Nutritional composition of cassava (Manihot esculenta Crantz) peel products

Oladimeji S O^1,2, Adeyemi A A¹, Mosuro A O³, Adebayo B F^1,4, Etop S C⁵, Adebiyi F G¹ and Ogunwole O A¹

¹ Agricultural Biochemistry and Nutrition Unit, Department of Animal Science, University of Ibadan
oladimejioo@gmail.com
² Animal Nutrition Department, Amo Byng Nigeria Limited, Awe, Oyo, Oyo State
³ Department of Human Nutrition and Dietetics, Faculty of Public Health, Lead City University, Ibadan, Nigeria
⁴ Department of Training and Internship, Nigeria Institute of Animal Science, Head Office, Abuja, Nigeria
⁵ Evonik Nutrition and Care GmbH, Germany (Abuja Office, Nigeria)

Abstract

The proximate composition, fibre fractions and amino acids of four cassava peel products: sundried cassava peel meal (SCPM), fine cassava peel mash (FCPM), whole cassava peel mash (WCPM) and coarse cassava peel mash (CCPM); were investigated in this study.

The products were processed from freshly peeled cassava peels. Results revealed that SCPM had crude protein (3.66g/100g), crude fibre (9.40g/100g), ether extract (1.37g/100g), neutral detergent fibre (27.78g/100g), hemicellulose (17.73g/100g) and cellulose higher than other cassava peel products studied. The CCPM had the highest dry matter (90.47g/100g), acid detergent fibre (16.70g/100g) and acid detergent lignin (12.60g/100g). The SCPM had the highest amino acid profile with glutamic acid (4.21g/100g) and aspartic acid (2.94g/100g) being the most abundant.

It was concluded that processing methods influenced the chemical composition of the cassava peel products.

Keywords: amino acid profile, fibre fractions, proximate composition, cassava peel products

Introduction

Cassava (Manihot esculenta Crantz) is a perennial crops found ubiquitous in the tropics and has ability to produce good yield even during climatic extremes (Echebiri and Edaba, 2008). It also has good performance under poor conditions which gives it the ability to be available all year round (Kolawole et al 2010). Morgan and Choct (2016), observed that cassava is one of the staple foods which have the potential to replace maize as an energy source and suggested it is central to food security in developing countries.

Cassava has significant role in the diets of Africans and was rated the fourth most consumed food crop in tropics after rice, wheat and maize (Cock, 1985). There is an increased use and consumption of cassava from subsistence to industrial consumption with most of the peel from cassava unutilized and unconsumed. FAO (2017) reported a significant growth in cassava production from 114 to 277 million tonnes from the year 1976 to 2016. The estimated 10 million tonnes annual production of garri in Nigeria would have at least doubled considering the increase in production of cassava and human population growth.

Increased production and consumption of cassava translates to higher production of cassava peel which are readily available and less competed for by human as food. It was also reported that cassava contributes 10-13% of fresh weight of cassava tubers (Tewe et al., 1976; Obadina et al. 2006). Also, tonnes of these cassava peel generated are released to the environment as waste especially during the wet season when it is very difficult to dry cassava peel to acceptable moisture content required for long term storage and feeding of livestock.

FAO (2017) also observed that meeting the future food demand would require technological and innovative approach to address the food challenge. The International Livestock Research Institute (ILRI) suggested combinations of several physical methods for the processing of cassava peel into a more attractive form which can be used in livestock feed (Okike et al 2015). However, knowledge of its chemical composition and the nutritive value are central to its use by nutritionist and feed-millers.

Previous reports on cassava were on performance and responses of animal fed diets based on cassava peels (Egbunike et al 2009; Abu 2015). There is therefore the need to determine the nutritive composition of the cassava peel and products which was the reason for the study.

Materials and method

Experimental site

The experiment was carried out at the Research and Demonstrations Farm, International Livestock Research Institutes (ILRI), located within the campus of the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. The chemical analyses were carried out at the Department of Animal Science Laboratories, University of Ibadan, Nigeria and Amino Lab Evonik Nutrition and Care GmbH, Germany.

Collection and processing of test materials

Fresh cassava peels were obtained from cassava processing plant located at Ajegunle, Oyo, Oyo State, Nigeria. The peels were from white varieties of cassava, predominantly TME 419 variety. The peels were transported to ILRI, Ibadan, sorted to remove foreign materials after which it was processed into various products, viz; Sundried Cassava Peel Meal (SCPM), Whole Cassava Peel Mash (WCPM), Fine Cassava peel Mash (FCPM) and Coarse Cassava Peel Mash (CCPM). The processing of test material has been succinctly described (Oladimeji et al 2020) and shown in Figure 1.

