Effect of Accessions of Colocasia esculenta -Based Diets on the Hepatic and Renal Functional Indices of Weanling Wistar Rats

Abstract

The liver and kidney functional indices of weanling albino rats (Rattus norvegicus) maintained on different accessions (offspring of a variety planted/collected at a specific location and time but differing in certain morphological characteristics) of cooked Colocasia esculenta (cocoyam)-based diets (UFCe1–UFCe7) for 28 days were investigated. All the accessions of C. esculenta-based diets did not significantly (P > .05) alter the serum levels of albumin, globulin, inorganic phosphorus, calcium, magnesium, and uric acid of the animals.The total protein and total bilirubin levels decreased only in the UFCe3- and UFCe4-fed animals, respectively. Whereas UFCe1 and UFCe2 significantly decreased the conjugated bilirubin levels, UFCe3 and UFCe6 increased it. While all the accessions of C. esculenta-based diet decreased the serum alkaline phosphatase activity, γ-glutamyl transferase activity was increased. UFCe1 and UFCe5 increased the serum alanine aminotransferase activity, whereas UFCe4 decreased the activity of the enzyme. Again, UFCe3 and UFCe1 increased the serum creatinine and aspartate aminotransferase activity of the animals. Furthermore, the computed blood urea nitrogen:creatinine ratio was higher in animals maintained on UFCe1-, UFCe3-, UFCe4-, and UFCe5-based diets. Whereas UFCe6 and UFCe7 increased the level of sodium in the serum of the animals, UFCe4 and UFCe5 decreased the chloride level. The serum urea level was decreased by UFCe1, UFCe3, UFCe4, and UFCe5, whereas the potassium level increased in the UFCe4-, UFCe6-, and UFCe7-fed animals. Overall, the results revealed that all the accessions of C. esculenta produced selective effects on the hepatic and renal functional indices of the weanling rats. The highest alterations were produced by UFCe4, whereas the least was from UFCe2. These alterations may have consequential effects on the normal functioning of the liver and kidney of the animals. UFCe2 exhibited the least toxicity risk among the accessions of C. esculenta growing in the KwaZulu-Natal Province of South Africa.

Introduction

C olocasia esculenta (Family Araceae) is an edible aroid commonly known as Taro cocoyam. It is an important crop in Hawaii, Japan, Egypt, Ghana, and Nigeria.¹ The crop is a staple food throughout the tropical and subtropical regions of the world, in particular, Asia and the Pacific Islands. It is cultivated mainly for its edible corms, cormels, leaves, and other traditional uses by subsistence farmers.^2,3 The leaves are also consumed as a vegetable.⁴ The tubers can be eaten boiled, fried, or pounded into paste and consumed with soup. It can also be made into porridge or pottage, as well as chips and flour. Cooked tubers can be eaten alone or with stew and also as soup thickeners. The crop can be processed into several food and feed products and industrial inputs, similar to that of potatoes in the Western world. In addition to being good sources of nutrients, cocoyam also has some medicinal properties.⁵

In South Africa, however, cocoyam, referred to as Amadumbe, is not well known despite having been cultivated for centuries in some remote parts of KwaZulu-Natal Province. The species is considered as food for the poor, and commercial farmers have not shown much interest in the crop. Previous studies on the chemical composition of cocoyam revealed that it is of high nutritional value.^6,7

The use of cocoyam as food for humans and animals has limiting factors like storage and the presence of antinutritional factors such as oxalates, phytates, tannins, and saponins.⁸ Oxalates have been implicated in the acrid or irritating quality found in cocoyam species when consumed. Boiling the tuber is a requirement for consumption as it helps to reduce the level of oxalates by inactivation.⁹ Similarly, Lewu et al.¹⁰ have shown that cooking significantly reduced the antinutrients such as oxalates, tannins, and phytates in cocoyam accessions growing in the KwaZulu-Natal Province of South Africa.

Despite all these results, and coupled with increasing consumption of the tubers, there is no information in the open scientific literature that addressed the toxic effect or safety of the cocoyam tubers in animals. The current work is a follow-up on the preliminary studies on the proximate, mineral, and antinutritional composition of the leaves and tubers of seven accessions (offspring of a variety planted/collected at a specific location and time but differing in certain morphological characteristics) used in this study.^10

–13 Therefore, there is the need to evaluate some of the different accessions of C. esculenta growing in the KwaZulu-Natal Province of South Africa for safety or toxicity.

