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Food science and technology


Traditional lactic acid fermentation, malt addition, and quality development in maize-cowpea weaning blends


M. A. Akpapunam and S. Sefa-Dedeh

Abstract

We studied the effects of traditional lactic acid fermentation and the addition of malt on the physicochemical properties of maize-cowpea blends. The products were high in protein (18.4%-19.4%) and low in fat (0.5%-1.3%) and fibre (0.5%-0.7%). Fermentation reduced the pH from 6.7 to 4.4. The unfermented sample without malt was about four times as thick in consistency as those containing it. Up to 5% malt in the blends did not reduce the viscosity of the cooked samples fermented for two days. Fermentation for three days further neutralized the known effects of reducing viscosity by the addition of malt. Two different effects occurred when fermented blends containing malt were cooked: malt addition caused a reduction in viscosity, whereas fermentation led to an increase.

Thus adding malt to maize-cowpea blends before fermentation does not reduce viscosity. Adding malt to the blend after fermentation should be tried.

Introduction

In most developing countries protein-energy malnutrition is fairly prevalent among infants and preschool children. It and its accompanying infectious diseases have long been linked to the high frequency of deaths for these groups. The supply of nutritious foods such as meat, eggs, milk, and milk products is inadequate, and animal sources of protein and commercially manufactured baby foods are usually too expensive for most families.

Many developing countries use supplementary foods made from cereals and vegetable proteins as one means of solving the problem. For example, vegetable protein sources such as legumes and oil seeds (fed to children as weaning foods) are high in lysine, an essential limiting amino acid in most cereals [1].

The problem with using cereals and legumes in weaning foods is the bulky nature of the porridge, which discourages many children from eating it. Thus attempts have been made to modify the starch structure to reduce bulk. These have included the use of enzymes (amylase), precooking, toasting, puffing, and extrusion processing of the raw materials. However, most of these methods are not culturally acceptable or are too technical for the rural population. To gain wider acceptance among the local population, simple and inexpensive technologies that can easily be adapted at the home level must be available [2]. Toward that end, traditional processes such as fermentation and malting of cereals and legumes have been tried with some success in reducing bulk in porridges [3-6]. The potential of fermentation to reduce bulk is still an open discussion [7]; however, malting seems to be successful [8-14].

The constraints posed by the long processing time, labour, and space associated with preparing fully malted cereals and legumes to reduce bulk led to research involving small quantities of amylase-rich flours (ARF) [9, 10,12,15]. The results showed that ARF has a great potential to reduce bulk in cooked starch porridge.

The high protein content of cereal-legume blends and their increased use in weaning foods makes it important to investigate the potential of ARF in them. Usually, ARF is added to the prepared porridge before it is heated, but this method has constraints in handling and proper application, particularly when done by illiterate mothers [7]. On the other hand, there is the danger of contamination when ARF is added after preparation. ARF has a short shelf life [10] and must be prepared often. It can be co-milled with unmalted cereal or cereal legume blends to obtain a unit pack. This would produce the desired reduction in the thickness of the porridge, and would also help overcome some of the problems of handling and application.

The objectives of this study were to formulate a high-protein weaning food based on maize, maize malt, and cowpeas, and to evaluate the effects of fermentation and malt addition on the product's characteristics.

 

Materials and methods

The raw materials used for the study were maize (Zea mays) and cowpeas (Vigna unguiculata), locally called asontem. The maize was purchased from a local market in Accra, and the cowpeas were obtained from the Crop Research Institute in Kumasi.

Product formulation

The maize was dehulled and the hulls separated. Cowpea seeds were dried in an air oven (70C) for one hour to facilitate dehulling using a disc attrition mill. The hulls were separated by winnowing, and the dehulled cotyledons steamed for eight minutes in a steam box.

Whole maize was soaked in water (1:3 w/v) at 29C for six hours and germinated in a sterilized woven cane basket lined with a sterilized moist jute sack. The grains were watered three times a day at regular intervals. After germinating for 72 hours, the grains were dried for eight hours in a solar drier (45-47C). The vegetative parts were removed by rubbing the grains between the palms and winnowing. The dried malted grains were milled in an attrition mill and sieved to remove the hulls.