Chemical composition determination

The samples of the four cassava peel products were prepared from different batch of production and analysed for proximate composition (crude fibre, dry matter, crude protein, ash, ether extract and nitrogen-free extract) using the method of AOAC (2000). Fibre fraction (acid detergent fibre, neutral detergent fibre, acid detergent lignin, hemicellulose and cellulose were determined using the method of Van Soest et al. (1991). Amino acid was determined using the standardized method of (EN ISO 13903:2005) as explained (Dalibard et al 2014).

Statistical analysis

The experimental design was completely randomized design. Data were subjected to analysis of variance using the procedure of SAS (2002) and means were separated, using Duncan’s Multiple range test option of the same software.

Results and discussion

Proximate composition of cassava peel products

The proximate composition of cassava peel products is shown in Table 1. There were significant differences (p<0.05) in the proximate composition of the analysed cassava products. The dry matter of WCPM (90.52 g/100g), CCPM (90.47 g/100g) were similar, but significantly higher (p>0.05) than 88.58 g/100g from SCPM. Though dry matter of 89.94 g/100g in FCPM was similar (p<0.05) to values in other cassava peel products.

Figure 1. Steps involved in the production of cassava peel mash

Crude protein (g/100g) was significantly higher in SCPM (3.66) (p<0.05) than in CCPM (3.03), WCPM (3.03) and FCPM (2.79). The crude fibres were significantly different (p<0.05) across the cassava products. The crude fibre (g/100g) was higher in SCPM (9.40) than in CCPM (7.80) and WCPM (6.33) while the least fibre content of 3.64 was recorded in FCPM.

The ash (%) compositions of the cassava peel products were significantly different (p<0.05). The ash in WCPM (5.73) and FCPM (5.39) were similar (p>0.05) but significantly higher (p<0.05) than 4.67 in SCPM and 3.55 in CCPM. Ether extracts varied significantly (p<0.05) with 1.37g/100g ether extracts in SCPM significantly higher (p>0.05) than in CCPM (1.15 g/100g), FCPM (0.86g/100g) and WCPM (1.01g/100g). The ether extract of FCPM and WCPM, were however similar.

The nitrogen free extract (NFE) in cassava peel products were significantly different (p<0.05). The FCPM had the highest NFE of 77.80g/100g which was similar (p>0.05) to 76.22g/100g in CCPM but significantly higher (p>0.05) than 75.90g/100g in WCPM and 70.52g/100g in SCPM.

Fibre fraction of cassava peel products (g/100g)

The fibre fractions of cassava peel products are presented in Table 2. A significant difference (p<0.05) was recorded for all the fibre fractions evaluated. The acid detergent fibre was highest (16.70g/100g) in CCPM and least (p<0.05) in FCPM. The WCPM and SCPM had acid detergent values of 8.85 and 10.05g/100g, respectively.

Neutral detergent was significantly different (p<0.05) among the cassava products evaluated. The highest value (27.78g/100g) was in SCPM and the least (15.30g/100g) in FCPM. The neutral detergent values recorded by CCPM and WCPM were 22.85 and 19.05g/100g, respectively.

Acid detergent lignin was significantly different (p<0.05) among the determined cassava peel products; the highest value, obtained from CCPM (12.60 g/100g) was significantly higher (p>0.05) than in SCPM (4.12 g/100g), WCPM (5.32 g/100g) and FCPM (3.61 g/100g). Each cassava peel products had significantly different (p<0.05) acid detergent lignin values but SCPM and FCPM values were similar.

Hemicellulose was significantly higher in SCPM (17.73g/100g), the lowest value of 6.15g/100g was in CCPM which was similar (p>0.05) to 7.93g/100 in FCPM and significantly higher (p<0.05) than in WCPM (10.20g/100). The highest cellulose was in SCPM (5.93g/100g) while the least was recorded by WCPM (3.53g/100g). The 4.10g/100g cellulose in CCPM and 3.76g/100g in FCPM were similar (p<0.05) to the values in WCPM.

Amino acids profiles of cassava peel products

The amino acids profile of cassava peel products is presented in Table 3. Significant differences (p<0.05) were observed for all the amino acids determined. The SCPM had significantly higher (p<0.05) amino acids compared to other cassava peel products. Methionine in SCPM (0.49g/kg) was significantly higher (p<0.05) than in CCPM (0.39g/kg), FCPM (0.37g/kg) and WCPM (0.39g/kg) which were similar (p>0.05). The lysine content of SCPM was the highest (1.64g/kg) while the least was in FCPM (1.42g/kg). Lysine in CCPM (1.51g/kg) and WCPM (1.55g/kg) were not significantly different (p>0.05) from the levels in SCPM and FCPM.

