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Energy-dense weaning foods liquefied by germinated-wheat amylase: Effects on viscosity, osmolality, macronutrients, and bacterial growth
M. A. Wahed, D. Mahalanabis, Mahfuza Begum, M. Rahman, and M. S. Islam
Providing the recommended food energy to children being weaned is not feasible using ordinary preparations of rice gruel or the traditional porridge khichuri because either the viscosity is too high or the volume needed is too large. One approach to preparing energy-dense weaning foods suitable for young children from cereals is to use amylase to reduce the viscosity. We evaluated the use of amylaserich flour (ARF) from germinated wheat. The flour reduced the viscosity of traditional cereal preparations by more than 90%. Osmolality was significantly higher in ARF-treated rice porridge (341 vs. 50 mosm/kg) and khichuri (526 vs. 154 mosm/kg). Clinical studies are needed to determine whether this increased osmolality causes osmotic damage in the intestine. When Shigella flexneri and enterotoxigenic Escherichia cold (LT) were added to both ARF-treated and untreated rice porridge, the multiplication of the micro-organisms was no greater in the treated porridge. Production of ARF is feasible and is a possible solution to the problem of formulating energy-dense food for young children.
In developing countries weaning-food mixtures based mainly on a cereal staple are thick and therefore are often diluted with water before being given to infants and young children ; the consequent low energy density of such foods leads to a reduced intake of calories and protein and is an important cause of growth faltering during the weaning period, from six months to two years of age .
The scarcity of animal milk in developing countries makes it difficult to provide weaning-food mixtures of adequate energy and nutrient content. Fortunately, in rural Bangladesh breast-feeding is common and is continued into the second and third years of life. Therefore, if children could eat enough of the porridge preparations made from traditional cereals, they might be able to overcome the problem of growth faltering during weaning.
One approach to preparing a suitable energy-dense weaning food is to use amylase produced in germinated cereals to liquefy a sticky porridge made of cereal and thus make it more acceptable [3, 4]. Although the viscosity-reducing property of amylase-rich flour (ARF) from a germinated cereal such as wheat has been studied, foods prepared with ARF have not been evaluated for feeding infants and young children during illnesses such as diarrhoea and acute respiratory infection. We therefore evaluated some aspects of energy-dense weaning-food mixtureslike those traditionally used in Bangladesh but liquefied by the addition of germinated wheat flourthat are relevant to their use in feeding sick children, particularly those with diarrhoea.
The amylase in germinated cereal flours, when added to a cereal porridge, breaks down complex starch into polymers of glucose with various chain lengths; consequently, the osmolality of the food is likely to increase. It is also possible that such a food containing starch may break down very quickly in the upper small intestine and cause a quick rise in osmolality in the lumen, and thus aggravate diarrhoea. Using a high concentration of glucose polymer in an oral rehydration solution can lead to severe osmotic diarrhoea in infants . Furthermore, we must ask whether pathogens may grow more readily in food modified with amylase when it is contaminated.
We evaluated the use of germinated wheat flour as a source of amylase to liquefy thick, sticky, energy-dense rice porridge and its effect on osmolality. In addition, we compared the growth of two enteric bacterial pathogens, Shigella flexneri and Escherichia coli, in a liquefied porridge and in an unaltered porridge. We also conducted a limited evaluation of the keeping quality of germinated wheat flour under ordinary conditions of storage. Our findings should assist in designing studies for further evaluation of energy-dense liquefied meals for feeding infants and young children with acute diarrhoeal illness, both in Bangladesh and in other populations with similar dietary practices.
Materials and methods
Preparation of study materials
Cleaned and picked grains of wheat (Triticum aestivum) were steeped in an equal volume of water at room temperature (23-25°C) for 12 hours. The grain was drained of water, wrapped in moist black cloth, and germinated for 36, 48, 56, and 72 hours at room temperature. Water was added occasionally to keep the environment moist. The well germinated grains (with shoots approximately 2-5 cm long) were spread on filter paper to remove surface moisture and air-dried for 12 hours under a ceiling fan until dry to the touch, then oven-dried at 50°C for 12 hours. The dried grain (both seeds and shoots) was ground to a fine powder with a laboratory blender. This constituted the ARF.
