Influence of storage life and variety on the micro-nutrient compositions of stored cocoyam-based products

NP David-Chukwu ,AG Amadi ,IC Onuabuchi ,MN Chukwu

1Department of Hospitality Management and Tourism,Abia State Polytechnic,Aba,Nigeria.2Department of Food Technology,Abia State Polytechnic,Aba,Abia State,Nigeria.

Abstract The micronutrient compositions of stored cocoyam-based products were determined using gas chromatography and atomic absorption spectrophotometry.The dried cormels and dried cocoyam leaves were pulverized with a locally fabricated machine and stored in various plastic containers for 0,1,2,3 months.The data obtained were analyzed statistically using SPSS version 21.Means were separated at P≤0.05 using Fisher’s Least Significant Differences.The vitamin contents (mg/100g) of achicha were as follows: cocoindia had total carotene(1.84),B1(0.071),B2 (0.044),B3(0.41),C (4.14) while edeofe had vitamin E (0.84)and total carotene (1.24),B1 (0.021),B2 (0.013),B3 (0.18),C (2.47) and E (0.57) after storage.The vitamin contents (mg/100g) of mpoto were as follows: cocoindia had B1 (0.53),B2 (0.31),B3 (1.75),C (18.46) and E (5.28) while edeofe had total carotene (3.44 µg/100g)and B1 (0.26),B2 (0.14),B3 (1.19),C (8.61) and E (2.46),and anampu had total carotene(2.56 µg/100g) after storage.The mineral composition (mg/100g) of achicha are as follows:anampu had Ca (48.78),Na (18.52),Mg (10.18),Mn (0.17) and P (19.61),Fe (2.47),Zn(2.60),I2(51.71);edeofe had P(26.27),Fe(3.66),Zn(2.91),and Ca(40.53),Na(10.67),Mg(6.29),K (285.77),Mn (0.075);and cocoindia had K (405.87) and I2 (69.34) after storage.The mineral compositions of mpoto (mg/100g) are as follows: anampu had Ca (157.57),Mg(95.84),K(485.52),P(45.52),I2(90.33) and Zn(2.61); edeofe had Fe(4.87),Zn(4.52),and Ca (152.29),Na (176.54),Mg (84.77),K (325.87),P (35.53),Mn (0.25),I2 (65.29) and cocoindia had Mg (95.84),Mn (0.63) and Fe (3.61) after storage.Micronutrients of the products reduced significantly (P≤0.05) during storage.Fortified Colocasia products with micronutrients will meet the required recommended dietary intake.

Keywords:achicha;mpoto;corm;cormel; edeofe; cocoindia;minerals;vitamins

Introduction

Micronutrients are nutrients required in small amounts that are essential for healthy development and growth.They have great importance for a healthy living [1].Micronutrients play a vital role in metabolism and in the maintenance of tissue function [2].Micronutrient deficiency is one of the major health challenges affecting the vulnerable groups (mainly children and pregnant women) in developing countries.This is due to cost of most animal foods which are major sources of these nutrients.However,these micronutrients are very vital to healthy living of man,and their deficiency can lead to acute or chronic diseases[3].

Vitamins are organic substances that function as regulators in the body.They are divided into two groups:fat soluble vitamins (vitamin A,D,E and K) and water-soluble vitamins (vitamin B1,B2,B3,B5,B6,B9,B12,vitamin C,folic acid,etc.).Fat soluble vitamins are stored in the fat tissues and liver;water soluble vitamins are found in the aqueous parts of the cells [2].They are required for normal growth,maintenance and functioning of the human body [4].A deficiency of vitamin A will cause physiological symptoms such as blindness.There are 13 vitamins,and most of them can be obtained by eating a variety of foods from each of the food groups,though the vitamins D,K,niacin,and biotin can also be synthesized in the body or by microorganisms in the intestinal tract.A chronic deficiency of any of the essential vitamins can cause a cascade of symptoms,from scaly skin to blindness.However,the consumption of excess amount of some vitamins can cause adverse effects as consuming too little.Moderate intake is always recommended to meet the daily vitamin requirement [5].Minerals are charged ions in our body fluids which help maintain fluid balance.Minerals can act as co-enzymes,support for body function [5].

The species ofColocasiaare often referred to as taro,while cocoyam ortanniais used for species ofXanthosoma.In the Pacific Island countries where taro is widely cultivated and consumed,two botanical varieties ofColocasiahave been identified asColocasia esculenta,many times calleddasheen,andColocasia esculanta,frequently callededdoe.Colocasiais believed to have originated in the Indo–Malaysian region,from where it spread into the Pacific Islands,finally to Africa [6].

About 60% of the World’s cocoyam production (5.7 million ton) is in Africa and majority of the remaining 40% in Asia and the Pacific[7].Eze and Okorji [7] also reported that Nigeria is the largest producer of cocoyam in the world,accounting for about 40% of the total world production output.Cocoyam,without any doubt,is an important food crop across many countries in Southern Sahara region,specifically in Nigeria,Ghana and Cameroon.Cocoyam is a major vegetable and source of income to farmers in Ghana.It is referred to as the third important staple root crop after yam and cassava in Nigeria and provides a cheaper yam replacement,especially during periods of insufficient food supply [8].

Cocoyam is rich in carbohydrates with nutritional value comparable with potato.Also,cocoyam is superior to cassava and yam in the possession of higher protein,mineral and vitamin contents as well as easily digestible starch [9].Cocoyam also contains higher noticeable quantities of essential minerals (Ca,Mg and P) than cassava and yam.It is to a great extent recommended for diabetic patients,the aged,children with allergies and for persons with intestinal disorders.The corms and cormels of cocoyam may be processed by boiling,baking or frying in oil.They may also be processed into different food products in many parts of West Africa and Central Africa [10].