Threonine content was significantly higher (p<0.05) in SCPM (1.36g/kg) and least in WCPM (1.03g/kg). The CCPM (1.12g/kg) had similar threonine content with SCPM and FCPM (0.96g/kg). The threonine of FCPM (0.96g/kg) was also similar (p>0.05) to the level in CCPM and WCPM. The isoleucine content of SCPM (1.34g/kg) was highest and least in FCPM (0.94g/kg). The Isoleucine in FCPM was similar (p>0.05) to 1.00g/kg in WCPM and 1.06g/kg in CCPM.

Leucine in CPM (2.22g/kg) was higher (p<0.05) than in CCPM (1.77g/kg), FCPM (1.56g/kg) and WCPM (1.67g/kg). The CCPM, FCPM and WCPM had similar levels (p>0.05). A similar trend was also observed with valine and phenylalanine which both had higher in SCPM (1.71g/kg) and phenylalanine (1.50g/kg). Valine content of CCPM (1.38g/kg), FCPM (1.23g/kg) and WCPM (1.31g/kg) were significantly different (p>0.05), while CCPM (1.10g/kg), FCPM (0.96) and WCPM (1.03g/kg) had similar (p>0.05) phenylalanine.

The histidine in SCPM (0.61g/kg) was significantly higher (p<0.05) than in CCPM (0.54g/kg), FCPM (0.50g/kg) and WCPM (0.56g/kg) which were similar. Glycine was significantly higher (p<0.05) in SCPM (1.49g/kg) than in CCPM (1.17g/kg), FCPM (1.04g/kg) and WCPM (1.10g/kg).

The serine content recorded significantly higher (p<0.05) (1.61g/kg) in sundried cassava peel meal while significantly lower value (p<0.05) was recorded by fine cassava peel mash (1.12g/kg). The coarse cassava peel mash serine content (1.34g/kg) is similar to the values obtained from whole cassava peel mash (1.22g/kg) while value recorded by whole cassava peel mash is similar to fine cassava peel mash. Similar trend was also observed in the proline content with sundried cassava peel meal recording the significant higher content of 1.42g/kg while the least proline was recorded by fine cassava peel mash (0.99g/kg). The proline content recorded by whole cassava peel mash (1.13g/kg) was significantly similar (p>0.05) coarse cassava peel mash (1.22g/kg) and fine cassava peel mash.

Alanine content had significant (p<0.05) higher value (1.73g/kg) in sundried cassava peel meal compared to coarse cassava peel mash (1.73g/kg), fine cassava peel mash (1.21g/kg) and whole cassava peel mash (1.28g/kg). The values recorded by coarse cassava peel mash, fine cassava peel mash and whole cassava peel mash are not significantly different from each other. Aspartic acid also recorded similar trend with alanine with sundried cassava peel meal (2.94g/kg) recording significantly higher aspartic acid compared with coarse cassava peel mash (2.32g/kg), fine cassava peel mash (2.11g/kg) and whole cassava peel mash (2.28g/kg). The aspartic acid values recorded by coarse cassava peel mash, fine cassava peel mash and whole cassava peel are no significantly different (p>0.05) from each other.

The glutamic acid was significantly higher (p<0.05) in sundried cassava peel meal (4.21g/kg) while the least amino acid was recorded by fine cassava peel mash (2.47g/kg). The value recorded by whole cassava peel mash (3.39g/kg) was not significantly different (p>0.05) from coarse (2.86g/kg) and fine cassava peel mash. The cystine content had sundried cassava peel meal recording the highest value (0.47g/kg) while the least value was recorded by fine cassava peel mash (0.33g/kg). The value recorded by fine cassava peel mash was not significantly different from whole cassava peel mash (0.35g/kg), though both values were significantly lower than the value obtained from coarse cassava peel mash (0.39g/kg).

Discussion

Proximate composition of cassava peel products

The different processing methods influenced the proximate composition of the cassava peel products. The result suggests that reduction of the particle size of cassava peel engendered lower moisture content of cassava peel products as observed. Also, processing may account for the lowered crude protein and crude fibre of the cassava peel products which was below the reported range of 4.90-5.60% (crude protein) and 10.46-16.26% (crude fibre) (Akpabio et al 2012) for oven dried cassava peel of sweet and bitter cassava varieties. The observed difference could be attributed to drying methods employed.

