Current Research Journal of Biological Sciences 1(3): 150-154, 2009
ISSN: 2041-0778
© M axwell Scientific Organization, 2009
Submitted Date: August 06, 2009
Accepted Date: August 28, 2009
Published Date: October 20, 2009
Effect of the Duration of Fermentation on the Quality of Gari
S.V. Irtwange and O. Achimba
Department of Agricultural and Environmental Engineering, University of Agriculture, Makurdi
Abstract: The effect of duration of fermentation on some prox imate and senso ry para meters wa s studied in
bitter cassava grated and fermented traditionally for a period of five days to de termine the optimum number
of days of fermentation for best quality gari. The statistical design used in studying the effect of duration of
fermentation on moisture content, ash content, crude fibre, crude protein, hydrogen cyanide (HCN ), swelling
index, HCN and crude fat was Complete Randomized Design (CRD) with three replications. Standard
procedures were used in the determination of all the parameters studied. A panel of thirty judges were invited
for the sensory evaluation of co lour, aroma and texture. Th e results of the study as indicated by analysis of
variance show that there is highly significant effect (P#0.01) of the duration of fermentation o f gari on moisture
content, ash content, crude fibre, crude fat, crude protein, HCN and sw elling index. The regression analysis
indicates that whereas moisture content, ash content, crude fibre, crude protein, HCN and swelling index
generally seems to increase with increase in duration of fermen tation, H CN and crude fat decreased with
increase in duration of fermentation. The study recommends that for industry application, ca ssava m ash for gari
shou ld be fermented for at least three days. Cassava mash fermented for three days has the HCN reduced to a
level tolerable for human consumption; there is an advantage of maximum swelling, in addition to desirable
colour, aroma and texture.
Key w ords: Duration, fermen tation, ga ri and quality
INTRODUCTION
Cassava (Ma nihot esculenta crantz) is a staple food
for over 500 million people in the dev eloping world
(Cock, 1985). In Nigeria, it appears to b e the m ajor stap le
food that matches the population growth. Nigeria’s
cassava production is by far the largest in the w orld, a
third more than production in Braz il and almost doub le
the production of Indonesia and Thailand (FAO , 2006).
The Food and Agriculture Organization of the United
Nations in Ro me estimated 2002 ca ssava prod uction in
Nigeria to be approxim ately 34 million tonne s wh ich in
comparison with other crops ranks first, followed by yam
production at 27 million tonnes, sorghum at 7 million
tones, millet at 6 million tones and rice at 5 million tonnes
(FAO, 2005). Cassava roots are highly perishable and
cannot be kept in fresh condition for more than a few days
after harvest without serious deterioration in quality
(Leakey and W ills, 1977 ). In orde r to extend the sh elf life
of the roots, ca ssava is processe d into dried products in a
variety of ways in different parts of the world to meet the
local needs, taste and tradition for use and storage
(Ingram and H umph ries, 1972; Onwu eme, 19 78). Of all
these, the main form in which cassava is eaten in West
Africa is a roasted granular product prepared from peeled,
grated and fermented cassava roots, known as gari
(Asiedu, 1989). The cassava root is processed into wet
chips, elubo from cassava flour, fufu (akpu) from cassava
starch and gari (eba) (NRCRI, 1987). Traditionally,
cooked gari and fufu are always served with rich
vegetable soup . As a snack, boiled cassa va is tak en w ith
roasted groundnut, coconut, fish or meat. Traditionally,
cassava salads are very good co mbin ations of high ly
nutritious food stuff such as ‘abacha’ (cassava noodles)
and wet chips and are often more than snacks. Thus the
emp hasis on protein deficiency of cassava is due to
ignorance of food habits in regions where cassava is the
people’s main food (Ihekoronye and Ngoddy, 1985)
Cassava is also used for the production of textiles, starch,
adhesive s, alcohols and acetone (N RC RI, 1987 ).
Gari is a convenience food with a short preparation
time. Its cheapness, ease of storage and preparation for
consumption have combined to make it extremely popular
among the urban dwellers in Nigeria and other West
African countries. A versatile product, gari can be
prepared in a variety of ways. It can be dispersed in cold
water and consumed directly with sweeteners, groundnut
and fish. The most widesprea d metho d of gari
consumption is preparing it into a paste by pouring into a
measured quan tity of boiling water. The paste, p opularly
called eba in Nigeria is eaten by dipping small balls of it
into soup or stew and swallowing with or without
mastication. Gari is by far the most popular form in which
cassava is consumed in W est Africa (O nwuem e, 1978).
