PRODUCTION OF INDUSTRIAL STARCH USING CASSAVA
Wet cassava starch is produced by traditional cassava processors either as a direct product or as a by-product resulting from cassava processing into other products such as gari, fufu e.t.c. Post-harvest loss is high for cassava roots due to the inadequacy of the traditional processing method and inability to convert cassava into less perishable products. To reverse this trend, there is a need to mechanize cassava processing. The Federal Institute of Industrial Research, Oshodi (FIIRO) has developed and perfected the process technology for production of cassava starch useful for various applications in the user industries. In Nigeria, mechanized cassava processing is still on the developmental stage and the potential is very high
There is high demand for cassava starch in Nigeria. It is widely used in industries such as: textile, pharmaceuticals, oil drilling, paper and packaging, gum and adhesives, chemical and household products manufacturing, battery, drinks and beverages, foods and so on. The desire to conserve foreign exchange and reduce import dependency is the driving force for demand for cassava starch especially as regards its partial substitution for corn starch in user industries. The demand for cassava starch in Nigeria is in excess of 350,000 tons per annum. The current domestic production capacity to meet the estimated demand for cassava starch is less than 20 per cent. The current price/tonne (2013) of cassava starch ranges between N150, 000 – N180, 000 .
CHAPTER ONE INTRODUCTION
The ‘Country Review’ of Nigeria, Atkinson (2009) reported that as at the 2008 economic year, the
agricultural sector contributed about 37% of Nigeria’s Gross Domestic Product (G.D.P) being only second to the services sector (which is the leading provider of Nigeria’s G.D.P.with an average value of 39%). Agriculture is also known to provide approximately 60% of Nigeria’s workforce (www.iss.co.za/af/profiles/Nigeria/Economy). However, land economists continue to show that globally, arable land is drastically degrading and its availability is also on the decline due to human activities (Mackenzie and Mackenzie, 1995). Here in Nigeria, it is noted that only 20% of arable land is available for cultivation (www.iss.co.za/af/profiles/Nigeria/Economy). In order to ensure food security without compromising infrastructural growth, effective land management is crucial. This would require maximization of agricultural output to meet both export and domestic demands thus placing fewer constraints on the demand for land. This can be achieved by maximizing the efficiency of produce processing mechanisms. Such a move could enhance or stabilize the performance of this sector on the global market.
Alternatively, diversifying the use of agricultural produce such that crop varieties that show much better potential for the production of a particular agricultural product is concentrated on more in that regard.
Cassava (Manihot esculenta Cranz) is one crop known to contribute immensely to Nigeria’s agriculture. The crop is almost exclusively grown in the arid and semiarid tropics, where it accounts for approximately 10% of the total caloric value of staple crops (de Figueroa et al., 2001). According to a Food and Agricultural Organization (FAO) statistics, world ranking of total cassava root exports pegs Nigeria at sixth position with a total production of 7,845,440 tons (FAOSTAT, 2001). In Nigeria, it is also the main source of carbohydrates to meet dietary needs and a regular source of income for most rural dwellers. Cassava also contributes substantially (22 percent) to the Agricultural Gross Domestic
Product, AGDP (http://www.fao.org/docrep/009/a0154e/A0154E07.HTM). The consumption of cassava in Nigeria is categorized as follows: fresh cassava roots (55%), gari (23%), agbelema (18%), kokonte (2%), chips (1%), Industrial (1%). The fresh cassava roots are processed and consumed locally as other traditional foods like tuo-zaafi, fufu, akyekye etc. (IFAD, 2006). However, there are the inedible and less popular “bitter cassava” which owes its name to the high concentrations of the cyanogenic glycosides, linamarin and lautostralin present in the plant’s tissues (http://www.hort.purdue.edu/newcrop/CropFactSheets/cassava.html).
