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International Journal of Biochemistry & Physiology Research Article 15 min read

Assessment of the Phytonutrient Content, Mineral and Proximate Compositions of Selected Yam Landraces (Dioscorea Rotundata Poir)

Nwankwo PO*
* Corresponding author
ISSN: 2577-4360  10.23880/ijbp-16000157  Received: April 05, 2019  Published: May 03, 2019
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Keywords
Dioscorea Rotundata Phytonutrient Mineral and Proximate Compositions
Abstract

The phytochemical screening, assessment of mineral and proximate compositions of eleven selected yam landraces were carried out using standard laboratory protocols with the view to gain insight to its nutritional and health potentials. Phytonutrient composition (mg/100g) analyses were carried out using different extraction solvents namely diethyl ether, ethanol, methanol, acetone and methanol. The results revealed that the eleven samples studied had alkaloid between the range of (0.22 – 0.40), flavonoid (2.96 - 3.51), saponin (2.89 - 1.89), tannin (0.03 – 0.05), phytate (0.001 – 0.02) and oxalate (0.04 – 0.06). All observed phytonutrients were below toxic level and thus essential for good health and vitality. Mineral elements (mg/100g) – calcium, magnesium, sodium, phosphorus, potassium, iron, zinc and copper were assessed. The eleven selected yam landraces had relatively high contents (within the WHO recommendations) of the assessed mineral elements such as calcium (16.47 – 91.32), magnesium (38.16 – 76.90), phosphorus (157.97 – 269.33), etc. The results of the proximate compositions showed that crude fibre was highest in Ogoja (2.36). Okpani had the highest content of crude protein (5.33) while Adaka had the highest content of crude fat (0.82). The caloric values (Cal/100g) ranged from 150.32 – 193.57 respectively

Introduction

Yams are important in the economic and social lives of Nigerians in particular and other tropical African countries in general; where they serve as one of the staple foods [1]. Yams contain mainly carbohydrate, thus are a cheap source of caloric energy. They also provide some minerals and essential vitamins, although a proportion of the minerals and vitamins may be lost during processing [2].

White yam (Dioscorea rotundata Poir) which originated in Africa is the most widely grown and preferred yam species. The tuber is roughly cylindrical in shape, the skin is smooth and brown and the flesh usually white and firm. A large number of white yam cultivars exist with differences in their production, nutritional qualities and post – harvest characteristics.

Landraces are those cultivars that have been in existence and have been in use over a long period of time. They could be regarded as accessions (i.e. yams that are not yet characterized). They are not hybrids. They are mostly disease resistant, high yielding and possess other preferred traits by the farmers. They make significant contributions in the diet of the people, or as varieties in the farming system of the people or even as progenitors in breeding program for the farmer preferred traits. The nutritional quality of the yam landraces have not been fully elucidated as to ascertain their food values. However, the analyses of the phytonutrient, mineral and proximate compositions of these landraces constitute an important index of their food quality and can elucidate useful information on the nutritional quality and authenticity of food products and sources of raw materials used in food manufacture. For one to stimulate the consumption and mass production of the various landraces there is therefore need for the research on their nutritional assessment. The aim of this research is to identify the need for the preservation of these yam Yam tubers ↓ Peeling ↓ Washing ↓ Chipping (manual) ↓ Drying (to brittleness at ≤ 70Oc) ↓ Milling ↓ Sieving (1mm, 250mm) ↓ Yam flour Flow chart for the production of yam flour Quantitative determination of phytochemical constituents: Phytochemical screening of the samples was carried out using standard phytochemical quantitative analyses.

Determination of Alkaloid

Quantitative determination of alkaloid was carried out according to the method of Harborne (1998) [4]. Exactly 200cm3 of 10% acetic acid in ethanol was added to each sample (2.50g) in a 250cm3 beaker and allowed to stand for 4hours. The extract was concentrated on a water bath to one-quarter of the original volume followed by addition of 15 drops of concentrated ammonium hydroxide drop landraces (based on their nutritional values) rather than completely replacing them with the new varieties. The results of this investigation will be useful information to the nutritionists, chemists, farmers and consumers who are constantly in search of additional food sources and products for the general wellbeing of mankind as well as animals.

