Fungal enrichment of cassava peels proteins

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African Journal of Biotechnology Vol. 5 (3), pp. 302-304, 2 February 2006
Available online at
ISSN 1684–5315 © 2006 Academic Journals

Short Communication

Fungal enrichment of cassava peels proteins

Obadina A.O.1*, Oyewole O.B.2 Sanni .L. O, 3 and Abiola S. S.4

1Department of Food Biotechnology, University of Technology, P.M.B 1015 Ota, Ogun State., Nigeria.
2Department of Food Science and Technology, University of Agriculture, Abeokuta, P.M.B. 2240, Ogun State, Nigeria.
3Department of Animal Production and Health, University of Agriculture, Abeokuta P.M.B.2240, Ogun State, Nigeria.

Accepted 12 December, 2005

About 60% of the cassava produced all over the world is used for human consumption. These peels
waste were found to contain 42.6% carbohydrate, 1.6% protein, 12.1% ether extract, 5.0% total ash and
22.5% crude fibre. With the advent of biotechnology approaches, there are opportunities for economic
utilization of agro-industrial residues such as cassava peels waste. The Microorganisms isolated from
the fermenting cassava waste were Aspergillus niger, A. flavus, and A. fumigatus. These and
Trichoderma sp. from soil were studied for their ability to increase the protein content of cassava peels

Keywords: Cassava peels, Aspergillus flavus, Aspergillus niger, Aspergillus fumigatus.


Cassava (Manihot esculenta Crantz) is the most
the peel as a substrate for microbial protein enrichment.
important crop in Nigeria and many tropical countries.

Cassava roots play an important role in the African diet

and they are processed using simple traditional methods
into products such as “gari” and fufu, of lafun flour, some

of which are fermented products (Odunfa, 1985). As a
Sample collection

rough estimate, about 10 million tones of cassava are
Solid cassava wastes were collected from solid waste dumping
processed for gari annually in Nigeria alone (Okafor,
sites at the University of Agriculture, Abeokuta (UNAAB) cassava
1992). In the processing of cassava fermented products,
processing site. The Trichoderma sp., originally isolated from soil,
the roots are normally peeled to rid them of two outer
was obtained from the Department of Microbiology, University of
coverings: a thin brown outer covering, and a thicker
Agriculture, Abeokuta, Nigeria.

leathery parenchymatous inner covering. These peels are

regarded as wastes and are usually discarded and
Enumeration and isolation of microorganisms
allowed to rot. With hand peeling the peels can constitute

20-35% of the total weight of the tuber (Ekundayo, 1980).
5 g of the collected solid wastes were taken under aseptic
The wastes generated at present pose a disposal
conditions. The samples were aseptically homogenized with 50 ml
problem and would even be more problematic in the
sterile 0.1% peptone under aseptic conditions. Appropriate dilutions
were plated on duplicate plates of Malt Extract Agar (MEA) for fungi
future with increased industrial production of cassava
counts. Plates were incubated at 30°C for 4 – 5 days. After
products such as cassava flour and dried cassava fufu.
incubation, the colonies on the plates were counted. Colony types
Since these peels could make up to 10% of the wet
and numbers were also noted. Representative colonies were picked
weight of the roots, they constitute an important potential
at random from the plates and streaked out to obtain pure cultures.
resource if properly harnessed by a biotechnological
The isolates pure cultures were also kept on slants of PDA for fungi
system. The objective of this work is therefore to utilize
before characterization.
The isolated fungi were classified according to their method of

(sexual) reproduction. They were identified according to their micro-

morphology as well as the colour and morphology of their

sporulating structures and conidia. Young, actively growing moulds
*Corresponding author E-mail: [email protected]
were picked with a sterile needle unto clean glass slides and prepa-

Obadina et al. 303

red for microscopic observation using lactophenol as mountant and
weights represented the crude fibre concepts which were
cotton blue as stain (Barnett and Hunters, 1992; Harrigan and
expressed as percentages of the original samples.
McCance, 1976). The slides were carefully covered with slips to

exclude air bubbles. Microscopic examination of the prepared slides

was carried out first using the low power objective followed by the
40 magnification objective lens for a closer examination of a
selected field. Microscopic identification was on the basis of the

structures bearing the spores and on the spores themselves. Other
Table 1 shows the microbiological assessment of the
features observed included presence or absence of septation,
cassava solid wastes, with a total aerobic count of 2.17 x
rhizoid and other tissues.
102, lactic acid bacteria of 1.6 x 102 and total fungal count
Trichoderma sp., originally isolated from soil, was obtained from
of 3.1 x 105. During the isolation the three moulds
the Department of Microbiology, University of Agriculture, Abeokuta,
frequently encountered were Aspergillus niger, A. flavus,

