Determination of Ascorbic Acid (Vitamin C) Content in Sprouted Brown African Yam Beans (Sphenostylis stenocarpa)

Omenna, E. C.^1* & Amadife, A. E.²

¹Institute of Agricultural Research and Training, Obafemi Awolowo University, Ibadan, Nigeria
²Enugu State University of Science and Technology, (ESUTECH), Enugu, Nigeria

*Correspondence to: Dr. Omenna, E. C., Institute of Agricultural Research and Training, Obafemi Awolowo University, Ibadan, Nigeria.

Copyright © 2019 Dr. Omenna, E. C., et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Introduction
In developing countries, the production of milk and other animal-based foods is highly inadequate to meet the nutritional needs of the teeming population. And humans who do not obtain enough vitamin C develop scurvy, which is characterised by haemorrhage under the skin and tissues, swollen and spongy gums from teeth are easily dislodges, poor wound healing, painful joints and common cold [1]. Human beings and non -human primates cannot synthesis vitamin C from other related hexose sugars and therefore there is need for the dietary intake of this essential welfare food. Furthermore, protein-energy and/or -nutrient malnutrition is the major affront to food and nutrition security in many developing countries like Nigeria [2]. However, legumes are the potential source of protein and calories since their seeds contain high amount of carbohydrate (50-67%) and protein (23-25%) [3]. But, it is worrisome to note that majority of leguminous crops are neglected and grossly underutilized. Meanwhile, studies have shown that combination of lesser –known-legumes with other conventional legumes can be used to combat food and nutrition insecurity particularly in Nigeria and the World at large [4].

African yam bean (Sphenostylis stenocarpo) is one of the grossly underutilized legumes with great nutritional potentials [5]. African yam bean is a climbing legume and also an annual crop with an exceptional ability to adapt low land tropical conditions. African yam bean (AYB) is largely cultivated in the Eastern and Southern parts of Nigeria [6]. AYB produces nutritious seeds as well as underground edible tubers. Like a cowpea, African yam bean have its seeds enclosed in pods. Each pod contains ten -thirty seeds of many colours ranging from brown, white, speckled, and marble [4,7].These pods are borne on a climbing stem with wide heart -shape-leaves, one at each node spaced apart long the stem [8]. Studies have shown that African yam bean is grown extensively in West Africa for various dietary preparations due to its potentials for supplementing protein requirement of many families [9]. Processing of African yam bean may bring about value-addition which can alleviate protein -energy malnutrition as well as nutrients deficiency. According to Ajibade et al. (2005) [10], African yam bean is a good source of protein, carbohydrate, minerals and vitamins but the major constraints to its utilisation are the presence of anti-nutrient factors and long cooking time. Many literatures highlighted that processing such as soaking or fermentation and heating can reduce the level of anti-nutrient factors to tolerable level [11,12,13]. This study aimed at the effect of sprouting on the ascorbic acid content in African yam bean.

Materials and Methods

Chemical reagents (such as 2, 6-dichlorophenolindophenol, phosphoric acid, tetraoxosulphate (VI) acid) used in this study were of analytical grade.

Preparation of Stock Solutions
0.58g of 2, 6-dichlorophenolindophenol was weighed on analytical balance. The 0.58g of 2, 6-dichlorophenolindophenol powder was dissolved in 2 litres (2000ml) of distilled water and was stored in a brown reagent bottle for future use.

Phosphoric Acid
85 percent of the acid was diluted to ten percent using the dilution formula

More water was added to 117.7cm³

Where C₁ is the initial concentration, V₁ is the initial volume, C₂ is the required concentration, and V₂ is the required volume.

