Cocoyam as Animal Feed 1: Production dynamics and nutrient composition
Published Date: 13th July 2020
Introduction
Cocoyam is a herbaceous perennial tropical crop primarily grown for its edible corms (roots) and leaves which are consumed as vegetables in some African countries. Two major types, Colocasia and Xanthosoma species are usually cultivated as food crops, and are generally composed of a large spherical corm from which few large leaves emerge. Two types of cultivated Colocasia are identified; those characterized by large edible main corm in addition to many cormels, which grow under variable conditions (C. esculenta var. esculenta), and the second type which produces small to medium-sized inedible corm in addition to a variable number of cormels and is often found growing close to watersheds or on irrigated lands. Only three Xanthosoma species are cultivated, with X. sagittifulium and X. mafafa being the most common. Colocasia species are referred to as taro and are known in southeast Nigeria as Ede ofe, ngbowa, akikara, ako noke, Coco-India, etc. Xanthosoma species are referred to as tannia and are known in the southeast as ede Oku, ede buji, or ako ahuri.
Cocoyam is one of the most widespread roots and tuber crops cultivated throughout the tropics. Africa as the major global producer recorded an output of 7.87 million tons of cocoyam in 2018. According to FAO (2019) estimates, Nigeria is the world largest producer, with an output of 3.46 million tons (about 37 percent of global production), followed by China (1.64 million tons), Ghana (1.510 million tons) and Cameroons (1.31 million tons) as the four major producers. The three African countries account for more than 60 percent of production in the continent. Cocoyam ranks third in importance after yam and cassava among the root and tuber crops of economic value in Nigeria. It is an important food crop for more than 400 million people worldwide, especially in developing countries. It is very important for the livelihood of poor farmers, and also serves as a food security crop for these farmers in many West and Central African countries, especially Nigeria, Ghana, and Cameroon. Cocoyam has superior nutritional qualities over other root and tuber crops such as cassava and yam and has specifically higher protein, vitamin, and mineral content. Cocoyam corm is highly prone to spoilage due to its inherent high moisture content which encourages the activities of pests and pathogens. This is exacerbated by poor harvesting techniques by farmers and a lack of appropriate storage techniques. Thus, global cocoyam post-harvest losses have been estimated at 15%. Processing of cocoyam into stable products is therefore essential in reducing post-harvest losses and enhancing its industrial applications.
Traditional uses of cocoyam
Traditionally, Colocasia and Xanthosoma species are mainly cultivated for their starchy corms and cormels. The corm is consumed after boiling, frying, or roasting. Boiled cocoyam corms and cormels are peeled, cut up, dried and stored or milled into flour, which can be used for soup thickening, and recently as biscuits, bread and puddings for beverages. The leaves are also consumed in some parts of Africa. Fresh leaves may be boiled and utilized as a vegetable supplement of carbohydrate meals or soups. In Ghana, for example, X. sagittifulium leaves are harvested and dried for utilization, especially during the dry season when vegetables are scarce. Cocoyam corms, peels, and leaves also serve as animal feeds, especially for the feeding of pigs in many Asian countries. The use of cocoyam as food or feed is however limited by its content of anti-nutritional compounds.
These anti-nutritional compounds lower palatability because of the acrid nature of the corms, which cause irritation in the mouth, throat, and skin, and is capable of causing inflammation of these tissues, especially when the corm is subjected to limited processing before consumption. Tannia cocoyam (Xanthosoma) in recent times has become more important than taro cocoyam (Colocasia), due to the superiority of its corms and cormels in terms of energy, proteins, and mineral elements. In most south Nigeria societies, however, X. mafaffa and many other cocoyam varieties have in recent years assumed the status of abandoned crops, and could be seen growing luxuriantly in the wild, especially at roadsides, palm plantations, compound bushes, and waste dump sites. This has engendered several research efforts on the possible uses of different cocoyam varieties, including the wild species as alternative feed raw materials for formulating livestock feeds.
Another highly abundant cocoyam is the genus Caladium which is found in the wild in South and Central America, India, and parts of Africa including southern Nigeria, where it grows in the open areas of the forest. Caladium bicolor or wild cocoyam is a high moisture tuberous rootstock, presently, not directly consumed by man and equally of no industrial value except as an ornamental plant, and is, therefore, being researched as an alternative feed ingredient for livestock.
Nutrient composition of the corm meals
Despite its nutritional qualities and importance to the livelihoods of many small-holder farmers, cocoyam generally has received limited attention in research. Xanthosoma species have been neglected in agricultural policies and research on root and tuber crops and remain underexploited food resources, with a reported decline of production figures in the three major African producing countries. Cocoyam has, however, been shown, on analysis to yield superior nutritional values over major root and tuber crops, especially in terms of their protein digestibility, vitamins, and mineral compositions. Compared to grains however, it is low in protein, fat, and most vitamins, but contains significant amounts of dietary fiber and minerals. Xanthosoma species root meal is particularly rich in starch and total dietary starch. The starch granules under the light microscope appear oval to kidney-shaped, with smaller granules appearing spherical. Leucine, lysine, and tryptophan are the three major essential amino acids found in Colocacia species root meal, although the amino acid values are relatively low. Aspartic acid, glycine, and arginine are the three dominant non-essential amino acids, while the dominant fatty acid in the corm is oleic acid.
