1. S. K. Mutayoba1,2,4, C.M. Fauquet3, and E S. Dierenfeld4
Title: Nutritional evaluation of Cassava (Manihot esculanta) Fractions (Flesh, Peels and Leaf) from select cultivars
S. K. Mutayoba1,2,4, C.M. Fauquet3, and E S. Dierenfeld4
1Sokoine University, Morogoro, TANZANIA; AWARD, Nairobi, KENYA;3Danforth Plant Science Center, St. Louis, MO USA; 4Novus International, Inc. St. Charles, MO USA
Abstract
Dried and ground fractions of peels, leaves and flesh samples of the improved (p746, p768 and p770) and unimproved (WT) cassava cultivars were assessed for their proximate composition, carotenoids, minerals, amino acids and HCN,
Crude protein on DM basis averaged 5.3, 9.6 and 28.5 % for the flesh, peels and leaves, respectively. Generally the genetically improved cassava cultivars contained higher levels of protein (2.4% (WT) and 8.1% (p746) for the flesh), TAA, and other macronutrients compared to unimproved variety. HCN varied in the flesh among varieties and was 96 in WT and 141 mg/kg in p746.
Fiber fractions (NDF, ADF and lignin) were highest in leaves and lowest in flesh. Both total amino acid and individual amino acids concentrations were 2 to 10 times higher in peels fractions compared to flesh of the same variety. Total carotenoid concentration in the flesh was 0.04 mg/kg in WT and 1.01 mg/kg in p746. ß-carotene was the primary carotenoid pigment in the flesh and peels, 75-93% whereas in cassava leaves lutein was 54-64%. Mineral levels were highest in leaves, followed by peels, and lowest in the flesh.
This study revealed nutritional differences between cassava cultivars and plant parts. Furthermore, cassava peels, normally thrown away contained higher nutrients and therefore could be a good source of nutrients in livestock diets
RESULTS
Nutrient Composition
The chemical composition, and nutritive values, for various plant parts in the cassava cultivars are presented.
Crude protein (CP) content in the various parts averaged 4.98, 8.85 and 26.67% for the flesh, peels and leaves, respectively, with widest variation observed in CP for the flesh (2.4% (WT) to 8.1% (p746)). CP concentration was lowest in the unimproved (WT) cultivar parts when compared to other cultivars. Soluble protein (SP) and NFC values were highest in the flesh, and lowest in leaves, whereas fiber fractions (NDF, ADF, and lignin) were highest in leaves and lowest in the flesh. With the exception for SP in leaves (only) and NFC (all parts), nutritive constituents were lowest in the WT variety.
HCN and Carotenoids
Differences among varieties were noted for HCN in the flesh, ranging from (96 to 141 mg/kg) in varieties WT and p746, respectively.
Total carotenoid content differed both among cassava cultivars and plant parts. Total carotenoid concentration was negligible in the WT flesh cultivar(0.04 mg/kg), and highest in p746 (1.01 mg/kg). ß-carotene was the primary carotenoid pigment detected in flesh and peels, comprising 75-93% of total carotenoids measured. In contrast, cassava leaves contained more of lutein, contributing 54-64% of total carotenoids measured. α-crypotxanthin and lycopene were not detected in all but zeaxanthin was less than 10% of total carotenoids in the plant fractions
Energy and Minerals
The energy content was flesh>leaf>peel fraction, although in Cultivar p746, peels contained higher calculated energy compared to leaves.
The mineral concentration of the different parts of cassava showed higher levels in leaves followed by peels and lastly flesh.
INTRODUCTION
The cassava plant originated in South America and has spread globally as an important food crop for million people in Africa, Asia and Latin America. It can be grown under harsh conditions such as low rainfall and poor soils. The major limitations to utilization are mainly due to sub optimal nutritional value including low protein content (average ~ 2-4% protein in cassava, although levels <1% have been reported; Nasser and Souza, 2007), low vitamin A value, and the presence of cyanogenic (hydrogen cyanide, HCN) and/or phenolic compounds (Montagnac et al, 2009). Additionally, cassava shows a strong tendency for post-harvest physiological deterioration (PPD). Recently targeted genetic studies to enhance the nutritional properties of specific cassava cultivars such as lowering cyanogens (Jorgensen et al., 2005), increasing ß-carotene (Akinwale et al., 2010), and/or increasing protein content (Stupak et al, 2006; Abhary et al., 2011) have been carried out. However the resulting nutritional value for the different cassava parts which can be useful to animals have not been investigated in detail.
Thus main objective of this preliminary study was to evaluate the nutritive value of root (flesh), peel, and leaf fractions of the four select cultivars of cassava (1) unimproved, 2) high-protein, 3) high-ß-carotene, 4) both high protein and high ß-carotene) as potential byproduct feed for livestock production.
