Nutritional potentials of cassava tuber wastes: A case study of a cassava starch processing factory in south-western Nigeria

S O Aro, V A Aletor, O O Tewe* and J O Agbede

Department of Animal Production and Health, The Federal University of Technology, P. M. B. 704, Akure, Nigeria
* Department of Animal Science, University of Ibadan, Ibadan, Nigeria
sambolaro@yahoo.co.uk

Abstract

A study of cassava tuber wastes (CTW) produced by a cassava starch-processing factory in Ondo State of Nigeria was made in which the types and quantity of these wastes were determined. This study revealed that five different types of CTW are produced on a daily basis and are subsequently discharged into the immediate environment. These categories of wastes with the corresponding quantities (fresh weight basis) produced by the factory are: the cassava starch residues (CSR) or pomace (17 metric tonnes/day), cassava peels (CAP) (5 metric tonnes/day), cassava effluent (CAE) (15.4 metric tonnes/day), cassava stumps (CAS) (8 metric tonnes/day) and cassava whey (CAW) (1.51 metric tonnes/day).

The proximate composition of samples collected in respect of these five types of wastes showed that moisture was highest in CAW (96.7%) and lowest in CAS (64.1%). Crude fibre was highest in CAP (29.6%) but was not detected in the whey (CAW). The CAS had the highest content of fat (5.35%) while it was not detected in CAW. Protein was highest in CAP (4.20%) and lowest in CSR (1.12%). Ash content was highest in CAP (7.47%) and lowest in CAW (1.88%). The nitrogen free extractives (NFE) were highest in CAW (95.7%) and lowest in CAP (55.5%).

The analyses of the anti-nutritional factors revealed that cyanide, phytate, oxalate, tannins, saponins and total alkaloids were highest in CAW (61.1mg/kg), CSR (15,926mg/kg), CAE (674mg/kg), CAP (3.90%) and CAS (0.15% and 0.52%) respectively while CAP had the highest content of Potassium (269mg/kg), Calcium (121mg/kg), Magnesium (236mg/kg), Sodium (261mg/kg) and Phosphorus (3233mg/kg). Iron content was highest (16.2mg/kg) in CAE. Copper (10.8mg/kg) and Selenium (1.27mg/kg) were highest in CSR while Manganese (0.43mg/kg) was detected only in CAP. Molybdenum, Cobalt and Arsenic were not detected in any of the cassava tuber waste samples.

These analyses revealed that CTW have appreciable levels of nutrients that could be tapped for beneficial use. The levels of anti-nutrients in some of them are below the normal toxic level but could still be reduced or removed through methods designed for such. Also the various options available for protein enrichment of these wastes could be explored in a bid to convert these wastes to wealth.

Key words: anti-nutrients, cassava tuber wastes, mineral profile, nutrient composition

Introduction

A new opportunity was opened for the utilization of cassava and its by-products by the immediate past democratic government of Nigeria. This has gone a long way to renew the interest of the farmers towards the cultivation of more hectares of the crop as a result of government’s commitment to self-sufficiency in food production coupled with an aggressive export drive. This new initiative of the government is in tandem with the Consultative Group of International Agricultural Research (CGIAR) mission to contribute to food security and poverty alleviation in developing countries through research partnership, capacity building and policy support.

The increased production and utilization of cassava has led to the release of huge wastes to the environment with consequent unwholesome implications. For example, year 2005 estimates indicated that Nigeria produced 34-40 million metric tonnes of cassava tubers with the leaves, according to Tewe (1996) constituting over 6% of the whole plant and the pomace (the starch residues) and the peels accounting for over17% and 8% respectively. This translated to the generation of more than 2.22 million metric tonnes of cassava leaves, 6.29 million metric tonnes of pomace and 2.96 million metric tonnes of the peel per annum, most of which are discarded as wastes and left to rot away in spite of their relatively high proteins, vitamins and nutritionally valuable mineral constituents. These figures are expected to rise in the light of the present development, which has propelled Nigeria from the third largest producer of cassava behind Brazil and Congo in the eighties to being the largest producer in the world today.

