Assessment of the nutritive value of bambara groundnut as influenced by cooking time

S O Omoikhoje

Ambrose Alli University, P.M.B 14, Ekpoma, Edo State, Nigeria
soomoikhojeaau@yahoo.com

Abstract

Sixty growing albino rats of the Wistar strain were used to assess the performance and protein quality of bambara groundnut as influenced by cooking time. Five treatment diets (1, 2, 3, 4 and 5) that contained raw bambara groundnut meal (RBGM), bambara groundnut meal cooked for 30, 60, 90 and 120 minutes (CBGM_a, CBGM_b, CBGM_c and CBGM_d) respectively were randomly assigned to five groups of 12 rats each in a completely randomized design (CRD).

Proximate analysis results showed that only the ether extract and ash were significantly (P<0.05) reduced as the cooking time increased. Performance data indicate that daily weight gain and feed to gain ratio were significantly (P<0.05) better in rats fed bambara groundnut meal cooked for 60 minutes and above than those on CBGM_a and RBGM based diets. Feed intake was highest significantly (P<0.05) in rats fed RBGM and decreased from CBGM_d to CBGM_a. Increase in cooking time significantly (P<0.05) increased the protein quality of bambara groundnut seeds as reflected in apparent digestibility, biological value, net protein utilization, net protein ratio and protein efficiency ratio values.

To enhance the nutritive value of bambara groundnut seeds therefore, an optimum cooking time of 60 minutes at 100^oC is adequate.                        

Key words: Albino rats, performance, protein quality, proximate composition

Introduction

Bambara groundnut (Vigna subterranea L. Verdc) is a novel legume of African origin grown mainly by subsistence female farmers intercropped with major commodities such as maize, millet, sorghum, cassava, yam, peanut and cowpea. Sellscope (1962) stated that bambara groundnut is the third most important legume after groundnut (Arachis hypogea) and cowpea (Vigna unguiculata) in Africa. Brough and Azam- Ali (1992) reported that bambaragoundnut seed makes a balance food as it contains sufficient quantities of carbohydrate (63%), protein (16.25%) and fats (6.3%) with relatively high proportions of lysine and  methionine as percentage of the protein (6.6 and 1.3% respectively).Brough and Azam- Ali 1992). The essential amino acid content of bambara groundnut such as lysine 6.82g/16gN, methoinine 1.85g/16gN and cysteine 1.24g/16gN is comparable to that of soyabean (6.24g/16gN lysine, 1.14g/16gN methionine and 1.80g/16gN cysteine) (Fetuga et al 1975).

The seeds can be consumed in different forms either in the immature green state or matured form. But at maturity, the seeds become very hard and therefore require boiling before any specific preparation can be carried out. However, it is a common knowledge that legume seeds generally require long cooking time for tenderization and the period varies from one legume to the other. Following the incessant increases in the prices of petroleum products in Nigeria, the cost of firewood or fuel for cooking the seeds has become a matter of immense concern. Against this backdrop, the study was designed to determine the effect of cooking time on the nutritive value of bambara groundnut seeds.

Materials and methods 

The feeding trial was conducted in the Department of Animal Science Laboratory of Ambrose Alli University, Ekpoma, Edo State, Nigeria.

Processing of bambara groundnut seeds

Enough quantity of raw bambara groundnut seeds purchased in Idah open market in Kogi State of Nigeria were divided into five groups of 0.5kg each. The first group was raw, while the second, third, fourth and fifth groups were cooked in water in a wide aluminum pot heated by naked fire from dried wood for 30, 60, 90 and 120minutes respectively at 100^oC. Thereafter, the cooked seeds were strained off the cooking water and they were sun- dried at atmospheric temperature of 28^oC for five days to obtain a constant moisture content of 10.99%. All the samples were then milled to form the bambara groundnut meal.

Experimental animals and design

A total of sixty (30male + 30female) growing albino rats of the Wistar strain with average initial weight range of 39.75 - 40.50g were used in a 21- day feeding trial. The rats were randomly selected into five groups of twelve (6 male + 6 female) each in a completely randomized design, based on their average initial weights. The groups of rats which were in three replicates of four rats (2 male + 2 female) each were housed in individual metabolic cages and assigned five treatment diets (1, 2, 3, 4 and 5). The test diets and clean water were supplied to the animals ad libitum.

Treatment diets

Five treatment diets were formulated in all with each diet incorporated in the nitrogen free corn starch basal diet comprising 75.75, 10, 5, 5,1, 2.50, 0.5 and 0.25% of cornstarch, groundnut oil, glucose, non-nutritive cellulose, mineral/vitamin premix, bone meal, oyster shell and common salt respectively (Oke et al 1999). Diet 1 was formulated to contain raw bambara groundnut meal (RBGM), while diets 2, 3, 4 and 5 were constituted by substituting RBGM in diet 1 with bambara groundnut meal cooked for 30, 60, 90 and 120 minutes (CBGM_a, CBGM_b, CBGM_c and CBGM_d) respectively. All the diets were constituted in a ratio necessary to maintain 10% crude protein on a dry matter basis. 

Performance study

During the feeding trial, weekly feed consumption and weight changes were measured, where weight gain, feed to gain ratio and protein efficiency ratio were estimated.