All major parts of cocoyam (corm and leaves) are edible.The young leaves are nutritious spinach-like vegetable,which supplies a lot of minerals and vitamins.This is particularly a major vegetable and source of income to farmers in Nigeria[11].The leaves of taro are rich in vitamins and minerals.They are suitable sources of thiamin,riboflavin,iron,phosphorus and zinc and a very good source of vitamin B6,vitamin C,niacin,and exceptionally in the leaves,also it is highly perishable that is it has a high content of water [12].Preliminary investigations have revealed that most vegetables are good sources of antioxidants,but some are definitely better than others.For example,when it comes to vitamins,minerals,carotenoids and cruciferous phyto-nutrients,which are all virtually important to good health,the most potent vegetable are dark green leafy vegetables,green leafy vegetables are greatly used for food in many countries of the world;they are good sources of β-carotene,ascorbic acid,minerals and dietary fibre [13].However,dark vegetables are more nutritious than those with lighter or yellowish leaves.They are much available shortly after rainy season but become scare during the dry season,these vegetables could be harvested at all stages in the process of growth or could be consumed fresh,semi-processed or processed forms [13].

Root and tuber crops contain a huge variety of minerals and trace elements,including comparatively considerable amounts of calcium,potassium,magnesium and iron.Root and tuber crops are usually good sources of vitamins,for instance,yellow varieties of the sweet potato or giant-swamp taro supplies large quantities of β-carotene[14].Starch is considered the most significant component (73.80%) ofColocasia esculenta[15].

Agrid[11]reported that cocoyam is a well-known food plant,which has a long history of cultivation.Its corms are vital sources of starch.They may also be cut up and boiled in curries or fried to make crispy chips.The leaf stalks can also be eaten.The leaves which are seldom used for food must be cooked.Every part of the raw cocoyam plant contains a toxic compound calcium oxalate,which must be destroyed through cooking before eating.The cocoyam (Colocasia esculenta) is considered as highly perishable root and leaves,crop as high as 40-60% post-harvest losses have been found [16].The high perishability of the harvested and stored cocoyam roots and leaves is a major barrier to the wider utilization of the crop and there is need to diversify the uses to enhance demand and increase the rate of turn over or sale of the product.Lack of adequate cocoyam processing technology inhibits production and processing.Over the years due to the high perishable nature of cocoyam local farmers had adopted sun-drying as a means of preserving the cocoyam.It becomes necessary to evaluate the effect of these processes and storage methods on the overall quality of cocoyam products [17].

Achicha(dried cocoyam corms/cormels) is a pre-cooked,sun-dried cocoyam corms/cormels and it lends its name to the vegetarian dish made with it.Achichadoes not only have enjoyable taste and satisfying but also low in calories.Achichacan be cooked in combination with pigeon pea or black beans,these are highly nutritional.Green leafy vegetables can also be added to it,for example,green amaranth,fluted pumpkin and scent leaf.Dry fish is also added which is an optional ingredient.Mpoto(dried cocoyam leaves) is a vegetable used in preparing soup delicacy.This is peculiar to the Igbo people of Eastern Nigeria[18,19].

The main objective of this work is to produceachichaandmpotofrom cormels and leaves of cocoyam.This could be achieved by evaluating the effect of period of storage and variety on micronutrient compositions of cocoyam-based products.Processing of cocoyam corms/cormel and leaves into more shelf-stable dry products such asachichaandmpotowill reduce post-harvest losses of cocoyam,provide a market for small scale farmers,and diversify the uses of cocoyam.Evaluation of the quality and shelf stability of theachichaandmpotowould give confidence to the producers and consumers of these products.

Materials and methods

Source of materials

Fresh cocoyam corms/cormels and leaves [edeofe(NCE 002),cocoindia(NCE 001) and ukpong/anampu(NCE 004)] were obtained from National Root Crop Research Institute,Umudike,Nigeria.The cocoyam corms/cormels and cocoyam leaves are shown in Figure 1 and Figure 2.

Processing of corms/cormels into achicha (dried cocoyam)

The cocoyam corms weighing 5 kg for each of the samples was sorted,washed,and boiled for 3 hours,cooled,peeled,and cut into small sizes of 2.0 cm by 1.5 cm dimension with a sharp knife.They were spread on a mat and dried under the sun for 5 days between 9 am-6 pm.The dried cocoyam corms (achicha) were pulverized (250 mm Mesh of US standard sieve) before storage with a locally fabricated machine and stored in various plastic containers for a period of three months and analyzed at zero,one,two-and three-month intervals.The pictures of the cocoyam plant,cocoyam corms and cocoyam leaves and the processedachichaare shown in Plate 1,2,3 and 4,respectively.Also,the flow chart of the production ofachichafrom cocoyam corms/cormels is shown in Figure 1 and 2.

Processing of cocoyam leaves into mpoto (dried cocoyam leaves)

A sample of 300 g of cocoyam leaves were plucked,sorted,washed,spread on a mat and sun-dried for 3 days between 9 am-6 pm.The steps taken in the preparation ofmpotosamples are shown in the flow chart in Figures 2 respectively.The dried cocoyam leaves (mpoto)were pulverized before storage with a locally fabricated machine and stored in various plastic containers for a period of 3 months and analyzed at 0-3 months.The picture of the dried cocoyam leaves is shown in Figure 4.Also,the flow chart of the cocoyam leaves is shown in Figure 2.