The objective of this study was to provide information on the toxic implications of the different accessions of C. esculenta growing in the KwaZulu-Natal Province of South Africa by evaluating the effects of the C. esculenta-based diet on the functional indices of the liver and kidney of weanling rats. Seven different farmlands located in four different villages in the main growing area of the KwaZulu-Natal Province of South Africa were sampled because those were the areas where the farmers cooperated. The sample obtained from each of the farmland was referred to as an accession. In this study, the use of accessions does not necessarily mean that C. esculenta may or may not belong to the same variety because the crop growing in South Africa has not been scientifically characterized for morphological properties.

Materials and Methods

Feed components

Seven accessions of cocoyam (C. esculenta) tubers designated as University of Fort Hare C. esculenta 1–7 (UFCe1–UFCe7) were obtained from four different villages (Umbumbulu, Makhathini, Mthwalume, and Maphumulo) in the KwaZulu-Natal Province of South Africa. Yellow maize (Zea mays) was obtained from Alice, South Africa, whereas soybean and its oil were obtained from Kei Seeds and Feeds Ltd. (East London, South Africa). Vitamin mix was a product of Ceva Animal Health (Pty) Ltd. (Midrand, South Africa). Component chemicals of the mineral mix were products of Sigma Chemical Co. (St. Louis, MO, USA).

Animals

Twenty-one-day-old, home-bred, weanling Wistar rats of both sexes (Rattus norvegicus) with a mean weight of 37.92 ± 3.19 g were obtained from the Animal House of the Agricultural and Rural Development Research Institute, University of Fort Hare, Alice. The animals were housed in clean metabolic cages placed in well-ventilated house with optimum conditions (temperature, 23 ± 1°C; photoperiod, 12 hours of natural light/12 hours of dark; humidity, 45–50%). This study was carried out following approval from the ethical committee on the use and care of animals of the University of Fort Hare.

Assay kits

The assay kits for creatinine, urea, calcium, sodium, potassium, chloride, phosphorus, albumin, bilirubin, alkaline phosphatase (ALP), γ-glutamyl transferase (GGT), and alanine and aspartate aminotransferases (ALT and AST, respectively) were obtained from Roche Diagnostic GmbH (Mannhein, Germany). All reagents used were of analytical grade and were supplied by Merck Chemicals (Pty) Ltd. (Bellville, South Africa).

Processing of feed components

The seven accessions of C. esculenta tubers were separately peeled, washed, sliced, and boiled at 100°C for 20 minutes and thereafter oven-dried at 60°C to constant weight. Yellow maize was soaked in distilled water for 48 hours at room temperature and later oven-dried at 40°C to constant weight. Dried soybean, maize seeds, and the cocoyam accessions were separately milled using a Fritsch Pulverisette 14^® Rotor-Speed mill (Fritsch GmbH, Laborgeraetebau, Germany) and stored in air-tight polythene bags. The milled soybean was later autoclaved at 120°C for 30 minutes. All the powdered samples were used as components of the formulated feed.

Composition of diet

The control (corn starch-based) and cocoyam (C. esculenta-based) diets were formulated using the components given in Table 1. The components were thoroughly mixed and made into pellets to ensure good handling by the animals. The feeds were packed in air-tight polythene bags and stored in the freezer to prevent microbial growth.

Table 1.

Components of the Diets

	Diet (g/kg)
Food component	Cocoyam-based	Cornstarch-based (control)
Soybean	250	250
Cornstarch	—	516
Cocoyam tuber	516	—
Soybean oil^a	40	40
Cellulose	40	40
Sucrose	100	100
dl-Methionine	4	4
Vitamin mix^b	40	40
Mineral mix^c	10	10

Soybean oil is composed of polyunsaturated fatty acids (58%), monounsaturated fatty acids (29%), and saturated fatty acids (13%).

Vitamin mix (per kg of diet): bioflavanoids, 500 mg; vitamin A, 1,000,000 IU; vitamin D3, 245,000 IU; vitamin E, 1,000 IU; vitamin K, 500 mg; d-pantothenic acid, 1,000 mg; riboflavin (vitamin B2), 500 mg; thiamine (vitamin B1), 300 mg; folic acid, 50 mg; niacin, 2,500 mg; pyrodixine (vitamin B6), 100 mg; vitamin B12, 3 mg; and ascorbic acid (vitamin C), 500 mg. Also contains 1.05% potassium dextrose and 20% sodium-21 (as salts).

