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close this book Applications of biotechnology to traditional fermented foods
View the document Notice
View the document Preface
close this folder I. Research priorities
View the document Research Priorities in Traditional Fermented Foods
close this folder II. Overview
View the document 1 Upgrading Traditional Biotechnological Processes
View the document 2 Genetic Improvement of Microbial Starter Cultures
View the document 3 Sudan's Fermented Food Heritage
View the document 4 Lesser-Known Fermented Plant Foods
View the document 5 Lactic Acid Fermentations
View the document 6 Mixed-Culture Fermentations
close this folder III. Milk derivatives
View the document 7 Fermented Milks Past, Present, and Future
View the document 8 Lactobacillus GG Fermented Whey and Human Health
View the document 9 The Microbiology Ethiopian Ayib
View the document 10 Moroccan Traditional Fermented Dairy Products
View the document 11 Fermented Milk Products in Zimbabwe
close this folder IV. Plant derivatives
View the document 12 Cassava Processing in Africa
View the document 13 Improving the Nutritional Quality of Ogi and Gari
View the document 14 Solid-State Fermentation of Manioc to Increase Protein Content
View the document 15 Leaf and Seed Fermentations of Western Sudan
View the document 16 Continuous Production of Soy Sauce in a Bioreactor
close this folder V. Animal derivatives
View the document 17 Using Mixed Starter Cultures for Thai Nham
View the document 18 Starter Cultures in Traditional Fermented Meats
View the document 19 Fermented Fish Products in the Philippines
View the document 20 Fish-Meat Sausage
View the document 21 An Accelerated Process for Fish Sauce (Patis) Production
close this folder VI. Human health, safety, and nutrition
View the document 22 Nutrition and Safety Considerations
View the document 23 Mycotoxic Flora of Some Indigenous Fermented Foods
close this folder VII. Commercialization
View the document 24 Commercialization of Fermented Foods in Sub-Saharan Africa
View the document 25 Biotechnology for Production of Fruits, Wines, and Alcohol
View the document 26 Future Directions
View the document Board on Science and Technology for International Development

14 Solid-State Fermentation of Manioc to Increase Protein Content

Nguyen Ngoc Thao and Nguyen Hoai Huong

Manioc (cassava) is grown extensively in Vietnam and other tropical countries for its high yields in infertile soil. Although manioc is high in carbohydrates, its use is limited by its low protein content (1 to 4 percent). Manioc has been used at levels of 10 to 15 percent in poultry feed and 35 to 50 percent in pig feed. Powdered dried fish debris (gills, scale, tail, etc., from the fish processing industry), oil cake (from coconut or peanut oil production), or soybean flour have been used to raise protein levels in such feeds, but these products raise the price of feed significantly.

To upgrade the protein content in manioc, yeast cells or fungi can be inoculated in a manioc-containing medium along with nutrients containing nitrogen, phosphorus, and potassium. The use of mycelial fungi has the following advantages:

The protein content in fermented product can increase to 30 percent.

Fungal protein can be substituted completely for animal protein.

The product has a low nucleic acid content.

The product contains a favorable spectrum of amino acids.

Solid-state fermentation and liquid-state fermentation are two methods used for cultivation of fungus. Liquid-state fermentation processes are well developed in industrialized countries but are not suitable for rural farms in developing countries. Solid-state fermentation is a simple process that does not require modern equipment, power supply, or sterile conditions. In addition, the capital investment is low, permitting countryside operation and the use of available manual labor.

Many studies of solid-state fermentation of manioc have been conducted. The cultivation of Aspergillus niger in a manioc medium at 35 to 40C for 30 hours has resulted in protein content increases of 5 to 18 percent; carbohydrate content decreased from 65 to 28 percent (1). The protein from this fermentation can be competitive with soybean protein.

In addition to A. niger, other fungi such as A. awamori, A. hennebegii, A. fugamitus, Rhizopus chinensis, and Sephalo sporium lichlorniae can be grown in acid medium at high temperatures. The protein content of the fermented product can reach 48 percent.

In Vietnam, A. niger and A. hennebegii were cultivated on a maltolized-manioc medium or a mixture of manioc and rice flour. This research comes from the demand of the husbandry industry and is designed to develop a fermentation process for on-farm use.

MATERIALS

Dried manioc pieces were ground to the size of 5 to 10 mm. Spores of A. niger were cultivated by surface fermentation on a medium containing rice hulls, rice bran, or manioc flour as carbohydrate, and urea (2 percent), ammonium sulfate (8 percent), and potassium phosphate (4 percent) at pH 4.5. Spores were collected after 7 days of cultivation.

METHODS

After a defined period of fermentation, the product was dried at 65 to 70C, ground, and analyzed. The moisture content was determined by drying at 105C to constant weight. The protein content was determined by precipitating with a solution of CaSO4 (6 percent) and NaOH (1.25 percent); the precipitate was analyzed by the Kjeldahl method. The starch content was determined by hydrolyzing the preparation with HCl and using the Bertrand method. The reduced glucose content was determined by the Bertrand method.