Protein quality study

On the 16^th day of the feeding trial, faeces and urine were collected from the rats for five consecutive days. At the end of the collection period, nitrogen in test diets, dry faeces and urine were determined by the method of A.O.A.C (2000). The nitrogen in dried faeces, test diets and urine were used to compute the apparent digestibility (AD), biological value (BV), net protein utilization (NPU), net protein ratio (NPR) and protein efficiency ratio (PER) as outlined for rats by NAS (1963).

Statistical analysis

Data generated were subjected to a one - analysis of variance (ANOVA) and treatment means that significantly differ were compared using the Duncan’s multiple range test as outlined by Steel and Torrie (1990) with the aid of SAS (1999).

Results and discussion  

The chemical composition of bambara groundnut as influenced by cooking time is shown in Table 1. The results indicate that only ether extract and ash were significantly (P<0.05) affected by cooking time, whereas crude protein, crude fibre and nitrogen free extract were not significantly (P>0.05) affected. Ether extract and ash values decreased as cooking time increases. Highest ether extract and ash values were obtained in raw bambara groundnut meal (RBGM) and least in bambara groundnut meal cooked for 120 minutes (CBGM_d). However, ether extract values of bambara groundnut meal cooked for 30, 60 and 90minutes (CBGM_a, CBGM_b and CBGM_c) were statistically similar to that in the raw state. Ash content in RBGM was comparable to that in CBGM_a, while comparable values were obtained between CBGM_a, and CBGM_b, CBGM_b, and CBGM_c.  However, the results in this investigation corroborates those of Temple and Aliyu (1994) and Osho et al (1995)

The performance data as influenced by cooking time is reflected in Table 2. Daily feed intake and weight gain as well as the feed to gain ratio of rats were significantly (P<0.05) affected by the cooking time. Rats fed CBGM_d had significantly (P<0.05) higher weight gain, but statistically similar to those placed on CBGM_b and CBGM_c based diets. Although, daily feed intake was highest in rats on RBGM than those on other treatment diets, but the feed to gain ratio was better in rats fed CBGM_b, CBGM_c and CBGM_d based diets.

The trend in this study in respect to performance indices showed that the longer the cooking time, the better the performance of rats in regards to growth promotion and feed utilization. However, the similarity in the performance of rats fed bambara groundnut meal cooked for 60minutes and above (CBGM_b, CBGM_c and CBGM_d) must have been mediated by the complete elimination of some anti-nutrient substances inherent in the intact seeds by the various cooking periods. This observation lends support from the earlier findings of Geevani and Theophilus (1980) who asserted that the nutritive value of a feedstuff does not only depend on the nutrient composition of the raw form, but also on the degree of nutrient loss or retained during processing. Thus, cooking can significantly enhance the bioavailability of nutrients in bambara groundnut seeds as reflected in this study (Abiola 1999).

Results on the effect of cooking time on the protein quality of bambara groundnut (Table 3) revealed that apparent digestibility (AD), biological value (BV), net protein utilization (NPU), net protein ratio (NPR) and protein efficiency ratio (PER) were significantly varied.

Cooking time significantly (P<0.05) improved the protein quality of bambara groundnut  seeds, but the extent of improvement was better and similar in rats fed bambara groundnut meal cooked for 60minutes and above (CBGM_b, CBGM_c and CBGM_d). Thus, it could be suggested that the optimum cooking time and temperature for bambara groundnut seeds is 60minutes at 100^oC. This corroborates the reports of Brenes et al (1973) who found the optimum cooking time and temperature for pigeon pea to be 20minutes at 120^oC. The poor protein quality of the raw bambara groundnut meal based diet must have been accounted for by the presence of some anti-nutrient substances (Oke et al 2004).

Conclusions

• Cooking time significantly improved the nutritive value of bambara groundnut with respect to performance and protein quality.

  
  

• To enhance bioavailability of component nutrients and performance of animals, an optimum cooking time of 60minutes at 100^oC is ideal for bambara groundnut seeds.

References 

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Brenes R G, Elias L G, Mohan M R, Delafuet G and Bressani R 1973 Changes in chemical composition and nutritive value of common beans and other legumes during house cooking. Proceedings of Latin Animal Nutrition Society 93: 75-81

Brough S H and Azam-Ali S N 1992 The effect of  soil moisture on the proximate composition of bambara groundnut (Vigna subterranea L. Verdc). Journal of Science. of  Food and Agriculture 60: 197-203

Fetuga B L, Oluyemi J A, Adekoya A A and Oyenuga V A 1975 A preliminary evaluation of rubber seed, beniseed and bambara groundnut as essential amino acid sources for chicks. Nigerian Agricultural Journal 12(1): 39-51

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Oke D B, Oke M O and Adeyemi O A 2004 Protein quality of autoclaved cowpea varieties as influenced by anti-nutritional factors. Nigerian Journal of Animal Production 31(1): 17-21

Osho S M, Ogundipe H O and Dashell K 1995 Soyabean processing and utilization in Nigeria. Tropical Post Harvest.(Osagie, A.U ed). Post Harvest Research Unit, University of Benin, Benin city. Pp 99-115                     

Sellscope J P F 1962 Cowpea (Vigna unguiculata L.Walp). Field Crop Abstract 15: 259-266

SAS 1999 Statistical Analysis System user’s guide; Statistics SAS Institute Inc. Cary, NC 27513, USA.

Steel R G D and Torrie J H 1990 Principles and procedures of statistics. A biometrical approach. (3^rd edition). McGraw Hill book Company, New York, USA.

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Received 29 November 2007; Accepted 8 January 2008; Published 4 April 2008

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