10. Cassava: Technological Interventions
10.1 Cassava Flour and Starch: Processing Technology and Utilization
Taofik A. Shittu1,2, Buliyaminu A. Alimi2, Bashira Wahab1, Lateef O. Sanni1, and Adebayo B. Abass3
1 Department of Food Science and Technology, Federal University of Agriculture, Abeokuta, Nigeria
2 Department of Bioresources Engineering, School of Engineering, University of Kwazulu-Natal, Pietermaritzburg, South Africa
3International Institute for Tropical Agriculture, Regional Hub for Eastern Africa, Dar es Salaam, Tanzania
10.1.1 Introduction
Cassava (Manihot esculentus, Crantz) is one of the root crops with growing food and industrial applications. It has been one of the mainstays of several tropical and sub-tropical countries of the world. According to FAO statistics, the world’s cassava production had been on the increase from about 176–277 metric tons per year from the years 2000–2013. Africa contributed between 54 and 58 % of the world’s cassava within these periods (Figure 10.1.1). Nigeria is the largest cassava root producer in the world. The impacts of cassava on the economies of different countries have changed in the last two decades. Previously, in some economies, it was an economic crop while in some others it constituted merely a poverty alleviation crop. Except in a very few countries, cassava has assumed a prominent position as an industrial crop with constantly growing utilization avenues.
Figure 10.1.1 Production of cassava between 2000 and 2013 (source: FAO, 2014).
The roots are highly perishable due to their high moisture content at harvest. Besides the advantage of preserving the root, processing is also used to add value to the raw roots by converting them to several primary and secondary products of varying economic importance. Primary products are those derived from raw roots without extensive transformation (or modification) of cassava tissue via chemical, enzymatic and microbial processes. Primary processing of cassava roots merely involves physical modification to achieve either root preservation, enhanced handling or storage stability. Such products are either consumed by humans or animals, or used as raw materials in some other processing applications. These include mainly chips (dried and boiled), flours and starch. The proportion of cassava root processed to specific end products differ from region to region. Overall, the extent, direction and capacity of cassava roots-value addition in any country depends on the level of economic and technological advancement.
Flours and starch powders are the two major primary products from cassava roots traded world-wide. They are essentially dried products, often packaged, stored or marketed at low moisture levels (10–14 %, wet basis). Numerous studies aimed at improving their quality and expanding their utilization have been conducted world-wide, especially in regions where cassava potentially have comparative economic advantaged over other root crops. This chapter seeks to describe the existing and emerging cassava processing technologies, and utilization of cassava flour and starch.
10.1.2 Cassava Flours
Cassava flour (CF) refers to the dry, fibrous and free-flowing particulate product obtained from cassava roots. It is either prepared from milled dried chips or wet mash. Mashing of cassava root can be achieved by grating, pounding or milling of peeled roots. The prepared mash may either be fermented or unfermented. When the unfermented mash is dried and milled, it gives rise to a bland, odorless, white or off-white particulate product also known as high-quality cassava flour (HQCF). The flours from fermented cassava root are also known as lafun, fufu or pupuru in Nigeria. Report of the Collaborative Study of Cassava in Africa (COSCA) indicated that CF and chip production consumed about 45 % of cassava roots produced in the sub-Saharan African region (Nweke, 1994).
10.1.2.1 Processing Technology
The main processing steps in CF production are summarized in Table 10.1.1. Similar to other sub-Saharan African countries, the CF processing technology has experienced tremendous improvement in Nigeria over the last four decades. Due to the changing status of cassava from poverty alleviation to an economically important crop, there has been a shift in the level of cassava processing technology. Nowadays, improved (mechanized) processing techniques are now replacing existing manual operation. The greatest drudgeries of manual peeling, size reduction, pressing, drying and milling have now been removed by the advent of various mechanical devices that perform these operations. It has given an opportunity to increase the throughput of many plants as well as improving the quality of product.
Table 10.1.1 Description of technological effect of processing steps during CF manufacture
Processing step | Technological effect | Authors and years of study
Root washing | Mainly to remove the adhering dirt and sand particles from the root surface prior to peeling. It is done with clean water. | -
Peeling | To separate the flesh from skin. | Ezekwe (1976); Igbeka (1985); Ohwovoriole et al. (1988); Oluwole and Adio (2013)
Washing | To further clean the peeled root from adhering dirt and incompletely removed skin during peeling | -
Root Size reduction | Might involve chipping, chunking or grating of peeled cassava root. The grating process leads to lower particulate wet mash while chipping and chunking leads to larger particulates more difficult to dry. | Jones et al. (1994) Doporto et al. (2012)
Fermentation | Allowing the wet mash to ferment for 3–5 days in sacks or fermentation vats | Westby (1991); Okolie and Ugochukwu (1988); Ampe et al. (1995)
Dewatering (or Pressing) | This is done to remove excess water from the wet cassava mash after root grating and/or fermentation, It gives rise to wet cake. This makes handling easy and enhances drying of the wet mash. | -
Drying | Wet cake is pulverized and either sun dried or flash dried to moisture content below 12 %. It gives rise to dry and coarse cassava meal. | Shittu et al. (2001); Osundahunsi (2005); Bindziet al. (2014).
Dry Milling | Dried meal is milled to fine particulates (flour) also known as CF or high quality cassava flour if the whole process is completed within 24 h. | Shittu et al. (2002); Adesina and Bolaji (2013); Defloor and Delcour (1993)
Cassava Peeling Peeling of cassava roots is one of the most tedious unit operations during cassava processing. It is done to remove the dark, rough skin. Women and children are the ones mainly involved in carrying out this operation by using sharp knives. The manual peeling is slow and burdensome due to the irregular shapes and sizes. The peel, which consists of periderm and cortex, also varies in thickness, texture and strength. The manual peeling operation is still predominantly used in most cottage, micro and small cassava processing outfits. Research efforts over the past four decades have been devoted to development of mechanical means of peeling cassava roots. Various designs of peelers have since been reported (Adetan et al., 2006; Ezekwe, 1976; Igbeka, 1985; Ohwovoriole et al., 1988; Oluwole and Adio, 2013). The peeling is actualized by either abrasive or cutting mechanism. About 75–97 % peeling efficiencies have been reported for these designs. Use of abrasive peeling requires more water for washing than cutting methods. Although chemical and steam peeling methods used for potatoes have been tried for cassava peeling, the ineffectiveness and attendant quality issues have not made them satisfactory for industrial cassava processing. Use of lye (hot sodium hydroxide solution) to loosen and soften the skin of cassava root requires longer immersion time. This consequently causes objectionable heat rings in cassava flesh as well as starch gelatinization (Igbeka, 1985), making chemical peeling unsuitable for food and starch manufacture.