Plate 1 Colocasia esculenta Plant

Plate 2 Colocasia esculenta corms/cormels

Plate 3 Raw achicha

Plate 4 Colocasia esculenta leaves

Figure 1 The Flow chart of the production of achicha

Figure 2 The Flow chart of the production of mpoto

Determination of micronutrient compositions of achicha and mpoto samples

Determination of the vitamin profile of achicha and mpoto samplesThe vitamin profile was analyzed using the method of AOAC[20].The sample was made to attain the atmospheric condition on the bench after removing it from the refrigerated storage chamber at less than 4°C.The sample was pressed and completely homogenized in the mortar carefully with pestle to avoid forming balls.A 0.10 g portion of the sample was weighed into a 10 mL capacity beaker and extracted as follows:0.1 g of the sample and 0.05 g ascorbic acid (as antioxidant)were weighed into a 16×126 mm test tube.Five milliliters of alcohol,made by mixing 90.2% ethanol,4.9% methanol and 4.9%isopropanol,and 0.5 mL of 80% KOH (W/V) were added and the test tube was vortexed for 30 seconds.The test tube was then flushed with nitrogen,capped and incubated for 30 minutes in a water bath at 70 oC with periodic vortexing.The tube was then placed in an ice-bath for 5 minutes.Three milliliters (3 mL) of deionized water and 5 mL of hexane were added to the test tube,vortexed for 30 seconds,and then centrifuged at 1000 rpm for 10 minutes.

The hexane in the upper layer was transferred to another test tube and the residue re-extracted two more times,each with 5 mL hexane.The extract was concentrated to 1 mL by evaporating it in a water-bath under the flow of nitrogen.The concentrated extract was analyzed for vitamin content under standard conditions in an HP(Hewlett Packard) Gas Chromatography equipped with 1206 Software;calibrated with selected standards under the instrument setting shown in Table 1.From the chromatogram of the extract and that of the mixture of standards,vitamins of the samples were identified and quantified by an enhanced integrator which gave the result in mg/100g sample.

Determination of the mineral profile of the samplesMineral contents ofachichaandmpotosamples were determined using the method described by Gyar and Owaku [21].About 0.2 g portion of the sample ash was weighed to a pre-cleaned borosilicate 250 mL capacity beaker for digestion.Thirty milliliters of concentrated nitric acid were added to the weighed sample in the beaker.The sample,with concentrated nitric acid,was placed on the hot plate for digestion in the fume cupboard.After digestion,the beaker and its content were allowed to cool.Another 20 mL of nitric acid was added and digested further in the fume cupboard and the mixture was allowed to cool to ambient temperature.The mixture was filtered into a 250 mL borosilicate beaker.The same procedure was followed,i.e.,the digestion of other samples.All the digested samples were transferred into pre-cleaned borosilicate beakers for Atomic Absorption Spectrophotometric(AAS) analysis.

Standards of iron,manganese,zinc,calcium,iodine magnesium,phosphorus,potassium and sodium solutions of 0.2,0.4,0.6,0.8 and 1.0 mg/L concentrations were made from each of the 100 mg/L stock solutions of the metal specimen.The set of standard solutions and the filtrate of the digested samples were analyzed by Atomic Absorption Spectrophotometry.The detection limit of the metals in the sample was 0.0001 mg/L using the UNICAM 929 London,Atomic Absorption Spectrophotometer powered by SOLAR software.Iron,manganese,zinc,phosphorus,calcium,magnesium,potassium and sodium cathode lamps were used for the analysis of the respective mineral ions in standards and the filtrates.Nitrous oxide-acetylene fuel was used in the generation of flame.The absorbance was read at 650 nm for the standards and sample filtrate.

Twenty-five milligrams of the sample were weighed into a Schoniger flask and digested with concentrated nitric acid.The content was boiled for a minute to ensure complete conversion of phosphorus pentoxide to orthophosphate.The solution was passed through a 10 cm long resin column,and the filtrate was collected.In a 10 mL Pyrex test tube,2 mL of ammonium molybdate was added and the absorbance read at 650 nm for both standards and filtrate.

Statistical analysis

Triplicate data obtained were subjected to statistical analysis using SPSS software of version 21.Mean values were determined and Three-Way ANOVA was done as well as Fisher’s Least Significant Difference[22] was used for the separation of the means (P≤0.05).

Results and discussion

Vitamin profile of achicha and mpoto samples for three months storage

The results in Tables 2 and 3 show the comparison of mean Vitamin Composition ofachichaandmpotoprocessed from three differentColocasiavarieties (edeofe,cocoindia,andanampu) stored from 0-3 months.

Fat-Soluble VitaminsThe fat-soluble vitamins are A,D,E,and K which are absorbed at the beginning of the small intestine.They are packaged with fatty acids and bile in micelles,small transport carriers that transport them close to the intestinal wall.Fat-soluble vitamins travel through the cells in the intestinal wall and are packaged with fat and other lipids in chylomicrons (one of the lipoprotein carriers).Vitamins then travel through lymph system before they enter bloodstream [5].

Table 1 GC Conditions for Vitamins Profile

Vitamin ATotal carotene contents ofachichasamples varied significantly (P<0.05) from 1.24 to 1.84 µg/100g.The highest total carotene content ofachichawas found incocoindia(1.84µg/100g)at 0 month,while the least total carotene content ofachichasamples occurred inedeofe(1.24 µg/100g) at three months (Tables 2).Total carotene contents ofmpotovaried significantly (P<0.05) from 2.56 to 3.44 µg/100g.The highest total carotene content ofmpotowas found incocoindia(3.44 µg/100g) at zero month,while the least total carotene content ofmpotooccurred inedeofe(2.56 µg/100g) at three months (Table 3).The over consumption of vitamin A damages cells thereby causing toxicity of cells [5].The daily requirement of vitamin A is provided from 75 % by retinol intake (as fatty acid esters,primarily retinyl-palmitate),while the remaining 25% is through β-carotene and other pro-vitamin active carotenoids [4,5].The recommended daily intakes (RDI) of vitamin A are 0.5-0.8mg/day for infants/children (0-10 years),0.8-1.0 mg/day for adults (25-65 years)while pregnant and lactating women take 1.1 mg and 1.5 mg respectively [4].Vitamin A from carotenoids in fruits and vegetables is the main source for most people in developing countries.It makes up 70-90% of their entire dietary vitamin A intake.Studies have indicated a significant reduction in maternal mortality and postpartum infection with β-carotene supplementation.β-carotene is a precursor of vitamin A;as a member of the carotenoids,also act as antioxidants that protect the body cells against free radicals by neutralizing them before they cause oxidative damage [23].Carotenoids found in plants,enhance the human health,immune response and reduce the risk of degenerative diseases such as cancer,cardiovascular diseases and so on;these have been attributed to their antioxidant and free radical scavenging activities [4]