In recent years, emphases have been shifted to the use of by-products of agro-industrial origin as low cost alternative carbohydrate sources for livestock nutrition (Delgado-Vargas and Parades-Lopez, 1997). Sucharita et al (1998) concluded that effective utilization of non- conventional feeds should be the major areas of research in the less developed countries due to shortage of conventional feedstuff. One of the constraints to the use of these non-conventional feeds especially in sub-Saharan Africa is their year- round non-availability. Though the cereal and legume by-products are somewhat seasonal and their utilization often consigned to offsetting the dry season’s short-fall of conventional feeds, cassava by-products enjoy year-round availability, unfortunately in Nigeria, such potential benefits are lost through rot or wastage (FAO, 1994).

The renewed interest in cassava production in Nigeria has led to the establishment of many cassava starch industries to cope with the export drive of the government. Three of such factories have been established in Ondo State. This initiative was first taken by a private ownership – the Matna Foods Limited, located at kilometre 19, Akure-Owo Express Way, Ogbese in Owo Local Government Area of Ondo State. This factory has been producing high quality grade multi-purpose cassava starch to the local and international market since 2004. With hindsight of the installed capacity of this factory, which is put at an average of 100 metric tonnes of cassava tubers per day, the amount of wastes being produced by this factory could be enormous and the impact on the environment could be devastating. In fact, a form of social attrition between the factory management and the host community is already in the offing concerning the discharge of this waste. A way out for the utilization of these wastes must be sought so as to avert this social rift between the factory management and its host. The scientific community must see this as a challenge. The response to this challenge has necessitated this scientific work aimed at quantifying the various types of wastes released from this site and the characterization of these wastes for their potential nutritive qualities for possible inclusion into livestock diet formulation.

Materials and methods 

The factory site

The cassava starch factory of Matna Foods Limited was located in Ondo State - one of the southwestern states in Nigeria. The factory is located at a vantage position i.e. in the centre of cassava growing areas of Ondo and Ekiti States and enjoys patronage in terms of supply of cassava tubers not only from these two states but also from the contiguous states of Oshun, Kogi, Edo and Delta states. The factory started operation in 2004 with an installed capacity of processing 120 metric tonnes of cassava tubers into cassava starch in two working shifts (day and night shifts) per day.

Categorization of wastes

Five categories of wastes from cassava tubers, which constitute the raw materials, are produced in the factory. These are: the cassava starch residues (CSR) or pomace, the cassava whey (CAW), the cassava peels (CAP), the cassava stumps (CAS) and the cassava effluent (CAE). The CSR is the fibrous component left after the starch content of the tuber has been extracted via the screen separators. The whey is the liquid pressed out of the tuber after it has been crushed mechanically. The peel is obtained after the tubers have been water-cleansed and peeled off mechanically. The stumps are the ends trimmed off the cassava tubers as they are manually prepared for onward transmission into the rotary washer and peeler. The effluent is made up of the whey and the fibre mixed together on their way to the slurry tank outside the factory premises.

Quantification of wastes

The quantities of the five categories of wastes produced were determined as follows:

Given that:

·        the factory has an average installed capacity of processing 100 metric tonnes of cassava tubers per day,

·        the CSR content in cassava tuber is 17% (Tewe, 1996),

·        the dry matter content of CSR is 15.82% (as determined in this trial),

·        the percentage composition of the peel in the tuber is 5% (as determined in this trial),

·        dry matter content of the wet cassava peel is 18.65% (as determined in this trial),

·        the percentage composition of the stumps in the tuber is 8% (as determined in this trial),

·        the percentage composition of dry cassava starch in the tuber is 23%,

·        volume of water consumed/tonne of cassava starch produced is 69m^3,

·        the percentage dry matter in the whey is 3.33% (as determined in this trial),

·        dry matter content of cassava effluent is 8.86% (as determined in this trial)

Therefore:

(a₁). Quantity of CSR produced/day (wet weight basis) = AIC x % composition of CSR  in the tuber (where AIC = Average installed capacity).

(a₂). CSR produced/day (dry matter basis) = DMC of CSR x Quantity of CSR produced/day. (where DMC = Dry matter content).