Mineral mix (in g/kg): CoCl₂ · 6H₂O (0.001), CuSO₄ · 5H₂O (0.079), MnSO₄ · 7H₂O (0.178), KI (0.032), NaCl (3.573), ZnCO₃ (1.60), CaSO₄ (11.610), MgSO₄ · 7H₂O (2.292), K₂HPO4 (10.559), and FeSO₄ · 7H₂O (1.078).

Animal grouping and feeding

Forty-eight rats of both sexes were completely randomized into eight groups (A–H) made up of six animals each. Group A consisted of the rats maintained for 4 weeks on cornstarch-based diet (control), whereas animals in groups B–H were maintained for the same period on the first, second, third, fourth, fifth, sixth, and seventh accessions of C. esculentum-based diets, respectively, and designated as UFCe1, UFCe2, UFCe3, UFCe4, UFCe5, UFCe6, and UFCe7. The animals were fasted (without food, but with water) for 6 hours before the beginnning of the experiment. The formulated feed and water were supplied to the rats ad libitum. The animals were sacrificed 24 hours after the 4-week feeding period.

Preparation of serum

Serum was prepared by adopting the procedure described by Yakubu et al.¹⁴ In brief, under ether anesthesia, rats were bled through their cut jugular veins, which were slightly displaced (to prevent blood contamination by interstitial fluid). An aliquot (5 mL) of the blood was allowed to clot for 10 minutes at room temperature and then centrifuged at 1,282 g for 5 minutes using a bench top centrifuge (model Z300, Hermle, Hamburg, Germany). The sera were later aspirated into sample bottles with Pasteur pipettes and used within 12 hours of preparation, for the analyses of the liver and kidney functional parameters.

Determination of functional parameters

The concentrations of sodium, potassium, chloride, calcium, magnesium, inorganic phosphorus, urea, creatinine, albumin, globulin, total protein, uric acid, ALP, GGT, ALT, AST, and total and conjugated bilirubin were determined in the serum of the animals by adopting the protocol outlined in the manufacturer's assay kit from Roche Diagnostics on the Roche modular system (model P800). The analyzer was calibrated for use on animal serum before the determinations were carried out. The blood urea nitrogen (BUN):creatinine ratio was computed as the ratio of serum urea to creatinine.

Statistical analysis

Data were mean ± SD values of six determinations and were subjected to one-way analysis of variance. Means were separated by the Duncan Multiple Range Test using SAS software (SAS Institute, Cary, NC, USA). Values were considered statistically significant at P < .05.

Results

Feeding of rats for 4 weeks ad libitum on the various accessions of C. esculenta-based diet produced varying alterations in the concentrations of serum liver and kidney functional indices investigated in this study (Tables 2 and 3). For example, all the accessions of C. esculenta-based diets did not significantly (P > .05) alter the levels of albumin and globulin in the serum of the animals, whereas the total protein and total bilirubin levels decreased only in the UFCe3- and UFCe4-fed animals, respectively (Table 2). Whereas UFCe1 and UFCe2 decreased the conjugated bilirubin levels, UFCe3 and UFCe6 increased it. Again, whereas all the accessions of C. esculenta-based diet decreased the ALP activity in the serum of the animals, GGT increased in all the diet groups. In contrast, UFCe1 and UFCe5 increased the serum ALT activity of the animals, whereas the activity of the enzyme decreased in the UFCe4-fed animals. All the other diets did not alter the activity of the enzyme. In addition, UFCe1 significantly increased AST activity in the serum of the animals, whereas the enzyme activity compared well with the control in all the other diet groups (Table 2).

Table 2.

