DESIGN AND PERFORMANCE EVALUATION OF A CASSAVA PEELING MACHINE

Cassava (manihot esculeta) is an edible root and a perennial woody shrub, which grows in tropical and sub-tropical areas of the world. Cassava originated from tropical America and was first introduced into Africa in the Congo basin by the Portuguese around 1558. Cassava is rich in carbohydrate, calcium, and vitamin B and C. However, according to variety, soil conditions, climate, other environmental factors during cultivation and age of the harvested crops, nutrients composition differs. It is a popular crop worldwide. It is known for drought tolerance and for thriving well on marginal soils, a cheap source of calories intake in human diet and a carbohydrate source in animal feed (Kordylas, 2002). Its importance as a major cheap source of calorie intake for both human and livestock in many tropical countries has been widely acknowledged. It is mostly processed traditionally into garri, fufu and abacha in Nigeria, and kokonte and agbelimain Ghana (Quaye et al., 2009).

Cassava has become one of the prominent crops that are required to be provided for both local consumption and export promotion. In 2004, the federal government of Nigeria initiated a policy to manufacture bread with wheat flour and cassava in the ratio of 9:1 in Nigerian bakery industry. Apart from human consumption, cassava is also used for animal feed and alcohol production (Cork, 1987). 

There is an ever-increasing global demand for cassava chips and pellets, particularly in China and Brazil. Cassava can thus be referred to as a versatile crop for man and livestock. 

The starch from cassava is an ingredient used in production of dyes, chemicals, drugs, carpets and in the coagulation of rubber latex (Odigboh, 1983). 

Since 1930, Nigeria overtook Brazil as the world’s leading producer of cassava with a projected yearly production of 26 million tons from a projected area of 1.7 million hectares of land (FAO, 1991). Some other main producers of cassava are Congo DR, Thailand, Indonesia, India, Malaysia, China, Malawi, Togo and Tanzania (Odigboh, 1983). 

Cassava tuber size depends on the choice and fertility of the soil. The cassava tuber can be separated into three regions. Namely: -

 

I. The periderm: - This is the outermost layer, which has a brown color and is made up of mainly dead cells, which cover the surface of the tuber. 

II. The cortern: - This is found below the periderm. It is generally about 1.5 – 2.5mm thick and has a white color. 

III. The central portion of the tuber: - This makes up the larger bulk of the cassava tuber and is made up of basically stored starch. 

In cassava peeling procedure both the periderm and the cortern are removed as waste, leaving the inner part of the root as the desired output. 

Numerous methods of peeling cassava roots have been adopted. They consist of manual, steaming chemical and mechanical methods. Each has its own merits and demerits. 

The manual method of peeling cassava root is ancient and burdensome. It is done by use of hand in peeling of the cassava root by means of sharp edged object like the knife. 

Chemical method is usually adopted in the industries, particularly in food processing companies. It involves thermal shock and chemical actions, which leads to softening and loosening of the skin using caustic soda (NaOH). The disadvantages of this method of peeling cassava include:

a. Cost of purchasing caustic soda. 

b. The complexity in controlling the penetration of chemical into the cassava tuber. 

c. The complexity in the removal of chemical traces as it may be poisonous. 

The roots are subjected to high steam pressure over a small period of time in other to prevent partial cooking (or eventual cooking). The problem of this method is that the tubers could be subjected further than the time required, which will lead to cooking. 

Mechanical peelers have diverse types of processes that interact directly with cassava skin which removes it in that way providing high quality fresh final products and they are environmentally friendly and nontoxic (Shirmohammadi et al., 2012). Most common prototype cassava root peelers have a functional system such as abrasive devices, peeling drums, rollers, knives, blades and milling cutters which eliminate the outer cortex using mechanical means to reduce drudgery and reduce hazards encountered in manual peeling. The drawback of this method includes the related mechanical damage, peeling off of improper percentage of useful cassava root flesh and decrease in peeling efficiency with improved time of operation with some of the peelers either too slow or too fast and cost ineffective (IITA, 2006). Jimoh et al., (2014) reported that most abrasive and impact peelers manufactured in Africa, China and Brazil is either manually operated, have poor peel removal efficiency or increased mechanical damage (Adetanet al., 2003 and Olukunle, 2005). 