The proportions of ingredients in the blends are shown in table 1. Figure 1 is a flow sheet for the preparation of the weaning blend. The dehulled maize grains were soaked in water (1: 3 w/v) at 29C for three hours, then mixed with the dehulled steamed cowpeas and the malted maize. The samples were milled together in a disc attrition mill and divided into three equal parts. One part was spread on a stainless steel tray and dried in an air oven for 14 hours at 60C, then lightly toasted at 105C for five minutes. The toasted samples were milled with a hammer mill (Christy and Norris Ltd., Chelmsford, England) to a flour of 60 mesh. Water was added to the two remaining portions to bring the moisture content to 50%. These were formed into a dough, placed in a plastic bowl, and allowed to ferment at room temperature (29C) for two and three days respectively. Fermented samples were dried and milled into flour as for the unfermented sample.

TABLE 1. Composition of maize-cowpea-malt blends

 

Ingredients (%)

Blend

Maize

Cowpeas

Maize malt

MCmalt0

60

40

0

MCmalt2.5

57.5

40

2.5

MCmalt5

55

40

5

MCmalt10

so

40

10

FIG. 1. Flow sheet for formulating weaning food

 

Chemical composition

The crude protein (N x 6.25), ether extract, crude fibre, ash, and moisture contents of the samples were determined by the AOAC methods [16]. Carbohydrate was estimated by difference, and energy was calculated using Atwater values (4 x protein, 9 x fat, and 4 x carbohydrate).

Water-soluble carbohydrates were determined by mixing 50 ml of distilled water with duplicate 5-g samples. The mixture was agitated for two hours at room temperature (25C), then filtered, and the residue was washed twice with 20 ml of distilled water. The combined extracts were made up to 100 ml in a volumetric flask. The total soluble carbohydrate content of the extracts was determined by the phenolsulphuric acid method [17].

The pH was determined by mixing duplicate 10-g samples with 100 ml of distilled water. The mixture was left at room temperature (26C) for 30 minutes, and pH was measured on supernatants. Titratable acidity as lactic acid was determined by dissolving duplicate 10-g samples in 100 ml of distilled water and titrating 10-ml aliquots with 0.1N NaOH to phenolphthalein end point.

Viscoamylographs

The cooked-paste viscosity of a 12% (dry matter) slurry of sample was determined with a Brabender viscoamylograph (Brabender Instruments Inc., Duisburg) equipped with a 700-cmg sensitivity cartridge. The sample was heated at 1.5C per minute to 95C, held for 30 minutes, cooled uniformly at the same rate to 50'C, and held for 30 minutes. Pasting temperature, peak viscosity, and viscosity at 95C, 95C-hold, 50C, and 50C-hold were measured from the viscoamylographs.

Statistical analysis

The data were analysed using Statgraphics software (STSC Inc., Rockville, Md., USA).

 

Results and discussion

Product description

The physicochemical properties of the maize-cowpea blends were affected by both fermentation and level of malt. The blends were free-flowing and cream-white in colour. Those that were fermented were slightly darker, and the intensity of the colour tended to increase with the length of fermentation and the level of malt.

Composition

The dry matter content of the blends ranged from 89.1% to 93.1% (table 2) and was not affected significantly (p < .05) by either fermentation or level of malt. The products had a relatively low moisture content and should have good storage properties. All the blends contained relatively high amounts of protein (18%-19%). This is in agreement with guidelines for commercial weaning foods [18]. Protein content was not significantly affected by fermentation or level of malt. The fat content ranged from 0.5% to 1%. The unfermented blends contained significantly more fat than the fermented ones; it appears that spontaneous lactic acid fermentation reduced the fat content, but malt addition had no effect. The ash content ranged from 3% to 4% and was not affected by either the addition of malt or fermentation.

