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Food science

Studies on a wheat- based amylase-rich food

Tara Gopaldas, Suneeta Deshpande, and Chinnamma John

Introduction

In most developing countries the first food to be introduced in a child's diet is a porridge prepared from a cereal or cereal flour. Such porridges are characterized by high viscosity and low energy content per unit volume of food, necessitating frequent feedings to meet the daily energy requirements of the child. This is not practical in tribal, rural, or urban slum areas where the mothers work the whole day away from home. Therefore a series of studies was undertaken in our laboratory to attempt to overcome this problem of dietary bulk.

Studies carried out on fully roasted and malted mixes indicated that the cooked-paste viscosity of a 10% (weight per volume) slurry of malted mix was significantly lower than that of its roasted counterpart [1]. In transferring this technology to the community level, however, the overriding constraints were the time, space, and labour involved in the production of the mix.

It was reported that 5% of malted barley could, because of its high amylase content, substantially reduce the viscosity of a 15% hot paste slurry of commercially available weaning foods such as Nestum, Cerelac, Balamul, and Farex [2]. On the basis of that hypothesis, Gopaldas et al. successfully developed an amylase-rich food (ARF) from bajra (Pennisetum typhoideum), which, when added at a level of 4 g% (weight per weight of total solids) to a 10% rice gruel, lowered the viscosity effectively [3].

Although the production of the ARF involved malting, it was a technology that could be transferred to the community and household levels since the ARF was required in very small amounts to thin the gruels. However, because the bajra ARF was subjected to high-temperature processing, it had low amylase activity and was ineffective in lowering the viscosity of slurries with solid concentrations higher than 10%. Therefore, the present study was planned to develop an ARF with optimum amylase activity from wheat and to study the effect of this ARF on wheat-based gruels with higher solid concentrations (up to 25%). Wheat was selected because it is the largest single crop produced in India, is consumed throughout the country except in a few tribal pockets, and is available in surplus amounts.

Since there was no information available on the development of a wheat ARF, the investigation was planned with the following specific objectives:

• to standardize conditions for preparing the ARF
• with respect to steeping, germination, and drying
• to obtain an ARF with optimum amylase activity;
• to study the shelf life of the ARF stored at ambient temperature and relative humidity;
• to conduct viscosity measurements and compare the catalytic activity of the ARF and pure enzyme takadiastase, and to study the effect of heat treatment on the reduction in viscosity;
• to evaluate the acceptability and measure the intake per sitting of porridge with and without the ARF by infants (612 months old) and toddlers (13-36 months old).

Methods and materials

Estimation of amylase activity

The method of Bernfield was used to estimate the amylase activity [4], which was reported in maltose units, corresponding to milligrams of maltose released by 1 g of ARF acting on 1 ml of 1% starch solution at 37 °C for 30 minutes.

Shelf-life studies

The moisture content, alcoholic acidity, peroxide value, and bacteriological count were estimated using standard procedures [1]. Organoleptic testing of the ARF was done using a hedonic rating test with a seven-point scale [5].

Viscosity measurement

The slurries were prepared by thoroughly mixing accurately measured amounts of water and weighed amounts of flour in a beaker and cooking the mixture over a boiling-water bath, stirring it continuously. The temperature of the slurries was noted, and they were cooked for five minutes after reaching 80 °C (the gelatinization temperature of starch).

The ARF was added at 1-7 g% at the cost of wheat flour, either before cooking or after cooking (when the cooked slurry cooled to a temperature of 70 CC). The slurries were cooled to 35-40 °C, and the viscosity was measured in a Brookfield Synchrolectic Viscometer.

Intake trials

A 20% wheat porridge with fat and jaggery at 10 g% and 100 g% respectively was used as the control porridge. (It was not possible to use higher solid concentrations of wheat flour, i.e. 25% or higher, as the control porridge at such concentrations became dough-like on cooking.) The experimental porridge contained ARF at 4 g%, added prior to cooking.

Initially, 50 ml of porridge was served; additional helpings of 50 ml were given subsequently on demand. The amount left over was noted, and the intake was calculated from the difference.

Results

Standardization of conditions for preparation of the ARF

Steeping

The picked and cleaned wheat grains were soaked in triple the volume of water for 6, 12, 18, and 24 hours. The percentage of moisture content was noted at the end of each period. There was no increase in water uptake after 12 hours of steeping, and spoilage set in after that (table 1). Therefore, a steeping period of 12 hours was adopted.