Crude fibre of feed materials is used by nutritionist to predict the quality of the feed ingredient. They are made up of cellulose and lignin which cannot be dissolved by water, dilute alkali and dilute acid (Souffrant, 2001). Detergent used for crude fibre dissolves some components of cellulose, lignin and hemicellulose summed with the NFE (Ngoc et al 2012). The NFE is a measure of water soluble carbohydrates and starch (Hall, 2000; Fuller et al 2004). The higher fibre content in SCPM compared to other cassava peel products could be attributed to the contamination from soil. Fibre in diet is mostly considered diluent and when high in poultry ration is believed to affect the birds negatively due to the presence of cellulose (Rougière and Carré, 2010). Cellulose, a component of fibre is not readily available to poultry because poultry do not produce cellulase required to digest cellulose. However, evidence that moderate levels of fibre in poultry diet would help improve digestive organ, gastric acid, bile acids and enzyme activity abound (Hetland et al 2003; Rougière and Carré 2010; Svihus 2011; Mateos et al 2012; Uchegbu et al 2017).

The WCPM and FCPM had higher ash content compared to CCPM. This is expected because the processing of cassava peel mash involve grounding to reduce particle size which during sieving will allow for the escape of soil contaminant to the fine fraction. The ash content of the cassava peel products was lower than 8.4% reported (Okike et al 2015). Authors submitted that ash content of less than 8.4% would not pose any significant challenge for pelleting.

The ether extract range of between 0.86 and 1.37 g/100g reported in this study was higher than 0.46 and 0.82% reported (Okike et al 2015) for grated cassava peel, sieved fractions, coarse fraction, fine and whole pellet. The FCPM appears to favour higher inclusion in monogastric diet, due to lower fibre and higher nitrogen free extract. Cassava peel or products have been suggested as replacement for maize in the diet of livestocks (Olorunsanya et al 2007; Aguihe et al 2016; Dayal et al 2018). However, cassava peel meals are lower in protein compared to maize which has protein ranges of between 9 and 14% (McDonald et al 2010).

Fibre fraction of cassava peel products

Fibre fraction have been considered to be synonymous to crude fibre. Van Soest et al (1991) classified fibre fraction as acid detergent fibre, neutral detergent fibre and lignin. Despite the acceptance of the classification of (Van Soest et al 1991), it was observed that soluble carbohydrates were not addressed (Ngoc et al 2012). The CCPM had the highest acid detergent fibre and acid detergent lignin while the lowest was in FCPM. This is expected as the CCPM is mainly the brownish cover of the cassava tuber, which contains little or no pulp compared with other cassava peel products. The FCPM is predominantly the white pulp from the generous peeling of cassava tuber. Lignins are polyphenolic compound of plant cell walls which are insoluble in water and make the plant cell wall to be rigid (Fuller et al 2004). High lignin in plant material has been consider a limitation in the digestibility of nutrients (Jung and Deetz, 1993). Campbell (1995) reported that binding ability of lignin to bind with cholesterol are used in reducing heart disease risk. The methoxyl content and molecular weight of lignin varied due to strong intramolecular bonding (Dhingra 2012).

The neutral detergent fibre is used to predict component of fibre that are slowly degraded in the gastrointestinal tract, and it is highly correlated to digestive properties (Hall 2000). The neutral detergent fibre in all the cassava peel products were higher than the reported value by Hall (2000) for maize (12.6%). The neutral detergent fibre recorded were within the range of 15.8 -35.5% reported for cassava peel by Heuze et al (2012).

Hemicelluloses are complex structural component of plant cell that can be solubilized by aqueous alkali after pectin have been removed (Dhingra et al 2012). They are mainly made up of xylans, glucomannans and arabinogalactans, though other type of polysaccharides may be found (Harborne 1984). The hemicellulose component of cassava peel products is expected to be made up of xyloglucan intermixed with 4-0-methylglucuronic acid residues. Xyloglucan intermixed with 4-0-methylglucuronic acid residues are more profound in dicotyledons while monocotyledons are usually made up of arabinoxylans (Harborne, 1984). Omode et al (2018) suggested that chemical treatment such as the use of organic acid could be employed as pre-treatment to reduce hemicellulose component of cassava peel. However, the reported hemicellulose content (34.4%) reported by Omode et al (2018) for cassava was almost twice higher than obtained values in this study. The difference could be attributed to cassava varieties used and the efficiency of the tuber peeling.