TABLE 2. Chemical characteristics of maize-cowpea weaning blends (% dry matter basis)

Blend Dry matter Proteina Ether extract Ash Crude fibre CHO Energy (kcal/100 g) pH Titratable acidityb Total soluble carbohydrateb

Unfermented

MCmalt0

90.1

19.0

1.31

4.3

0.6

65.1

348

6.8

0.5

8.1

MCmalt2.5

92.4

18.7

1.29

4.1

0.7

67.7

357

6.6

0.6

8.9

MCmalt5

92.1

19.2

1.33

4.2

0.5

65.9

352

6.6

0.7

8.4

MCmalt10

90.6

19.4

0.92

4.4

0.6

65.3

347

6.6

0.7

8.8

Fermented 2 days

MCmalt10

91.6

18.9

0.60

3.4

0.6

68.1

353

5.3

1.7

7.3

MCmalt2.5

89.2

19.4

0.68

3.7

0.7

64.7

343

4.4

2.6

7.0

MCmalt5

93.1

18.4

0.85

3.9

0.6

69.3

359

4.9

2.2

6.8

MCmalt10

92.0

18.8

0.88

3.9

0.6

68.1

353

6.6

0.7

8.8

Fermented 3 days

MCmalt0

89.1

19.2

0.49

3.8

0.6

65.2

342

4.9

1.7

6.9

MCmalt2.5

90.6

19.1

0.77

3.9

0.6

66.2

348

4.6

2.9

6.8

MCmalt5

92.4

19.1

0.87

3.7

0.5

68.3

357

4.6

2.3

6.8

MCmalt10

91.3

19.2

1.06

3.9

0.6

66.5

353

4.6

2.8

6.9

a. N x 6.25.
b. Grams per 100 g dry matter.

The fibre content of the blends ranged from 0.5% to 0.7%. These levels were low because dehulled ingredients were used in the formulation. The total carbohydrate content ranged from 65% to 69% and was not affected by fermentation or addition of malt. The energy content varied from 342 to 359 kcal/100 g (dry matter). These values are slightly lower than the 375 kcal/100 g recommended as a minimum for high-quality weaning foods [19].

pH and titratable acidity

Fermentation generally caused a reduction in pH of all blends. The pH ranged from 4.4 to 6.7 and was significantly affected (p < .05) by fermentation. There were, however, no significant differences between the pH values of the two- and three-day fermented blends, and malt had no significant effect.

Titratable acidity tended to increase with increased fermentation time. The acid content was significantly lower in unfermented blends than in fermented ones. There were no significant differences between the acid content of the blends fermented for two or three days. Malt had no significant effect on the acidity of the blends. It has been reported that fermented foods with low pH have some antimicrobial activities [6]; therefore the low pH of the fermented blends reported here could be beneficial.

The soluble carbohydrate content of the blends decreased significantly with fermentation time. There was no significant difference in the soluble carbohydrate of blends fermented for two and three days, but the two differed significantly from the unfermented blends. Similar reduction in the soluble sugars of fermented cowpea meal has been reported [20]. It is possible that micro-organisms in the blends converted some of the carbohydrates to alcohols and organic acids.

FIG. 2. Viscoamylograph of unfermented maize-cowpea blends containing (A) 0%, (B) 2.5%, (C) 5%, and (D) 10% malt

FIG. 3. Viscoamylograph of maize-cowpea blends containing (A) 0%, (B) 2.5%, (C) 5%, and (D) 10% malt fermented for two days

Viscoamylographs

Viscoamylographs provide useful information on the hot-and cold-paste viscosity of starch-based foods. In the unfermented blends malt reduced all the viscosity parameters (fig. 2), most significantly after holding at 50C for 30 minutes. The maize-cowpea blend prepared without added malt was about four times as thick as that containing malt. This has implications for infant feeding.

After two days of fermentation the samples containing malt did not show any clear trend on cooked-paste viscosity (fig. 3). Unlike the unfermented blends, the addition of up to 5% malt did not reduce the cooked-paste viscosity. The sample containing 10% malt, however, showed a reduced viscosity (280 BU) comparable to that of the unfermented sample containing the same amount of malt. It appears that a high level of malt is required to cause a comparable reduction in cooked-paste viscosity.

The samples fermented for three days showed comparable viscosities (fig. 4). The combined effects of fermentation (three days) and malt addition (2.5%-10%) are products with relatively similar viscosities. Two different effects seem to occur when fermented blends containing malt are cooked. Whereas malt addition causes a reduction in viscosity, fermentation causes an increase. The sample containing 10% malt and fermented for two days was the only one showing viscosity similar to the unfermented samples.