Germination and drying

After 12 hours of steeping, the seeds were germinated for 24, 36, 48, 72, and 96 hours. Three methods of drying were used: sun drying (40±2 °C), oven drying (50 °C), and toasting in a shallow iron pan (80 ± 4 °C). The dried grains were devegetated and milled to a fine flour to obtain the ARF. The amylase activity of each ARF was determined. The sun-dried ARF with 72 hours of germination had the highest amylase activity (table 2). However, mould growth was observed after 48 hours of germination. Therefore, a germination period of 48 hours and sun drying were found suitable for preparing an ARF with optimum amylase activity.

TABLE 1. Effect of the length of the steeping period on the moisture content of the grain

TABLE 2. Effect of the period of germination and the method of drying on the amylase activity of the ARF

a. Milligrams of maltose liberated by 1 g of ARF acting on 1 ml of 1% starch solution at 37 °C for 30 minutes.

Shelf life

The keeping quality of the ARF was studied at intervals of 10 days over a period of 30 days. The toasted ARF had a shelf life of 30 days, while the sun-dried and oven-dried ARF had a shelf life of only 10 days on the basis of IS/PFA specifications (table 3). However, the scores obtained on organoleptic testing indicated that all the ARFs were highly acceptable throughout the storage period of 30 days; scores were more than 80% of the maximum for taste and smell.

Viscosity trials

Trials were carried out to study the effect of the concentration of solids (15%, 20%, and 25% weight per volume) on viscosity and the comparative thinning on addition of oven-dried ARF, toasted ARF, and pure enzyme takadiastase to the slurries. The catalytic agent was added at 1-7 g%. Optimum thinning was observed at the 4% level, and this level of ARF was used subsequently. All three agents had similar catalytic effects (table 4). A different trend was observed in the case of 15% slurry, however, which is difficult to explain. All the catalytic agents could effectively turn even the thick, dough-like 25% slurry into a semi-solid, pour-batter consistency suitable for child feeding.

TABLE 3. Shelf life of ARF

a. The day after which thc ARF exceeded the IS/PFA specification for the specific variable.

TABLE 4. Effect of solid concentration on viscosity of wheat slurries, and viscosity reduction on addition of a catalytic agent

a. Solid concentration (weight per volume).
b. Incorporated at 4 g% (weight per weight of total solids).
c. Control.

We studied the effect of adding fat and jaggery, the two important constituents of the traditional wheat porridge, on viscosity and caloric content. These substances lowered the viscosity by approximately 66% and increased the caloric content 2.4 times in the case of each slurry (table 5).

We also studied the effect of heat treatment on reducing viscosity. ARF was added to the slurries at 1-7 g% before and after cooking (as described above), and the reduction in viscosity was noted. There was significantly greater reduction in viscosity in all cases when the ARF was added after the slurry was cooked, even at a low 1 g% level (table 6).

Intake trials

Intake trials were carried out for three consecutive days on infants 6-12 months old and toddlers 13-36 months old in an urban slum, using 20% wheat porridge without ARF (control) and with ARF. The infants and toddlers fed the experimental porridge had significantly higher caloric intake per sitting than those fed the control porridge (table 7).

Discussion

The preparation of a wheat ARF was simple. Steeping the wheat grains overnight (12 hours) was found to be optimum. Steeping for longer periods resulted in the water becoming slimy, and by 24 hours starch was leached from the grains because of rupture of the seed coat. The optimum period for germination was 48 hours. A germination period of 72 hours and sun drying was found to yield an ARF with the greatest amylase activity. However, after 48 hours of germination mould growth was observed, and there was only a marginal increase in amylase activity.

TABLE 5. Effect of adding fat and jaggery to wheat slurries on their viscosity and caloric content

a. Slurry with fat incorporated at 10 g% and jaggery at 100 g% (weight per weight of wheat flour)

TABLE 6. Effect of heat treatment on reduction in viscosity of wheat slurries by ARF

Oven-dried ARF added to slurry at 1 g %

TABLE 7. Intake of porridge with and without ARF per sitting by infants and toddlers

The control group were fed 20% wheat porridge with 10 g% fat and 100 g% Jaggery; the experimental group were fed the same porridge with 4 g% ARF added before cooking.

a. 6-12 months old
b 13-36 months old.

*Significantly different from control at P < .05.

