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ISSN: 2157-7110
Journal of Food Processing & Technology

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Amino Acid Profiles of Some Varieties of Rice, Soybean and Groundnut Grown in Ghana

Eshun Naomi Amankwah1, Emmanuel Adu2,3*, Barimah John2, Dossou VM2 and Van Twisk C4

1Assistant Standards Officer, Ghana Standards Authority, Legon-Accra, Ghana

2Lecturer, Department of Biochemistry, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

3Biomass Refinery and Process Dynamics, WUR, Agrotechnology and Food Science, Wageningen, The Netherlands

4Assistant, Research and Education, Food Quality and Design, Wageningen University and Research Centre, EV, Wageningen, The Netherlands

*Corresponding Author:
Emmanuel Adu
Lecturer, Department of Biochemistry
Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
E-mail: [email protected]

Received date: November 27, 2014; Accepted date: January 22, 2014; Published date: January 29, 2015

Citation: Amankwah EN, Adu E, John B, Dossou VM, Van Twisk C (2015) Amino Acid Profiles of Some Varieties of Rice, Soybean and Groundnut Grown in Ghana. J Food Process Technol 6:420. doi:10.4172/2157-7110.1000420

Copyright: © 2015 Amankwah EN, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Amino acid profiles of some Ghanaian varieties of rice, soybean and groundnut were investigated to augment existing data on their physicochemical properties and provide information to guide their application in weaning foods formulation. Five varieties of rice and four varieties each of groundnuts and soybeans were analyzed. Amino acids were separated using HPLC. Without postcolumn derivatization, Evaporative Light Scattering Detector (ELSD) was used to determine their concentrations against standard amino acids. Local rice varieties lacked tryptophan, valine, glycine, glutamic acid and lysine and histidine was present in only Nerica-2 variety but Nerica-1 variety had the highest total essential amino acid content of 36.42 g/kg. Quarshie soybean variety expressed all the amino acids under study and also had the highest total essential amino acids content of 169.14 g/kg. Sinkarzie and F-Mix groundnut varieties expressed all amino acids except tryptophan, with Sinkarzie having the highest total essential amino acids content of 100.62 g/kg.


Amino acids profiles; Evaporative light Scattering Detector (ELSD); Grain legumes; HPLC


The weaning of infants on gruels made from traditional cereal or root tuber staples like rice, maize or yam has made protein-energy malnutrition prevalent in infants in most developing countries [1,2]. Gruel made from cereals like maize, millet, sorghum or guinea corn is the major traditional weaning food in most developing countries, known as koko in Ghana and Ogi in Nigeria [3]. These gruels, although low in proteins and deficient in some essential amino acids still persist because the commercial weaning foods available for infant feeding are too expensive for low income families.

In an attempt to combat the persistent protein-energy malnutrition challenge, especially among children, in Africa, several strategies have been developed to produce healthy nutritious food, rich in proteins, for infant feeding; Rice, soybean and groundnut composites yielded diets with improved nutritional composition [3]. Malted cereals, soybeans and groundnuts composites yielded diets rich in proteins and minerals [4]. Germinated sorghum, soybean, sesame and groundnut composited diet had high protein contents. Cowpeas, common beans and green peas served as good protein supplements for sorghum and finger millet based diets [5]. Rice, soybeans and groundnuts are cheap and readily available in Ghana and have been recommended as composites for infant weaning diets.

Cereal-legume combinations could therefore yield low-cost diets with improved nutritional contents for infant weaning in Africa. However information for the right proportions of cereals and legumes for infant weaning food formulation is limited. This is because the exact nutritional profiles of traditional cereals and legumes are not known. Thus, weaning foods formulated from cereals and legume composites could still be deficient in some essential micro or macro nutrients. The study seeks to determine the amino acid profiles of the predominant varieties of rice, soybean and groundnuts grown in Ghana. This is necessary to provide information to facilitate the formulation of lowcost weaning foods with the optimum protein and amino acid profile, for infant growth and metabolism.

