Перейти в украинский интерфейс (версию)/Change to Ukrainian interface versionПерейти в английский интерфейс (версию) / Change to English interface versionПерейти в русский интерфейс (версию) / Change to Russian interface versionначальная страница / Home pageОчистить / Clear last query resultsсправочная страница / Help page
поиск конкретных документов / Search for specific termsпросмотр по тематическим категориям / Browse by subject categoryПросмотр списка заголовков по алфавиту / Browse alphabetical list of titlesПросмотр по организациями / Browse by organizationпросмотр конкретного тематического вопроса / Browse special topic issues

Закрыть книгу / close this bookApplications of Biotechnology to Traditional Fermented Foods (BOSTID; 1992; 188 pages)
Просмотр документа / View the documentNotice
Просмотр документа / View the documentPreface
Открыть папку и просмотреть содержание / Open this folder and view contentsI. Research priorities
Открыть папку и просмотреть содержание / Open this folder and view contentsII. Overview
Открыть папку и просмотреть содержание / Open this folder and view contentsIII. Milk derivatives
Закрыть папку / close this folderIV. Plant derivatives
Просмотр документа / View the document12 Cassava Processing in Africa
Просмотр документа / View the document13 Improving the Nutritional Quality of Ogi and Gari
Просмотр документа / View the document14 Solid-State Fermentation of Manioc to Increase Protein Content
Просмотр документа / View the document15 Leaf and Seed Fermentations of Western Sudan
Просмотр документа / View the document16 Continuous Production of Soy Sauce in a Bioreactor
Открыть папку и просмотреть содержание / Open this folder and view contentsV. Animal derivatives
Открыть папку и просмотреть содержание / Open this folder and view contentsVI. Human health, safety, and nutrition
Открыть папку и просмотреть содержание / Open this folder and view contentsVII. Commercialization
Просмотр документа / View the documentBoard on Science and Technology for International Development
 

13 Improving the Nutritional Quality of Ogi and Gari

T. G. Sokari

Ogi is a blancmange-like product processed by fermenting the slurry from wet-milled maize (or sorghum or millet). Used as both a weaning food for infants and as a breakfast food by adults, ogi is one of the most important food items in Nigeria. Yet it is nutritionally inferior to maize, which is deficient in certain essential amino acids, because of the maize-milling process that is an integral part of ogi production.

Cassava, another very important food crop, has the problem of possible nutritional complications because it contains the cyanogenic glucosides linamarin and lotanstralin. Although the cyanogens in cassava are hydrolyzed to hydrogen cyanide during processing by the endogenous enzyme linamarase (1,2), not all processes are equally effective. It has even been suggested that traditional processing techniques are unlikely to remove all the cyanide from cassava (3,4).

In view of this, studies were undertaken to increase the protein content of ogi relatively inexpensively and to develop a technique for processing cassava into gari that would eliminate cyanogens from the product or reduce them to innocuous levels.

PROCESSING OF OGI

The traditional technique for processing maize into ogi is summarized in Figure 1. Also shown in Figure I is an alternative to this procedure; a 20-minute boiling step is substituted for the normal 24- to 28-hour steeping of maize prior to wet milling (5). Cowpea can be combined with maize to increase the protein content of ogi.

Substituting 20 minutes of boiling for the traditional 24 to 28 hours of steeping prior to wet milling maize reduced processing time from 72-76 hours to about 24 hours.


FIGURE 1 Processing of maize into ogi including cowpea protein enrichment; dotted lines show a bypass by which processing time can be reduced.

There was, however, no significant difference ( p> 0.05) in the aroma, color, taste, and overall acceptability between the products obtained by the short-time processing and traditional processing (5). The same was also true for unenriched and protein-enriched ogi except for color (6).

CYANIDE REDUCTION DURING CASSAVA PROCESSING

Two foods processed from cassava (gari and ijapu) were studied. Adding water to grated cassava at the 75 percent (v/w) level and heating at 50°C for 6 hours resulted in linamarin reduction of >99 percent (Figure 2). The pH of the mash fell from 6.4 to 6.3 during the period (7). After dewatering, the mash was adjusted to a pH below 4 by equilibrating with a 3-day fermented cassava liquor (40 percent, v/w) at 50°C for 12 to 18 hours. The equilibrated mash was then dewatered and toasted (Figure 3). A panel of tasters who were familiar with gari but otherwise untrained could not differentiate between the product and traditionally processed gari. Both sets of products were equally acceptable to the panel.


Figure 2 Effect of added water at 0% - i.e., control o-o, 25% D-D, 50% v-v, 75% - levels on linamarin hydrolysis in grated cassava at (a) 30°C, (b) 40°C, (c) 50°C.


FIGURE FIGURE 3 Processing of ijapu and gari from cassava.

The modified procedure for processing cassava into gari reduced the processing time from >96 hours to about 24 hours. Cyanogens were not detectable in the product by the method of Cooke (8,9).

The study of the traditional production of ijapu (Figure 3) was intended to aid in understanding the loss of cyanogens during cassava processing. About 54 percent of the cyanogens in raw cassava were lost after boiling peeled cassava, but a substantial proportion remained in the water (Table 1). After slicing the boiled cassava and steeping the slices, a substantial proportion of the cyanogens was again lost.