Material and Methods

The current study was conducted in Biochemistry Laboratory of National Root Crops Research Institute, Umudike. Yam source: The selected yam landraces were obtained from the yam barn of National Root Crops Research Institute, Umudike. Chemicals: All chemicals used in the investigation were of analytical grade. Production of yam flour: Yam four was produced according to the method of Ukpabi and Oti [3].

wise to the extract until the precipitation was complete. After 3hours of mixture sedimentation, the supernatant was discarded and the precipitates were washed with 20cm3 of 0.1M ammonium hydroxide and then filtered using Whatman filter paper. The residue was dried in an oven and using an electronic weighing balance, the alkaloid content was calculated.

Determination of Flavonoid

Flavonoid determination was carried out by the method of Ejikeme, et al. [5] and Boham and Kocipai [6]. Exactly 50cm3 of 80% aqueous methanol was added to 2.50g of each of the samples in a beaker covered and allowed to stand for 24 hours at room temperature. After discarding the supernatant, the residue was re-extracted (thrice) with the same volume of ethanol. Whatman filter paper (125mm) was used to filter whole solution of each sample. Each sample filtrate was later transferred into a crucible and evaporated to dryness over a water bath. The content in the crucible was cooled in a desiccator and weighed until constant weight was obtained.

Determination of Saponin

Quantitative determination of saponin was done by the method reported by Obadoni and Ochuko [7] and Ejikeme, et al. [5]. Exactly 100cm3 of 20% aqueous ethanol was added to 5g of sample in a 250cm3 conical flask. The mixture was heated over a hot water bath for 4hours with continuous stirring at a temperature of 55oC. The residue of the mixture was re-extracted with another 100cm3 of 20°C aqueous ethanol after filtration and heated for 4 hours at a constant temperature of 55°C with constant stirring. The combined extract was evaporated to 40cm3 over water bath at 90°C. 20cm3 of diethyl ether was added to the concentrate in a 250cm3 separator funnel and vigorously agitated from which the aqueous layer was recovered while the ether layer was discarded. This purification process was repeated twice. 60cm3 of n- butanol was added and extracted twice with 10cm3 of 5% sodium chloride. After discarding the sodium chloride layer, the remaining solution was heated in a water bath for 30minutes, after which the solution was transferred into a crucible and was dried in an oven to a constant weight.

Determination of Tannin

Four hundred milligram (400mg) of each of the samples was placed into two conical flasks. 40ml of diethyl ether containing 1% acetic acid was added and centrifuged to remove the pigments. The precipitate was dissolved in 20ml of 70% acetone. The flasks were sealed with cotton plug covered with aluminum foil, then kept in a shaker for 2hours. Each of the contents in the flask was filtered through Whatman filter paper. 0.5ml of filtrate was made up to 1ml with distilled water. 0.5ml of folin ciocalteau reagent was added and mixed with 2.5ml of 20% sodium carbonate solution and mixed. The mixtures were kept for 40 minutes at room temperature. The absorbance was measured by spectrophotometer using tannin as standard.

Determination of Oxalate

Oxalate content was determined using the method described by Harborne [4]. One gram (1g) of the sample was dissolved in 190ml of distilled water. 10ml of 6M HCl was added to it and the mixture was warmed in water bath at 90°C for 4 hours. The mixture was then centrifuged at a speed of 2000rpm for 5 mins. The supernatant was diluted and evaporated. The precipitate was filtered off and titrated with ammonium solution until the methyl orange colour changed to faint yellow. The solutions were heated at 90oC and the oxalate was precipitated with 10ml of 5% calcium chloride solution. Each precipitate was washed with 25% H2SO4, diluted to 125ml and warmed at 90°C. It was titrated against 0.05M potassium permanganate.

Determination of Phytate

The phytate content was determined according to the method of Ejikeme, et al. (2014) [5]. Two grams (2g) of each of the samples was weighed and soaked in 100ml of 2% HCl for 3hours, the filtered through a double layer thick filter paper. 50ml of each filtrate was made up to 150ml with distilled water. 10ml of ammonium thiocyanate solution was added as indicator. Each solution was titrated against standard iron chloride solution which contain 0.00195g of iron per ml till a constant coloration was obtained. The phytate content was calculated.

