Cassava Waste as Feedstuff 1: Cassava peel production, processing, and nutrient composition

Published date: 8^th June 2020

Introduction

Cassava is an extensively farmed annual crop in the tropical and subtropical countries of the world for its edible root tuber and leaves. It is a stable crop well adapted to the agro-ecological conditions of sub-Saharan Africa. According to FAO (2014) estimates, global cassava production has been put in recent times at 290 million tons per annum, with Africa accounting for 158 million tons or about 57 percent of global production. Nigeria is currently the world's highest producer of cassava, with an annual production estimate of about 54 million tons according to FAO (2015). The Nigerian Cassava Master Plan of 2006 had the overall objective of sustaining the country's global position as a major player in cassava production and also to upgrade the use of cassava into primary industrial products such as starch, ethanol, chips, and flour, and to create an industrial basis for national economic diversification. The current global average harvest of cassava roots is 12.8 tons per hectare, however, there is the prospect of this increasing to an average of 23.2 tons. This would average more than 500 million tons a year, while yield could reach 80 tons per hectare under optimal conditions.

This growth in the cassava production is driven principally by escalating food demands in the African continent and its growing industrial applications in Asia, particularly for ethanol and starch production. In African countries, cassava serves as a daily source of energy when processed into a wide variety of granules, pastes, and flour or when consumed freshly boiled. In some of these countries, the cassava leaves are also eaten as a green vegetable for their energy, fiber, and vitamin contents. The crop, therefore, plays a vital role in alleviating African food insecurity through its efficient food energy production and storage, year-round availability, tolerance of varied climatic conditions and pest attacks, as well as suitability to the peculiar farming and food systems in the continent.

Cassava and its wastes as animal feed

According to FAO (2013) estimates, 34.4 percent of the global cassava production of about 76 million tons was annually used as animal feed. The figures for Africa and Western Africa were 37 and 24 million tons respectively, indicating that West Africa accounted for about 66.0 percent of African usage. The African data are probably underestimated because cassava roots and leaves are also routinely fed to small ruminants and pigs in the cassava producing areas, either as fresh or cut-and-dried forms. Cassava and livestock farming are particularly complimentary in most rural communities because by-products of cassava processing are also fed to sheep, goats, and chicken as a major part of their diets. FAOSTAT (2012) cassava utilization data showed that cassava produced in Nigeria was used mainly for animal feed (45.6 percent) and human food (45.7 percent), while the remaining 11.7 percent was wasted due to poor post-harvest and processing methods adopted by producers.

The proportion of cassava being used for animal feeding in Africa is however mostly utilized in a fresh form as cassava foliage (stems and leaves), cassava peel (fresh, dried, boiled or ensiled) and broken cassava roots or as by-products of cassava processing such as cassava meal (powdered residue), cassava pomace (also called bagasse, bran or pulp) and cassava whey. Only a limited amount is directly processed whole cassava root tuber into feedstuffs such as cassava pellets, cassava chips, gelatinized cassava grains, and fermented cassava products. The presence of cyanogenic glycosides in cassava products meant for animal feeding limits cassava use in non-ruminant feeds. Elimination of the toxic glycosides is, therefore, a prerequisite to the acceptance of cassava as a major ingredient in commercial animal feeds.

Cassava peels production and processing for animal feeding

The major by-products of cassava processing into human food or industrial products are cassava peels and sieviate (chaffs resulting from the processing of cassava into fufu). These constitute about 25 percent of the processed root tuber and are used traditionally either as animal feedstuff or discarded as waste. Cassava peels constitute about 5 – 15 percent of the cassava root. It is generated as a waste from both small and large-scale cassava processing into garri, starch, and flour. An estimated 50 million tons of cassava peel waste per year are produced in Africa. This according to estimates could form the stock for producing 15 million tons of feed grade cassava peel products for feeding livestock and aquaculture in the continent. In Nigeria, the 14 million tons of cassava by-products including peels and undersized tubers and accounting for 26 percent of annual production are described as waste, constituting environmental problems at several cassava processing locations.

The nutritional drawbacks to the use of these cassava by-products in non-ruminant animal feeding are their low protein content, high fiber (cellulose and hemicelluloses) content, and presence of anti-nutritional cyanogenic glucosides, which limit their utilization due to high water absorption and cyanide poisoning respectively. Several tropical studies have reported practicable methods of improving the nutrient composition and utilization of cassava peels and other cassava by-products both at the small-scale and commercial-scale farms.