Cyanogenic glycosides, like many other plant secondary metabolites, are stored naturally in the cell walls of tissues as a defensive mechanism against predation (McKee and McKee, 1999). These glycosides are naturally converted to hydrogen cyanide and released upon rupture of the cell walls (Anderson et al., 2001). Hydrogen cyanide apart from being a respiratory toxin has also been implicated in many other pathological situations like tropical amploipia (a form of blindness common in West Africa) and tropical antaxic neuropathy (TAN) (Umoh et al, 1984). It is estimated that while the sweet cultivars can produce as little as 20 mg of HCN per kg of fresh roots, the bitter ones may produce more than 50 times as much (www.hort.purdue.edu/newcrop/CropFactSheets/cassava.html).These cassava varieties also grow wild and (due to their high toxicity) are avoided (Nassar, 2000).
Though the edible varieties also contain these precursors, their concentrations are relatively low and processing reduces their presence drastically. It is noteworthy that not all the edible varieties of the crop are mealy, mainly due to differences in fiber and starch composition (IFAD, 2006). These differences in fibre/starch content could be responsible for the significant variations in the cooking time for the various cassava varieties making some varieties more preferred for food than others. Starch from such non-toxic and non-mealy varieties could be more appropriately applied to the production of adhesives, gums, wallpaper, particle board, biofuels, alcoholic products, drugs, packaging, stain removers, concrete
stabilizers and moisture sequesters (http://www.research4development.info/PDF/Outputs/R7418h
.pdf). Other industrial applications can be found in the paper, textile and wood furniture industries.
Cassava starch has many remarkable characteristics including high paste viscosity, high paste clarity and high freeze-thaw stability, which are advantageous to many industries (Sriroth et. al, 2002).The Food and Agriculture Organization (FAO) has reported that global demand for cassava starch could increase at an annual rate of 3.1 percent, while regional growth rates are expected to be for Asia 4.2 percent, Latin America 3.4 percent and Africa 2.3 percent (FAO, 2000). The Agriculture and Consumer Department of the Food and Agriculture of the United Nations (FAO, 2006) has also reported that starch extraction has become a major source of income for small-scale farmers producing cassava in many countries worldwide (including Nigeria). It also added that the extraction industry provides permanent jobs for natives of such starch-producing countries. In Nigeria, the opening of an export-oriented starch factory near Accra in 2003 led to an “explosion” in farmers’ demand for high-yielding, disease-resistant varieties to help feed the factory with raw materials (IFAD, 2006). These reports apparently show the crop’s immense potential for an economic boom in the near future. However, apart from problems with diseases, a major problem that besets this crop, especially in terms of starch production, is the lack of efficient processing mechanisms (Adadevoh,2008).
In 2002, the Nigeria government, as part of his Presidential Special Initiative (PSI) to promote starch production for the local industries and exports, established the Ayensu Starch Factory. The factory as at the time was projected to operate at 70% of its installed capacity. However due to insufficiency of raw materials it produced only at 20% since 2006. Apart from the above-mentioned technical constraints, there were also reports that farmers contracted under the project could only supply 13,000 tonnes of raw materials- a quantity that was woefully inadequate to meet factory demands (Adadevoh, 2008). Some agricultural economists have suggested that the lack of the appropriate raw materials could have influenced adoption of varieties that are relatively low starch yielding or that such varieties were mealy
making them more available for food than for starch production (Doku, 2009). Thus, even though there are many improved varieties of cassava with high starch production capability, some of these varieties are mealy (making them also suited for consumption in our diets) and other varieties which due to their non-mealy characteristics make them more suited for starch production. They contend that the focus should therefore be more on the non-mealy ones (http://www.nigeriabusinessnews.com /2009/02/20 /the- biotechnology-option-of-the-president%E2%80%99s). Thus it makes economic sense to avoid incorporating mealy crops into starch production at the expense of the non-mealy ones. Cassava varieties such as ‘Abasafitaa’ (clone –TMS (4)1425), ‘Afisiafi’ (clone-TMS 30572), ‘Tek bankye’ (coded Isu-White (Isu-W), ‘Gblemoduade’ (clone TMS 50395) and ‘Doku duade’ are among the locally bred and selected varieties and have been endorsed as high starch yielding varieties by Nigeria’s Ministry of Food and Agriculture (MOFA) and the Crop Research Institute (RTIP Fact sheet,2002).