Vitamin E (Tocopherol)Vitamin E contents ofachichavaried significantly (P<0.05) from 0.57 to 0.84 mg/100g.The highest vitamin E content ofachichawas found inedeofe(0.84 mg/100g) at zero month,while the least vitamin E content ofachichaoccurred inedeofe(0.57 mg/100g) at 3 months (Table 2).Vitamin E contents ofmpotovaried significantly (P<0.05) from 2.46 to 5.28 mg/100g.The highest vitamin E content ofmpotowas found inedeofe(0.84 mg/100g) at zero month,while the least vitamin E content ofmpotooccurred inedeofe(0.57 mg/100g) at three months (Table 3).Vitamin E is a fat-soluble vitamin essential to health.It is a fat-soluble vitamin,usually found in plants and act as an antioxidant [24].Vitamin E is a natural antioxidant,acting as a chain breaking,primary antioxidant to intercept peroxyl free radicals in biological systems [25].Vitamin E helps to protect the Low-Density Lipoprotein cholesterol carrier from being oxidized and reduces the buildup in the arteries,called atherosclerosis.Vitamin E also alters the stickiness of the cells that line lymph and blood vessels.This decreases the ability of blood components to stick to these walls and clog the passageways [4].The recommended daily intakes of vitamin E are 3-4 mg/day for infants(0-12 months),6-14 mg/day for children and teenagers,12-13 mg/day for adults (˃52 years),while pregnant and lactating women take 13 mg/day and 17 mg/day respectively [4,24].

Vitamin KThere are two forms of vitamin K:menaquinone and phylloquinone.Menaquinone is synthesized by the bacteria that exist naturally in the intestinal tract.Phylloquinone is found in green plants,and is the primary source of vitamin K in our diet.Vitamin K plays a major role in blood coagulation,or clotting.Blood clotting is a complex chain of events involving substances in blood,many of which are proteins,called clotting factors.Vitamin K plays a role in synthesizing four of these clotting factors.Acting as a coenzyme,vitamin K aids an enzyme that alters the bone protein osteocalcin.Vitamin K enables osteocalcin to bind with the bone-strengthening mineral calcium[4].The RDI of vitamin K are 4-10 mg/day for infants(0-12 months),15-50 mg/day for children and teenagers,50-80 mg/day for adults (˃52 years),while pregnant and lactating women take 60 mg/day [4].However,vitamin K was not detected in the samples.

Water-Soluble VitaminsThe B-vitamins and vitamin C are water soluble which are absorbed with water and enter the bloodstream directly.Most water-soluble vitamins are absorbed in the upper portion of the small intestine,although vitamin B12 is absorbed in the lower part of the small intestine.Water-soluble vitamins are typically not stored in the body for long periods of time (vitamin B12 is the exception),and excess amounts are excreted,so it is important to consume adequate amounts of them every day [4].

Vitamin B1 (Thiamine)Thiamine contents ofachichavaried significantly (P<0.05) from 0.021 to 0.071 mg/100g.The highest content ofachichawas found incocoindia(0.071 mg/100g) at zero month,while the least content ofachichaoccurred inedeofe(0.021 mg/100g) at three months (Table 2).Thiamine contents ofmpotovaried significantly (P<0.05) from 0.26 to 0.53 mg/100g.The highest thiamine content ofmpotowas found incocoindia(0.53 mg/100g) at zero month,while the least content ofmpotooccurred inedeofe(0.26 mg/100g) at three months (Table 3).Thiamine (vitamin B1),in the form of its pyrophosphate,such as pyruvate dehydrogenase,transketolase,phosphoketolase and α-ketoglutarate dehydrogenase,in reactions involving the transfer of an activated aldehyde unit.The RDI of vitamin B1are 0.2-0.4 mg/day for infants (0-12 months),0.6-1.3 mg/day for children and teenagers,1.0-1.2 mg/day for adults (˃ 52 years),while pregnant and lactating women take 1.2 mg/day and 1.4 mg/day respectively [4].The B1vitamins are known for their significant role in energy metabolism and several body functions [5].

Vitamin B2 (Riboflavin)Riboflavin contents ofachichavaried significantly (P<0.05) from 0.013 to 0.44 mg/100g.The highest Vitamin B2content was found incocoindia(0.071 mg/100g) at zero month,while the least vitamin B2content occurred inedeofe(0.021 mg/100g) at three months (Table 2).Riboflavin contents varied significantly (P<0.05) from 0.17 to 0.31 mg/100g.The highest vitamin B2 content ofmpotowas found incocoindia(0.31 mg/100g) at zero month,while the least vitamin B2content ofmpotooccurred inanampu(0.17 mg/100g) at three months (Table 3).B vitamins are known for their significant role in energy metabolism and several body functions.Riboflavin helps the body cells use fat,protein and carbohydrate.Riboflavin also helps in the production of niacin(vitamin B3) and pyridoxine(vitamin B6).

