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Food science

Weaning foods with improved energy and nutrient density prepared from germinated cereals. 1. Preparation and dietary bulk of gruels based on barley

Marianne Hansen, Birthe Pedersen, Lars Munck, and Bjorn O. Eggum

Editor's note

The article "Studies on a Wheat-Based Amylase-Rich Food" by Tara Gopaldas et al. (Food and Nutrition Bulletin, vol. 10, no. 3, Sept. 1988) described the use of germinated (malted) wheat for making a weaning food of low viscosity. In response to the interest generated by that article, we are publishing the following two papers, discussing the application of this principle using barley. The three works taken together should provide sufficient guidance for those wishing to produce weaning foods from barley or other cereal that are locally available or preferred.

Introduction

In most developing countries traditional weaning foods are based on local staples, usually cereals. For use as weaning foods, cereals are normally made into gruel. During the cooking process, the starch granules swell and bind a large amount of water, resulting in gruels of high viscosity. A gruel of satisfactory feeding consistency will contain a great deal of water and have a large volume relative to its content of solid matter. If the concentration of solids is raised to increase the nutrient and energy density, the gruel will be too thick and viscous for a small child to eat easily. This high volume/high-viscosity characteristic, referred to as dietary bulk, which makes it difficult for small children to fulfil their energy requirement, is considered a major factor in the development of malnutrition in areas where cereals and starchy staples are the main food [1].

There are various ways of reducing the viscosity of gruels, and among the low-cost methods, germination (malting) seems to be the most effective [2]. During the germination of grains, r-amylase activity is developed. The enzyme degrades the starch granules, reducing their water-binding capacity and consequently lowering the viscosity of the gruel. When germinated cereals are used, therefore, liquid gruel can be prepared with a higher flour concentration than that of gruels made from ungerminated cereals [3]. As children are able to consume more of a liquid weaning gruel than of a stiff porridge in one meal [4], they can obtain much more energy and other nutrients per meal from such a gruel than from one prepared in the traditional way from ungerminated flour.

Malting is a traditional practice in many developing countries, where it is used primarily in the production of beer. Although the viscosity-reducing effect is recognized in some communities in India and Africa, germination is not widely used in making weaning foods, perhaps because the preparation of germinated flour is rather time consuming [3].

Recently it has been shown that adding just a small amount of flour made of germinated grain (malt) to a gruel of ungerminated cereal produces a remarkable reduction in viscosity. Thick porridges can be liquefied in this way, and the energy density can be increased while an acceptably low viscosity is maintained [5].

The use of sorghum malt as an additive has been introduced at the village level in Tanzania [4], and several studies have been carried out with sorghum, millet [3; 4; 6], and rice [7], but no information seems to be available for barley.

Barley is the fourth most important cereal, accounting for 12% of the world's total cereal production [8]. It is grown over a broader environmental range than any other cereal, much of it in areas unfavourable for growing other major cereals. It is drought-resistant, and almost two-thirds of the total crop comes from subhumid or semiarid lands. It is an important food in semiarid regions from North Africa through the Middle East to Tibet and is also grown in the Andean region of South America. In areas of deficient rainfall and poor soils, it is often the only cereal from which a harvest, however meagre, can be obtained [9].

The present study was undertaken to examine the dietary bulk of barley gruels and their value as a source of energy for small children. The possibility of reducing their bulk by using germinated barley flour as an additive was investigated. As cereals are usually milled before they are consumed, the effect of refining was also examined. An improved, high-lysine barley variety was used in the study. The nutritional aspects of the gruels are further described in the following paper [10].

Materials and methods

Barley of the high-lysine variety Ca 700202, harvested in Denmark in 1986, was used in the experiment. Ca 700202 is a cross between a high-lysine barley mutant (Riso 1508, carrying the lys 3a gene) and Triumph, a normal barley commonly grown in Denmark. The seed quality of Ca 700202 is acceptable and the yield is close to that of normal varieties [11|. Triumph was used as a control.

Ungerminated flours

The high-lysine barley was milled into three different flours: wholemeal, semi-refined, and refined. The outer layers of the kernels were removed successively by abrasive milling (Schule, LVSM mash no. 2002182), and the decorticated kernels were then ground into flour in a hammer mill (Alpine, type 100LU, mesh 500 am). The wholemeal was produced after the husk was removed. The semi-refined flour was prepared after further removal of the fibrous pericarp and testa, and this fraction thus contained the nutrient-rich aleurone layer. The refined white flour consisted of the inner part of the kernel, the starchy endosperm. The extraction rates for the wholemeal, the semi-refined fraction, and the refined flour were 84%, 72%, and 58% respectively. For comparison, a refined flour was produced from Triumph; its extraction rate was 73%.

Germinated flours

The grains were germinated at 15 °C for three, five, or seven days. Water was added continuously to the kernels, and there was no preliminary soaking. During the first 24 hours the moisture content of the kernels was gradually increased to 40%-45%, and this level was maintained throughout the germination process. After germination the kernels were dried at a temperature that was raised from 25 °C to 60 °C during eight hours and kept at 60 °C for four hours. The shoots were removed; the malted kernels were ground; and the fibrous outer layers were removed by sifting to a degree of refining comparable to that of the semi-refined fraction.