Materials and Methods

The rice, soybean and groundnut varieties were obtained from the Crops Research Institute, Fumesua, Kumasi and the Savannah Agriculture Research Institute, Tamale.

Rice varieties: Sikamo, Digang, Jasmine-85, Nerica-1 and Nerica-2

Soybean varieties: Salintuya, Quarshie, Anidaso and Jenguma

Groundnut varieties: Sinkarzie, F-mix, Chinese and Manipinta

Sample preparation

Moisture content of all samples were between 4-5%. About 40 mg previously milled sample (using the Retchmill machine) was mixed with 5 ml of 3% Phenol in 6 N Hydrochloric acid in glass tubes. Samples were incubated at 110°C for 16 hours in a heating block (Liebisch), cooled and 1 ml of standard solution (0.656 mg/ml norleucine) was pipetted into the glass tube and mixed. The mixture was filtered using Whatman 595½ filter paper and washed repeatedly with water. The resulting supernatant was divided into 1 ml portions and dried in a Rotavap centrifuge (Thermo Electron, Asheville, NC, USA) under vacuum at 60°C for 2-3 hours to remove the excess water and HCl. After complete drying the hydrolysate was suspended in 1 ml buffer A (5 mM Heptafluorobutyric acid/0.7% Trifluoroacetic acid) and untrasonicated for 15 minutes. Subsequently the samples were filtered through 0.45 um filter for HPLC analysis. Measurements were conducted in duplicates for each variety.

HPLC Analysis of Amino Acids in Samples

In this research, sample concentration for HPLC was 6.67 mg/ ml, injected volume, 20 μl and flowrate, 1 ml/min. Chromatographic analysis was performed using the HPLC (SP thermo separation products) and ELSD (Polymer laboratories, PL-ELS2100, USA). The solvent system consisted of two buffers. Buffer A (0.653 ml 5 mM 98% heptafluorobutyric acid in 7 ml 0.7% trifluoroacetic acid solution) and buffer B (acetonitrile). Samples were injected onto the HPLC column (Grace Alltech Prevail C18 5 μm column, 4.6×250 mm). Stepwise elution was used beginning with 0% B or 100% A for 6 mins, followed by 15% B for 2 mins then 35% B for 17 min and finally held at 0% B for 5 min. The nebulisation and the evaporation temperatures, and the nitrogen flow rate were optimised at 60°C and 2.0 l/min, respectively.

Calibration curves were prepared for each amino acid standard. Area was plotted against concentration. Power trend lines were calculated from 5 dilutions. Regression coefficients were found in the range of 0.95-1.0. No correction factor was used for the internal standard because recovery was approximately 100%.

Statistical analysis

The data obtained was analyzed using ANOVA. The significant differences between factors were determined using the Tukey’s HSD test at 95% confidence level (p<0.05). The statistical tool used was STATGRAPHICS Centurion Version XIV.I.

Results and Discussion

A total of sixteen (16) amino acids, eight (8) essential and seven (7) nonessential, were detected using the HPLC-ELSD. Glutamic acid and Lysine however, eluted together for soybean and groundnuts and were recorded as such. The method could not detect glutamic acid and lysine in rice. This may be due to the hydrolyses procedure which causes variation in the determined and composition of aminoacids. Asparagine and glutamine were converted to their corresponding acids during the hydrolysis procedure. Cysteine and Methionine were oxidized into cystic acid and methionsulphon in the rice samples but could not be extracted from soybean and groundnut samples.

All rice varieties investigated were deficient in the essential amino acids (EEA) tryptophan, valine and lysine as well as the nonessential amino acids (NEEA) glycine and glutamic acid. All varieties, except Nerica-2, were deficient in histidine while Digang was deficient in proline. Threonine was the most predominant essential amino acid in the rice varieties, ranging from 10.70 g/kg for Digang and 21.17 g/kg in Nerica-1 while the predominant nonessential amino acid was Serine, ranging from 1.53 g/kg for Jasmine-85 to 29.30 g/kg in Nerica-1. The total EEA for all five varieties ranged from 36.42 g/kg to 20.52 g/kg while total NEEA ranged from 26.16 g/kg to 54.90 g/kg with Nerica-1 having the highest and Digang the lowest in both cases. The amino acid profile of the different rice varieties is shown in Table 1.