The merit of mechanical peeling is that the edible portions of the products are kept clean and harmless. For this reason, many attempts have been made to develop optimized peeling processes. Analysis of root movement in a mechanical peeling system to achieve high peeling efficiency was idealized by Jimoh et al. (2014) so as to form the basis for near 100 % peel removal as well as whole root flesh recovery. The cassava root movement inside the cassava root peeler may be achieved by incessant collision between the cassava root and peeling tool, linear movement of the cassava root in the path of the auger, displacement of cassava root by kinetic energy, cylindrical barrel circular motion at which peeling tool tract the root, material flow as a result of continuous feeding in the hopper governed by the combine action of the auger, root monitor on each side and the driving force. However, cassava root loss of up to 42 % has been a major disadvantage of mechanized peeling in Nigeria (Olukunle and Jimoh, 2012).

Cassava is one of the most outstanding crops that are vital for mutually local consumption and export promotion in Nigeria. In 2004, a policy was initiated by the Federal Government of Nigeria (FGN) to produce Nigerian bread with cassava and wheat flour in the ratio of 1:9. Apart from human consumption, cassava is also used for animal feed and alcohol production (El-Sharkawy and Cock, 1987). However, it is at the moment one of the most significant food crop in Nigeria from the point of view of both the area under cultivation and the tonnage produced. It has distorted significantly into a high yielding cash crop, a foreign exchange earner, as well as a crop for world food security and industrialization. Freshly harvested cassava tuber would start deteriorating almost instantaneously after harvest and can only last for about three days (Kolawole et al., 2011). This is due to its high moisture content of about seventy percent. The most excellent form of preserving cassava root and the decrease of post-harvest losses of cassava roots is its immediate processing into various shelf stable products such as abacha, starch, garri, flour, pellets, chips, akpu,  etc. (Igbeka, 1985; Oriola and Raji, 2013; Ugwu and Ozioko, 2015). Alternatively, farmers desire to delay harvest of the root until it is really needed, thereby allowing it to remain in the ground for up to two years and beyond since it stores well in-ground. Efforts at developing modern storage technologies to store cassava root beyond few days are still on-going (Oriola and Raji, 2013). 

Lack of mechanization is responsible for the long time required for processing cassava root. Therefore, the drudgery in post-harvest processing of cassava root into products that can be utilized can be reduced or eliminated through sufficient mechanized cassava root processing. Survey of previous literatures on the Nigeria research institutions revealed an amount of mechanized cassavas root peelers (Aniedi et al., 2012). These peelers have not been advanced and put to use commercially for the farmers and stakeholders in the cassava industry and value chain to benefit from, due to the low efficiency of the machines. 

Apart from the above-named stable products, cassava roots are also utilized for other food products such as bread, lafun,  food for babies, glucose, biscuits, gravies, etc. or industrial products: livestock feed, , glue, etc, (Aniedi et al., 2012;  Echebiri and Edaba, 2008). Syrup concentrates used soft drinks production,  pre-gelled starch for making adhesives, hydrolysates for manufacturing pharmaceuticals drugs and seasoning are also derived from cassava.  (FAO, 2007; Ilori and Adetan, 2013). It also serves as a constituent in dyes production, industrial chemicals, carpets production, used as binder for  textile industries and  additive for rubber latex (Ugwu and Ozioko, 2015; Kamal and Oyelade, 2010;  Odigboh, 1983a). There has been an increase in the demand for this product; arising the interest of Government in cassava research with strong importance on mechanization (IITA, 2006). 

According to Oriola and Raji (2013) cassava processing into finished or semi-finished products usually involves all or several of the subsequent operations, depending on the preferred end-product: peeling of the cassava root, washing of the peeled root, grating/chipping, dewatering, fermentation, pulverizing, sieving, pelletizing, and drying/frying (Kolawole et al., 2010; Jimoh et al., 2014).