Preparation of gruels and viscosity measurements

Gruels, with dry-matter content varying between 5% and 40%, were prepared from ungerminated flours, from germinated flours, and from ungerminated flours mixed with 1% (dry basis) of the flour made from grain germinated for seven days. The gruels were cooked and the viscosity measured in an amylograph (Brabender, type 801201, 75 rpm). The weight of flour plus water was kept constant. The temperature was increased by 1.5 °C per minute from 25 °C to 95 °C, kept constant at 95 °C for 10 minutes, and then lowered by 1.5 °C per minute to 40 °C. The viscosity was recorded in Brabender units (BU) at this temperature, and standard curves relating the viscosity to the dry-matter content of the gruels were prepared.

Analytical methods

The level of a-amylase in the germinated grains was determined as described by Hejgaard and Gibbons [12]. The energy content of the gruels was determined as described in the following paper [10].

Results

The level of a-amylase increases with time of germination, the maximum level being reached after five to seven days (fig. 1). The enzyme level is affected by the raw material as well as the conditions during the germination process.

FIG. 1. Level of a-amylase in barley grain (Ca 700202) as affected by germination time

FIG. 2. Influence of dry-matter content on the viscosity of barley gruels at 40 °C.

Based on ungerminated flours (curves 1-4), ungerminated flours with 1% of germinated flour added (curves 5-7), or germinated flours (curves 810). I = normal barley, refined (control). 2 = high-lysine barley, refined. 3 = high-lysine barley, semi-refined. 4 = high-lysine barley, wholemeal. 5 = high-lysine barley + malt, wholemeal. 6 = high-lysine barley + malt, semi-refined. 7 = high-lysine barley + malt, refined. 8 = high-lysine barley germinated 3 days. 9 = high-lysine barley germinated 5 days. 10 = high-lysine barley germinated 7 days.

TABLE 1. Dry-matter content of barley gruels with acceptable viscosity, energy densities, and estimated amounts need to provide 60% of the daily energy requirement of a one-year-old infant

a. Concentration resulting in an acceptable viscosity-400 BU. b. Based on available energy determined as described in the following paper [10]. c. Volume to provide 60% of daily energy requirement. d. Number of meals of 250 ml each to provide the indicated volume. e. Ungerminated, refined normal barley (Triumph variety).

As the enzyme is the key to the reduction in viscosity and dietary bulk, it is important to consider the time course of enzyme development.

The viscosity of the various gruels at different levels of dry-matter content is shown in figure 2. It was recorded at 40 °C because that is a typical eating temperature [13]. Germination had a remarkable reducing effect on viscosity, and the effect increased with germination time. To obtain a gruel with a viscosity of 400 BU, which is considered acceptable for small children, using ungerminated, semi-refined flour, the dry-matter concentration was 13%. The corresponding concentrations for flours from grain germinated for three, five, and seven days were 28%, 34%, and 37% respectively (table 1). Addition of a small amount (1%) of germinated flour to gruels prepared from ungerminated flour also had a pronounced effect on viscosity. The dry-matter content of these gruels at a viscosity of 400 BU was 24%. Thus, it is possible to increase dry-matter content some two to three times by using flour from grain germinated for three to seven days, or to double it by including a small amount of germinated flour.

The viscosity of gruels made from ungerminated flours increased rapidly with increasing content of dry matter. It was also affected by the degree of refining, being lower in wholemeal gruel than in gruels made from more refined flours because wholemeal has a higher content of fibre and a correspondingly lower content of starch capable of binding a large amount of water. The normal barley, Triumph, has a higher content of starch than the high-lysine variety, and refined flour produced from it is consequently very high in starch [10]. When gruel is made from such a refined, starch-rich fraction, the viscosity becomes extremely high.

The volume of gruel needed to provide 60% of the energy requirement of a one-year-old child was estimated on the basis of the available energy content of the flour fractions (table 1). The amount of available energy in the flour fractions was determined as described in the following paper [10], and the energy requirement was based on the FAO/WHO/UNU recommendations [14]. Furthermore, it was assumed that (i) a one-year-old consumes about 300 ml of breast milk a day [13; 15; 16], providing approximately 20% of the energy requirement, and (ii) one-fourth of the remaining calories needed are obtained from such foods as sugar, oil, pulses, and meat. Using these assumptions, the volume of gruel required to satisfy the child's energy needs varied from 430 ml a day to as much as 2,770 ml, a volume that is obviously impossible for a small child to consume. A total daily intake of 800-1,000 ml has been reported for children of this age group [17]. Consequently, infants consuming germinated barley gruel or gruel made from ungerminated barley with a small amount of malt should be able to consume sufficient quantities to fulfil their energy requirements. The ungerminated barley flours, however, seem to be inadequate as a source of energy for small children, especially when highly refined.