TABLE 1 Cyanide Content of Cassava During Processing Into Ijapu

Cyanide Content (ppm)

Material analyzed

pH

Total

Free

HCN

Bound

Cyano

Unprocessed peeled cassava

6.3

76.1+15.3

5.5+2.2

2.9+0.4

70.6

2.6

Boiled cassava

6.0

35.1+8.7

2.4+1.2

2.0+0.7

32.7

0.4

   

(53.9)

   

(53.7)

 

Boil water

6.2

12.8+2.1

1.1+0.2

0.5+0.2

11.6

0.5

"Ijapu"

           

(after 24 hours steeping)

ND

11.8+1.4

4.2+1.4

3.1+1.4

7.6

 
   

(84.5)

   

(89.2)

 

Steep water

4.0

16.2+3.9

5.7+3.4

5.6+3.4 7.8

0.1

 

Note: Cyano, Cyanohydrin; numbers in parenthesis, percent loss; ND, not determined

Much of the loss could, however, be accounted for in the steep water, and the proportion lost depended on the duration of steeping and the cassava: water ratio (Tables I and 2).

ROLE OF FERMENTATION

The reduction of >99 percent in the linamarin content of grated cassava within 6 hours of adding water, with little or no change in the pH of the mash, would imply that fermentation had nothing to do with the detoxication. Linamarin breakdown is essentially a hydrolytic process catalyzed by the endogenous enzyme linamarase (1,2). The results of the present study indicate that the addition of water aids in the hydrolytic process. Apparently not all of the water normally in raw cassava tuber is available for hydrolysis.

During the boiling of cassava for processing into ijapu, linamarase would be inactivated. Yet a substantial proportion of the linamarin in cassava was still lost, appearing to a large extent in the water used for boiling and for steeping (Tables 1 and 2). This would suggest that leaching could be an important factor in cyanide loss during cassava processing. This would be true not only during the boiling and steeping of cassava for ijapu production but also during the dewatering of grated cassava for gari production.

CONCLUSION

Cassava detoxication during processing is essentially an enzymic hydrolysis of cyanogens in cassava (1,2,8). Fermentation has little role

TABLE 2 Effect of Sliced Boiled Cassava: Steep Water Ratio on Cassava Detoxification

Ratio

(w/v)

Material analyzed

pH

Total

Free

HCN

Bound

Cyano

1:1

Unboiled cassava

6.4

90.2

4.5

3.0

85.7

1.5

 

Boiled cassava(a)

ND

51.7

1.5

0.5

50.3

1.0

   

(42.7)

     

(41.3)

 
 

Boil water

6.1

20.2

0.5

0.3

19.7

0.2

 

Sliced, boiled

ND

5.6

1.1

0.6

4.5

0.6

 

cassava(b)

(93.8)

     

(94.7)

 
 

Steep water

4.3

25.5

5.7

4.5

19.7

1.3

1:2

Sliced boiled

ND

5.7

1.7

0.6

4.0

1.2

 

cassava(b)

(93.7)

     

(95.3)

 
 

Steep water

4.3

21.3

1.9

1.4

19.4

0.5

1:3

Sliced, boiled

ND

4.2

1.6

0.5

2.6

1.0

 

cassava(b)

(95.3)

     

(97.0)

 
 

Steep water

4.2

11.5

2.1

1.1

9.4

1.0

(a) Prior to slicing and soaking in water.
(b) After 24 hours soaking; other notes as in Table 1.

in this process and may even be antagonistic to it (10). Leaching is another important process for cyanogen reduction during cassava processing. Although fermentation does not aid in cassava detoxication during processing, it is important in flavor development (11,12) and preservation of the product.

REFERENCES

1. Conn, E.E.1969. Cyanogenic glucosides. Journal of Agricultural and Food Chemistry 17:519-526.

2. Nartey, F. 1978. Cassava: Cyanogenesis, Ultrastructure and Seed Germination. Copenhagen, Denmark: Munksgaard.

3. Cooke, R. D., and E. N. Maduagwu. 1978. The effects of simple processing on the cyanide content of cassava chips. Journal of Food Technology 13:299-306.

4. Oke, O. L. 1983. Processing and detoxication of cassava. Pp. 329-336 in: Proceedings: 6th Symposium of the International Society for Tropical Root Crops, Lima.

5. Sokari, T. G., P. S. Karibo, and L. F. F. Manuel, 1991. Substitution of boiling for steeping in ogi production. Discovery and Innovation (In press).

6. Manuel, L. F. F. 1990. Microbiological, Nutritional and Sensory Evaluation of the Effects of Cowpea Fortification of Ogi. M.Phil. thesis, Rivers State University of Science and Technology, Port Harcourt, Nigeria.

7. Sokari, T. G., P. S. Karibo, and C. K. Wachukwu. 1991. Reevaluation of the role of fermentation in cassava detoxification during processing into foods. Proceedings: Workshop on Traditional African Foods, Dar-es-Salaam, Tanzania (In press).

8. Cooke, R. D. 1978. An enzymatic assay for the total cyanide content of cassava. Journal of the Science of Food and Agriculture 29:345-352.

9. Cooke, R. D. 1979. Enzymatic assay for determining the cyanide content of cassava and cassava products. Cassava Information Center, Centro Internacional de Agricultura Tropical, Cali, Colombia, 05EC-6, 14 pp.

10. Maduagwu, E. N. 1983. Differential effects on the cyanogenic glucoside content of fermenting cassava activities. Toxicology Letters 15:355-359.

11. Vasconcelos, A. T., D. R. Twiddy, A. Westby, and P. J. A. Reilly. 1990. Detoxification of cassava during gari preparation. International Journal of Food Science and Technology 25:198-203.

12. Dougan, J., J. M. Robinson, S. Sumar, G. E. Howard, and D. G. Coursey. 1983. Some flavoring constituents of cassava and of processed cassava products. Journal of the Science of Food and Agriculture 34:874-884.

Предыдущая секция / to previous section Следующая секция / to next section

[Украинский]  [английский]  [русский]