(b₁). Quantity of CAP produced/day (fresh weight basis) = AIC x % composition of CAP in the tuber.

(b₂). CAP produced/day (dry matter basis) = DMC of CAP x Quantity of CAP produced/day.

(c₁). Quantity of CAS produced/day (fresh weight basis) = AIC x % composition of CAS in the tuber.

(c₂). CAS produced/day (dry matter basis) = DMC of CAS x Quantity of CAS in the tuber.

(d). Quantity of CAE discharged/day (dry matter basis) = Quantity of CSR x % DMC of CAE.

(e). Quantity of CAW produced (dry matter basis) = Quantity of CAE x % DMC of CAW.

From all these formulae, the quantity of these wastes produced per month and per year (of 300 working days) was calculated.

Collection of waste samples

The five categories of wastes designated as CSR, CAP, CAS, CAE and CAW were collected in the fresh form from the factory site. Two kilogrammes (2kg) of each solid waste and two litres (2l) of each liquid waste were collected in clean cellophane bags and subsequently carried to the laboratory within 30 minutes of collection for analysis.

Chemical analyses of the waste samples

Proximate analysis of the samples 

The proximate analysis of the wastes for crude protein, ash, nitrogen free extractives, ether extracts, crude fibre and dry matter was carried out according to AOAC method (1990). Triplicate samples were taken for all the analyses.

The mineral content determination was carried out by ashing (dry ashing). Atomic absorption spectrophotometer (Buck Scientific, 2004) was used in the determination of the concentration of these minerals: Copper (Cu), Iron (Fe), Calcium (Ca), Magnesium (Mg), Selenium (Se) and Manganese (Mn). Potassium (K) and Sodium (Na) were determined by flame photometry using the specific metal bulbs while Phosphorus (P) was determined by the Vanado-molybdate method (A.O.A.C., 1990).

Determination of the anti-nutrient contents of cassava tuber wastes

Some anti-nutrients whose contents were analyzed in the CTW are cyanide, phytate, oxalate, tannins, saponin and total alkaloids. These anti-nutrients were all assayed by the standard laboratory procedures established for them.  

Statistical analysis

The results were presented as the mean values of three replicates per observation. A one-way analysis of variance (ANOVA) and Duncan Multiple Range Test (DMRT) were carried out using SPSS 15 (2006) package. Significance was accepted at P<0.05.

Results and discussion  

Quantification of wastes

The result of the various quantities of wastes discharged to the environment from the factory is given in Table 1.  

The largest amount of wastes produced by the factory on fresh weight basis was CSR (17,000kg or 17 metric tonnes/day). On dry matter basis, the stumps provided the largest quantity of wastes (2,872.80kg or 2.87 metric tonnes/day). This quantification revealed that a huge amount of wastes is being discharged into the environment with untoward consequences. Daily emission of CTW in this way as revealed by this study stood at 47.00 metric tonnes of fresh wastes (8.05 metric tonnes of dry wastes) or 1,175.01 metric tonnes of fresh wastes per month (201.29 metric tonnes of dry wastes) or 14,100 metric tonnes of fresh wastes per annum (2,415.32 metric tonnes of dry wastes). FAO (1994), in its monthly report gave the estimated total roots and tubers availability (fresh weight) for Nigeria as 8,480 metric tonnes with a conclusive remark that most of these crop residues, despite their abundant availability, are poorly utilized and are mainly left to rot away or at worst are burnt off to create space for the accumulation of new generation of waste heaps.

Bakrie (2002) reported on the abundant amount of cassava fibre or pomace (CSR) from cassava starch industries in Indonesia but concluded that they are under-utilized and are being wasted. He reported that more than 70 tapioca factories located in a district produce over 1.3million tonnes of cassava fibre per year. This translates to 18,571.43 tonnes per factory per annum. The factory under this study (Matna Foods Ltd) produces 5,100 metric tonnes of fresh CSR/annum or 806.82 metric tonnes of the same by-product on dry matter basis. This factory also produces 1,500 metric tonnes of cassava peels (279.75 metric tonnes on dry matter basis) and 2,400 metric tonnes (861.84 metric tonnes on dry matter basis) of cassava stumps. All these by-products are currently being wasted as no commercial value has been found for them. All these five categories of wastes have either potential or real economic uses. The effluent and the whey could be used for the production of ethanol, single cell protein and industrial enzymes. Literature is replete with the use of CAP in the nutrition of different livestock species (Iyayi and Tewe, 2003; Belewu and Jimoh, 2005). The only waste whose potentials have not been fully exploited is the CSR mainly because of its relatively low protein content and high fibre level (Balagopalan and Padmaja, 1988).  Research focus has been directed therefore towards protein enrichment of the CSR.