Cellulose is the insoluble component of plant which is made up of β-D-glucopyranose units linked by β(1 → 4) bonds, forming a long straight chains which are hardened by cross-linked hydrogen bond (Campbell 1995). It cannot be digested by monogastric due to the absence of enzyme that will cleave the β linkage and therefore a good source of bulk in diet of monogastric (Mayes and Bender 2003). The cellulose in SCPM (5.93 g/100g) indicated that it would require more exogenous enzyme to digest the cellulosic component by monogastrics compared to other cassava peel products. The reduction in particle size employed for coarse, fine and whole cassava peel mash could help to significantly reduce the cellulose component.

Amino acids profile of cassava peel products

Amino acids are obtained from the breakdown of protein. Amino acids along with other nutrients are required in the diet of livestock for optimal production and health. Amino acids of feed ingredients are of interest to nutritionist. They are required for the formulation of balanced feed which will promote the health and production of the animal especially when the cost of supplemental source of amino acids are high. Protein contains only L-α-amino acids while amino acid synthesized from microbes could either be L- or D- α-amino acids (Rodwell and Kennelly 2003).

Methionine is considered the first limiting amino acid in poultry and ruminant diets (Dalibard et al 2014). Methionine is required for several metabolic reactions in the body especially those that require methyl group. Cysteine level of a diet will determine the level of methionine requirement (McDonald et al 2010). The methionine content of all the cassava peel products except in SCPM were similar to value documented by Nassar and Sousa (2007) for cassava tuber from cassava varieties ICB 300 (0.41g/kg), SCPM had a higher methionine value (0.49g/kg). The methionine in cassava peel products were higher than reported for SCPM (0.30g/kg) by Aro and Aletor (2012). However, observed methionine content was within the range of 0.32 to 0.69 g/kg reported by Ogunwole et al (2017). Ogunwole et al (2017) observed that methionine in cassava peels or peelings were influenced by cassava varieties and ranged from 0.32g/kg in oven-dried cassava peelings of TMS 01/1371 cassava variety to 0.69g/kg in oven-dried cassava peels from TMS 07/0593. Evonik (2015) reported average methionine content of yellow maize and soyabean meal to be between 1.8g/kg and 6.4g/kg, respectively. The methionine in the cassava peel products indicated that it was 3.6-4.9 times lower in methionine than in maize and 13.0-17.3 times lower than in soyabean meal. Omode et al (2018) also noted that methionine was required for detoxification of cyanide, and was considered the first limiting amino acid in cassava based diets.

Lysine is a basic amino acids and considered the second limiting amino acids after methionine in poultry and ruminant (Dalibard et al 2014). Increasing dietary lysine in diets of chickens have been reported to result in corresponding improvement in feed conversion ratio and weight gain (Weurding et al 2003). The lysine content (1.42-1.64 g/kg) of the cassava peel products was similar to 1.43g/kg reported for potato tuber (Solanum tuberosum) by Blair (2008) and doubled the lysine content of 0.70g/kg in dried cassava roots reported (Bayata, 2019). In SCPM, lysine content of 1.22g/kg has been reported (Aro and Aletor 2012). The values in cassava peel products were consistent with the reported 1.52g/kg in TMS 01/1371 to 2.27g/kg in TMS 07/0593 (Ogunwole et al 2017). Replacement of maize with any of the cassava peel products studied would require low supplemental lysine when used to replaced maize. Evonik, (2015) reported a lysine content range of 2.4-2.5 g/kg for maize which showed higher levels than in the cassava products.

Threonine is considered the third limiting amino acids after methionine and lysine, it plays an important roles in the production and maintenance of body protein (Kidd et al 1997). Threonine is a component of mucin protein and helps the development of the gastrointestinal tract (Le Floc’h et al 2012). The threonine obtained for the cassava peel products revealed that sun drying of cassava peel promote higher threonine. Threonine of 0.96 to 1.36 g/kg recorded for the cassava peel products were higher than 0.5g/kg in cassava sifting but lower than reported 2.9 g/kg in yellow maize (Evonik 2015). Natural fermentation could be used to improve the threonine content and other amino acids of cassava peel products. The natural fermentation employed by Aro and Aletor (2012) was used to improve the amino acids of cassava peel except for valine and proline which was reduced. The threonine content of cassava peel was improved from 1.16g/kg in SCPM to 2.7g/kg when fermented naturally. The threonine content of 1.16g/kg reported by Aro and Aletor (2012) was higher than values recorded for the cassava peel products studied except SCPM. The lower threonine of 0.30g/kg reported (Bayata 2019) for cassava roots corroborates the lower threonine recorded for fine cassava peel mash compared to other cassava peel products. The FCPM had higher volume of pulp compared to other cassava peel products studied, which could obviously influence the lower content of threonine.

