcal/kg). This higher energy intensity is due to the slower solubilization of the proteins in the flour, which are required to form and sustain foam. Longer soaking of the flour paste before aeration could reduce the energy required by promoting the solubility of residual proteins. This might also improve the quality of the akara by making it lighter and fluffier. Even without such soaking, however, a substantial amount of energy is saved using dehulled pea flour.

Conclusion

It is noteworthy that vendors spent 1.7 times more energy preparing akara by the traditional pasting processes than using flour and 1.9 times more energy preparing moimoi by the traditional process. The production of pea flour should be seen as a time-and energy-saving measure. Therefore, nutritionists and extension workers should endeavour to teach vendors and householders to use the flour in their daily food preparation and to incorporate it into other dishes such as weaning foods. It could also be used to enrich staple starchy foods (roots and tubers) [6].

References

1. Durnin JVGA, Passmore R. Energy, work and leisure. London: Heineman Publishers, 1967.

2. Adams MW. Bean-cowpea production constraints and national programmes. Ann Arbor, Mich, USA: Bean-Cowpea Collaborative Research Support Programs, Michigan State University, 1984.

3. McWatters KH. Compositional, physical and sensory characteristics of akara processed from cowpea paste and Nigerian flour. Cereal Chem 1983;60:97-105.

4. McNeil G. Cox MD, Revers JPW. The Oxylog oxygen consumption meter: a portable device for measurement of energy expenditure. Am J Clin Nutr 1987;45(6):1415-19.

5. Dovlo FE, Williams CE, Zoaka L. Cowpeas: home preparation and use in west Africa. Ottawa, Canada: International Development Research Centre, 1976.

6. Okeke EC, Nwachukwu FC. Traditional root crop enrichment with legumes for sustainable development with reference to cocoyam (Xanthosoma maffa). Paper presented at the 25th annual conference of the Nutrition Society of Nigeria, Calabar. Nov 1992.

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