Table 2 Vitamin Composition (mg/100g) of Achicha during Three Months Storage

Table 3 Vitamin composition(mg/100g) of mpoto during three months storage

Vitamin B3(nicotinamide or niacin)Nicotinic acid amide,in the form of nicotinamide adenine dinucleotide (NAD+),or its phosphorylated form (NADP+),is a coenzyme of dehydrogenases.The daily requirement is covered to an extent of 60–70 % by tryptophan intake.Hence,milk and eggs,though they contain little niacin,are good foods for prevention of pellagra because they contain tryptophan.It substitutes for niacin in the body,with 60 mg L-tryptophan equaling 1 mg nicotinamide.The RDI of vitamin B3 are 2-5 mg/day for infants (0-12 months),7-18 mg/day for children and teenagers,13-16 mg/day for adults (˃ 52 years),while pregnant and lactating women take 15 mg/day and 17 mg/day respectively [4].Niacin contents ofachichavaried significantly (P<0.05) from 0.18 to 0.41 mg/100g.The highest niacin content ofachichawas found incocoindia(0.41 mg/100g) at zero month,while the least niacin content ofachichaoccur red inedeofe(0.18 mg/100g) at three months(Table 2).Niacin contents ofmpotovaried significantly (P<0.05)from 1.19 to 1.75 mg/100g.The highest niacin content ofmpotowas found incocoindia(1.75 mg/100g) at zero month,while the least vitamin B1 content ofmpotooccurred inedeofe(1.19 mg/100g) at three months (Table 3).Niacin is a water-soluble B-vitamin that helps the body use fat,protein and carbohydrates from foods to make energy.Niacin helps over 200 enzymes (natural chemicals in the body) to function normally in the body by helping the body use other B vitamins and make DNA.The vitamin B3contents of the samples could not provide adequate dietary intakes for all ages.

Vitamin B5 (pantothenic acid)Pantothenic acid is the building unit of coenzyme A (CoA),the main carrier of acetyl and other acyl groups in cell metabolism.Acyl groups are linked to CoA by a thioester bond.Pantothenic acid occurs in free form in blood plasma,while in organs it is present as CoA.The RDI of vitamin B5are 2-3 mg/day for infants(0-12 months),4-6 mg/day for children and teenagers,6 mg/day for adults,pregnant and lactating women [4].However,vitamin B5 was not detected in the samples.

Vitamin B6 (pyridoxine or pyridoxal)Vitamin B6activity is exhibited by pyridoxine or pyridoxol (R=CH2OH),pyridoxal (R=CHO) and pyridoxamine (R=CH2NH2).The metabolically active form,pyridoxal phosphate,functions as a coenzyme of amino acid decarboxylases,amino acid racemases,amino acid dehydrases,amino transferases,serine palmitoyl transferase,lysyloxidase,δ-aminolevulinic acid synthase,and of enzymes of tryptophan metabolism.The RDI of vitamin B6are 0.1-0.3 µg/day for infants(0-12 months),0.4-1.6 µg/day for children and teenagers,1.2-1.5µg/day for adults,pregnant and lactating women take 1.9 µg/day [4].However,vitamin B6was not detected in the samples.

Vitamin B9 (folate/folic acid)Vitamin B9is a micronutrient necessary for key metabolic processes,mental and emotional health and,in conjunction with vitamin B12and vitamin C,is important in the formation of red and white blood cells.Folate is the naturally-occurring form of vitamin B9,although“folate”is actually a generic name for a group of related compounds with similar nutritional properties.Folic acid is a synthetic form of vitamin B9,also known as pteroyl-monoglutamic acid and is the component commonly present in vitamin B supplements and vitamin B-complex supplements[27].Mammals cannot synthesize folate and rely on dietary sources(fruit,vegetables and grains) for this essential micronutrient [28].Low serum levels of folate are associated with an increased risk of several health conditions,including elevated homocysteine,birth defects and an increased cancer risk [29].The RDI of vitamin B9 are 60-80 mg/day for infants (0-12 months),200-400 mg/day for children and teenagers,400 mg/day for adults while pregnant and lactating women take 600 mg/day [4].However,vitamin B9was not detected in the samples.

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Vitamin B12 (cobalamine/cyanocobalamin)Cyanocobalamin is formed as an artifact in the processing of biological materials.Cobalamins occur naturally as adenosylcobalamin and methylcobalamin,which instead of the cyano group contain a 5-deoxyadenosyl residue and a methyl group respectively.Adenosylcobalamin (Coenzyme B12) participates in rearrangement reactions in which a hydrogen atom and an alkyl residue,an acyl group or an electronegative group formally exchange places on two neighboring carbon atoms.Reactions of this type play a role in the metabolism of a series of bacteria.In mammals and bacteria,a rearrangement reaction that depends on vitamin B12is the conversion of methylmalonyl CoA to succinyl CoA.The recommended daily intakes (RDI) of vitamin B12 are 0.4-0.8 µg/day for infants (0-12 months) and 1.0-3.0 µg/day for children and teenager,3.0 µg/day for adults (˃ 65 years),while pregnant and lactating women take 3.5µg/day and 4.0µg/day respectively [4].However,vitamin B12was not detected in the samples.

Mineral Composition of Achicha and Mpoto during Three Months Storage

The results in Table 3 and 4 shows the comparison of mean values of Mineral Composition ofachichaandmpotoprocessed from three differentColocasiavarieties (edeofe,cocoindia,andanampu) during to three months’ storage.

The Major MineralsThe main elements (Na,K,Ca,Mg,P) are essential for human beings in amounts>50 mg/day[4].