Extraction and Determination of Ascorbic Acid
1 gram of sprouted brown African yam bean sample was weighed out on analytical balance and then ground in a mortal with a spatula of acid -washed -sand followed by the addition of 5ml of diluted phosphoric acid and then triturated [14]. After triturating, the macerate was filtered, using cotton wool placed in the plastic funnel into a conical flask. The separation was aided by pressing the residue. The residues returned to the mortar and the extraction was repeated for two more times using the same quantity (i.e. 5ml) of phosphoric acid. The filtrate was poured into 100ml of volumetric flask and then distilled water was added to make up the marks of 100ml.The mixture was shaking for few minutes.10ml of the extract solution was taken into a beaker and was titrated with 2, 6-dichlorophenolindophenol solution from a micro-burette until the last drop that discharges a pink colouration, which persisted for the next 30 seconds. The titration was repeated for two times and the average titres of the two readings were calculated using the formula.

Where D1 is the difference between final reading and the initial reading of the first titration;

D2 is the difference between final and initial readings of the second titration for each sprouting day.

Calculation for the Determination of Ascorbic Acid Content in Brown African Yam Bean
The ascorbic acid content of African yam bean for each sprouting day was evaluated according to Stroev and Makarova (1989) [15] using the formula:

Where Y = ascorbic acid concentration (mg/kg),

Ma = mass of ascorbic acid (i.e.0.088mg) titrimetrically equivalent to 1ml of 0.001M 2, 6-dichlorophenolindophenol solution,

100 = the dilution ratio of the sample taken,
1000 = the scaling factor for conversion to per kilogram of raw material,
10 = the titre volume in ml
V = titrant volume (i.e. 2, 6- dichlorophenolindophenol solution) in ml, and b = the sample weight in gram.

Statistical Analysis
Data obtained were analysed using analysis of variance and means were separated using Duncan’s Multiple Range Test at P =0.05. Statistical Package for Social Science package (version 16) was used.

Results and Discussion

The ascorbic acid content of sprouted brown African yam bean is presented in Figure 1. From the results, it was observed that sprouting had significantly increased the amount of vitamin C in African yam beans. At day zero, there was no trace of ascorbic acid found in the dry brown African yam beans. The amount of ascorbic acid had increased as the number of sprouting days last. The first sprouting day had the lowest amount of ascorbic acid (13.2mg/100g) while the fifth sprouting day had the highest amount of ascorbic acid (22.0mg/100g). The data obtained from this study were strongly in agreement with the publication report by Colditz et al. (1985) [16] that sprouting improves the level of vitamin C in dry seeds. In addition, the observation of this study supported the research findings by Boehringer (1997) [17] which emphasized that sprouting supplies food in pre-digested form as the enzymes would have acted upon the food materials. And as starch is broken down into simple sugars like glucose, fructose, sucrose) and proteins are converted to amino acids and amides as well as fats and oils are converted to free fatty acids. Sprouting is a novel and cheap processing-method that can enhance the nutritional value of beans. In the light of this, Pezacka and Walerych (1991) [18] reported that sprouting makes beans to lose its objectionable gas-producing quality which causes stomach flatulence. The findings of this study were in consonance with Pezacka and Walerych (1991) [18] that sprouting was extremely an inexpensive method of obtaining a high concentration of vitamins, minerals and enzymes. The results of this study was also at par with other literature reports which stated that dried seeds, grains, and legumes do not contain any discernible traces of ascorbic acid yet when sprouted, they revealed quite significant quantities with corresponding decrease in calories and carbohydrate content [19]. Sprouts are the freshest and most nutritious of all vegetables available to human diet. Sprouts were also considered as wonder foods [19,20]. Eating of sprouts was described as the best and safest way of getting the advantage of both fruits and vegetables without the contamination of harmful insecticide [19]. The results of this study vehemently supported the observation from the literature publication bys Onyeike et al. (1995) [21] that animal fed on the germinated cooked mash bean gained more weight than those fed on the ungerminated beans.