Effect of C. esculenta-Based Diet on Liver Functional Indices of Weanling Wistar Rats

Parameter	Control	UFCe1	UFCe2	UFCe3	UFCe4	UFCe5	UFCe6	UFCe7
Total bilirubin (μmol/L)	7.00 ± 0.82^ab	6.00 ± 0.82^bc	7.00 ± 0.82^ab	7.75 ± 0.96^a	5.25 ± 0.50^c	7.75 ± 0.96^a	6.00 ± 0.82^bc	7.25 ± 0.96^ab
Conjugated bilirubin (μmol/L)	2.25 ± 0.96^abcd	1.50 ± 0.58^cd	1.25 ± 0.50^d	3.25 ± 0.50^a	2.50 ± 0.58^abc	2.00 ± 0.82^bcd	3.00 ± 0.82^ab	2.25 ± 0.50^abcd
Albumin (g/L)	14.50 ± 1.29^a	14.75 ± 0.96^a	13.50 ± 1.00^a	13.25 ± 1.50^a	13.50 ± 1.73^a	14.50 ± 1.29^a	13.25 ± 0.50^a	12.75 ± 0.96^a
Globulin (g/L)	32.75 ± 0.96^ab	35.00 ± 2.16^a	32.75 ± 2.06^ab	30.25 ± 1.26^b	34.75 ± 1.26^a	32.75 ± 0.96^ab	34.50 ± 1.92^a	32.25 ± 2.22^ab
Total protein (g/L)	47.25 ± 2.22^ab	49.75 ± 1.89^a	46.25 ± 2.63^bc	43.50 ± 1.29^c	48.25 ± 2.75^ab	47.25 ± 0.96^ab	47.75 ± 1.71^ab	45.00 ± 2.31^bc
Alkaline phosphatase (U/L)	1,362.30 ± 80.04^a	1,030.00 ± 99.05^c	669.00 ± 81.29^e	835.25 ± 68.03^d	1,053.50 ± 72.33^c	1,213.00 ± 92.64^b	1,214.50 ± 77.04^b	799.50 ± 56.69^d
γ-Glutamyl transferase (U/L)	6.25 ± 0.96^a	8.00 ± 0.82^b	8.25 ± 0.96^b	9.50 ± 1.29^bc	13.50 ± 1.29^d	10.75 ± 1.50^bc	10.75 ± 1.71^bc	12.50 ± 1.00^de
Alanine aminotransferase (U/L)	116.00 ± 9.42^a	149.50 ± 14.01^b	122.00 ± 14.45^c	121.00 ± 10.49^c	98.25 ± 6.08^d	135.75 ± 11.62^e	115.75 ± 8.14^cd	108.25 ± 7.46^cd
Aspartate aminotransferase (U/L)	214.00 ± 12.73^ad	278.50 ± 19.54^b	231.75 ± 14.89^c	235.00 ± 31.61^c	199.00 ± 14.67^d	215.00 ± 16.97^ad	197.50 ± 16.84^d	208.00 ± 14.86^ad

Data are mean ± SD values (n = 6).

abcde

Values with different superscripts along the row for each diet are significantly different (P < .05).

Table 3.

Effect of C. esculenta-Based Diet on Kidney Functional Indices of Weanling Wistar Rats

Parameter	Control	UFCe1	UFCe2	UFCe3	UFCe4	UFCe5	UFCe6	UFCe7
Sodium (mmol/L)	139.25 ± 1.71^a	139.25 ± 1.71^a	140.25 ± 1.26^a	139.75 ± 0.96^a	140.75 ± 1.71^a	140.50 ± 1.73^a	143.00 ± 2.45^b	142.75 ± 0.50^b
Potassium (mmol/L)	5.80 ± 0.08^a	6.03 ± 0.33^a	6.05 ± 0.31^a	5.90 ± 0.80^a	6.43 ± 0.44^b	6.15 ± 0.71^a	6.70 ± 0.66^b	6.43 ± 0.50^b
Chloride (mmol/L)	108.50 ± 2.89^a	105.00 ± 2.16^a	104.50 ± 2.52^a	107.50 ± 1.29^ab	103.25 ± 2.50^c	103.25 ± 1.26^c	105.50 ± 3.32^abc	105.25 ± 1.71^abc
Inorganic phosphorus (mmol/L)	2.95 ± 0.30^a	2.70 ± 0.28^a	2.75 ± 0.19^a	2.88 ± 0.10^a	2.75 ± 0.06^a	2.70 ± 0.27^a	2.85 ± 0.27^a	2.70 ± 0.14^a
Urea (mmol/L)	7.45 ± 0.51^a	5.40 ± 0.59^bc	7.55 ± 0.95^a	5.23 ± 0.76^bc	5.70 ± 0.85^bc	5.03 ± 0.97^c	7.55 ± 0.65^ab	7.65 ± 0.93^a
Creatinine (mmol/L)	35.50 ± 2.89^abc	38.25 ± 1.50^d	37.00 ± 4.90^abc	41.25 ± 2.06^e	36.00 ± 2.58^abc	32.25 ± 0.96^c	34.25 ± 2.99^bc	36.50 ± 2.89^abc
BUN:creatinine ratio	1:4.8	1:7.0	1:4.9	1:7.9	1:6.3	1:6.4	1:4.5	1:4.7
Calcium (mmol/L)	2.37 ± 0.09^a	2.37 ± 0.07^a	2.40 ± 0.12^a	2.31 ± 0.11^a	2.37 ± 0.09^a	2.39 ± 0.03^a	2.38 ± 0.04^a	2.38 ± 0.09^a
Magnesium (mmol/L)	1.08 ± 0.06^a	1.06 ± 0.03^a	1.07 ± 0.03^a	1.03 ± 0.08^a	1.01 ± 0.08^a	1.02 ± 0.03^a	1.03 ± 0.05^a	1.01 ± 0.07^a
Uric acid (mmol/L)	0.06 ± 0.02^a	0.09 ± 0.03^a	0.07 ± 0.01^a	0.09 ± 0.01^a	0.09 ± 0.01^a	0.08 ± 0.01^a	0.08 ± 0.01^a	0.08 ± 0.01^a

