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JOURNAL OF RESEARCH IN NATIONAL DEVELOPMENT VOLUME 8 NO 1, JUNE, 2010


EVALUATION OF THE QUANTITY AND QUALITY OF GARI PRODUCED FROM
THREE CULTIVARS OF CASSAVA 
E. A. Komolafe
Department of Food Science and Technology
E-mail: komodeji@yahoo.com
and
  J. O. Arawande       
Department of Science Laboratory Technology, Rufus Giwa Polytechnic, Owo
E-mail: joawande1@yahoo.com

 

Abstract
Three prominent cassava cultivars (TMS 30572, Isunikankiyan and Odongbo) cultivated by farmers in Owo, Ondo- State, Nigeria were obtained and used to produce gari (common staple food) and their quantity and quality were evaluated. The percentage yield, proximate composition, physico-chemical and sensory properties of gari samples produced from these cultivars were investigated. The result showed that TMS 30572 and Isunikankiyan   had the highest (37.00±1.44%) and lowest (28.00±1.00%) yield respectively. The proximate composition result revealed that the values of crude protein (1.40±0.35%), ash (1.25±0.04%) and crude fibre (2.25±0.37%) of Odongbo were highest while moisture content (11.81±0.21%) of Isunikankiyan was highest; and carbohydrate (83.31±0.81%) and fat (1.10±0.10%) of TMS 30572 were highest. The pH values of the gari samples were approximately 4.00±0.00 and the total titratable acidity (g/100mg lactic acid) of TMS 30572, Isunikankiyan and Odongbo were 0.54±0.01, 0.65±0.03 and 0.84 ±0.03 respectively. The total hydrogen cyanide concentration (mg/100g) of the three cultivars was within the range 1.36±0.02 to 2.15±0.05. The physico-chemical properties showed that TMS 30572 had the highest swelling index of 4.15±0.07 followed by Odongbo gari with a value of 3.00±0.05 and Isunikankiyan gari had the lowest swelling index of 2.15±0.04. The bulk density (g/cm3) of the gari samples were 0.55±0.10, 0.65±0.10 and 0.82±0.21for Odongbo, Isunikankiyan and TMS 30572 gari respectively. Organoleptic assessment of the gari samples from the three cultivars tested showed that there was no significant difference (P > 0.005) in the sensory attributes evaluated. However, there was high acceptability and preference for gari produced from TMS 30572 and Odongbo above that of Isunikankiyan gari which equally had the lowest swelling capacity.  TMS 30572 and Odongbo could be recommended for rapid multiplication and distribution to farmers as quality cultivars for gari production.

Keywords: Cassava cultivars, proximate composition, physico-chemical, sensory properties.

 


Introduction
Cassava (Manihot esculenta Crantz) is a very popular high energy root crop consumed in the tropics and many regions of the developing world. It is the seventh most important crop of the world and constitutes a stable food for about 12.50% of the world population (Halin and Keyser, 1985). Cassava is the most important root crop in Nigeria in terms of food security, employment creation, and income generation for crop producing households (Ugwu and Ukpabi, 2002). The consumption of cassava has currently been on the increase, and the growing of cassava is expanding to semi-arid areas where cassava was not cultivated some thirty years ago (Omodamiro et al., 2007).The adoption of disease and pest resistant varieties released by the International Institute of Tropical Agriculture, (IITA), Ibadan and the National Root Crops Research Institute (NRCRI), Umudike, have increased cassava production in many African countries to such an extent that Nigeria has become, since 1989, the largest cassava producer in the world (Bokanga and Otoo, 1994; FAO, 1991; FAOSTAT, 2002). The current production figure of cassava in Nigeria is about 34 million metric tonnes per annum.
Cassava root is normally processed before consumption to detoxify, preserve and modify it (Oyewole, 1991). Several products are derived from processed cassava root; prominent amongst these products is gari. Gari is by far the most popular form in which cassava is consumed in Nigeria and indeed in West Africa (Ikediobi et al., 1980, Odoemelam, 2005). Gari is a starchy staple with high dietary energy and it is consumed by both young and old in almost all parts of Nigeria and many African countries (Ernesto et al., 2000; Oluwole et al., 2004). Processing of cassava roots into gari consists of peeling, washing and grating followed by fermentation and dewatering in a jute bag for at least seventy-two hours. Thereafter, the cake formed is broken into small lumps, sieved and toasted. It could be eaten as snacks with coconut or groundnut by adding cold water and sugar, or it could be prepared into dough (eba) with hot water and eaten with soup.