Boakye, and coworkers in a review of the food and nutrient values of edible cocoyam reported that X. sagittifolium has appreciable levels of dietary energy, proteins, and vitamins. It is also high in potassium, zinc, and nicotinic acid, but low in trypsin inhibitor compared to another edible cocoyam. Researchers at the Wolaita Sodo University, Ethiopia reported a range of 8.48 - 10.10 percent crude protein and 2.14 - 2.66 percent fiber contents in X. sagittifulium root meals. Fat content ranged from 0.85 - 0.22 percent, ash ranged from 2.27 - 3.25 percent, while carbohydrate and gross energy values were 84.76 - 85.36 percent and 378.47 - 380.27 kcal/100 g respectively. Similarly, mineral contents in mg/100 g were Fe (8.20 -9.88), Zn (3.07 - 3.12), Cu (1.04 - 1.14), Mg (78.77 - 82.00), Mn (2.48 - 3.74), P (120.93 - 129.87), Na (24.33 - 29.22), K (1085.70 - 1223.30) and Ca (56.57 - 44.90), indicating richness in the macro-minerals, potassium, phosphorus, magnesium, and calcium, and the micro-minerals, iron, zinc, and manganese.
Recent studies on the nutrient composition of raw X. mafafa root meal at the Federal University of Technology Owerri, Nigeria recorded 10.38 percent crude protein, 6.75 percent crude fat, 6.64 percent crude fiber, 3.66 percent total ash and 62.04 percent carbohydrate. The macro-mineral values were calcium (2345.00 mg/kg), magnesium (2361.33 mg/kg), potassium (11815.00 mg/kg) phosphorus (783.67 mg/kg) and sodium (1246.00 mg/kg). The nutrient constituents of C. esculenta root meal was also reported by Adeyanju and coworkers to be protein 1.8 g, fat 0.1 g, carbohydrate, 23 g, fiber 1.0 g, calcium 51 mg, phosphorus, 88 mg and iron 1.2 mg in 100g of edible part. Vitamin values were thiamine 0.10 mg, riboflavin 0.03 mg Niacin 0.8 mg, and vitamin c 8 mg in 100g of edible part. Again, research reports from the University of Zululand, South Africa, showed that raw C. esculenta root meal, on analysis yielded 3.3 – 4.4 g/100%DM total ash, 0.28 – 0.8 g/100%DM crude fat, 4.5 – 5.04 g/100%DM crude protein and 25 – 28 g/100%DM starch.
Few studies have also been carried out on the nutrient composition of the wild cocoyam, C bicolar. Researchers at Imo state University, Owerri, Nigeria, reported 7.21 percent crude protein, 1.48 percent crude fiber, 4.69 percent ether extract, 5.13 percent ash, 81.58 percent Nitrogen free extract, and 5.21%. gross energy in its root meal. These results seem to mimic the values recorded in the Xanthosoma species.
Anti-nutrients in cocoyam root meal
The scratchiness and off-taste problems associated with cocoyam consumption have been attributed to the presence of needle-like calcium oxalate crystals and other anti-nutritional compounds like tannins and phytate in the corm. Among the toxicants commonly found in cocoyam corm are phytate, oxalate, tannin, saponin, hydrogen cyanide, trypsin, and alpha-amylase inhibitors. Research reports from the University of Calabar, Nigeria, showed the levels of anti-nutritional compounds in raw X. sagittifulium root meal as 1.29, 33.32, 1.52, 6.40, and 1.07 mg/kg for phytate, oxalate, tannin, saponin, and cyanide respectively. Ethiopian studies on X. sagittifulium root meal also recorded high levels of anti-nutritional factors such as phytate (187.57 - 167.76 mg/100 g) and tannin (156.11 - 39.62 mg/100 g).
A recent study at the Federal University of Technology Owerri, Nigeria, reported that the phytochemical contents of X. mafafa root meal in mg/kg were 1066.19 for tannin, 270.49 for phenol, 21.28 for hydrogen cyanide, 632.02 trypsin inhibitor, 1.97 for alkaloids and 24.47for phytate. Other researchers at the University of Calabar, Nigeria, reported 0.19, 3.52, 0.14, and 2.30 mg/100g of phytate, oxalate, tannin, and saponin respectively in raw C. esculenta. South African studies also revealed high levels of trypsin inhibitor (16.5 – 19.7 mg.g-1), amylase inhibitor (21 – 25 mg.g-1), total phenol (11.5 - 13 mg.g-1), alkaloids (0.18 – 0.19 mg.g-1), oxalate (0.10 - 0.13 mg.g-1), phytate (2.8 – 3.1 mg.g-1), saponin 0.14 – 0.15 mg.g-1) and traces of cyanogens in raw C. esculenta. These studies show that the major anti-nutrients in cocoyam root meal are the oxalates, tannins, enzyme inhibitors, and saponins. Similar high levels of tannin and trypsin inhibitor have also been reported in the wild cocoyam, C. bicolor, indicating that their liberal use in animal feeding would be encumbered by the presence of anti-nutrients, which would adversely affect protein and energy utilization, especially in monogastric animals.