In Nigeria, it is consumed primarily by the urban dwellers
and the scale of gari processing in West Africa has been
found to involve individual family units producing less
than 0.5 ton/hr. The end p roduct (gari) is consu med in
varying amounts by approximately 50 million Nigerians
(NR CR I, 1987). W hethe r gari can be relied upon as staple
Corresponding Author: S.V. Irtwange, Department of Agricultural and Environmental Engineering, University of
Agriculture, Makurdi, Nigeria. Tell: +234-803-5885567
150
Curr. Res. J. Biol. Sci., 1(3): 150-154, 2009
food will to a large ex tent depend on how well it can be
processed in safe fo rms (B okanga, 1995 ). Market
expansion for gari, to some extent; depend largely on the
degree to which the quality of the processed gari can be
improved upon to make it attractive to potential
consumers. Quality is the degree of excellence and
acceptance. Products with superior quality can get higher
prices and can also sell larger quantities. The quality of
gari availab le in the local market varies from ba tch to
batch amo ng the traders. Variations are observed in the
colour, fiber content, moisture, particle size, starch
content and residual cyanide. These v ariations are caused
by cassava variety, age at the time of harvest, processing
methods and equipment, and duration of fermentation.
The use of cassa va as a food is limited b y its
perishability, low protein content and poten tial toxicity
(Cooke and Coursey, 1981). Processing methods have
been devised to reduce their toxicity and at the same time
convert the highly perishable roots to more stable
products. These processes include sun drying , soaking and
fermentation followed by drying or roasting.
The toxicity is due to the cyanogenic glucosides,
linagm arin and lotaustralin present in all parts of the plant
with the possible exception of the seeds (C oursey, 19 73).
Fermentation is one method by which cyanogenic
glucosides in gari can be reduced. Fermentation also
results in the production of volatile compounds that give
gari its unique flavour. Most of the juice from the cassava
pulp is expressed during this period. The time allowed for
fermentation is critical; too short and the detoxification
process is incom plete, resulting in a potentially toxic
product, too long and the product will have a strong sour
taste and the texture will be poo r (Aza m-A li et al., 2003).
Commercial gari processors in Nigeria ferment for
different durations. Collard and Levi (1959) reported that
the acceptability of gari is influenced by its sourness and
is directly related to the degree of fermentation. Akinrele
(1964) reported that hydrogen cyan ide is liberated during
fermentation through the spontaneous hydrolysis of the
cyan ogenic gluco sides of cassava at low pH. The
cyan ogenic glucoside content of gari is an important
quality parameter of gari, due to its toxicity, if consumed
in amounts greater than 30ppm (Olarewaju and
Boszoromanyi, 1975). If processing is adequate, the
cassava roots w ill be detoxified from about 300mg
hydrogen cyanide (HCN) per kg fresh weight of cassava
to 10mg/kg (Akinrele et al., 1962). Of interest is the
report that gari toasted with p alm oil contain s practically
no detectable cyanide. Ukpabi and Ndimele (1990)
reported that moisture content w as direc tly related to the
aggregate sizes and tha t gari with aggregate sizes greater
than or equal to 1 mm and moisture content greater than
or equal to 16% did not store well and showed decreased
swelling index. In recent years, consumers have placed
increased emph asis on food safety and expect that food
would not contribute to chronic diseases. The expectation
of food supply include that it be nutritious, wholesome,
pure and safe. Therefore, investigation into an appropriate
duration of cassava fermentation that will yield the best
quality of gari is imperative.
MATERIALS AND METHODS
This study w as carried out in March 2008 in the
Department of Agricultura l and E nviro nme ntal
Engineering, University of Agriculture, Makurdi, Nigeria.
Cassava tubers obtained in M akurdi were immed iately
peeled, washed and allowed to drain, after which the
tubers were grated using locally manufactured perforated
meal sheet. The g rated meals were bagg ed in a cloth sack
and heavy stones placed on the sack for dew atering while
it fermented for a period of five days. For the five days
that the ferm entation lasted , a quantity from the mash was
taken, sieved , fried and ana lyzed for proximate and
sensory parameters.
The proximate composition of each sample of gari
was determined using standard analytical procedures. The
amount of HC N w as calculated in milligram per kilogram
of gari based on AO AC (1984) method. The ash content
of the samples were also determined similarly using
methods described in AOAC (1984) after burning the gari
sample on a Bunsen burner and incinerating the charred
material in a muffle furn ace set at 550ºC until a whitish
grey ash remains, then cooling in a desiccator and
weighing. The percentage moisture content of the gari
was determined based on weight loss of w ater due to
evaporation during drying in an oven at 50ºC for four
hours until constant weight is obtained. The sorhlet
extraction method as described by Egan et al. (1981) was
used in determining the crude fat. The extraction under
reflex was carried out with petroleum ether at a
temperature range of 40-60ºC for 5 hours, followed by
drying in an oven for 30m ins at 10 0ºC for the so lvent to
evaporate, cooling and weighing. Crude fibre was
determined as difference between the oven dry weight and
weight after ashing divided by the sam ple w eight w hile
crude protein was determined using the kjedahl method.