There are over thirty different cassava cultivars in Nigeria, which the extension workers recommend to farmers because of their per hectare tuber yield (Achinewhu et al., 1998). However, only a few cultivars are dominant among the many used in Owo, Ondo State. Among the popular or dominant cultivate grown in the farmers’ fields in Owo locality are Odongbo, Isunikankiyan and TMS 30572. The Odongbo and Isunikankiyan are local cultivars while TMS 30572 is an elite cultivar released by IITA.

The high yield of the cassava cultivars are based on tuber yield, which may not necessarily reflect the actual gari yield and its quality. The usefulness of any cassava to the processor and the ultimate consumer will be determined by the quantity and quality of its gari. The present-study therefore seeks to investigate the quantity and quality of gari produced from these three prominent cultivars (Odongbo, Isunikankiyan and TMS 30572) planted in Owo community in order to enhance utilisation and industrial potential.

Materials and methods
Ten kilograms each of 15 months old cassava tubers (Manihot esculenta Crantz) of three cultivars; TMS 30572, Isunikankiyan and Odongbo were harvested from a staff farms at Rufus Giwa Polytechnic, Owo, Ondo-State, Nigeria and used for the experiment.

Gari was produced by the process described by IITA (1990) illustrated in the flow chart below.The cassava root (10 kg) of each cultivar was peeled manually using a stainless steel kitchen knife. The peeled roots were washed and grated in a 5Horze Power diesel powered grater. The grated meal was then packed into Hessian bag and allowed to ferment for 72 hours. The fermented pulp was dewatered using the hydraulic press. The pressed cake was broken into pieces with hand and sieved with a wire mesh screen. The sieved pulp was garified inside a wide shallow cast iron pot and stirred constantly over a low fire until well dried. It was cooled, packaged, labelled and sealed.



Morphological characteristics and pulp/peel ratio determination
The morphological characteristics such as the colour of the cassava, root peel, shape of the root and the character were determined for each variety. The pulp/peel ratios were determined by peeling five kilogram’s of each cassava cultivar manually with a kitchen knife .The peeling was carefully done to ensure that the fleshy inner part (pulp) was not removed with the peel. The pulp and the peel of each cultivar were weighed separately for the pulp/peel ratio determination.   

Yield of gari from fresh cassava roots
The percent yield of Gari samples obtained from fresh cassava roots of each cultivar was determined by using the expression


 

% Gari yield =                                     weight of Gari                                     x    100
Weight of fresh cassava root                                  1


Chemical analysis
The moisture, protein (N x 6.25), fat, fibre, ash and carbohydrate (by difference) contents were analysed according to the AOAC (2000) method. The hydrogen cyanide was determined using Knowles and Wathins (1990) method of analysis. The pH and total titratable acidity (TTA) were determined as described by Oyewole and Odunfa (1989), pH meter (model Jenway) was used.

Physical properties
The swelling index was determined according to the procedure described by Ukpabi and Ndimela (1990). Bulk density was determined according to the method described by Okaka and Potter (1979).  A 50 g sample was put into a 100 ml graduated cylinder. The cylinder was tapped 40 times and the bulk density was calculated as weight per unit volume.

Sensory evaluation
The Gari samples produced from the different cassava cultivates were subjected to organoleptic evaluation using 10-man experienced panellists in the consumption of gari in the various consumable forms. The sensory evaluation was based on colour, texture, taste, flavour and overall acceptability. Each panellist’s score was reflected on a nine point hedonic scale ranging from nine (like extremely) to one (dislike extremely) as described by Masen (1982).

Statistical analysis
Scores from the hedonic rating tests were averaged to obtain mean scores which were subjected to analysis of variance. The Duncan (1955) multiple range test was then used to determine the significance of any difference between samples.
Results and discussion
The results of the tuber characteristics and chemical composition of the cassava cultivars used in this experiment are presented in Table 1. Isunikankiyan had the highest percent pulp of 87.80±1.01% closely followed by TMS 30572 with 85.90±1.86% pulp while Odogbo cultivar recorded the lowest value of 83.85±1.53% pulp. The dry matter of the cassava roots ranged from 27.20±0.34% for Isunikankiyan to 30.60±0.58% for TMS 30572. However, the total hydrogen cyanide content (mg/100g) of the peeled roots used was 4.52 ±0.09, 9.00±0.11 and 18.70±0.14 fresh weight for Isunikankiyan, Odongbo and TMS 30572 cultivars respectively. Based on the total cyanide level in each cultivar and the classification of Coursey (1973), Isunikankiyan can be classified as a low cyanide (sweet) cassava since its total cyanide content was less than 5 mg HCN/100g fresh weight while Odongbo and TMS 30572 can be classified as high cyanide (bitter) cassava since their total cyanide levels was above 5 mg/100g fresh weight. The advantage of Isunikankiyan (low cyanide cultivar) over the Odongbo and TMS 30572 (high cyanide cultivar) was that it required minimal amount of processing time and can be boiled, roasted, grated and made into different dishes straight from the field, whereas the Odongbo and TMS 30572 must be given elaborate processing (3 to 5 days) to reduce the HCN content before consumption as inadequate processing of the cultivars before consumption can lead to cancer or ill health.