Data are mean ± SD values (n = 6).

abcde

Values with different superscripts along the row for each diet are significantly different (P < .05).

BUN, blood urea nitrogen.

The serum inorganic phosphorus, calcium, magnesium, and uric acid levels of rats maintained on all the accessions of C. esculenta-based diet were not significantly altered by the end of the feeding period (Table 3). However, all other kidney functional indices investigated in this study were affected by specific diet. For example, UFCe6 and UFCe7 increased the level of sodium in the serum of the animals, whereas UFCe4 and UFCe5 decreased the chloride level. In contrast, these electrolytes were not significantly altered by the remaining accessions of C. esculenta-based diets. The serum urea level was decreased by UFCe1, UFCe3, UFCe4, and UFCe5, but all other C. esculenta accession-based diets did not affect the urea level of the animals. UFCe1 and UFCe3 increased the serum creatinine content of the animals, whereas the value produced by the other accession of C. esculenta-based diet groups compared well with the control (Table 3). Again, the computed BUN:creatinine ratio was higher in animals maintained on UFCe1, UFCe3, UFCe4, and UFCe5. In addition, only the animals maintained on UFCe4, UFCe6, and UFCe7 had their serum potassium levels elevated, whereas the level of the electrolyte in the other formulated diet groups were not significantly altered (Table 3). The animals maintained on UFCe4 showed the highest (38.89%) alteration in all the functional indices investigated, whereas UFCe2 altered the least number (16.67%) of parameters.

Discussion

C. esculenta is an important staple food throughout many regions of the world. Despite the increasing consumption of the crop, data on toxicological implication in animals appear to be scanty in the open scientific literature. Feeding of animals with accessions of C. esculenta growing in the KwaZulu-Natal province of South Africa revealed that the crop could alter some of the liver and kidney functional indices of the weanling rats.

The biochemical indices monitored in the serum in this study are useful “markers” for assessing the functional capacities of the organs. Biochemical indices of organ function if altered may indicate an adverse effect on the normal functioning of the organs.¹⁵

Albumin, bilirubin, and total and conjugated bilirubin are mixtures of biomolecules that can be used to assess the functional capacity of the liver. Albumin, synthesized in the liver, is the most abundant serum protein, representing 55–65% of the total protein.¹⁶ Bilirubin formed from the breakdown of hemoglobin in the liver is conjugated with glucuronic acid to form a soluble compound, which passes down the bile duct and is excreted into the gastrointestinal tract. The absence of an effect on albumin and globulin by some of the formulated diet and coupled with alterations in the level of total protein and bilirubin might imply a selective and diet-specific effect on the liver. In contrast, however, the reduction in the total protein and total bilirubin content of the serum by UFCe3 and UFCe4 as well as the decrease in conjugated bilirubin level by UFCe3 and UFCe6 may imply adverse effects on the synthetic, secretory, and rapid clearance of the bilirubin without commensurate synthesis of the compounds.