Determination of the Mineral Composition

The mineral composition was determined according to the method described by Larrauri, et al. [8]. The ash was dissolved in HNO3 with 50g/l of LaCl3 and the mineral contents Calcium (Ca), Magnesium (Mg), sodium (Na), iron (Fe), and potassium (K) were analyzed separately using an atomic absorption spectrophotometer. One gram (1g) of sample was digested with 20ml of 2:1 HNO3/HClO4 and heated until white fumes were evolved. The digested samples were then filtered into standard 50ml volumetric flask and made up to the mark with distilled water. The minerals, copper (Cu) and zinc (Zn) were determined using air acetylene flame atomic absorption spectrometry. Glassware used for analyses were thoroughly cleaned and all reagents used were of analytical grade. Phosphorus content of the samples was determined colorimetrically according to the method described by Obadoni and Ochuko, [7].

Determination of the Proximate Composition

The ash, crude fat, crude fibre and moisture contents of the eleven selected yam landraces were determined using the standard method of AOAC, 1990. Crude protein was determined by the Kjeldahl method as described by Okalebo, et al. [9], and expressed as (%N X 6.25), where %N represents percentage nitrogen. Carbohydrate content was obtained by difference. Carbohydrate = 100 – (moisture + ash + crude protein + crude fat + crude fibre).

The caloric values of the selected landraces were obtained using the Atwater factor method: (4 X Carbohydrate) + (4 X Crude protein) + (9 X Crude fat).

Statistical Analysis

The experiments were carried out in five determinations and data collected were expressed as the mean ± standard deviation.

Results and Discussions

The eleven yam land races collected from the yam barn of National Root Crops Research Institute, Umudike were selected for the present studies to characterize for phytonutrient, mineral and proximate compositions.

The results of the phytonutrient contents of the eleven selected yam landraces are presented in Table 1. The eleven selected yam landraces have alkaloid ranging from (0.22 – 0.40). Alkaloids are a diverse group of secondary metabolites and show antimicrobial activity by inhibiting DNA topoisomerase [10]. Alkaloids affect a lot of metabolic activities in the body, but when in high concentration is toxic to man [7]. The flavonoid content of the samples was relatively high with Okpani (3.94) having the highest content of flavonoid followed by Miyango (3.51). In vitro studies have shown that flavonoids have a wide range of biological and pharmacological activities such as anti-inflammatory [11], antioxidant [12], antimicrobial [13], antidiabetic [14], etc. This shows that Okpani as well as the other landraces could serve as useful sources of antioxidants due to increased content of flavonoids. The highest content of saponin (2.89) was found in Okpani followed by Adaka (2.80). Saponins are components of glycosides and are often referred to as natural detergents, because of their foamy nature. They are known to have both beneficial and deleterious properties depending on their concentrations. They have been reported to possess anticarcinogenic properties [15], immune modulation activities, regulation of cell proliferation as well as health benefits such as inhibition of the growth of cancer cells and cholesterol lowering activity [16]. Both Ogoja and Gwagwa had the highest value of tannins (0.05) respectively, followed by Aloshe, Amola, Dorban, Hemba and Okpani which had (0.04 mg/100g of tannin).Tannin is one of the important secondary metabolites which reduce the risk of coronary heart diseases [17]. The eleven selected yam landraces had oxalate ranging between (0.04- 0.06). Studies have shown that oxalate may play various roles in plants including calcium regulation, ion balance, plant protection, tissue support and heavy metal detoxification Nakata [18]. However when in excess, oxalate poisoning occurs. Ingested oxalate complexes with other mineral elements such as calcium to form calcium oxalate. This can lead to disturbances in calcium and phosphorus metabolism, involving excessive mobilization of bone minerals thus causing dimineralized bones [19, 20]. The phytate content of the selected samples were also below toxic levels and range from (0.01 – 0.02). Phytates are phytic acid bound to a mineral. Phytic acids are the storage forms of phosphorus [21]. Phytic acid has a strong ability to chelate multivalent metal ions, especially zinc, calcium and iron. The binding can result in very insoluble salts with poor bioavailability of minerals [22]. These low contents of phytochemical contained in these yam landraces show that they are not harmful to health but rather are useful sources health-maintenance components. However, only inositol pentaphosphate (IP5) and inositol hexaphosphate (IP6) have a negative effect on bioavailability of minerals. Besides its well- known negative properties IP6 by complexing iron may bring about a favourable reduction in the formation of hydroxyl radicals in the colon and also positive effect against carcinogenesis have been shown with in vitro cell culture systems [23]. All studied samples are rich in phytochemical and thus could be recommended for nutritional balances and health management.