Proximate composition of processed gari samples from the different cassava cultivars is shown in Table 2. The moisture content of the gari samples ranged from 11.78±0.18% to 11.81±0.20%. The moisture content was generally low; it is indicative of the level of processing (roasting) and will probably confer longer shelf life on the gari in storage. The fat content of the gari samples ranged from 0.40±0.02% for gari produced from Odongbo to 1.10±0.10% for gari produced from TMS 30572. Given the low fat content, rancidity of stored gari would not be a problem. The crude fibre of the gari samples ranged from 1.65±0.34% (TMS 30572) to 2.25±0.37% (Odongbo) and is within the nutritionally maximum level of 3.0% (Ibe, 1981). However, the crude fibre content of 2.25±0.37% recorded in gari sample from Odongbo is slightly higher than 2.0% crude fibre recommend by the Nigerian Industrial Standard, NIS (1988). The increased fibre content could be attributed to the cultivar of cassava used. The protein content and the mineral level of the gari samples were slightly higher than those reported in literature. The protein content ranged from 1.04±0.15 to 1.40±0.35% for the gari samples from TMS 30572 and Odongbo respectively. According to Obatolu and Osho (1992) gari should contain 0.7 to 1.2% protein. The difference in protein content observed in the gari samples could be attributed to varietal differences. Gari would not be eaten as a protein source and for a balanced dish it should be combined with legumes or meat and vegetables. The gari from the different cultivars had high carbohydrate content. The value ranged from 82.92±0.58% for gari from Odongbo to 83.31±0.81% for gari from TMS 30572.

All the gari samples were acidic with pH ranging from 3.6 to 4.0. The acidity of fermented cassava roots and its products has been found to be caused by the synthesis of lactates, acetates and some volatile organic acids (Oyewole and Odunfa, 1989). The acid contributes to the desirable sourness of gari and is also an indication of the duration and effectiveness of the fermentation step in gari processing.
The total titratable acidity (TTA) expressed as percentage lactic acid of gari samples are 0.65±0.03, 0.84±0.03 and 0.54±0.01 for Isunikankiyan, Odongbo and TMS 30572 cultivars respectively. These values were in agreement with NIS recommendation of less than 10g/100ml TTA for gari samples. This shows that the period of fermentation of the various samples was adequate.

The results of analysis on the gari yield, hydrogen cyanide content, swelling index and bulk density of gari made from the three cassava cultivars were summarised in Table 3.  Isunikankiyan cultivar recorded the lowest gari yield of 28.0% while TMS 30572 cultivar recorded the highest yield of 37.0% and Odongbo cultivar recorded 34.0%. The changes in the gari yield could be attributed to varietal differences since the same processing technique and processor were used in the production. The cyanide concentration of the gari samples ranged from 1.36 mg HCN/100g to 2.15 mg HCN/100g. The gari produced from Isunikankiyan had the least cyanide value of 1.36 mg HCN/100g while TMS 30572 gari had the highest value of 2.15 mg HCN/100g and Odongbo gari had a value of 1.85 mg/HCN/100g. These values are far below the estimated lethal dose of 4-6 mg/100g reported for gari by Bokanga (1995); Bokanga and Otoo, (1994); Tewe and Maner (1981). Also the values are within the 2-3 mg/100g regarded as acceptable level of cyanide in gari (IITA, 1989). The gari processing technique employed in this study reduced the HCN content in the cassava pulp by 88.5%, 79.4% and 69.9% for TMS 30572, Odongbo and Isunikankiyan cultivars, a safe level for human consumption.