and A. fumigatus. The morphological and physiological

properties of the major lactic acid bacteria isolated from
Production of protein

the cassava solid waste were used in identifying the
100 g sample of cassava solid wastes were collected from the local
strains. The isolates were identified and the organisms
processors dump site and mixed thoroughly with 5 ml of isolated or
are Lactobacillus brevis, L. delbrueckii, La. sake, L. casei
obtained growing culture. The fermentation was carried out in 250
and L. plantarum.
ml conical flasks for 72 h. At intervals of 24 h the waste
fermentation medium was centrifuged at 4000 rpm for 30 min. The

sediment waste residue was dried in an oven at 105°C for 24 h and

ground in a mortar. The crude protein, crude fibre and total

carbohydrate were determined on duplicate samples
Table 1. Microbiological assessment of solid cassava wastes.

Amount of microbes
Chemical analysis of solid cassava wastes inoculated with
Total aerobic count
2.17 x 102

Lactic acid bacteria
1.6 x 102
These were determined by the methods of Association of Official
and Agricultural Chemists (A.O.A.C., 1990) on dry matter basis.
Total fungal count
3.1 x 105

Determination of crude protein content

An amount of 10 g finely ground dried samples were each
Chemical changes in cassava peels inoculated with
transferred into a 50 ml Kjedhal flasks. 2 ml distilled water were
different moulds
added and the flasks were allowed to stand for 30 min. 0.02 g

powdered pumice, 1.33 g K2SO4 catalyst mixture and 1.5 ml
Table 2 shows the changes in the protein, crude fibre
concentrated H2SO4 were then added. Heating was done on the
carbohydrate yield of the fermented peeled cassava
digestion rack until frothing stopped. Heating was again increased
to gentle boiling so that the H
wastes inoculated with different moulds. The fermentation
2SO4 condensed to about one third
way up the neck of the flask. The isolated particles were washed
of the wastes with moulds caused an increased in the
with 30% H202 solution before boiling again for 1 h. On cooling, 10
protein content. The highest protein yield was in the
ml deionized water was added slowly with swirling. 2 ml aliquots of
medium fermented by Trichoderma sp. followed by A.
each diluted solution were measured and total nitrogen determined
fumigatus, A. flavus and A. niger.
spectrophotometrically using Technicon Auto – analyzer. The
Crude protein contents were determined from total nitrogen values

using the conversion method of A.O.A.C. (1990).


Determination of crude fibre

All the moulds isolated from the cassava solid wastes (A.
Two grams each of dried samples were transferred into clean filter
niger, A. flavus and A. fumigatus) are effective in
crucibles. 150 ml of 0.128 M H2SO4 previously preheated in the
producing feed of high protein, but their used for this
reagent system were added to prevent foaming. The contents of the
purpose is limited due to the toxic materials produced by
beakers were boiled for 30 min and filtered through a Buchner
these organisms. These fungi have been implicated in
funnel with the aid of a suction pump. The residues were washed
with hot deionized water until acid free. The residues left after acid
animal diseases (Richard et al., 1985) and mycotoxin
digestion were carefully transferred into a 400 ml beaker. 150 ml of
production (Mossel, 1982). A. fumigatus has been
0.22 M KOH solution and a few drops of octanol were added to
previously found to produce high amount of microbial
each sample. The mixtures were again heated for 30 min with
proteins (Odunfa, 1987). The results of microbial protein
constant stirring. The contents of the beaker were filtered through a
yield in this work can be compared to that of other
Buchner funnel and 15 cm No 4 Whatman filter paper on cooling.
The residues were washed several times with hot water and once
studies. Odunfa (1987) obtained overall yields of 7.2 –
with methylated spirit until free from KOH. Finally, the residues
19% using different moulds to ferment cassava peels
were transferred into porcelain crucibles and dried at 130°C for 2 h.
while overall yields of 12.6 – 25.5% were obtained in this
They were allowed to cool in desiccators before weighing. The
work. The moulds make used of the fibre to produce the

304 Afr. J. Biotechnol.

Table 2. Protein, crude fibre and carbohydrate yield of cassava solid wastes inoculated with different moulds.

Crude protein (%)
Total carbohydrate (%)
Crude fibre (%)
Aspergillus niger
Aspergillus flavus
Aspergillus fumigatus
Trichoderma sp.

microbial protein and this is responsible for the reduction
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From this study it can de deduced that a protein
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Odunfa SA, Shasore SB (1987). Saccharification of Cassava Peels
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hydrolysate could serve as a good substrate for

production of value-added products.


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