The temperature at which the first detectable viscosity is measured in the amylogram is the pasting temperature, which is a reflection of the swelling of the starch paste and is affected by the starch concentration [22]. Generally a high starch concentration leads to a low pasting temperature. The presence of monosaccharides and oligosaccharides has been reported to lead to a shift upward of pasting temperature [23]. The pasting temperature of the blends increased with the level of malt (table 3). Malt may reduce starch concentration and promote the production of monosaccharides and oligosaccharides. Fermentation also caused an increase in the pasting temperature, with the samples fermented for three days showing the highest pasting temperatures.

The peak viscosity in the amylogram is cited regardless of the temperature at which it occurs. Cooking must proceed through this stage for a usable paste to be formed. The addition of malt resulted in a reduction in the peak viscosity of all samples. Unfermented blends had a lower peak viscosity than fermented ones.

The effect of malt and fermentation on viscosity at 95C was similar to that observed for the peak viscosity. The data suggest that fermented samples are easier to cook, as shown by the relatively high viscosity at 95C. The presence of malt, however, caused a reduction in this index. A similar effect of fermentation on viscosity at 95C has been reported for fermented traditional maize dough [24]. It appears that the spontaneous solid-state lactic acid fermentation in cereal processing practiced in West Africa makes the resulting material easy to cook.

After holding at 95C for 30 minutes, the viscosity (V95C-hold) of the unfermented blends increased and that of the fermented samples decreased. The most significant viscosities with respect to the eating quality of weaning foods were those measured on cooling the sample to 50C (V50C) and holding at 50C for 30 minutes (V50C-hold). The viscosity of the unfermented blends without malt showed a drastic increase in V50C; those containing it also increased but to a lesser degree. The presence of malt in the unfermented blend allowed a reduction of the thickening effect on cooling.

Fermentation for two and three days led to samples with very high V50C, producing samples too thick to be used as weaning foods. Except for the sample containing 10% malt and fermented for two days, the addition of malt did not appear to have much influence on V50C and V50C-hold.

FIG. 4. Viscoamylograph of maize-cowpea blends containing (A) 0%, (B) 2.5%, (C) 5%, and (D) 10% malt fermented for three days

TABLE 3. Viscoamylograph indices on maize-cowpea blends

Blend   Viscosity (BU)

Pasting temperature (C)

Peak

95C

95C-hold

50C

50C-hold

Unfermented

MCmalt0

65.2

540

490

490

1,480

1,720

MCmalt2.5

68.2

120

118

126

360

430

MCmalt5

72.2

140

130

150

408

440

MCmalt10

75.8

70

70

85

270

270

Fermented 2 days

MCmalt0

70.8

400

342

359

640

710

MCmalt2.5

72.2

650

620

480

1,180

1,130

MCmalt5

74.1

380

370

285

900

960

MCmalt10

74.1

100

90

85

280

260

Fermented 3 days

MCmalt0

73.3

500

500

380

1,090

1,150

MCmalt2.5

72;1

460

460

360

1,010

960

MCmalt5

78.1

448

448

365

1,140

1,120

MCmalt10

77.2

365

365

260

920

900

 

Conclusions

Simple traditional solid-state lactic acid fermentation of cereals reportedly has a positive effect on the safety of gruels used for weaning [6]. However, the resulting product can be too thick for infants to consume in sufficient amounts to satisfy their nutritional requirements. The process described here combines supplementation with cowpeas, lactic acid fermentation, and the addition of malt. Whereas adding malt leads to a reduction in product viscosity, fermentation leads to an increase. The cumulative effect of combining fermentation with malt addition is that the desired product consistency is not achieved. Further work must be done to establish a process to take advantage of the reported benefits of lactic acid fermentation and malt addition.

 

Acknowledgements

We are grateful to the United Nations University for granting author M. A. Akpapunam a study fellowship. This study was supported by the US Agency for International Development, Bean/Cowpea Collaborative Research Support Program, grant DAN-1310-G-SS-6008 00. Recommendations do not represent an official position of USAID.

 

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