As small children generally are able to consume about 200 to 300 ml of gruel at a time [4; 13; 18], the number of meals a one-year-old would need to eat to meet 60% of the energy requirement ranged from 2 to 11 (table 1). Two or three meals a day of the gruels made from germinated flour or to which malt was added would be enough. If the corresponding ungerminated flours were used, the number of meals needed ranged from four to seven a day, depending on the degree of refining: the more refined the flour, the higher the number of meals required. If a highly refined, starch-rich fraction, very low in fibre, is used, the number of daily meals needed will be exceedingly high.

Discussion

The viscosity of barley gruels and the effects of germination

Barley does not seem to be different from other cereal grains with respect to gruel viscosity and the effects of germination [4; 17]. The energy density of the barley gruels could be increased two to three times by germination, and twice by the addition of malt. Our results are in accordance with those of Mosha and Svanberg [3], who found that the volume of white sorghum gruel needed to cover 60% of the daily energy requirement of a one-year-old child was 2,500 ml. This volume could be reduced by about two-thirds if the sorghum was germinated, and by half if 5% of sorghum malt was added to the ungerminated flour. Similarly, Taal et al. [17] reported that the required volume of millet-groundnut gruel could be halved by either germination or the addition of germinated flour at a 5% level.

The development of a-amylase with time illustrated in figure 1 is typical for barley [19]. Thus, to obtain an acceptable viscosity in gruel made from germinated flour, the grain should be germinated for two or three days. There is little to be gained in further reducing the viscosity by prolonged germination; and, to minimize losses due to respiration and the growth of sprouts during malting, the time should be kept as short as possible. In our study 8% of the dry matter was lost after seven days of germination; however, malting losses can be considerably higher [20].

Food-intake studies have shown that the energy density of weaning foods should exceed 0.7 kcal per gram and preferably be about 1.0 kcal per gram [5]. The doubling of the energy density of barley gruels made possible by adding a small amount of germinated flour to ungerminated flour brings them within this range of 0.7-1.0 kcal per gram. Thus, only gruels made from germinated flours or those prepared by adding malt to ungerminated flour can be considered to have acceptable energy densities for weaning foods.

The addition of malt

In a preliminary experiment we found that it made no difference whether the germinated barley flour was added before or after cooking in the amylograph. The result was the same when gruels were cooked in a pot. However, if the gruel is heated very quickly, the a-amylase might be inactivated before the gruel has been liquefied. For this reason it might be better to add the malt after cooking. If the microbiological quality of the added germinated flour is questionable, it is possible to reheat the gruel, as this will not affect the final viscosity [3]. For technical reasons we chose to add the malt to the ungerminated flours before cooking.

We found the optimum level of malt to be about 1%. Preliminary experiments in which inclusion levels of 1.5%, 2.5%, and 5% were tested showed that it was not possible to reduce the viscosity further by adding more malt. Thus, there is no linear relationship between the quantity of enzyme and the decrease in viscosity. Under limited conditions, however, a doubling of the a-amylase quantity causes reduction to the desired viscosity in half the time [21].

Apparently very few studies have assessed the optimum level of inclusion. In similar studies with other cereals, higher levels (5%-10%) have generally been used [3; 17]. According to Gopaldas et al. [7], as much as 16% of malted pearl millet was required to bring about a maximum reduction in viscosity when added to a 25% rice-flour gruel. This might have been because the malt was roasted and part of the a-amylase activity destroyed.

The liquefying effect of malt appears to be caused solely by the action of alfa-amylase, whereas b-amylase has no liquefying effect [22]. Thus, all germinated cereals have potent liquefying potential due to the presence of aamylase. However, wide differences may occur between varieties, and both the germination time and the conditions during germination are important [21]. In our experiment at least three days of germination was required to produce a barley malt with high levels of a-amylase activity.

Effects of refining

The energy density of wholemeal gruel was almost twice as high as that of gruel made from refined flour at an acceptable viscosity, 0.65 and 0.35 kcal per gram respectively. Thus, if wholemeal is used for gruel, four meals a day are sufficient, whereas seven meals are needed when the corresponding refined flour is used. This difference between flours of different degrees of refining disappears when germinated flour is added. The lowest energy density, 0.20 kcal per gram, was found in gruel made of refined conventional barley flour. Hence, dietary bulk is primarily related to the starch content of the diet rather than to the content of dietary fibre.

Wholemeal seems to be superior to refined flours with respect to dietary bulk. The reduction in available energy caused by the fibre in wholemeal was rather small, about 5% when determined in rats [10], and this reduction is well compensated for by the lower viscosity of the wholemeal gruel. Wholemeal also has a higher content of vitamins and minerals than refined flours [10; 23; 24]. Finally, refining results in loss of food for human consumption.

Unfortunately, little is known about the ability of infants and small children to digest and tolerate dietary fibre, and this needs to be investigated. In addition to reducing available energy, fibre may interfere with the digestion and absorption of nutrients and result in excessive losses in faeces [25]. Until recently a very low level of fibre in weaning food has generally been recommended [2], but the recent interest in fibre has changed attitudes on this subject, and whole-grain gruels are now recommended for small children above the age of eight months in some countries [26].

Acknowledgement

The authors thank Dr. S. Aastrup, of the Department of Brewing Chemistry, Carlsberg Research Centre, for his advice regarding the malting procedure.

References

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