ALP is a “marker” enzyme of damage to the plasma membrane and endoplasmic reticulum.¹⁷ It is often used to assess the integrity of the plasma membrane.¹⁸ Although tissue enzyme activity was not studied, the decrease in ALP activity in the serum of the animals by all the accessions of C. esculenta-based diet may be attributed to inactivation or inhibition of the enzyme molecule at the cellular/molecular level.¹⁸ The decrease in ALP activity may also be due to reduction in the production of the enzymes. In contrast, the increase in serum GGT suggests leakage from the tissue into the extracellular fluid, the serum. The increase in the activity of GGT may also be due to de novo synthesis of the enzyme molecule. Because tissue enzymes were not determined in this study, it is impossible therefore to really ascertain this school of thought. The enhanced levels of serum GGT could possibly indicate an adverse effect on the mechanism responsible for the maintenance of the normal level of the enzyme in the blood of the animals.

ALT and AST are useful “marker” enzymes of liver cytolysis.¹⁹ They play a key role in the metabolism of amino acids. The increase in serum ALT by UFCe1 and UFCe5 as well as the decrease in the activity of AST by UFCe4 are indications of alterations in the cytosolic content of the animals. Whereas the increase in serum ALT suggests contribution from the tissue enzymes, the decrease in the activity of ALT suggests inactivation of the enzyme molecule at the molecular level or reduction in the production of the enzyme molecule. All these alterations may have consequential effect on the amino acid metabolism of the animals.

It is noteworthy that the levels of inorganic phosphorus, calcium, magnesium, and uric acid were not affected by the various accessions of C. esculenta-based diets. However, the increase in sodium level by UFCe4 as well as the decrease in the chloride levels by UFCe5 implies selective effects by the diets on the normal functioning of the kidney. The alterations in these electrolytes may affect processes dependent on these ions. Urea, a major catabolic product of protein, is one of the principal indices for assessing kidney function. It is derived from general protein metabolism and is always at least partially reabsorbed passively in the renal tubules.²⁰ The decrease in the level of urea by UFCe1, UFCe3, UFCe4, and UFCe5 suggests an enhanced rate of excretion/clearance of the kidney parameter from the blood, which is not commensurate with the rate of production arising from deamination of protein. Therefore, the reduction in the serum ALP, the increase in GGT activity, and the reduction in the level of urea in the serum of the animals may not likely be due to bile duct effect, but a combinatorial effect on the liver and kidney. Creatinine, a commonly used test of renal function, is an endogenous, nitrogenous waste product derived from creatine and creatine phosphate in muscle tissue. The increase in serum creatinine level by UFCe3 might be an indication of dysfunction at the glomerular and/or tubular levels.²⁰ The serum BUN:creatinine ratio measures the amount of nitrogen in the blood, and an increase in the serum levels reflects dehydration, a high protein diet, or renal dysfunction. Furthermore, a low BUN:creatinine ratio may indicate liver damage or overhydration. Therefore, the higher levels of computed BUN:creatinine ratio in the animals maintained on UFCe1-, UFCe3-, UFCe4-, and UFCe5-based diets may be an indication that the kidneys of the animals were not able to remove urea from the blood normally. Urea is synthesized in the liver, and it is excreted by the kidney. Therefore, the corresponding increase in the serum creatinine contents of the animals maintained on UFCe1 and UFCe3 may be an indication that the diets may prone the animals to renal damage.²¹

The reduction in the levels of potassium by UFCe4, UFCe6, and UFCe7 might imply an adverse effect on the pump responsible for regulating and maintaining the constancy of the ion in the blood. All these alterations suggest that the accessions of C. esculenta could adversely affect the normal hepatic and renal functioning of the animals.

In conclusion, the accessions of C. esculenta have selectively altered the biochemical indices of liver and kidney function in the weanling rats. The highest alterations were produced by UFCe4 (38.89%), whereas the least was from UFCe2 (16.67%). UFCe2 exhibited the least toxicity risk among the accessions of C. esculenta growing in the KwaZulu-Natal Province of South Africa. These alterations may have consequential effects on the normal functioning of the liver and kidney of the animals.

Footnotes

Acknowledgment

The authors acknowledge with thanks the research grant provided by the National Research Foundation of South Africa.

Author Disclosure Statement

No competing financial interests exist.

References

Iwuoha

, Kalu

. Calcium oxalate and physico-chemical properties of cocoyam (Colocasia esculenta and Xanthosoma sagittifolium) tuber flours as affected by processing. Food Chem, 1995; 54:61–66.