Sodium,NaSodium is the major electrolyte outside the cell;helps regulate body water and blood pressure [5].It is present mostly as an extracellular constituent and maintains the osmotic pressure of the extracellular fluid.It activates some enzymes,such as amylase.Sodium absorption is rapid;it starts 3–6 min after intake and is completed within 3 hours.The adult’s average requirement ranges from 1.3–1.6 g/day (equal to 3.3–4.0 g/day NaCl).The intake of too little (low blood pressure) or too much sodium can result in serious disorders.From a nutritional standpoint,only the excessive intake of sodium is of importance because it can lead to hypertension [4].Higher sodium intakes have been known to have stronger effects on blood pressure and risk of subsequent cardiovascular diseases due its ability to absorb moisture from the blood which resists the flow of blood to other parts of the body [30].Sodium contents ofachichavaried significantly (P<0.05) from 10.67 mg/100g to 18.52 mg/100g.The highest sodium content ofachichawas found inanampu(18.52 mg/100g) at zero month,while the lowest sodium content ofachichaoccurred inedeofe(10.67 mg/100g) at three months (Table 4).Ndabikunzeet al.[31] reported that sodium contents ofColocasia esculentafrom different countries ranged from 6.87 to 19.49mg/100g Sodium contents ofmpotovaried significantly (P<0.05) from 176.39 mg/100g to 190.56 mg/100g.The highest sodium content ofmpotowas found incocoindia(190.56 mg/100 g) at zero month,while the lowest sodium content ofmpotooccurred inedeofe(176.39 mg/100g)stored for three months (Table 5).Ogbujiet al.[32] reported that Na content found inugu(Telfaria occidentalis) was 25 mg/100g.The values of Na obtained in some leafy vegetables ranged from 15.01 mg/100g to 88.00 mg/100g [33].The result revealed that cocoyam corms/leaves contain significant amount of sodium;whose salts regulate the acid-base balance of the body [34].

Potassium (K) contentPotassium is localized mostly within the cells.It regulates the osmotic pressure within the cell.It is involved in cell membrane transport and also in the activation of a number of glycolytic and respiratory enzymes.The minimum daily requirement is estimated to be 782 mg.Potassium causes the kidneys to excrete excess sodium from the body,and keeping sodium levels low can help lower blood pressure.Potassium plays a buffering role in the blood;hence it helps the bone strengthening minerals,calcium and phosphorus,from being lost from the bones and kidneys [4,5,24].Potassium contents ofachichavaried significantly (P<0.05) from 285.77 mg/100g to 405.87 mg/100g.The highest potassium content ofachichawas found incocoindia(405.87 mg/100g) at zero month,while the lowest potassium content ofachichaoccurred inedeofe(285.77 mg/100g) stored for 3 months (Table 4).Potassium contents ofmpotovaried significantly (P<0.05) from 325.87 mg/100g to 485.52 mg/100g.The highest potassium content ofmpotowas found inanampu(485.52 mg/100g) at zero month,while the lowest potassium content ofmpotooccurred inanampu(325.87 mg/100g)stored for 3 months (Table 5).Ogbujiet al.[32] reported that K content found inugu(Telfaria occidentalis) to be 76 mg/100g.The values of K obtained in leafy vegetables ranged from 16.85 to 168.96 mg/100g [33].Ndabikunzeet al.[31] reported potassium contents ofColocasia esculentafrom different countries ranged from 760.21mg/100g to 1048.98mg/100g.The values of potassium may have resulted from the type of the soil and the processing methods ofColocasia esculenta.Higher potassium intakes have been shown to have strong effects on blood pressure and risk of subsequent cardiovascular diseases [30].Salts of potassium are known to regulate the acid-base balance of the body [34].Potassium occurred in abundance more than other mineral elements,which suggests that cocoyam could be a good source of dietary potassium.Based on an earlier study,high dietary potassium in humans plays a protective role against hypertension,stroke,cardiac dysfunctions,renal damage,hypercalciuria,kidney stones and osteoporosis[35].

Phosphorus,PPhosphorus contents ofachichavaried significantly (P<0.05) from 19.61 to 26.27 mg/100g.The highest Phosphorus content ofachichawas found inedeofe(26.27 mg/100g) at zero month,while the least phosphorus content ofachichaoccurred inanampu(19.61 mg/100g) stored for 3 months (Table 4).Ndabikunzeet al.[32] reported phosphorus contents ofColocasia esculentafrom different countries varied from 114.32 mg/100g to 154.27 mg/100g.Njoku and Ohia [34] reported lower values of phosphorous (44.39 mg/100g to 72.2 mg/100g).The difference in values may be as a result of processing methods,soil type and water composition [24].Phosphorus contents ofmpotovaried significantly (P<0.05) from 32.77 mg/100g to 45.52 mg/100g.The highest phosphorus content ofmpotowas found inanampu(45.52 mg/100g) at zero month,while the least phosphorus content occurred inedeofe(32.77 mg/100g) stored for 3 months (Table 5).Ogbujiet al.[32] reported that P content found inugu(Telfaria occidentalis) to be 53.00 mg/100g.The values of P obtained in leafy vegetables ranged from 12.5291 mg/100g to 36.91 mg/100g [33].Phosphorous contents were appreciably high.Phosphorous plays numerous roles in cells [36].The phosphorus contents of the samples could provide adequate dietary intakes for persons.Phosphorus combines with calcium to form hydroxyapatite,the strengthening material found in bones and teeth.Phosphorus is part of phospholipids,which give cell membranes their structure.Phosphorus helps the body to store energy generated from the metabolism of carbohydrates,protein,and fat for later use and the body can draw upon these stores as needed.Adults need 700-1000 mg of phosphorus daily [5,37].