Yam LandracesAlkaloidFlavonoidSaponinTanninOxalatePhytate
Adaka0.29 ± 0.013.05 ± 0.012.8 ± 0.010.03 ± 0.010.06 ± 0.010.01 ± 0.01
Aloshe0.34 ± 0.013.01 ± 0.011.99 ± 0.020.04 ± 0.010.05 ± 0.010.02 ± 0.01
Ameh0.36 ± 0.013.07 ± 0.022.79 ± 0.020.05 ± 0.010.06 ± 0.010.00 ± 0.00
Amola0.26 ± 0.022.99 ± 0.022.01 ± 0.010.04 ± 0.010.04 ± 0.010.02 ± 0.01
Dorban0.28 ± 0.013.66 ± 0.062.62 ± 0.020.04 ± 0.010.04 ± 0.010.00 ± 0.00
Gwagwa0.40 ± 0.023.07 ± 0.012.41 ± 0.380.05 ± 0.010.05 ± 0.010.02 ± 0.01
Heabalo0.24 ± 0.013.11 ± 0.012.19 ± 0.020.03 ± 0.010.04 ± 0.010.01 ± 0.01
Hemba0.22 ± 0.023.01 ± 0.011.99 ± 0.030.04 ± 0.010.04 ± 0.010.01 ± 0.01

Table 1: Phytonutrient composition (mg/100g) of the selected yam landraces. * Mean of five determinations ± standard deviation.

Miyango0.36 ± 0.013.51 ± 0.022 ± 0.020.03 ± 0.010.05 ± 0.010.00 ± 0.00
Ogoja0.32 ± 0.012.96 ± 0.061.89 ± 0.020.05 ± 0.010.04 ± 0.010.01 ± 0.01
Okpani0.35 ± 0.053.94 ± 0.022.89 ± 0.020.04 ± 0.010.05 ± 0.010.00 ± 0.00

Table 2: Phytonutrient composition (mg/100g) of the selected yam landraces. * Mean of five determinations ± standard deviation.

YamCalciumMagnesiumSodiumPhosphorusPotassiumIronZincCopper
Landraces(Ca)(Mg)(Na)(P)(K)(Fe)(Zn)(Cu)
Adaka29.5 ± 0.0261.5 ± 0.0261.14 ± 0.03164.51 ± 0.02614.45 ± 0.120.23 ± 0.022.61 ± 0.010.17 ± 0.02
Aloshe62.52 ± 0.0276.9 ± 0.0281.61 ± 0.03189.91 ± 0.03670.03 ± 0.030.48 ± 0.041.93 ± 0.070.11 ± 0.02
Ameh16.47 ± 0.0441.52 ± 0.0260.53 ± 0.02157.97 ± 0.46474.8 ± 0.380.32 ± 0.021.69 ± 0.020.11 ± 0.01
Amola20.48 ± 0.0367.51 ± 0.0269.42 ± 0.08211.62 ± 0.02611.3 ± 0.020.43 ± 0.021.35 ± 0.020.09 ± 0.02
Dorban74.3 ± 0.0255.49 ± 6.3370.28 ± 0.09239.13 ± 0.06623.53 ± 0.10.34 ± 0.022.12 ± 0.020.12 ± 0.02
Gwagwa89.61 ± 0.0440.04 ± 0.0362.54 ± 0.01219.19 ± 0.07711.3 ± 0.020.3 ± 0.012.42 ± 0.020.11 ± 0.02
Heabalo27.3 ± 0.1273.01 ± 0.0172.1 ± 0.03190.5 ± 0.03704.54 ± 0.120.21 ± 0.021.72 ± 0.040.1 ± 0.05
Hemba91.32 ± 0.0554.11 ± 0.0473.8 ± 0.06224.78 ± 0.03804.32 ± 0.10.48 ± 0.041.48 ± 0.030.1 ± 0.02
Miyango40.1 ± 0.0338.16 ± 0.0766.74 ± 0.08193.13 ± 0.02760.01 ± 0.030.27 ± 0.031.72 ± 0.020.09 ± 0.03
Ogoja78.73 ± 0.0243.5 ± 0.0253.33 ± 0.03200.15 ± 0.02900.09 ± 0.170.21 ± 0.011.88 ± 0.010.1 ± 0.02
Okpani80.11 ± 0.0243.62 ± 0.0261.51 ± 0.03269.33 ± 0.03795.82 ± 0.020.34 ± 0.041.81 ± 0.020.11 ± 0.02