Bibliography

1. Wagner, A. F. & Folker, K. (1994). Vitamins and Co-enzymes. Inter Sci., New York, (pp. 42-46).
2. FAO (2000). Protein quality evaluation (Report of joint FAO /WHO expert consultation held in Bethesda, MD, USA), FAO. Rome, Italy.
3. Olapade, A. A., Oluwole, O. B. & Aworh, O. C. (2012). Physico-chemical properties and consumer acceptance of instant cowpea (Vigna unguiculata) powder for complementary food. African Journal of Food Science and Technology, 3(4), 102-106.
4. Ajibola, G. O. & Olapade, A. A. (2016). Physical, proximate and anti-nutritional composition of African yam bean (Sphenostylis stenocarpa) seed varieties. Journal of Food Research, 5(2), 67-72.
5. Adewale, B. D. & Odoh, N. C. (2013). Review on genetic Resources, Diversity and Agronomy of African yam beans (Sphenostylis sternocarpa). A potential Future Food crop. Sustainable Agricultural Research, 2(1), 32-43.
6. Njoku, H. O., Ofuya, C. O. & Eli, L. (1991). Development of cheese like products from African African yam beans. Food Chem., 39(2), 197-204.
7. Edem, D. O., Amugo, C. L. & Eka, U. O. (1990). Chemical composition of African yam beans. Trop. Sc., 30, 59-63.
8. Asoiro, F. U. & Ani, A. O. (2011). Determination of some physical properties of African yam beans. The Pacific Journal of Science and Technology, 12(1), 14-25.
9. Ajayi, A. O. (2011). Sustainable Dietary Supplements: An Analytical Study of African yam bean-Sphenostylis sternocarpa and Corn-Zea mays. European Journal of Experimental Biology, 1(4), 189-201.
10. Ajibade, S. R., Balogun, M. O., Afolabi, O. O., Ajomale, K. O. & Fasoyiro, S. B. (2005). Genetic Variation in nutritive and anti-nutritive content of African yam bean. Trop. Sc., 5, 144-148.
11. Fasoyiro, S. B., Ajibade, S. R., Omole, A. J., Adeniyan, O. N. & Farinde, E. O. (2006). Proximate, mineral and anti-nutrient factors of some underutilized grain-legumes in South-Western Nigeria. Nutr. Food Sci., 36(1), 18-23.
12. Ndidi, U. S., Ndidi, C. U., Abbas, O., Aliyu, M., Francis, G. B. & Oche, O. (2014). Proximate, antinutrients and mineral composition of raw and processed (Boiled and roasted) Sphenostylis sternocarpa seeds from Southern Kaduna, Northwest Nigeria.
13. Verderames, M. (1995). Hand book of Hormones, Vitamins and Radiopaques. C.R.C. Press Inc., (pp. 245-307).
14. 14. AOAC. (2005). Official methods of Analysis (18^th Ed). Association of Official Analytical Chemists. Washington D.C. USA. (pp. 118-120).
15. Stroev, E. A. & Makarova, V. G. (1989). Laboratory Manual in Biochemistry. Mir Publisher Moscow, (pp. 197-199).
16. Colditz, G. A., Branch, I. G. & Lipnick, K. J. (1985). Increased green and yellow vegetables intake and lowered cancer deaths in elderly population. American Journal of Clinical Nutr., 41(1), 32-36.
17. Boehinger, M. G. (1997). Methods of enzymatic bioanalysis and food analysis. Mannheim, Germany, (pp. 66-79).
18. Pezacka, E. & Walerych, W. (1991). Biosynthesis of Vitamin C: Roles of microsomal enzymes in vitamin C biosynthesis. Biochem. Biophs. Aceta., 678, 300.
19. Helen, M. & Barker, C. (1999). Nutrition and Dietetics for health care. Longman Group Ltd. (pp. 47-50).
20. Hurst, J. W. (2002). Methods of analysis for functional foods and nutraceuticals. C. R. C. Press, New York, London, (pp. 291-294).
21. Onyeike, E. U., Ayalogu, E. O. & Uzogara, S. G. (1995). Influence of heating processing of African yam bean seed flour on growth and organ weight of rats. Plant Foods for Human Nutrition, 48(2), 85-93.