Garri Processing Operations include:

Most of these operations are still done manually particularly peeling, and they are generally labor intensive, difficult in nature, consumes time and inappropriate for vast scale production due to having a low product output (Adetan et al., 2003; Davies et al., 2008; Quaye et al., 2009).

Cassava is a tropical plant which has a fibrous root system. Some of these roots develop into root tubers by the process of secondary thickening. These roots develop radials about the base of the plant forming five to ten root tubers per plant. These are the main economically useful parts of the plant (Ajibola, 2000). It often elongated, depressed and crevices along its length and tapers to one end. In the majority of cases, the center part has a moderately even diameter. Whereas the head end has a relatively large diameter, the tail end has a considerably smaller diameter compared to the middle part. The head and tail ends are generally referred to as the proximal and distal ends respectively. At its proximal end, the tuber is joined to the rest of the plant by a short woody ‘neck’ (Adetan et al., 2003). A transverse section of the root shows that it consists of central core called the pith. This is enclosed by the starchy flesh that makes up the mass of the root and constitutes the major storage region. Covering the cambium layer is the root peel. The peel is made up of a corky periderm on the outside which has a dark color and can be detached by brushing in water as it is being done in the washers in large factories. The internal part of the peel contains the cortex. The cortical region usually has a white color (Adetan et al., 2003), as shown in fig 1.1.

Fig.1.1: Morphology of cassava root: (a) general morphology and (b) transverse section      Source: Adetan et al.,(2003)

The loosening of the whole peel from the central part facilitates the peeling of the roots. As the diameter of the root increases continuously, the continuity of the cork layer is broken, so that longitudinal cracks or fissures appear on the cassava root surface. However, new corks soon form underneath the cracks to bring back the integrity of the protective corky layer (Igbeka, 1984).

Cassava root processing operations are often preceded by peeling which makes it a very important operation. Peeling the root of the cassava is the first procedure carried out after harvesting the cassava and debris has been removed. It entails peeling off the outer skin of the cassava roots or the thin layer elimination (more often called the peel) from the cassava root. Peeling, therefore, must make sure which layer to take out, so that the cassava root peeled and the peels can be used for various purposes. Other problems presently faced in peeling of cassava root include: 

i. Peeling off of improper proportion of useful cassava root flesh when peeling mechanically. 

ii. Decreased peeling efficiency with increasing operational time and speed. 

iii. Peeling manually, is moreover slow, labor intensive or cost ineffective. 

iv. Inadequate technological information on cassava roots engineering properties necessary for designing the machine and also the operational parameters of the machine and crop essential for the modeling and design of the peeling process. 

v. cassava root age and range (Oriola and Raji, 2013; Olukunle et al., 2010; IITA, 2006; Adetan et al., 2006;) that affect the properties of the root. 

To these ends, the need to develop a cassava peeling machine that would remove the cortex of the cassava root without substantial cassava root loss of useful flesh is needed.

This work is aimed at developing a machine capable of peeling cassava roots, with the following specific objectives to:

The study is limited to:

When processing cassava into garri or cassava flour, cassava peeling is one of the first steps. After cassava peeling, it will be easy to process cassava into garri or cassava flour, but the drudgery associated with peeling cassava manually (using of knife) has always been a challenging task. Thus, the need for mechanization of cassava root peeling is of great importance. 

In order to engage in large scale production of garri and cassava flour, cassava peeling system must be mechanized due to the negative factors associated with manual peeling, because it is normally rigorous, tough in nature, consumes time and inappropriate for production of large scale because it has a low output.

According to Kadurumba and Aririguzo (2021), several made attempts to solve these problems, has resulted in the development of various cassava peeling machines. However, the common setback with these cassava root peelers is that cassava root are reduced to a uniformly cylindrical profile with large amount of useful flesh wastage before achieving adequate peeling, having an efficiency as low as 45%. Therefore, a machine that can peel cassava effectively and efficiently is important for those who want to engage in small- and large-scale cassava processing.