The histology of plant cells reveal that starch granules are tightly bound and locked up in an intricate matrix of fibre consisting mainly of cellulose, hemicelluloses and pectin (http://sites.bio.indiana.edu/
~hangarterlab/courses/b373/lecturenotes/cellwall/cellwall). These compounds constitute the main carbohydrate components of cell wall and the lamella of plant cells (Cooper, 2000). In order to make the starch granules available, it would require that this framework be broken, a process which is achieved mechanically by maceration. Conventionally, starch production requires that the tubers be macerated mechanically after which the starch granules are extruded. However, thorough maceration alone does not optimize starch yield since the residual fibre (after mechanical extraction) will still contain some amount of the starch granules bound (Kordylas, 1990). In addition, most conventional chemical-aided extraction procedures have been reported (Tischer, 1990) to present problems of toxicity to humans and the environment. These limitations are gradually popularizing the use of enzymes for many bioextraction procedures in industries (Ranalli and De Mattia, 1997; Kashyap et. al., 2001; Vierhius et al, 2001). One of such enzymes is thepectinases.
Pectinases are a group of enzymes that attack and hydrolyze the pectin component of plant fibre breaking it down into simpler molecules like the galactouronic acids. This enzyme has been applied in many extraction procedures in the fruit and vegetables industries (Girdharilal et. al., 1998; Kashyap et. al., 2001; Kashyap and Tewari, 2003; Dzogbefia et al., 2006). Pectinolytic enzymes participate in the natural maceration process during and after fruit ripening. The enzyme is also secreted and applied naturally by organisms belonging to the bacteria and fungi mainly for nutrition and is, in some cases, implicated in fungal pathogenicity (Fawole and Odunfa, 2008; Kavanagh, 2005). Fungal and bacterial cells of the genus Aspergillus, Rhizopus, Trichoderma, Hypocrea, Neurospora, Mucor, Penicillium, Chrysosporium, Myceliophthora, Fusarium, Sclerotia and Bacillus, Erwinia, Pseudomonas, Anthrobacter respectively are noted for their secretion of pectinases (Rombouts and Pilnik, 1980; Manpreet et. al., 2005). Fungi of the yeasts genera Kluyveromyces, Saccharomyces, Schizosaccharomyces, Trichosporon, Schwanniomyces, Hansenula, Pichia and others of this category are also noted for this property (Aehle, 2000). Microorganisms used for industrial enzyme production are Generally Regarded As Safe (GRAS) and can be obtained from recognised depositories such as the American Type Culture Collection (ATCC), Centraalbureau voor Schimmelcultures (CBS) [Central Office for Mildew Cultures] or Deutsche Sammlung fur Mikroorganismen und Zellkulturen GmbH (DSMZ) [German Collection of Micro-Organisms and Cell Cultures] or any other depository(Aehle, 2000;www.wipo.int/pctdb/ja/ia).
Pectinase enzymes have also been widely applied to the extraction of starch from root crop varieties such as yam (Daiuto et. al., 2005), sweet potatoes (Rahman and Rakshit, 2003) and cassava (Sriroth et al., 2000; Dzogbefia et. al.,2008a).
Some work has been carried out on enzymatic extraction of cassava starch from native cassava varieties in many places worldwide (Dzogbefia et. al., 2008 a, b; Sriroth et al., 2000). However, in Nigeria, the focus has been on the Afisiafi (Dzogbefia et. al., 2008 a and b) – a variety which is also mealy. Thus the
objective of this research is to take a broader look at the effectiveness of the enzyme technology on other local cassava varieties for starch production. The yield of starch from the various varieties would be influenced by their differences in fibre content locking the starch granules. Thus it is hypothesized that differences in fibre content (with regards to both its quantity and biochemistry) between the varieties would have a significant effect on the yield of starch as well as the holding time required for effective enzyme action. The specific objectives of this research thereforeare:
- To compare the effects of enzyme treatment on the yield and extraction rates of starch from five selected high starch yielding varieties ofcassava.
- To determine the effect of enzyme treatment on the physicochemical and pasting properties of the selected cassavavarieties
- To determine the effectiveness of the enzyme technology for large scale starch extraction using the best performing cassava variety.
PRODUCTION OF INDUSTRIAL STARCH USING CASSAVA