Magnesium,MgMagnesium is a constituent and activator of many enzymes,particularly those associated with the conversion of energy-rich phosphate compounds,and as a stabilizer of plasma membranes,intracellular membranes,and nucleic acids.It is needed for the metabolism of carbohydrates,proteins,and fats.Magnesium supplements may help lower blood pressure slightly.Also,a diet with higher amounts of magnesium may help decrease the risk of type 2 diabetes mellitus.In a normal diet,the daily intake is 300–500 mg [4,5,35].Magnesium contents ofachichavaried significantly (P<0.05)from 6.29 mg/100g to 10.1 8mg/100g.The highest magnesium content ofachichawas found inanampu(10.18 mg/100g) at zero month,while the lowest magnesium content ofachichaoccurred inedeofe(6.29 mg/100g) stored for 3 months (Table 4).Ndabikunzeet al.[31] reported that magnesium content ofColocasia esculenta(81.16mg/100g).Magnesium contents ofmpotovaried significantly (P<0.05) from 84.77 mg/100g to 95.84 mg/100g.The highest magnesium content ofmpotowas found inanampu(95.84 mg/100g)at zero month,while the lowest magnesium content ofmpotooccurred inedeofe(84.77 mg/100g) stored for 3 months (Table 5).Ogbujiet al.[32] reported that Mg content found in fluted pumpkin (Telfaria occidentalis) to be 94.00 mg/100g.The values of Mg obtained in leafy vegetables ranged from 27.51 to 249.92 mg/100g [33].Magnesium is important in the regulation of blood pressure,improvement of serum lipid profile,prevention of stroke and skeletal growth and development [38].

Calcium (Ca) contentCalcium is an essential nutrient because it is involved in the structure of the muscular system and controls essential processes like muscle contraction (locomotor system,heartbeat),blood clotting,activity of brain cells and cell growth.The desirable calcium intake(g/day)is stipulated as:birth to 6 months(0.4),6 to 12 months(0.6),1 to 5 years(0.8),6 to 10 years (0.8–1.2),11 to 24 years and pregnant women (1.2 to 1.5),25 to 65 years (1.0) and above 65 years (1.5) [4,5,35].Calcium contents ofachichavaried significantly(P<0.05) from 40.53 mg/100g to 48.78 mg/100g.The highest calcium content ofachichawas found inanampu(48.7 8mg/100g) at zero month,while the lowest calcium content ofachichaoccurred inedeofe(40.53 mg/100g) at 3 months storage (Table 4).Calcium contents ofmpotovaried significantly (P<0.05) from 145.39 mg/100g to 157.57 mg/100g.The highest calcium content ofmpotowas found inanampu(157.57 mg/100g) at zero month,while the lowest calcium content ofmpotooccurred inedeofe(145.39 mg/100g)stored for 3 months (Table 5).Ogbujiet al.[32] reported that Ca content found inugu(Telfaria occidentalis) was 255 mg/100g.The values of Ca obtained in leafy vegetables ranged from 61.19 mg/100g to 110.16 mg/100g [33].The salts of calcium regulate the acid-base balance of the body [34].Consumption of calcium-rich foods helps in building a strong immune system,thereby helping the body to absorb,utilize and digest nutrients.Ndabikunzeet al.[31] reported that calcium was the third most abundant mineral in both varieties of cocoyam amounting to 110.2 mg/100g and 68.7 mg/100g forX.sagittifolllium and C.esculenta,respectively.The value obtained for Ca in this study are less than the daily requirement (Adults between 19-50 years is 1000mg/day and adults between 51 and older is 1200mg/day) [24] but could be augmented by either increasing the quantity of cocoyam consumption or complementing it with other food sources that are rich in calcium.A severe calcium deficiency leads to rickets in children and osteomalacia in adults.

The Trace MineralsTrace elements (Fe,Zn,Se,Cu,Mn,Co,Ni) are essential in concentrations of<50 mg/day;their biochemical actions have been elucidated [4].

Iron,FeIron is present in the hemoglobin (the oxygen carrying transport protein in your red blood cells blood) and myoglobin(muscle tissue) pigments.The metal is also present in a number of enzymes (peroxidase,catalase,hydroxylases and flavine enzymes),hence it is an essential ingredient of the daily diet.Iron helps enzymes that are involved in the synthesis of neurotransmitters in the brain,which send messages to the rest of our body.The iron requirement depends on the age and sex of the individual,it is about 1.5–2.2 mg/day [4].Iron supplied in the diet must be in the range of 15-18 mg/day in order to meet this daily requirement [5].A sufficient supply of iron to persons who require higher amounts (children,women before menopause and pregnant or nursing women),cereals(flour,bread,rice,pasta products) fortified with iron to the extent of 55–130 mg/kg are recommended [4,5,35].Iron (Fe) contents ofachichavaried significantly (P<0.05) from 2.47 mg/100g to 3.66 mg/100g.The shighest iron level ofachichawas found inedeofe(3.66 mg/100g) at zero month,while the lowest iron content ofachichaoccurred inanampu(2.47 mg/100g) after 3-months storage (Table 4).Iron (Fe) contents ofmpotovaried significantly (P<0.05) from 3.61 mg/100g to 4.87 mg/100g.The highest iron level ofmpotowas found inedeofe(4.87 mg/100g) at zero month,while the lowest iron content ofmpotooccurred inanampu(3.61 mg/100g) after 3-months storage(Table 5).The values of Fe obtained in leafy vegetables ranged from 16.39 mg/100g to 39.04 mg/100g [31].Ndabikunzeet al.[32]reported Fe level inColocasia esculentafrom different countries varied from 3.24 mg/100g to 11.72 mg/100g.The value obtained for Fe in this study is less than the daily requirement (male:8 mg/day and female:18 mg/day) as reported by Eze and Njoku [24];but could be augmented by either increasing the complementing it with other food sources that are rich in iron or consumption of enriched or fortified cocoyam products.