Arginine is a basic amino acid which is found naturally in animal cells and has anti-inflammatory and anti-oxidative properties (Birmani et al 2019). It is important for growth and maintenance of the body (Geng et al 2011). Poultry depend on dietary arginine to meet their requirement for immune response and synthesis of protein (Birmani et al 2019). However, pigs and rats do not require dietary arginine for maintenance (Mcdonald et al 2010). The higher arginine content recorded in SCPM compared to others could be attributed to combination of different physical methods employed for other cassava peel products which was not employed in SCPM. The arginine content of 0.39% reported (Evonik, 2015) for maize was 10 times higher than values recorded for cassava peel products studied except for SCPM which was 2.75 times lower in arginine compared to maize. The arginine content for all the cassava peel products determined were all lower than 1.8g/kg recorded for unfermented cassava peels (Aro and Aletor 2012) and 2.9g/kg recorded for oven-dried cassava roots (Bayata 2019). The difference observed could be attributed to drying and physical method employed, especially the use of hydraulic press to extract the moisture.

Isoleucine is an amino acid considered to be ketogenic and glucogenic (Moore and Langley, 2008). Four isomers of isoleucine have been reported, namely L-isoleucine, D-isoleucine, L-alloisoleucine and D-alloisoleucine. The D-alloisoleucine have been reported to have 60% activity of L-isoleucine while commercially sold DL-isoleucine contains 25% of each of the isomer and observed to have 40% relative bioavailability (Lewis and Baker, 1995). The isoleucine recorded for sundried cassava peel (1.34g/kg) was similar to value recorded for yeast fermented cassava chips (1.3g/kg) reported (Polyorach et al., 2012). The results suggests that fermentation could help to improve the isoleucine content of cassava products. Processing methods also influenced the isoleucine content of the cassava peel products as sundried cassava peel recorded a higher isoleucine content compared with other cassava peel studied. The lower isoleucine in cassava peel products could have contributed to the lower cyanide observed. Hydrocyanide synthesis from linamarin and lotaustralin in cassava require amino acids such as isoleucine and valine (Omode et al., 2018). The isoleucine in cassava peel products was lower compared to 2.7g/kg in maize (Evonik, 2015). This submission agrees with the findings of Buitrago et al. (2002) on lower value for cassava compared to maize. The isoleucine in the cassava peel products was similar to values reported for unfermented cassava peels (1.2g/kg) (Aro and Aletor, 2012).

Leucine is a ketogenic amino acid (Moore and Langley 2008). Leucine aids the synthesis of protein in the muscle and involve in the generation of gluconeogenic precursors from the muscle (Mero, 1999). Excess leucine consumption should be avoided due to its strong regulatory role in the catabolism of branch chain amino acid such as valine and isoleucine (Dalibard et al 2014). Bioavailability of leucine in mammals is reported to be below 50%, however, both D and L-methionine are readily available in chicks (Lewis and Baker 1995). The value recorded for the cassava peel products obtained were similar to reported 2.38g/kg (Aro and Aletor 2012) for unfermented cassava peels. However, this study showed that processing methods of cassava peel has influence on leucine content of cassava peel products. The use of hydraulic press to ensure rapid removal of water may have contributed to lower leucine in coarse, fine and whole cassava peel mash compared to sundried cassava peel meal. The leucine content of cassava peel products when compared to the value reported for maize (Evonik 2015) showed maize was 4.1-5.9 times richer.

Valine is a glucogenic and hydrophobic amino acid (Moore and Langley 2008). Dalibard et al (2014) noted that knowledge of quantity of branched chain amino acids such as valine, is important to nutritionist as it point to how much decrease could be accommodated in a diet. In humans, D-valine is considered very low in biological value, however, in chick it is observed that D-valine has a relative bioavailability of 70% when compared with the L-valine (Lewis and Baker 1995). In cassava, valine as well as isoleucine are required for the formation of cyanogenic glucosides (Bokanga 1995). The valine recorded in cassava peel products were higher than 0.4g/kg reported for cassava root (Bayata 2019). The valine value of 1.86g/kg reported by Aro and Aletor (2012) for unfermented cassava peel was similar to 1.71g/kg in SCPM. The value reported by Aro and Aletor (2012) was higher than in coarse, fine and whole cassava peel mash, indicating that the processing method has great influence on valine content of cassava peel products. The valine content for maize reported (Evonik 2015) was 2-2.5 times higher than values obtained for cassava peel products studied.