Amino Acid Digang Nerica-1 Jasmine-85 Nerica-2 Sikamo
Glutamic acid+Lysine - - - - -
Histidine - - - 0.92 -
Threonine 10.70a 21.17e 11.86b 17.58d 13.49c
Isoleucine 1.96a 3.55e 2.04b 3.51d 2.98c
Leucine 4.13a 6.81d 4.82b 7.27e 5.95c
Phenylalanine 3.55a 4.91d 3.80b 5.03e 4.45c
Tryptophan - - - - -
Valine - - - - -
Total EAA 20.72 36.42 22.5 33.36 26.88
Glycine - - - - -
Serine 13.69b 29.30e 12.53a 17.03d 15.71c
Aspartic acid 4.72a 7.56e 5.07b 7.50d 5.86c
Alanine 3.46a 7.27e 4.22b 7.14d 5.32c
Tyrosine 1.07a 2.93e 1.50b 2.70d 2.10c
Proline - 2.11c 1.52a 2.28d 1.68b
Arginine 3.17a 5.76e 3.88b 5.71d 4.44c
Total NEAA 26.16 54.9 28.68 42.36 35.16

Table 1: Amino Acid Composition of Ghanaian rice varieties (g/kg).

The amino acid profile of Nerica-1 rice compared well to Thai rice having total essential amino acid content of 34.68 g/kg [6]. The rice variety, environment and/or soil type for rice cultivation as well as preharvest and postharvest practices account for differences in nutritional composition.

All the local soybean varieties had good amino acid profiles. All the essential and nonessential amino acids were detected in Quarshie soybeans, while Salintuya and Anidaso soybeans were deficient in tryptophan and Jenguma soybean was deficient in histidine and proline. Threonine was the most abundant essential amino acid in the soybean varieties, ranging from 54.36 g/kg to 58.80 g/kg while alanine was the predominant non essential amino acid ranging from 63.96 g/kg to 75.30 g/kg. Total EEA ranged from 154.32 g/kg to 169.14 g/kg while total NEEA ranged from 218.10 g/kg to 233.34 g/kg with Quarshie having the highest and Jenguma the lowest in both cases as shown in Table 2.

Amino Acid Quarshie Salintuya Anidaso Jenguma
Glutamic acid+Lysine 23.70c 20.16a 24.24d 20.28b
Histidine 7.32c 7.02b 6.78a -
Threonine 57.48c 58.80d 54.36a 54.72b
Isoleucine 20.16d 20.04c 19.38b 19.14a
Leucine 32.40d 31.44b 31.56c 30.60a
Phenylalanine 21.36d 20.64b 20.76c 19.98a
Tryptophan 2.46a - - 3.12b
Valine 4.26b 6.78D 3.90a 6.48c
Total EAA 169.14 167.94 160.98 154.32
Glycine 16.86d 15.18A 16.68c 15.60b
Serine 46.08a 48.30B 55.92d 52.44c
Aspartic acid 41.53d 39.36B 39.00a 39.78c
Alanine 69.12c 67.98B 63.96a 75.30d
Tyrosine 14.52d 14.10c 13.38b 13.20a
Proline 21.18a 21.48c 21.24b -
Arginine 16.80a 23.58d 23.16c 21.78b
Total NEAA 226.09 229.98 233.34 218.1

Table 2: Amino Acid Composition of Ghanaian soybean varieties (g/kg).