Table 4 Mineral composition (mg/100g) of mpoto during three months storage

Table 5 Mineral Composition (mg/100g) of achicha during three months storage

Zinc,ZnZinc is found in almost every cell of our body.It is involved in the function of more than 100 enzymes.Zinc is a component of a number of enzymes (e.g.,alcohol dehydrogenase,lactate dehydrogenase,malate dehydrogenase,glutamate dehydrogenase,carboxypeptidases A and B,and carbonic anhydrase).Other enzymes,e.g.,dipeptidases,alkaline phosphatase,lecithinase and enolase,are activated by zinc and by some other divalent metal ions.Zinc plays a role in the structure of both RNA and DNA in the cells and in gene expression.Zinc is needed for adequate growth in developing infants and throughout the adolescent years.Zinc is needed for production of white blood cells,so it helps keep our immune system healthy thereby reducing the inflammation that can accompany skin wounds.The daily requirement of 5–10 mg is provided by a normal diet (6–22 mg zinc/day)[4,5,35].Zinc contents ofachichadid not vary significantly(P>0.05).The values ranged from 1.92 mg/100g to 2.91 mg/100g.The highest zinc level ofachichawas found inedeofe(2.91 mg/100g)at zero month,while the lowest zinc content ofachichaoccurred incocoindia(1.92 mg/100g) stored for 3 months (Table 4).Ndabikunzeet al.[31] reported Zn level inColocasia esculentafrom different countries varied from 1.35 to 3.24 mg/100g.Njoku and Ohia [34]reported lower values of zinc(2.49 to 310 mg/100 g).Zinc contents ofmpotodid not vary significantly (P>0.05).The values ranged from 2.61mg/100g to 4.52 mg/100g.The highest Zinc level ofmpotowas found inedeofe(4.52 mg/100g) at zero month,while the lowest zinc content ofmpotooccurred inanampu(2.61 mg/100g) stored for 3 months(Table 5).The value of Zn obtained by Asaolu and Asaolu[39]and Ayoolaet al.[40] ranged between 3.73 and 24.64mg.

Manganese,MnManganese is the metal activator for pyruvate carboxylase and,like some other divalent metal ions,it activates various enzymes,such as arginase,amino peptidase,alkaline phosphatase,lecithinase or enolase.It is involved in the metabolism of carbohydrates,fats,and amino acids and the formation of bone.Manganese,even in higher amounts,is relatively nontoxic.The daily requirement,2–5 mg,is met by the normal daily food intake(2–48 mg manganese/day) [4,5,35,41].Manganese contents ofachichavaried significantly (P<0.05) from 0.075 mg/100g to 0.17 mg/100g.The highest manganese level ofachichawas found inanampu(0.17mg/100g) at zero month,while the lowest manganese content ofachichaoccurred inedeofe(0.075 mg/100g) stored for 3 months(Table 4).Ndabikunzeet al.[31] reported manganese level inColocasia esculentafrom different countries varied from 3.12 mg/100g to 6.82 mg/100g.Manganese contents ofmpotovaried significantly (P<0.05) from 0.25 to 0.63mg/100g.The highest manganese level ofmpotowas found incocoindia(0.63 mg/100g)at zero month,while the lowest manganese content ofmpotooccurred inedeofe(0.25 mg/100g)at three months (Table 5).The values of manganese obtained in leafy vegetables ranged from 2.54 to 10.06 mg/100g [33].Consumption of foods rich in micronutrients helps in building a strong immune system,thereby helping the body to absorb,utilize and digest nutrients [29].

Iodine (I) contentThe content of iodine in the body is about 10 mg,of which the largest portion (70-80%) is covalently bound in the thyroid gland.Iodine absorption from food occurs exclusively and rapidly as iodide and is utilized in the thyroid gland in the biosynthesis of the hormone thyroxine (tetraiodothyronine) and its less iodized form,triiodothyronine.The iodine requirement of humans is 100-200 µg/day;pregnant and nursing women require 230 µg/day and 26 µg/day respectively [4,5,35,41].Iodine contents ofachichavaried significantly (P<0.05) from 2.47 mg/100g to 3.66 mg/100g.The highest iodine level ofachichawas found inedeofe(3.66 mg/100g) at zero month,while the lowest iodine content ofachichaoccurred inanampu(2.47 mg/100g) stored for 3 months (Table 4).Iodine contents ofmpotovaried significantly (P<0.05) from 65.29 mg/100g to 90.33mg/100g.The highest iodine level ofmpotowas found inanampu(90.33 mg/100g) at zero month,while the lowest Iodine content ofmpotooccurred inedeofe(65.29 mg/100g) after three months(Table 5).Ndabikunzeet al.[31]reported iodine level in flours produced fromColocasia esculentafrom different countries varied from 3.24 mg/100g to 11.72 mg/100g.

Conclusion and Recommendations

Conclusion

The results of vitamin profile ofachichaandmpotoshowed that vitamins A,E,C,B1,B2,B3were detected.However,the amounts of vitamins obtained in theachichaandmpotowere not adequate to provide recommended daily intakes for all ages.Vitamin C had the highest contents inachicha(2.71 mg/100g) andmpoto(10.75 mg/100g) ofcocoindiavariety after 3 months storage.The vitamins occurred more predominantly in thempotothanachichasamples as there was significant change in the amounts of vitamins caused by the variety and the storage time (month).Therefore,enrichment of theachichaandmpotoduring food preparations would yield food rich in vitamins for humans.

The result of mineral profile ofachichaandmpotoshowed that sodium,potassium,phosphorus,magnesium,calcium,iron,zinc,manganese and iodine were present.All these minerals obtained in this research could not provide adequate daily intakes for all ages especially the adults.Potassium had the highest contents inachicha(294.31 mg/100g) ofcocoindiaandmpoto(485.52 mg/100g) ofanampu.The major minerals in the products were Na,K,P,Mg,and Ca which are the major elements while the trace minerals were Fe,Zn,Mn and iodine.these minerals occurred more predominantly in thempotosamples.

Recommendations

Based on the findings of this research,it is recommended that the rich micronutrient potentials of the cocoyam-based products could be harnessed as a source of micronutrients in food industry if fortified or enriched.The study has revealed the micronutrients potential ofachichaandmpotowhich are presently considered as foods for the poor or low earners.