Proximate composition of cassava tuber wastes

The results of the proximate composition of the five different types of cassava wastes are as presented in Table 2.

The dry matter ranged from 3.34% in CAW to 35.9 % in CAS. Since the dry matter content of any feed or food sample is a determinant of its exploitable value from the commercial point of view, it then means that CAS as a waste product of cassava starch factory has the highest potentials for livestock feeding followed by CAP, CSR, CAE and CAW in that order. The values obtained for crude protein were 4.20% for CAP, 2.92% for CAE, 2.46% for CAW, 1.12% for CSR and 1.71% for CAS. The CAP contained the highest level of crude fibre (29.6%) while the fat content was highest in CAS (5.35%) but was not detected CAW. The highest ash content (7.47%) was obtained with the CAP. The moisture content of the CTW ranged from 64.1% in CAS to 96.7% in CAW. The values for N.F.E also ranged from 95.7% (CAW) to 55.5% (CAP).

The feeding potentials of these wastes as revealed by their dry matter content are indeed very substantial. The statement made in respect of the utilization of crop residues by FAO (1994) that there are enormous potentials for a better utilization of crop residues as livestock feed corroborates the findings in this study. Okafor (1998), while commenting on the volume of cassava peels released into the environment annually in Nigeria, opined that the peels could constitute an important potential resource if properly harnessed by a bio-system. All the five CTW had very low crude protein content. This is reflective of the various findings in literature that cassava root and its by-products are generally low in crude protein content (Bakrie, 2002, Nwafor and Ejukonemu, 2004). It is however possible to solve this low crude protein content through biotechnological option (Israelides et al, 1998). The high level of crude fibre in CAP (29.6%) obtained in this trial may not be unconnected with the mechanical peeling used in the factory, which removed only the outer fibrous covering of the tuber without the adhering pulps.

Generally speaking, all these wastes contain a high level of moisture that could constitute transportation problem in terms of their bulkiness and hence an implied higher transportation cost. Also, the keeping quality or shelf life of these wastes could be heavily compromised because of their rapid rate of deterioration and spoilage under this high moisture content level. The NFE values of CSR (74.4%) and CAS (72.3%) showed that these wastes contain appreciable level of carbohydrates that could qualify them as good candidates for microbial fermentation as the soluble carbohydrates they contain could serve as suitable substrates for the growth of the microbial inoculums.

Anti-nutrients composition of the cassava tuber wastes

The anti-nutrient composition of the five representative samples of the CTW is as presented in Table 3.

CAW had the highest level of cyanide (61.1mg/kg) while (CSR) contained the highest level of phytate (15926mg/kg). The level of oxalate was highest in CAE (674mg/kg). The values of saponin in the CTW ranged from 0.02% in CAW to 0.15% in CAS. Saponin contents in all the CTW were generally low. Values for tannins content in the CTW were 3.90% (CAP), 2.16% (CAE), 0.98% (CAW), 2.53% (CSR) and 3.44% (CAS). The CAS had the highest concentration of total alkaloids (0.52%).