Materials and Methods:
Cassava materials
Samples of dried and ground fractions (tuber flesh, peels, and leaves) of 4 cassava cultivars (WT (unimproved), p746 (high protein), p768 (high ß-carotene) and p770 (both high protein & ß-carotene) from ITLAB Danforth Center, St Louis, USA were analyzed to determine proximate composition and amino acid profiles (tuber fractions only), cyanide,, carotenoid pigments, and mineral content using standard laboratory methods.
Laboratory analysis
Dried, ground fractions (flesh, peel, leaf) were subjected to laboratory analyses to determine proximate composition (crude and soluble protein, crude fat, non-fiber carbohydrates (NFC), ash), fiber fractions (neutral detergent fiber, NDF; acid detergent fiber (ADF), and lignin), and macro- and trace mineral concentrations, as well as calculated energy content using standard (AOAC, 1990) methods.
Amino acids were characterized using AOAC Official Methods of Analysis (2006) method E (a,b,c).
Anti-nutritional properties (cyanic acid and HCN were characterized using picrate paper kits for determination of total cyanogens in cassava roots and all tuber products described by Bradley et al (1999) total polyphenols were measured as catechins using a Folin-Ciocalteu UV methodology (Singleton et al, (1999) and the carotenoids profile was determined using spectrophotometer.
Macro- and trace minerals concentrations in cassava (Manihot esculanta) cultivars/parts. (air-dry basis)
Cultivar/ Part
WT Tuber
p770 Tuber
p768 Tuber
p 746 Tuber
WT Peel
p770 Peel
p768 Peel
p746 Peel
WT Leaf
p770 Leaf
Ash, %
2.26
1.94
3.76
6.15
4.14
6.23
5.91
5.45
5.81
5.54
Macrominerals, %
Calcium
0.06
0.14
0.19
0.69
1.15
1.25
0.85
0.99
0.76
Phosphorus
0.13
0.18
0.11
0.15
0.12
0.33
0.36
Magnesium
0.07
0.08
0.20
0.17
0.32
0.27
Potassium
1.13
0.87
1.73
3.04
1.52
1.30
1.46
1.34
1.70
Sodium
0.02
0.04
0.01
0.03
Sulfur
0.09
0.29
0.42
Trace Minerals, mg/kg
Copper
3.00
4.00
5.00
<1.0
6.00
2.00
7.00
Iron
14.00
9.00
10.00
12.00
52.00
66.00
44.00
86.00
73.00
Manganese
23.00
25.00
97.00
63.00
43.00
217.00
133.00
Molybdenum
<0.1
0.10
0.30
0.80
0.50
1.10
1.00
Zinc
8.00
20.00
40.00
35.00
57.00
51.00
Amino Acids
The mean values for amino acid (AA) composition in the flesh and peel samples from 4 cassava cultivars are presented in Fig. 2.
Variation in the distribution of AA, both among varieties and between plant parts, was noted; variation was higher between peel compared to flesh fractions.
Both total amino acid (TAA) and individual AA concentrations were 2 to >10X higher in peel fractions compared to flesh of the same cassava varieties, depending on the individual AA. Differences in AA distribution between plant fractions, however, did not appear to be directly correlated.
The total concentrations of most AAs were consistently lower in the WT variety for both plant parts.
The essential amino acid levels relative to nutrient requirements of livestock (Ideal Protein (AA) Ratios), both flesh and peels of cassava were below Ideal AA ratios in all AA except ARG, HIS and TRP for poultry. In both plant parts, MET, CYS, TYR and TRP were relatively low while ASP, GLU and ARG were high.
Discussion:
Crude protein content of 2.4% for WT was within the range of unimproved varieties ( %) reported in the literature. Higher CP noted in the other cultivars did conform to findings reported by Abhary et al., A change in the distribution of nutrients was also noted. Differences in CP content between cassava varieties are normally observed and in most cases the bitter varieties have slightly higher protein content. The higher CP content in the peels observed in the present study was similar to findings reported by Okigbo 1980) and was slightly higher for the sweet variety.
Conclusion
This study showed nutritional differences between cassava cultivars and plant parts. The transgenic varieties contained high protein compared to normal cassava cultivars. Additionally cassava peels, normally thrown away contained higher nutrients compared to the flesh and therefore could be a good source of nutrients in livestock diets. Further studies to determine nutrient utilization are recommended.
Acknowledgments
The authors would like to thank ITLAB Danforth Center, USA for providing the research materials, NOVUS International, Inc, USA for laboratory analyses and AWARD program, for granting research fellowship to S.K.Mutayoba.