When the thinning effect of the ARF prepared from grain germinated for different lengths of time was evaluated visually, as described below, it was found that the optimum effect was obtained with the ARF from grain germinated for 48 hours or more, and therefore that was used for the study.
To prepare 20% rice porridge, 60 g of rice flour was mixed thoroughly with 300 ml of water in a glass beaker, heated in a boiling-water bath to reach a temperature of 100 °C, and cooked for about 15 minutes with occasional stirring.
Wheat-flour porridge was prepared similarly.
Khichuri, a traditional porridge, was prepared by mixing 20 g of rice flour, 6 g of lentils, 3 g of oil, and 0.5 g of salt in sufficient water, and heating in a boiling-water bath for 15 minutes with occasional stirring. Hot water was added to bring the final volume to 100 ml, and the porridge was blended after cooking to make a homogeneous mixture.
Measurements and evaluations
Thinning effect and the reduction of viscosity
The thinning effect of ARF was evaluated by placing cooked porridge in a beaker, adding 2 g of ARF per 100 g of porridge while still warm (50-60 °C), and stirring with a glass rod for a few minutes. The thinning effect was observed visually and recorded.
The viscosity of each of the three porridge preparations, thinned as described, was measured on a Brookfield viscometer (Brookfield Engineering Laboratories, Stoughton, Mass., USA) using spindle RV no. 2 at speeds of 1, 2.5, 5, and 10 rpm. Similar portions of untreated porridge were also tested for viscosity, using a smaller spindle, TD (because of the non-Newtonian nature of the fluid). For the sake of uniformity we present the results at a speed of 2.5 rpm.
To evaluate the optimum time for liquefication, we measured the viscosity of the same porridge at five-minute intervals for up to two hours.
Osmolality and macronutrient measurements
The osmolality of both ARF-treated and untreated rice porridge and khichuri was measured with a freezing point-depressing osmometer (Advanced Measurements, Inc., Needham, Mass., USA).
Glucose was estimated by the enzymatic method  using commercial kits (Boehringer Mannhein GmbH, Germany) both before and after acid hydrolysis in rice porridge and khichuri. The total energy content of the rice porridge and khichuri with and without ARF was measured with an adiabatic bomb calorimeter (Gallenkamp, UK). Protein as nitrogen was estimated by the micro-Kjeldahl technique .
S. flexneri and enterotoxigenic E. cold (LT) were used to study the multiplication of pathogenic bacteria in rice porridge with and without added ARF. Fifty grams of rice porridge with or without ARF was placed in separate beakers, and 1 ml of a bacterial suspension containing a bacterial inoculum of 103 organisms per milliliter was added to each beaker and mixed. The beakers were then incubated for up to eight hours at room temperature. Quantitative cultures were performed by dilution in phosphate-buffered saline onto MacConkey and blood agar. The concentrations of bacteria were expressed as colony-forming units (cfu).
The effect of storage on the viscosity-reducing capacity of ARF
To check its stability, ARF from the same batch was packaged in heat-sealed polyethylene bags and stored at room temperature. One bag was tested for efficacy of viscosity reduction each month from November to February, using 20 g% rice porridge.
November-February is the cooler season of the year in Dhaka, with mean monthly temperatures and ranges of 23°C (11-330°C) in November, 19°C (7-31 °C) in December, 15 °C (6-36 °C) in January, and 15°C (5-36 °C) in February. The humidity always fluctuates widely during this period (50%90%), but the monthly means are 76% in November and December, 69% in January, and 63% in February.
Variability in viscosity reduction in the same batch of ARF was not checked in the true sense, but, apart from instrument variation, variation could be due to the length of cooking, the amount of rice flour used, the volume of water, and the length of time between preparation and analysis.
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