In determining the swelling test, 25mg of gari was
measured into a 100m l measuring cylinder. The
measuring cylinder was then filled with water to 100ml
bench mark. The measuring cylinder was shaken several
times and allowed to settle. The volume of the gari was
recorded after 15 minu tes. The percentage swelling in the
volume was determined by the difference in volume
divided by the initial vo lume.
For the sensory evaluation (colour, aroma and
texture), the gari obtained on zero fermentation was
poured into container labelled 0 th day, gari of the 1 st day
of fermentation into container labelled 1 st day, gari of the
2 n d day of fermentation into the container labelled 2 n d day,
and so on till all the six containers we re filled with gari.
A panel of thirty judges w ere invited for the sensory
evaluation of colour, arom a and texture. The samples in
the container were presented to the jud ges at rando m. The
judges were asked to award scores for each sample after
observing the colour, aroma and texture of each sample of
151
Curr. Res. J. Biol. Sci., 1(3): 150-154, 2009
Table 1: Prox imate, sensory and regression an alysis as affected by duration of fermen tation (days)
Parameter
Du ration of F ermen tation (D ays)*
Linear Regression Equation
---------------------------------------------------------------------0
1
2
3
4
5
C ru de fib re (% )
2.70
2.70
2.35
2.70
3.10
3.10
2.521+0.101D
S w ellin g te st (% )
225
300
355
400
400
400
259.524+34.857D
HCN content (mg/kg)
12.67
9.48
7.60
5.72
4.50
3.82
11.660-1.745D
Moisture content (% w.b)
8.98
10.91 10.83
10.55
9.91
10.33
10.004 +0.099D
A sh co nte nt (% )
1.87
1.69
2.20
1.65
2.27
2.46
1.728+0.118D
C ru de fa t (% )
3.23
2.91
2.82
2.60
2.54
2.48
3.126-0.145D
C ru de pro te in (% )
2.33
2.40
2.45
2.55
2.50
2.48
2.370+0.033D
C olo ur (% )
13 .3
72 .4
82 .5
85 .3
80 .1
70 .4
45.090+8.897D
A ro ma (% )
20 .7
57 .1
78 .3
79 .8
78 .8
75 .9
40.629+9.789D
T ex tu re (% )
28 .6
68 .5
80 .8
83 .8
85 .2
73 .9
50.162+7.989D
*V alue s of s ens ory a ttribute s are m ean s of 3 0 pa nelists wh ile all oth er va lues a re m ean s of trip licate m easu rem ents
R 2 = coefficient of determination, r=correlation coefficient, D= duration of ferm entation (days)
Table 2: Sum mary of A NO VA for proximate
Source of
Degree of
M oisture
Variation
Freedom
Content (%w b)
Duration of
Fermentation
(Days)
5
779.065**
Error
12
* *H ig hly sig nific an t d iffe re nc e (1 % )
param eters as affected by duration of fermen tation (days)
HCN
Swelling
Ash content
Crude
content (mg/kg) te st (% )
(% )
fib re (% )
1802.44**
7675**
gari. The best sample had 6 points, the next in quality 5
points, and so on. The least had 1 poin t. The total poin ts
for each of the samples were added.
42.734**
Crude
fa t (% )
R2
r
0.4405
0.8311
0.9493
0.0662
0.4398
0.9232
0.6239
0.3774
0.6142
0.4921
Crude
p ro te in (% )
123.464** 115.008** 38.936**
0.6637
0.9117
0.9743
0.2574
0.6632
0.9608
0.7899
0.6143
0.7837
0.7015
5%
1%
3.11
5.06
of heat on hydro cy anic acid content. Generally therefore,
gari should be properly dried as a w ell dried g ari wo uld
have the HCN ‘burn off’ in heat during the drying
process be cause heat destroy s HC N.
The duration of fermentation also had hig hly
significant effect (P#0.01) on the moisture content of the
gari (Table 2). However, the r value is very low as shown
in Table 1. Th is indicates a very poor relation ship
between moisture content and duration of fermentation.
Moisture removal in gari is a function of many factors
such as temperatu re, time, humid ity, etc. Th e available
moisture in gari solely depends on the degree of dryness
during frying. Generally, a well dried gari stores well as
there would be no free moisture to encourage microorganisms multiplication in gari w hich o therw ise would
have had adve rse effect on the qua lity of gari.