The local soybean varieties contained lower lysine, valine, histidine and tryptophan (from 2.46 g/kg to 24.24 g/kg) when compared with Brazillian and USA soybeans which ranged from 4.51 g/kg-100.58 g/kg. Threonine and alanine levels were about three times higher in the local varieties than soybeans from Brazil and USA while isoleucine, leucine and phenylalanine contents in the local soybeans were comparable to that of Brazil and USA [7].

Tryptophan was not detected in all four groundnut varieties. F-Mix and Sinkarzie expressed all the other amino acids investigated. Co-eluting Glutamic acid and lysine as well as serine were not detected in Manipinta and Chinese. Histidine and threonine were also not detected in Manipinta while Chinese was lacking in glycine. Threonine (34.74 g/kg to 41.64 g/kg) and alanine (20.94 g/kg to 31.68 g/kg) were the predominant amino acids in Sinkarzie, F-Mix and Chinese while leucine (2.12 g/kg) and glycine (26.22 g/kg) were predominant in Manipinta as shown in Table 3. Sinkarzie groundnuts had the highest total EEA and total NEA of 100.62 g/kg and 147.94 g/kg respectively while Manipinta expressed the least total EEA and total NEA of 67.08 g/kg and 70.60 g/kg respectively.

Amino Acid Manipinta Sinkarzie F-Mix Chinese
Glutamic acid+Lysine - 10.32a 10.20b -
Histidine - 4.08a 3.64b 2.10c
Threonine - 41.64a 34.74b 38.58c
Isoleucine 12.78a 10.14b 10.32c 8.10d
Leucine 24.12a 18.12b 17.82c 14.28d
Phenylalanine 18.90a 13.08b 13.74c 12.06d
Tryptophan - - - -
Valine 11.28a 3.24b 3.72c 6.30d
Total EAA 67.08 100.62 94.2 81.42
Glycine 26.22a 17.40b 16.14c -
Serine - 31.73a 30.48b -
Aspartic acid 14.60a 27.30b 25.26c 22.02d
Alanine - 31.68a 24.18b 20.94c
Tyrosine 12.96a 9.90b 8.64c 7.08d
Proline 11.16a 7.30b 7.32c 6.78d
Arginine 5.46a 22.63b 22.62c 16.92d
Total NEAA 70.6 147.94 133.4 73.74

Table 3: Composition of amino acids in four Ghanaian groundnut varieties (g/kg).

All the groundnut varieties had lower total EEA than Indian JL groundnut variety (121 g/kg) and USA peanuts (127.43 g/kg) but threonine levels of the local groundnut varieties were about four times higher than in the Indian or USA groundnuts.

Tryptophan is essential in the manufacture of serotonin, needed for balancing mood and sleep patterns but was the least expressed amino acid in all the local rice, groundnut and soybean varieties [8]. Alanine was expressed in high amounts in almost all the rice, soybean and groundnut varieties. Alanine however can be produced by the body and is thus nonessential. Excess alanine in the diet may result in flushing and tingling in the muscles of humans and must therefore be regulated in weaning foods [9].

The FAO [10] recommends weaning foods to contain not less than 42 g/kg each of lysine, leucine, isoleucine and valine, 28 g/kg each of threonine, tyrosine and phenylalnine and 14 g/kg tryptophan. With the exception of tryptophan requirements, weaning diets formulated with the local rice, soybean and groundnut varieties will not meet all other essential amino acid requirements. Thus, there is the need for fortification of the weaning diets with protein isolates.


While rice varieties were lacking in valine, glycine, glutamic acid and lysine and histidine, soybean and groundnut varieties expressed most amino acids investigated. Nerica-1 rice, Quarshie soybean and Sinkarzie groundnut had the highest total EAA. The predominant amino acids in all varieties tested were threonine and serine. However, composites of rice, soybean and groundnut varieties in weaning foods will still present some deficiencies in the essential amino acid requirements of infants. Fortification of weaning diets, formulated with the local rice, soybeans and groundnut varieties investigated, with protein isolates is necessary to meet the protein energy requirement of infants.


The authors like to thank Lettink, F., for the technical assistance during this project.


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