Miyasaka

, Ogoshi

, Tsuji

, Kodani

. Site and planting date effects on taro growth: comparison with aroid model predictions. Agron J, 2003; 95:545–557.

Ekanem

, Osuji

. Mitotic index studies on edible cocoyams (Xanthosoma and Colocasia spp) Afr J Biotechnol, 2006; 5:846–849.

Aregheore

, Perera

. Dry matter, nutrient composition and palatability/acridity of eight exotic cultivars of cocoyams-taro (Colocasia esculenta) in Samoa. Plant Foods Hum Nutr, 2003; 58:1–8.

Saldanha

. Fibre in the diet of U.S. children: results of national surveys. Pediatr, 1995; 96:994–996.

Onayemi

, Nwigwe

. Effect of processing on the oxalate content of cocoyam. Food Technol, 1987; 20:293–295.

Niba

. Processing effects on susceptibility of starch to digestion in some dietary starch sources. Int J Food Sci Nutr, 2003; 54:97–109.

Agwunobi

, Angwukam

, Cora

, Isika

. Studies on the use of Colocasia esculenta (taro cocoyam) in the diets of weaned pigs. Trop Anim Health Prod, 2002; 34:241–247.

Njintang

. Studies on the production of taro (Colocasia esculenta) flour for use in the preparation of achu—a taro base food [Doctoral/Ph.D. Thesis] University of Ngaoundere: Ngaoundere, Cameroon, 2003; 298.

10.

Lewu

, Adebola

, Afolayan

. Effect of cooking on the minerals and antinutrient contents of the leaves of seven accessions of Colocasia esculenta (L.) Schott growing in South Africa. J Food Agric Environ, 2009; 7:359–363.

11.

Lewu

, Adebola

, Afolayan

. Effect of cooking on the proximate composition of the leaves of some accessions of Colocasia esculenta (L.) Schott in KwaZulu-Natal province of South Africa. Afr J Biotechnol, 2009; 8:1619–1622.

12.

Lewu

, Adebola

, Afolayan

. Effect of cooking on the proximate composition of seven accessions of Colocasia esculenta (L.) Schott tubers growing in South Africa. Int J Food Sci Nutr, 2009; 60,Suppl 4:81–86.

13.

Lewu

, Adebola

, Afolayan

. Effect of cooking on the mineral contents, anti-nutritional factors in seven accessions of Colocasia esculenta (L.) Schott growing in South Africa. J Food Compos Anal 10.1016/j.physletb.2003.10.071. Epub ahead of print,23 June 2010.

14.

Yakubu

, Akanji

, Oladiji

. Aphrodisiac potentials of aqueous extract of Fadogia agrestis (Schweinf Ex Heirn) stem in male albino rats. Asian J Androl, 2005; 7:399–404.

15.

Afolayan

, Yakubu

. Effect of Bulbine natalensis Baker stem extract on the functional indices and histology of the liver and kidney of male Wistar rats. J Med Food, 2009; 12:814–820.

16.

Cameron

, Greger

. Renal function and testing of function. Oxford Textbook of Clinical Nephrology. Davison

, Cameron

, Grunfeld

, Kerr

DNS

, Rits

, Winearl

. Oxford University Press: Oxford, 1998; 36–39.

17.

Wright

, Plummer

. The use of urinary enzyme measurement to detect renal damages caused by nephrotoxic compounds. Biochem Pharmacol, 1974; 12:65–67.

18.

Akanji

, Olagoke

, Oloyede

. Effect of chronic consumption of metabisulphite on the integrity of rat cellular system. Toxicology, 1993; 81:173–179.

19.

Shahjahan

, Sabitha

, Mallika

, Shyamala-Devi

. Effect of Solanum trilobatum against carbon tetrachloride induced hepatic damage in albino rats. Indian J Med Res, 2004; 120:194–198.

20.

Chawla

. Kidney function tests. Practical Clinical Biochemistry. Methods and Interpretation, 2 ^nd. JAYPEE Brothers Medical Publishers (P) Ltd.: New Delhi, India, 1999; 90–92.

21.

Morgan

, Carver

, Payne

. Plasma creatinine and urea: creatinine ratio in patients with raised plasma urea. Br Med J, 1977; 2:929–932.