Such sophisticated items of equipment as ovens are not generally available at the community level in India, but there is abundant sunshine for nine to ten months a year, and it would therefore be easy to introduce the simple technology of ARF preparation by sun-drying. Though sun-dried ARF had the optimum amylase activity, however, it had a poor shelf life (10 days). Toasted ARF had a good shelf life because of a lower initial moisture content (due to the higher temperature of processing). Low moisture content inhibits the growth and proliferation of microorganisms, thereby extending the keeping quality. In addition, a higher processing temperature (80 ± 4 °C in the case of the toasted ARF) may itself lower the initial surface microbial load.

Since the toasted ARF was found to have a longer shelf life, which is a desired characteristic for any processed food and makes the product more readily acceptable, the viscosity measurements were carried out to study the comparative catalytic activity of oven dried ARF, toasted ARF, and pure enzyme takadiastase. The results were comparable for all three agents, indicating that amylase activity on the order of 600700 maltose units is enough for effective reduction in viscosity. This suggests that an ARF with good shelf life and catalytic activity can be prepared by the simple procedure of steeping (12 hours), germination (48 hours), and toasting in a shallow iron pan at a low temperature (80 °C).

Addition of fat and jaggery had a twofold benefit. First, they lowered the dietary bulk, and, second, they increased the energy content significantly, thus enabling a child to ingest more calories per unit volume of food consumed. This would result in less frequent feedings being needed to meet the energy requirements of the child. To test this hypothesis, intake trials were carried out on infants and toddlers, using a 20% porridge with 10 g% of fat and 100 g% of jaggery added, without ARF and with ARF at 4 g%. The children fed the experimental gruel had a caloric intake 2 to 2.5 times as high per sitting as those fed the control gruel.

It was observed during the feeding trials that the mothers preferred thicker porridges (of spoonable consistency) for the older children (10 months old or over). Since the 25% slurry with ARF has a suitable consistency for child feeding and a higher energy density, it would be the most appropriate product to use. A serving of 195 ml of this porridge can meet one-third of a child's total energy requirements [61, whereas 490 ml of a 10% porridge, 325 ml of a 15% porridge, or 245 ml of a 20% porridge would be required to provide the same calories.

The observations on the effect of heat treatment on the reduction in viscosity were very interesting and encouraging. It was noted that 1 g% of ARF added to a cooked slurry reduced the viscosity by 92%, while 6-7 g% was required for similar viscosity reduction when it was added before cooking. This is because cooking at 80 °C drastically reduces the level of the potent amylase which can act on starch and lower the viscosity. When the amylase was added to a cooked slurry cooled to 70 °C, or when the porridge was taken off the fire, a major portion of the potent amylase was conserved, resulting in a greater reduction of viscosity. Such a procedure has two benefits: much less ARF needs to be prepared in bulk, and it would be much easier for a housewife to add a small amount of ARF to an already cooked and hot gruel.

Conclusions

Several conclusions emerge from this study: The procedure for preparing toasted ARF from wheat is simple and inexpensive. Toasting the germinated grains is necessary, and the toasted ARF has more than enough amylotic power to reduce thick traditional gruels. Low-bulk, high-energy wheat porridges can be prepared by just adding a pinch of ARF to a big cup of hot cooked porridge. Thus it should be feasible to transfer this technology from the laboratory to the household level in rural, tribal, and slum areas.

References

1. Gopaldas T. Malted versus roasted weaning mixes: development, storage, acceptability. and growth trials. In: Achaya KT. Interfaces between agriculture, nutrition, and food science. Food and Nutrition Bulletin supplement 9. Tokyo: United Nations University, 1984:293-306.

2. Desikachar HSR, Malleshi NG. Formulation of a weaning food with low hot paste viscosity based on malted ragi (Eleusine coracana) and green gram (Phaseolus radiatus). J Food Sci Tech 1982;19:193-97.

3. Gopaldas T, Mehta P, Patil A, Gandhi H. Studies on reduction in viscosity of thick rice gruels with small quantities of an amylase-rich cereal malt. Food Nutr Bull 1986;8(4):42-47.

4. Bernfield P. Amylases alpha and beta. In Colowick SP, Kaplan NO. Methods in enzymology, vol 1. New York: Academic Press, 1955:149-51.

5. Amerine MA, Pangoorn RM, Roseler HB. The principles of sensory evaluation of food. New York and London: Academic Press, 1965.

6. Indian Council of Medical Research. Recommended dietary intakes for Indians. New Delhi: ICMR, 1981:7.

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