All the cassava wastes were below the maximum tolerable level of cyanide (IITA, 1990). The relatively high concentration of HCN in the CAW and CAE should be expected. This is because the whey is the liquid pressed out of the CSR after its separation from the starch milk. It contained the bulk of dissolved HCN. The phytate content of all the cassava wastes revealed that all these wastes have appreciable level of phytate.  A solution to this high phytate level has however been found by way of microbial fermentation (Reddy and Pierson, 1994).  Oxalates were most concentrated in CAE (674mg/kg), CAS (610mg/kg) and CAW (520mg/kg). Its concentration in all the waste samples however would not compromise their nutritional potentials according to the works of Mathams and Sutherland (1992) who concluded that plants must contain 10% or more (i.e. 100,000mg/kg) of oxalate on dry weight basis to be potentially dangerous thereby implying the potential for use of these wastes in livestock ration with regard to oxalate. The concentration of saponin in CTW revealed the low level of this anti-nutrient in all the waste samples. From the standpoint of the low saponin content of the various CTW, the overall thriftiness of livestock would not be threatened as a result of the saponin content of these CTW. The concentration of tannins in all the CTW samples could be described as very low to moderate when compared with the typical concentration reported by D’Mello (2000) in some legumes. It is therefore safe to conclude that none of these CTW contains tannic acid levels that could compromise the growth and general well being of farm animals.

The mineral profile of cassava tuber wastes

The mineral constituents of the CTW are as presented in Table 4.

CAP contained the highest level of Potassium (269mg/kg). The Calcium content of the wastes ranged from 122mg/kg in the CAP to 5.17mg/kg in CAW. CAP also had the highest content of Magnesium (236mg/kg). The CAE contained the highest level of Iron (16.2mg/kg). Manganese was only detected in traceable amount (0.43mg/kg) in CAP. This showed that these CTW are generally poor in Manganese. The level of Sodium ranged from 261mg/kg in CAP to 7.54mg/kg in CAW. Copper was found in trace amount in CAP (0.24mg/kg), CAE (0.13mg/kg) and CAS (0.19mg/kg) while it was not detected in the whey, it however occurred at a level of 10.8mg/kg in the CSR. Selenium was not detected in any traceable amount in CAW. Phosphorus content in the CTW was very high in comparison with all the other mineral elements. Values of more than 1000mg/kg (1g/kg) were recorded in all the CTW samples except in the CAW. CAP had the highest concentration of Phosphorus (3233mg/kg). Potassium was found in appreciable levels in all the waste samples especially in those relatively high in dry matter content (the CAP, CSR and CAS).

The use of three of these CTW i.e. CAP, CAS and CSR which all contain well above 100mg/kg of Magnesium will meet a good proportion of Magnesium requirement in livestock species when mixed with other ingredients in the diet. Three of these CTW (CAP, CAE and CSR) could also contribute substantially towards meeting the Iron requirement of pigs when incorporated into feed formulation with other feed ingredients. Because of the appreciable content of Cu in CSR, its utilization in livestock ration formulation will generously contribute to the Cu content and hence to increased growth rate especially in growing pigs (McDowell, 1992). It could be observed that Selenium is highly concentrated in these wastes. This high concentration of Selenium in these CTW especially in the CSR and CAP could be as a result of contamination of these wastes with the soil particles that adhere to the outer covering of the cassava tubers. CAP, CAE, CSR and CAS could be said to have appreciable content of Phosphorus. It would be observed that Molybdenum, Cobalt and Arsenic were not detected in any of the CTW samples. The utilization of CAP, CAS and CSR could meet a sizable proportion of the requirement of livestock for Potassium, Calcium and Magnesium; also these three categories of wastes are capable of substantially meeting the Iron requirement of many farm animal species.

Conclusion 

• This trial revealed that five types of wastes from cassava tubers with ample nutritional potentials are being discharged to the environment on a daily basis.  The quantification of these wastes showed that at least three of them could be used as non-conventional feed resources to alleviate the perennial scarcity of feed for livestock and the unhealthy competition between man and his livestock for the available conventional feed ingredients. Their direct usage in livestock nutrition could also rid the environment of the attendant environmental problems. The proximate composition and mineral analyses showed that they have a lot of dry matter and ash available for use all the year round.

  
  

• Nutritional consideration of these CTW to mitigate high cost of conventional livestock feed ingredients could therefore yield huge financial dividends and research focus into the improvement of their nutritive quality to meet the various nutritional and physiological needs of farm animals would not be a waste of time. 
   

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Received 8 August 2010; Accepted 17 September 2010; Published 1 November 2010

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