ABSTRACT
The effect of variety and
processing methods on the physicochemical and sensory properties of gari in
three districts of the Brong Ahafo region was studied. The study aimed at
investigating the effect of cassava varieties and processing methods on the
proximate, functional, physicochemical and sensory properties of gari. Gari was
processed from Bankyehemaa, Ampong and Bensre cassava varieties.
Each of the varieties was processed using both traditional and modern
processing methods to obtain six gari samples. Physicochemical, proximate and
functional analyses were conducted on all the six samples, after which sensory
evaluation was carried out using a thirty member panel based on ratings on
bases of colour, taste, aroma, texture and overall acceptability. The results
showed that carbohydrate, protein and moisture content of gari from all the
varieties were significantly different (P < 0.01). Bankyehemaa had
the highest carbohydrate (90.31%) and protein (3.41%) contents. Processing
methods did not have any significant impact (P > 0.01) in making variation
among the functional properties of gari. The hydrocyanic acid level of the
varieties was not significantly influenced (P > 0.01). However, the
interaction of variety and processing methods influenced significantly
differences among pH and hydrocyanic acid of gari. Traditionally processed gari
had the least cyanide content as compared to gari obtained from modern
processing method. Overall acceptability from sensory evaluation showed that Bankyehemaa
gari samples processed through both methods were the most preferred, and the
traditionally processed Bensre gari was the least preferred. From the
results, it was concluded that variations in physicochemical properties were
due to both genetic variation and processing methods. Traditionally processed
gari is safer for consumption due to low hydrocyanic acid content.
CHAPTER ONE
1.0 INTRODUCTION
Cassava is a popular root crop widely cultivated in the
tropical areas. It is scientifically known as Manihot esculenta which belongs
to Euphobiaceae family. The plant is a woody shrub usually cultivated as
perennial. The enlarged tuberous roots are highly perishable and can be stored
only for a few days after harvest. The root provides a lot of carbohydrates to
consumers. The crop is highly resistant to drought and has the ability to
survive on poor soils. Variation in yield depends on cultivar, planting season,
soil type and fertility of soil. Yields of improved varieties can reach 20-25
tonnes per hectare when cultivated under proper management practices. It is
mainly cultivated for the roots but its leaves are also used as vegetables. The
tuber contains 25 to 30% starch but poor in minerals, protein, vitamins
(Ayankumbi et., al 1991). Both the leaves and roots are for human consumption
and for feeding animals which are important source of carbohydrates, protein
and minerals in the diet.
Cassava provides food security in Africa. More than two
billion people living in Africa, Asia and Latin America will depend on roots
and tubers such as cassava, yam and sweet potato for their nutrition and tax
income by 2020 (Scott et al., 2000). Also, Food and Agriculture Organization
Corporate Document Repository entitled “The World Cassava Economy” produced by
Agriculture and Consumer Protection indicated that almost 70 % of the world
cassava production is produced in Nigerian, Democratic Republic of Congo,
Brazil, Thailand and Indonesia .The report added that more than 50 % of the
present global production of cassava is cultivated in Africa of and about 70%
of the region’s production is harvested in Nigeria, Democratic Republic of
Congo and Tanzania.
According to Egesi et. al. (2006) Nigeria is the leading
cassava producer worldwide which produces about 45 million metric tonnes and
cassava transformation in Nigeria is the most advanced in Africa. Globally,
Ghana is and the sixth highest cassava producer and the third in Africa, with
about 70 percent of local farmers producing over 14 million metric tonnes every
year. Production of cassava in Ghana increased from 14,270,000 metric tonnes in
2011 to 14,547,000 metric tonnes in 2012 and went up to 14, 990,000 metric
tonnes in 2013(www.theafricareport.com/West-africa/
Ghana).
Recently there is an increasing demand for quality products
processed from fresh cassava such as gari, flour, dough, starch and alcohol.
This has enhanced the production of cassava because farmers have ready market
for their produce. Generally, roots of cassava mature 6 -18 months depending on
the cultivar. The crop is popular because of its use in producing food such as gari,
fufu and kokonte. The root deteriorates quickly after harvesting and has to be
processed within 24 hours after harvest (Hahn, 1998). Gari is a fermented
product of fresh cassava tubers which is an important source of energy for
consumers in Tropical Africa (Ihekoronye and Ngoddy, 1985). Gari is also widely
consumed because it has a longer shelf life as compared to other products
produced from fresh cassava. Its wide consumption is also attributed to the
ease of preparation for eating. The popularity of gari in rural and urban communities
is due to its ease and ready- to-eat-form (Flach, 1990).