Processing of cassava peel for animal feeding

Cassava peel can be used to produce good quality silage for ruminant and pig feeding. The peels are first chopped into short lengths of about 2 cm for easy compaction and wilting for two days to reduce the moisture content from 70 – 75 percent to about 40 percent. They are then ensiled under those conditions for 21 days so that they turn light brown, firm in texture, and possessing a pleasant odor, a pH of 4.4, with no observable fungal growth. Sun-dried cassava peel could also be milled to produce cassava peel powder, which could be inculcated in poultry and pig diets. It will usually require 2 to 3 days of intense sun drying to reduce the moisture content of cassava peel from 60 to 20 percent, which can still support fungal growth.

Recently, researchers at the International Livestock Research Institute (ILRI) at Ibadan, Nigeria developed a new technology for harnessing cassava peels as a sustainable source of animal feed in Nigeria and Africa. This involves subjecting the peels to particle size reduction by grinding using a normal garri grinder and pressing with a hydraulic press to reduce the moisture content. The product is thereafter sun-dried to 12 to 15 percent moisture content. This innovation reduces the drying time of the peel from three to less than a day to produce various types of high-quality cassava peel for ruminants, poultry, and aquaculture. A highly informative 10-minutes video titled “ILRI transforming cassava peels into livestock feed using garri-making processes” was created from the project and could be viewed on YouTube at https://youtu.be/JwfgyHkLE

Nutrient composition of cassava peels

On a dry matter basis, cassava peels constitute about 8 to 10 percent of the cassava roots tuber. Nutritionally, it contains 62 percent soluble carbohydrate, 10 percent fiber, and only about 4.8 percent crude protein. Akpabio and coworkers reported that cassava peels also contains 1.59 and 1.02 mg/100g of vitamin A in fresh peels of bitter and sweet varieties, respectively which increased to 8.15 and 6.72 mg/100g respectively with drying, indicating that the bitter cassava variety contains the highest concentration of vitamin A. Freshly produced bitter and sweet cassava varieties were equally found to contain 30.43 and 34.8 mg/100g, respectively of vitamin C in their cassava peels, which increased considerably to 50.97 and 45.10 mg/100g, respectively when dried. Table 1 shows the chemical composition of cassava peel meal on a dry matter basis.

Table 1: Chemical composition of cassava peels (%DM)

Cassava peels harbor cyanogenic glucoside in various concentrations depending on the variety and growing condition. The cyanide levels range from 310 to 650 mg/kg for the peel and pulp in bitter varieties, and 38 to 200 mg/kg for the peel and pulp respectively in sweeter varieties. The presence of cyanogenic glucosides and their breakdown products remains a cause of concern to a nutritionist because of their limiting effects on the use of cassava peels in the feeding of most animals. Cassava peels have a high phytate content that causes low phosphorus availability in non-ruminant animals since phytic acid has the potential to bind calcium, iron, and other minerals, thereby reducing their availability to the body. Again, the tannin content of cassava peels increases with the maturity of the plant and has been reported to be as high as 1.1 to 120 mg/100mg. The oxalate content has been put at 330 mg/kg for freshly milled cassava peels and may be detrimental to animal health depending on the level of calcium in the ration.  

Improving the nutritive value of cassava peel

Several approaches apart from processing methods have been used to improve the nutritive value of cassava peels. Drying is the most common method used to reduce cyanide content of cassava peel and has been found more effective than oven-drying because, during sun drying, the cyanide is in contact with the enzyme that metabolizes cyanogenic glucoside for a longer period. The cyanide levels are about 815 mg/kg, in fresh cassava peel samples, 1,250 mg/kg in the oven-dried samples, and 322 mg/kg in the sun-dried samples.

A study carried out at the Federal College of Animal Health and Production Technology, Moor Plantation, Ibadan, determined the effects of submerging, fermenting, ensiling, boiling, and sun-drying treatments of fresh cassava peel and further sun drying for 3 - 5 days on its proximate composition and hydrogen cyanide concentration. Ensilage (10.69 percent) and fermentation (9.25 percent) improved the crude protein of cassava peel better than boiling (4.92 percent) and sun drying (4.86 percent). Similarly, fermentation (16.88 mg/kg) and ensilage (21.62 mg/kg) reduced the hydrogen cyanide content of the peels to permissible levels better than boiling (55.21 mg/kg) and sun-drying (46.44 mg/kg), indicating that fermentation and/or ensilage enhances the nutritional value and utility of cassava peel as animal feed raw material.