Histidine is a basic amino acid which its reaction is easily affected by pH changes (Moore and Langley, 2008). D-isomers of histidine is poorly utilized (Lewis and Baker 1995). In humans’ histidine is considered non-essential amino as it is not required in their diets (Mcdonald, 2010). The histidine content of 2.4g/kg reported for maize and 4.1g/kg for wheat bran (Evonik 2015) were higher than from 0.5-0.61g/kg recorded for cassava peel products. The histidine content of cassava roots (0.7g/kg) reported (Bayata, 2019) and 0.9g/kg for unfermented cassava peel (Aro and Aletor 2012) were higher than histidine content in studied cassava peel products. The cassava sifting had lower histidine of 0.3g/kg compared to the cassava peel products.

Phenylalanine is a glucogenic and ketogenic amino acid which when present in adequate amount in the diet would make tyrosine non-essential (Moore and Langley 2008). Phenylalanine is considered an essential amino acids required for normal growth of chicks, rats and pigs (Mcdonald et al 2010). Phenylalanine in diet has a sparing effect on tyrosine as it could be converted to tyrosine, however, tyrosine cannot be converted to phenylalanine. (NRC 1998). Phenylalanine and tyrosine are part of the building blocks of catecholamines, which are component of hormones and neurotransmitters (Lerner and Lerner 2003). The deficiency of phenylalanine 4-monoxgenase (enzyme responsible for breakdown of phenylalanine) will results to hyperphenylalaninemia. Phenylalanine in high quantity will stimulate transamination resulting in high level of phenylpyruvate which have been noted to cause damage to the brain of infants (Moore and Langley 2008). Hyperphenylalaninemia induced through high dietary intake have also been reported to result in reduced learning behavior of offspring of rhesus monkeys (Chhazllani 2008). The high level of phenylalanine in SCPM compared with other studied cassava peel products agrees with the findings of Omode et al (2018). Aro and Aletor (2012), observed that fermentation of cassava chips and cassava peels helped to increase the phenylalanine content. The phenylalanine recorded for cassava peel products were higher than 0.3g/kg reported for cassava roots by Bayata (2019). The reported phenylalanine (Aro and Aletor 2012) for unfermented cassava peel (1.4g/kg) was similar to that reported for SCPM. However, 2.96g/kg in naturally fermented cassava peels reported (Aro and Aletor 2012) was higher than the reported value for all the studied cassava peel products.

Glycine is a glucogenic amino acid which is classified as non-essential amino acid (Moore and Langley 2008). However, in chicks’, glycine is considered an essential amino acid (Mcdonald et al 2010). Formation of purine and porphyrins requires glycine as precursor for it ring system (Moore and Langley 2008). Glycine is the only symmetrical amino acid and without stereoisomers (Hogg 2005). In plants, glycine is one of the free amino acids abundantly found. The requirement of glycine in chicks is increased with low level of arginine, methionine and B-vitamins, though, glycine and serine can be converted to one another (McDonald et al 2010). The glycine content obtained for cassava peel products analysed were higher than 0.1g/kg reported for cassava root by Bayata (2019). The 1.3g/kg of glycine reported by Aro and Aletor (2012) for unfermented cassava peels was lower than value reported for sundried cassava peel meal in this study which was 1.49g/kg. The observed difference in glycine content could be attributed to varieties of cassava. The peels may be obtained from different cassava varieties, this was corroborated by Ogunwole et al (2017) where they observed differences in amino acids of cassava products from different varieties. Whole, fine and coarse cassava peel mash had lower glycine content compared to findings of Aro and Aletor (2012) for unfermented cassava peel meal.

Serine is a glucogenic, non-essential and hydrophilic amino acid, which function as a base in the formation of cysteine (Moore and Langley 2008). In chicken liver, choline could be synthesized from serine and methyl donor such as methionine (Barroetta et al 2012). Serine and glycine have been identified as important for growth when diet with less than 20% crude protein are fed to broiler chicken aged less than 21-days (Siegert et a 2015). The serine content of 6.6g/kg reported for maize (Evonik 2015) was higher than for all the studied cassava peel products. The higher serine content (1.61g/kg) recorded for sundried cassava peel meal compared to fine, coarse and WCPM showed that the processing methods may influence serine content of cassava peel mash. The serine content reported for all the cassava peel products studied were higher than reported (Aro and Aletor, 2012) for unfermented cassava peel (0.93g/kg) and 0.4g/kg reported for cassava roots (Bayata 2019). The difference in serine content in SCPM and unfermented cassava peel meal reported by Aro and Aletor (2012) could be attributed to varieties of cassava tuber used, since both samples were subjected to sundrying.