The analysis of variance further indicates that there
is a highly significant effect (P#0.01) of duration of
fermentation on crude fibre content of gari (T able 2) with
a correlated r value of 0.6637 (Table 1). Gen erally, there
appears to be an increase in crude fibre as duration of
fermentation increases. The duration of fermentation also
had highly significant effect (P#0.01) on crude fat
(Table 2) with highly correlated r value of 0.9608
(Table 1) indicating that crude fat decreased with increase
in duration of ferm entation. At the onset, i.e. 0 th day, the
crude fat value was 3.23%.
On the 1st day of
fermentation, the value decreased to 2.91% and it further
decreased to 2.82% on the 2 n d day. The decreasing trend
did not abate on the 3rd day as it further decreased to
2.60% and continued until it finally fell to 2.48% on the
5 th day of fermentation. This behavior could be attributed
to the rising temperature of fermentation.
As
fermentation duration increases the temperature also
increases (Collard and Levi, 1959). Temp erature is
known to have an effect on phy sical characteristics of
food fats.
W eiss (19 83) has established that as
temperature increases the solid fat index of certain foods
Experimental Design: The experimental design for the
study on the effect of duration of fermentation on
moisture content, ash conten t, crude fibre, crude protein,
HCN, swelling index, H CN and crude fat is Co mplete
Randomized Design (CRD) with three replications. The
Analysis of Variance (ANOVA) and regression analyses
were carried out using Microsoft Office Excel 2007.
RESULTS AND DISCUSSION
From the result of the proximate analysis of gari
sample shown in Table 1, it was observed that the HCN
content decreased with increase in days of fermentation
with highly correlated r value of 0.9743. The analysis of
variance indicates highly significant effect (P#0.01) of
HCN as affected by duration of fermen tation (Table 2).
This could be as a result of two reasons: Firstly, the
grating of the peeled cassava roots/tubers to obtain the
mash disrupts the structural integrity of plant cells, thus
allowing the cyanogenic glucosides from storage vacuoles
to com e in contact with the enzyme linamarase on the cell
wall (Bokanga, 1995). When plant tissues are crushed
(mashed roots), the plant cell structure may be so
damaged that the enzymes can meet with and act on the
cyanogenic glucoside (Bokanga, 1995). The action of
linamarase on linamarin and lotaustralin is the hydrolytic
release of acetone cyanohydrin an d 2-butano ne w hich is
unstable. At pH abov e 5, they spontaneously decompose
to the corresponding ketone and HCN w hich is lost by
volatilization (Bokanga, 19 95). The second reason co uld
be the high temperature at which gari is roasted and dried.
The heat resulting from high temperature reduced the
HCN content of the gari. This is in agreement with the
observation of Meuser and Smolnik (1980) on the effect
152
Curr. Res. J. Biol. Sci., 1(3): 150-154, 2009
decreases. Temp erature could probably be the reason for
the rate of decrease of crud e fat in ga ri.
The result of the study further indicates that increase
in days of fermentation appears to have highly significant
effect (P#0.01) on the crude protein content in the
samples (Table 2). The crude protein increased with
increase in duration of fermentation between the 0 and 3 rd
day but decreased with increase in duration of
fermentation afterwards, thus giving a correlated r value
of 0.7899. The du ration of fermentation had a highly
significant effect (P#0.01) on the ash content (Table 2)
which gene rally appears to increase w ith increase in
duration of fermentation (Table 1). T he results sho wn in
Table 2 indicate that swelling index of gari is highly
affected by duration of fermentation (P#0.01). The
swelling index increased with increase in duration of
fermentation from 225% on day zero to 400% on day 3
and remained constant afterwards (Table 1). Carmago
et al. (1988) reported that the organic acids and amylase
released by micro-organisms degrad e starch granu le. A
breakdown of starch granules invariably loosens up the
starch network and allow s for a higher mo isture
absorption capacity. It could therefore be assumed that
prolonged fermentation period s (up to 3 days) for proper
degradation of starch led to a higher absorptive/swelling
capacity of the gari on reconstitution.
The effect of duration of ferm entation on the colour,
aroma and texture of gari is shown in Table 1. From the
percentage sensory evaluation of gari samples, it could be
seen that the gari fermented between 3-5 days yielded best
quality. The gari fermented for 3 days have the desirab le
colour and aroma while the gari fermented for 4 days was
voted the best gari with the best texture.
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CONCLUSIONS
The following conclusions may be drawn from the
study:
C
C
C
There is highly significant effect (P#0.01) of the
duration of fermentation of gari on moisture content,
ash content, crude fibre, crude fat, crude protein,
HCN and swelling index.
W hereas moisture content, ash content, crude fibre,
crude protein, HCN and sw elling index ge nerally
seems to increase with increase in duration of
fermentation, HC N and cru de fat decreased w ith
increase in duration of fermentation
The gari of best quality was obtained from the mash
fermented for 3 days. The gari was the best in terms
of colour and aroma, the gari fermented for 4 days
was the best in terms of texture.
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