Researchers at the Federal Polytechnic, Bida, Nigeria, have also reported a seasonal influence on the anti-nutrients content of X. sagittifulium root peels in the guinea savannah zone. Dry season values of phytate, hydrogen cyanide, soluble oxalate, and tannin were lower than the rainy season values. A similar seasonal influence on the proximate compositions of cocoyam peel was also reported, with dry season values for crude protein and fat being higher than wet season values, while carbohydrate values were the opposite. The protein content of the peels ranged from 6.3 – 17.2 percent, while fiber and carbohydrate values ranged from 10.7 – 19.7 percent and 41.2 – 46 percent respectively.
Processing to improve the nutrient value of cocoyam root meal
Several studies have shown that the major limiting factors to the utilization of cocoyam corms in animal feeding are the low protein content and presence of anti-nutrients, especially the oxalates, which impart acrid taste or cause irritation when cocoyam root meal-based diets are consumed. Ingestion of feeds containing high levels of oxalates has been reported to cause corrosive effects, irritation to the intestinal tract, absorptive poisoning, and interference with the bioavailability of calcium. The use of cocoyam in diets formulation is therefore constrained by the acrid nature of the root meal that reduces palatability and feeds intake, indicating the need for some form of processing and/or treatment before use.
The common approaches to overcoming these nutritional limitations of cocoyam corms, both for human and animal consumption has been peeling, boiling, roasting, fermenting, baking, frying in oil, pasting, milling, pounding, and ethanol extraction. These treatments essentially eliminate or reduce the anti-nutrients in the cocoyam, improve its palatability, and increase nutrient digestion and utilization. Researchers at the University of Zululand, South Africa, studied the effect of different methods of heat treatment such as boiling in water for 30 minutes, frying in vegetable oil for 15 minutes, and roasting in an oven at 180OC for 30 minutes on the anti-nutrients contents of C. esculenta corm. All treatment methods completely eliminated the trypsin inhibitors, while roasting and frying also eliminate all the oxalates, while only 40 – 54 percent was eliminated by boiling. Cyanide, amylase inhibitors, and alkaloid contents were reduced by about 70 percent by all treatment methods, while saponin, phytate, and phenolic contents were not seriously altered by heat treatment. Therefore, to eliminate the major anti-nutrients in cocoyam corm, especially oxalate and enzyme inhibitors, roasting in an oven, frying in oil, or boiling in water for longer than 30 minutes is recommended.
In another study at the Federal University of Technology Owerri, Nigeria, X. mafafa root meal was blanched in palm fruit bunch ash derived mineral electrolyte solutions at different concentrations (0.25, 0.50, 0.75 and 1.00 percent). Blanching was achieved by heating the electrolyte solution to 100OC before adding the freshly pulped cocoyam meal and then allowing it to boil for 3 minutes. The set up was cooled before decanting the electrolyte solution and drying the blanched cocoyam pulp meal in the sun. Most of the proximate constituents of the cocoyam tuber meal were not overly affected by the treatments, except total ash that expectedly increased with increasing electrolyte concentration. Anti-nutrients (tannin, phenol, cyanide, trypsin inhibitor, and alkaloids) concentrations were reduced averagely by 60 percent, while phytate content increased as the electrolyte concentration increased. Blanching in the ash electrolyte solution is, therefore, another good heat processing method for cocoyam tubers, although a longer blanching period may yield better results. Studies at Imo state University Owerri, Nigeria, in which the wild cocoyam C. bicolar root was cooked in water at 100OC for 30 minutes, however, did not report any significant changes in the proximate values due to the treatment.
A Nigerian study at the Federal College of Animal Health and Production Technology, Ibadan, also investigated the effects of urea treatment alone; cooking and urea treatment; and fermentation and urea treatment on proximate composition and anti-nutrient concentrations in Colocasia esculenta root meal. These treatments did not significantly influence any of the proximate values, although crude protein and crude fiber values were a bit elevated by the fermentation and urea treatment. Similarly, phytate and saponin concentrations were slightly depressed by the urea/boiling and urea/fermentation treatments, while a slight reduction in tannin concentration was also achieved by the boiling/urea treatment. Slight increases in oxalate concentrations were observed as a result of the treatments, with the urea/fermentation treatment recording the highest value. These treatment methods may, therefore, be adopted for processing Colocasia esculenta root meals into feed ingredient for ruminants but not monogastric animals.
Conclusion
Despite the position of cocoyam as one of the important tuber and root crops cultivated in the tropics, many species previously used as human food have become abandoned and could be harnessed as alternative energy feedstuff for animals. The presence of anti-nutrients such as phytate, oxalate, tannin and saponin, hydrogen cyanide, trypsin, and alpha-amylase inhibitors in the root tuber makes its further processing necessary before inclusion in animal feeds. Blanching with an ash electrolyte solution, roasting in an oven, and frying with vegetable oil reduced the levels of these anti-nutrients much more than just boiling in water.
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