Table I shows that A. niger could not grow in medium containing urea as the only nitrogen at a concentration of 4.5 percent because of the resultant alkalinity. With (NH4)2SO4 as the N source, the pH was maintained at 4 to 5 during the fermentation. The maximum protein content was attained in medium containing urea (4 percent) and ammonium sulfate (5.8 percent). The content of protein can reach 17 percent in comparison with the one cultivated in only urea-containing medium. However, 1.55 percent N protein was achieved in the culture medium containing 3.1 percent N with the transformation efficiency of 49 percent.

TABLE 1 Effect of Nitrogen Sources on Protein Formation

N Protein

Percent Percent N Protein

N in Culture in Fermented in Fermented

N

Source

Medium

Product

Preparation

1 Urea

2.0

0.93

5.2

0.83

3.3

1.54

8.0

1.28

4.0

1.86

8.2

1.3

4.5

2.10

no growth

--

5.0

2.33

no growth

--

         

2 Ammonium sulfate

       

(AS)

7.4

1.54

4.4

0.70

Urea 2% + AS 10%

 

3.05

7.2

152

Urea 3.3% + AS 4%

 

3.10

9.36

1 49

Urea 4.0% + AS 5.8%

 

3.1

9.7

1.55

Urea 4.5% + AS 7.4%

 

3.1

no growth

 

The transformation efficiency was 70 percent in medium containing only urea (4 percent).

The P and K elements (Table 2) were added to the medium containing urea 3.3 percent and ammonium sulfate 4.4 percent (1-5) or urea 3.3 percent (6-9), respectively. The results suggested that the P and K sources had no clear effect on protein formation.

In Table 3, the effect of humidity on the protein content is shown. Table 4 illustrates the effect of sterilizing conditions on the yield of protein. Table 5 shows the effect of the amount of inoculum culture on protein synthesis.

RESULTS

Manioc flour cannot be used as a carbohydrate source in the culture medium because it agglomerates and excludes air necessary for the growth of the fungal mycelium.

Manioc pieces of 0.5 to 1.0 centimeters are best for this solid fermentation method. The protein content of fermented preparation decreased 50 percent when using manioc pieces that were 1.0 to 2.0 centimeters in size.

The analysis of a fermented preparation after 2 days of fermentation, drying at 65 to 70C, and grinding is shown in Table 6.

TABLE 2 Effects of Nutrients on Biosynthesis of Protein (The P and K elements were from chemical fertilizers)

Chemical Fertilizer

P Percent + K Percent

Protein Percent

1

3.3 + 1.0

10.21

2

2.3 + 0.5

11.34

3

2.3 + 1.5

10.41

4

4.3 + 0.5

11.46

5

4.3 + 0.5

9.3

6

3.3 + 1.0

10.0

7

2.3 + 0.5

10.0

8

1.3 + 0.5

11.25

9

0.3 + 0.5

9.62

TABLE 3 Effect of Initial Humidity on Protein Content

Humidity of

Protein

 

N

Culture Medium(a)

Percent

Notes

1

45

7.9

The change of humidity from

2

50

9.36

60 to 70 percent occurred

3

55

9.64

depending on the atmospheric

4

60

11.08

temperature and humidity.

5

65

11.23

 

6

70

11.37

 

7

75

Poor growth

 

a The medium for this experiment contained urea (4 percent), P (1.3 percent), and K (0.5 percent).

TABLE 4 Effect of Sterilization Conditions on Protein Production

, ,

N

Temperature C

Time Minutes

Percent Protein

Notes

1

100

45

8.6

The culture medium

2

100

90

7.35

can be sterilized

3

120

30

7.6

at 100C in

4

120

45

7.50

45 minutes.

5

120

60

6.30

 

 

TABLE 5 Effect of the Amount of Inoculum Culture on Protein Synthesis

Percent of Inoculum

Percent

Notes

N

Culture

Protein

 

1

0.5

6.0

The maximum percent of

2

1.0

8.6

protein was achieved in 2 percent

3

1.5

10.0

of inoculum culture. There was

4

2.0

12.5

formation of black spore in

5

3.0

12.0

fermented preparation when using more than 2 percent of inoculum culture.

TABLE 6 Product Analysis

   

Fermented

 

Manioc Pieces

Preparation,

N

Index

Culture-Medium, Percent

Percent

1

Protein

1.5-2.0

10.0-13.3

Starch

33

11

Reduce sugar

4.4

8.11

Total sugar

8.4

13.00

CONCLUSION

This solid-state fermentation method can be used to upgrade by six to seven times the protein content in manioc pieces. The resulting fermented product contains 10 to 13 percent protein, which is suitable for use as a feed additive.

REFERENCE

1. Raimbault, M.J. 1985. Fermentation Technology 63(4):395-399.