From Table 3, the swelling indices ranged from 2.15±0.04 to 4.45±0.07 for gari from Isunkakiyan and TMS 30572 cultivars respectively. According to Ingram (1975), Ajibola et al., (1987) and IITA (1989), a good quality gari should swell when soaked in water, to at least three times its dry volume, only Isunikankiyan produced gari has less swelling capacity of 2.15±0.04. The bulk density of 0.55 g/cm3 to 0.82 g/cm3 is within the limit reported is within the limit reported by previous workers. According to Ukpabi and Ndimele (1990), good gari should have bulk density of 0.56 g/cm3 to 0.908 g/cm3. High bulk density increases the rate of dispersion (Brennan et al., 1976) which is important in the reconstitution of flours in hot water to produced dough.

Results of the sensory evaluation scores of the gari produced from the three cultivars tested revealed that there were no significant differences in all the quality parameters evaluated. However, the results showed high acceptability for gari produced from TMS 30572 and Odongbo cultivars.

Conclusion
This study shows that the gari yield from TMS 30572 (an improved cultivar) was 80% and 24% higher than the quantity recovered from Odongbo and Isunikankiyan cultivars respectively. However, Odongbo cultivar had an improvement of 17.6% gari yield over its Isunikankiyan local cultivar. Although Isunikankiyan cultivar has the least swelling capacity, its low total hydrogen cyanide value is highly desirable.

The results obtained in this study equally show that the potential exists for selecting cassava cultivars that are suitable for specific products among the existing cassava cultivars grown in each locality in Nigeria. The variability in the percent of gari cyanide content of the cassava pulp from the cultivars and their corresponding gari samples, swelling index and bulk density are clearly useful for the plant breeders that may select cultivars based on certain desirable quality characteristics.
On the basis of low cyanide level, Isunikankiyan could be selected for processing and utilisation in products that require less processing time while the Odongbo and TMS 30572 cultivars are well suited for gari production judging from the quantity and quality of gari produced from both.


                                        
Table 1: Root Characteristics/Chemical Composition of Different Cultivars of Cassava


Root characteristics/constituents

TMS 30572

Isunikankiyan

Odongbo

Colour of the peel

White

Pink

White

Shape

Oblong

Oblong

Oblong

Average diameter (cm)

30.00±1.20

26.25±0.92

32.10±1.32

% peel

14.10±0.87

12.20±0.42

16.15±0.68

% pulp

85.90±1.82

87.80±1.01

83.85±1.53

Dry matter (%)

30.60±0.58

27.20±0.34

29.70±0.67

HCN (mg/100g)

18.70±0.14

4.52±0.09

9.00±0.11

Values of mean ± standard deviation of triplicate determinations.

 

Table 2: Proximate composition, pH and TTA of Gari Produced from Different Cultivars of Cassava


Constituents

TMS 30572

Isunikankiyan

Odongbo

Moisture content (%)

11.80±0.23

11.81±0.20

11.78±0.18

Fat (%)

1.10±0.10

0.62±0.05

0.40±0.02

Crude Protein (%)

1.04±0.15

1.25±0.20

1.40±0.35

Ash (%)

1.10±0.07

1.13±0.04

1.25±0.04

Crude Fibre (%)

1.65±0.34

1.90±0.42

2.25±0.37

Carbohydrate

83.31±0.81

83.29±0.77

82.92±0.58

pH

4.00±0.00

3.90±0.00

3.60±0.00

Total Titratable Acidity (TTA)

0.54±0.01

0.65±0.03

0.84±0.03

Values of mean ± standard deviation of triplicate determinations.

 

 

 

Table 3: Yield and Some Selected Physicochemical Properties of Gari Produced
    Different Cultivars of Cassava


Cultivar

% Yield

HNC (mg/100g)

Swelling Index

Bulk Density (g/cm3)

TMS 30572

37.00±1.44

2.15±0.05

4.15±0.07

0.82±0.21

Isunikankiyan

28.00±1.00

1.36±0.02

2.15±0.04

0.65±0.10

Odongbo

34.00±1.08

1.85±0.00

3.00±0.05

0.55±0.10

Values of mean ± standard deviation of triplicate determinations.

Table 4: Sensory Evaluation Scores of Gari Produced From Different Cultivars of Cassava


Samples

Colour

Texture

Taste

Odour

General acceptability

TMS 30572

4.8a

4.6a

4.4a

4.4a

4.6a

Isunikankiyan

4.3a

4.4a

4.6a

4.3a

3.7a

Odongbo

4.5a

4.6a

4.5a

4.4a

4.5a

Means with the same letters in the same column are not significantly different (P > 0.05). Higher values indicate greater preference.


 

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