Table 3: Mineral composition (mg/100g) of the selected yam landraces (Dioscorea rotundata Poir). * Mean of five determinations ±

YamCaloric value
(Cal/100g)
MoistureAshCrude fibreCrude proteinCrude fatCarbohydrate
Species
Adaka56.45 ± 0.120.49 ± 0.341.57 ± 0.034.01 ± 0.020.82 ± 0.0236.56 ± 0.14169.61 ± 0.57
Aloshe55.77 ± 0.060.68 ± 0.021.25 ± 0.013.04 ± 0.030.42 ± 0.0138.85 ± 0.09171.31 ± 0.35
Ameh54.53 ± 0.280.64 ± 0.011.74 ± 0.013.81 ± 0.030.81 ± 0.0238.46 ± 0.29176.36 ± 1.17
Amola59.12 ± 0.030.64 ± 0.011.65 ± 0.034.25 ± 0.020.45 ± 0.0133.9 ± 0.08156.61 ± 0.22
Dorban50.97 ± 0.380.64 ± 0.011.43 ± 0.033.16 ± 0.030.51 ± 0.0143.29 ± 0.35190.4 ± 1.48
Gwagwa52.91 ± 0.220.64 ± 0.011.4 ± 0.013.7 ± 0.020.5 ± 0.0240.85 ± 0.22182.67 ± 0.8
Heabalo61.05 ± 0.470.48 ± 0.031.71 ± 0.012.88 ± 0.010.65 ± 0.0433.24 ± 0.52150.32 ± 1.9
Hemba56.61 ± 0.041.09 ± 0.012.26 ± 0.024.18 ± 0.030.74 ± 0.0135.12 ± 0.05163.88 ± 0.31
Miyango50.43 ± 0.080.35 ± 0.021.4 ± 0.025.12 ± 0.020.47 ± 0.0142.23 ± 0.09193.57 ± 0.22
Ogoja58.32 ± 0.050.44 ± 0.012.36 ± 0.013.69 ± 0.010.53 ± 0.0334.67 ± 0.08158.18 ± 0.24
Okpani60.02 ± 0.310.69 ± 0.012.02 ± 0.025.33 ± 0.020.46 ± 0.1631.48 ± 0.38151.56 ± 1.66

Table 4: Proximate composition (%) of the selected yam landraces. * Mean of five determinations ± standard deviation

Conclusion and Recommendation

Phytonutrient, mineral and proximate compositions assessment of the eleven selected yam landraces showed that the landraces are endowed with phytochemical and nutritional constituents that could play a role in health maintenance. The landraces contain appreciable quantities of phytochemical which possess lots of medicinal properties and thus may be useful in pharmaceutical industries. The findings may also be useful for quality control and nutrient-health promotion campaign. Furthermore, this study presents the landraces for future pharmacological and therapeutic studies in related research field.

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@article{nwankwo2019,
  title   = {Assessment of the Phytonutrient Content, Mineral and Proximate Compositions of Selected Yam Landraces (Dioscorea Rotundata Poir)},
  author  = {Nwankwo PO},
  journal = {International Journal of Biochemistry & Physiology},
  year    = {2019},
  volume  = {4},
  number  = {3},
  doi     = {10.23880/ijbp-16000157}
}
Nwankwo PO (2019). Assessment of the Phytonutrient Content, Mineral and Proximate Compositions of Selected Yam Landraces (Dioscorea Rotundata Poir). International Journal of Biochemistry & Physiology, 4(3). https://doi.org/10.23880/ijbp-16000157
TY  - JOUR
TI  - Assessment of the Phytonutrient Content, Mineral and Proximate Compositions of Selected Yam Landraces (Dioscorea Rotundata Poir)
AU  - Nwankwo PO
JO  - International Journal of Biochemistry & Physiology
PY  - 2019
VL  - 4
IS  - 3
DO  - 10.23880/ijbp-16000157
ER  -