A safety concern in the eating of cassava based products such
as gari is due to the presence of cyanohydrins which breaks down to produce
hydrogen cyanide (Ernesto et al., 2002; Bokanga, 1994). Some cassava varieties
contain large quantities of cyanide which is toxic to human health and gives the tuber a
bitter taste. Cassava varieties are classified as sweet or bitter based on the
cyanide level.
Bitter varieties have high starch content and are usually
used for industrial purposes. The sweet varieties are normally consumed as
food. Gari processing methods vary from locality to locality and from processor
to processor. However, the two most common methods are the traditional and
modern methods. Both methods of processing bring about reduction in the cyanide
content of the fresh cassava tubers. The traditional gari processing method
reduces the cyanide content in gari through prolonged period of fermentation up
to seven days which is a vital strategy for producing a safe product (Sanni,
2001).
According to Nweke et. al. (2002), gari processed by the
traditional method contain varied amounts of cyanide because different
processors tend to shorten fermentation period in order to meet the increasing
market demand. The traditional method of processing gari is tedious and usually
used to produce gari in small quantities, as compared to the modern method
which is used to produce gari in commercial quantities. It is therefore
important that the use of modern method should aim at reducing the period of
fermentation and still eliminate cyanide so as to obtain gari quality and also
produce quantities that would meet the ever increasing market demand for gari.
Gari is produced from any available cassava variety. Since different cassava
varieties differ in quality characteristics, the interactions between cassava
variety and the method of processing may affect the physicochemical properties
of the gari, and consequently the quality of the gari produced. Studies have
shown that the major processes involved in gari processing (peeling, grating,
fermentation, pressing and roasting) vigorously effect cyanide elimination, as well
as other physicochemical properties of the product (gari).
Not much research have been done on the effect of cassava
variety and gari processing methods on the physicochemical properties of gari.
Therefore understanding the effect a particular cassava variety and processing
methods have on the proximate functional and physicochemical properties of gari
will greatly aid the production process of gari. In recent times, improved
cassava varieties such as Ampong, Bankyehemaa, Sika bankye and Esam bankye have
been introduced to farmers for cultivation within the Wenchi Municipality,
Techiman Municipality and Techiman North District, all in the Brong Ahafo
Region.
Most gari processors now use these new varieties alongside
popular local varieties like Kentema, Bensre, Asuma, Ahenemma, Buoyam and
others .The gari processors in the study area complain that even though the
improved varieties are high yielding, they do not produce the best quality gari
as compared to some of the local varieties. Some cassava growers have therefore
threatened to stop the cultivation of these new varieties. This can be a threat
to food security because the demand for cassava, and for that matter gari,
would be high as a result of low production of cassava.
More often than not, most gari processors use a mix of both
the local and improved varieties in processing gari. Since each variety has
different physicochemical properties, there is the need to conduct a study into
the physicochemical properties of selected local and improved cassava varieties
commonly cultivated and used for gari processing in the study area so as to
ascertain the claim by the processors. In addition, research on the methods of
processing gari, and making appropriate recommendations with reference to a particular variety would be of great
benefits especially to the people within the study area and the nation as a
whole.
The study would provide a solution to the inability of gari
processors to identify varieties which would produce gari of the best quality
so that farmers would know which varieties to cultivate based on demand of the
gari processors. It may also provide information for government, financial
institutions and Non-Governmental Organizations (NGOs) who would be interested
to support cassava farmers and gari processors in the study area.
1.1 OBJECTIVE
The main objective of this research was to determine the
proximate, functional and physicochemical properties of selected local and
improved cassava varieties using two different gari processing methods.
1.1.1 Specific Objectives
The specific objectives were to:
i. To investigate the effect of cassava varieties on the
proximate composition and of gari.
ii. To investigate the effects of cassava varieties on the
functional properties of gari.
iii. To investigate the effect of processing methods on the
physicochemical properties of gari.
iv. To determine the interactive effect between cassava varieties
and processing methods on the physicochemical properties of gari.
v. To determine the relationship among physicochemical
properties and sensory attributes of gari.
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