Proline is a glucogenic and hydrophobic amino acid (Moore and Langley, 2008). Findings of Patra and Saxena (2010) suggests that in ruminant, proline rich protein could help to subside the negative effect of tannin in nitrogen metabolism. Also, poultry has a limitation of synthesizing proline (Mcdonald et al 2010). The higher proline content in sundried cassava peel meal compared with other studied cassava peel products confers advantage in the formation of collagen, proline is required in the synthesis of collagen (Bender 2003). The proline levels of all the cassava peel products were higher than 0.48g/kg reported for fermented cassava chips by Polyorach et al (2012). The higher protein in cassava peel products could have contributed to the higher proline recorded. The proline values recorded were also higher than reported values (Aro and Aletor 2012) for unfermented cassava peel.

Alanine is a glucogenic, hydrophobic and non-essential amino acid to poultry and pigs (Moore and Langley, 2008; Dalibard et al 2014). Alanine and glutamine play essential roles in the transport of amino group to the liver from extra-hepatic tissues in form which are not toxic (Nelson and Cox, 2017). The alanine recorded for cassava peel products were higher than 0.7g/kg reported for fermented cassava chips (Polyorach et al 2012). However, 1.6g/kg alanine level (Aro and Aletor 2012) for unfermented cassava peel and 1.5g/kg in cassava root (Bayata 2019) were higher than values obtained in coarse, fine and whole cassava peel mash but lower than 1.73g/kg observed in sundried cassava peel meal. The difference in the profile could be varietal difference in the cassava source. Alanine content of cassava chips (1.14g/kg) and cassava pellet (1.12g/kg) reported by Bhuiyan and Iji (2015) were lower than value obtained for cassava peel products studied.

The aspartic acid of 0.7g/kg in fermented cassava chips (Polyorach et al 2012) is lower than value recorded for cassava peel products in this study. The aspartic acid levels recorded in this study for cassava products, were higher than 1.5g/kg obtained in cassava root (Bayata 2019), 2.97g/kg in unfermented cassava peel (Aro and Aletor 2012) were higher than values obtained in this study. The highest value obtained in this study was 2.94g/ kg in SCPM.

Glutamic acid is the most abundant amino acid in the analysed cassava peel products, in line with earlier submission (Mcdonald et al 2010) that glutamic acid is one of the amino acids found in large quantity in plants. The result indicates that glutamic acid and aspartic acid were the most abundant amino acids in cassava peel products. This results obtained also agrees with the findings of Omode et al (2018), that free amino acid were predominantly glutamic and aspartic acids. In fermented cassava chip, Polyorach et al (2012) observed that lysine was the most pronounced amino acids in cassava root. However, Bayata (2019), reported leucine as the most abundant amino acid in cassava roots. The observed differences could be due to fermentation employed by Polyorach et al (2012). Glutamic acid recorded for the analysed cassava peel products were higher than reported 1.5g/kg (Bayata, 2019) for cassava peel products. Bayata (2019) observed that alanine and glutamic acid in cassava roots were the same, however, in cassava peel products analysed, glutamic acid was 1.48-2.43 times higher than alanine.

The 0.05g/kg reported for cystine (Polyorach et al 2012) was lower than observed for cassava peel products in this study. Cystine in analysed cassava peel products were higher than 0.1g/kg reported (Bayata 2019) for cassava roots. The 0.39g/kg cystine obtained for coarse, (0.33g/kg) fine and (0.35g/kg) WCPM were similar to values obtained for unfermented cassava peel meal determined (Aro and Aletor 2012).

Conclusion

• The processing methods employed helped to reduce the crude fibre, crude protein and amino acid content of the cassava peel products relative to sundried cassava peel meal.
  
  
• Fibre fractions was highest in SCPM except for acid detergent fibre and acid detergent lignin.
  
  
• Also, glutamic acid and aspartic acids were the most abundant amino acids in cassava peel products studied.

Acknowledgements

Authors appreciate the contributions of the Management of International Livestock Research Institute, Idi Ose, Ibadan for assisting with the machinery used in the production of the cassava products. We also thank the Technical hub of Evonik Nutrition and Care GmbH, Germany for providing the template and technical assistance for the analyses of the cassava peels. Finally, the doggedness and scholarly roles of the erudite teacher, mentor and patriarch, Professor Olumide Odeleye Tewe at the inception, collaboration and eventual execution of this masterpiece remained indelible. Prof OOT, sweet is your memory, continue to rest in perfect peace, Sir.

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