In another study at the Federal University of Technology Owerri, Nigeria, in which the effect of fermentation with Baker’s yeast (Saccharomyces cerevisiae) on the Physico-chemical composition of cassava peels was carried out, it was found that crude protein and gross energy content of fresh peels increased with increasing levels of Baker’s yeast in the substrate. A similar increase in crude protein content has been reported by other workers who studied the effect of mixed cultures of Saccharomyces cerevisiae and Lactobacillus spp solid media fermentation of cassava peels. Experiments with three species of fungi (Saccharomyces cerevisiae, Mucor spp. and Rhizopus spp) in a solid substrate that contained 80 g of cassava waste powder also recorded increased crude protein levels. The fermentation process has also been shown to reduce both the cyanide and phytate content of cassava peels to safe levels for both broiler and layer feeding. Fermentation not only reduces toxicity, but the enzyme resistant lignocellulose material is converted into the more digestible substrate by fermentation processes.

Researchers at the University of Ibadan, Ibadan, Nigeria, investigated the effect of submerged fermentation using Trichoderma viride on the protein content and amino acid profile of enzyme and non-enzyme pre-treated cassava peel. The T. viride treatment improved the crude protein, true protein, crude fat, crude fiber, ash, and total dietary fiber of the cassava peels. Crude protein increased from 4.21 to 37.63 percent (31.6 percent as true protein) and 36.52 percent (29.03 percent as true protein) for the enzyme and non-enzyme fermented samples respectively, while the starch contents reduced considerably in both samples. The products contained all the essential amino acids, although essential amino acid score showed that methionine was the limiting amino acid.

Conclusion

Cassava wastes and peels, in particular, are abundantly available animal feed raw materials at all cassava producing and processing locations in the world. Present research knowledge suggests that these wastes could be easily and cheaply processed into nutrient-rich feedstuff for feeding all classes of livestock and aquaculture. There is however the need to promote the appropriate technologies among would-be entrepreneurs to meet the expected demands from the animal feed industry. Information on feeding trials with processed cassava peels in poultry and other livestock will be discussed in the next blog.

Bibliographic References

Akpabio U.D., Akpakpa A.E., Udo I.E. and Nwokocha, G.C. (2012). Comparative study on the physiochemical varieties of cassava peels (Manihot utilissima Pohl). International Journal of Environment and Bioenergy, 2 (1): 19 -32

Aro. S.O. Aletor V.A., Tewe O.O. and Agbede J.O. (2010). Nutritional potentials of cassava tuber waste: A case study of a cassava processing factory in southwestern Nigeria. Livestock Research for Rural Development, 22 (11):  http://www.irrd.org/irrd22/11/aro22213.htm. accessed February 3, 2013.

Etuk, E.B., Obasi, I.U., and Ezeokeke, C.T. (2017). Nutrient composition and feeding value of cassava peels in livestock and poultry production. In: Okoli, I. C., and Udedibie, A.B.I. (Eds.). The science and technology of cassava utilization in poultry feeding. Proceedings of a NIPOFERD Workshop on Knowledge Transfer towards Cost-Effective Poultry Feeds Production from Processed Cassava Products to Improve the Productivity of Small-Scale Farmers in Nigeria, June 27 – July 1, 2016, Asaba, Nigeria. Pp:  85 – 102.

Ezekiel, O.O., Aworh, O.C., Blaschek, H.P., and Ezeji, T.C. (2010). Protein enrichment of cassava peel by submerged fermentation with Trichoderma viride (ATCC 36316). African Journal of Biotechnology, 9(2): 187-194.

FAO (2014). Food outlook. Biannual report on global food markets. Food and Agriculture Organization of the United Nations, Rome.

FAO (2015). Production: Crops’ [Online] http://faostat3.fao.org/browse/Q/QC/E [Accessed 23 May 2020]

Obasi, I.U. (2017). Physico-chemical composition of cassava peels fermented with Baker’s yeast, its metabolizable energy, and true digestible protein for poultry. MSc. Thesis, Federal University of Technology, Owerri, Nigeria.

Okike, I., Anandan, S., Lawrence, K., Claude, F., Joseph, A., Ranajit, B., Peter, K., Alan, D., Tunrayo, A. and Micheal, B. (2015). Technical innovations for small-scale producers and households to process wet cassava peels into high-quality animal feed ingredients and aflasafeTM substrate. Food Chain, 5:1-2.    

Okoli, I.C., Osuji, M.N.  and Chikaire, J.U.  (2017). Analysis of global and Nigerian cassava production and utilization dynamics. In: Okoli, I. C., and Udedibie, A.B.I. (Eds.). The science and technology of cassava utilization in poultry feeding. Proceedings of a NIPOFERD Workshop on Knowledge Transfer towards Cost-Effective Poultry Feeds Production from Processed Cassava Products to Improve the Productivity of Small-Scale Farmers in Nigeria, June 27 – July 1, 2016, Asaba, Nigeria. Pp: 151 – 168.
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