Effect of Processing on In–Vitro Protein Digestibility and Anti–Nutritional Properties of Three Underutilized Legumes Grown in Nigeria
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British Biotechnology Journal 14(1): 1-10, 2016, Article no.BBJ.22581 ISSN: 2231–2927, NLM ID: 101616695 SCIENCEDOMAIN international www.sciencedomain.org Effect of Processing on in–vitro Protein Digestibility and Anti–nutritional Properties of Three Underutilized Legumes Grown in Nigeria M. O. Aremu 1* , H. Ibrahim 2 and B. E. Ekanem 3 1Department of Chemical Sciences, Federal University Wukari, PMB 1020, Taraba State, Nigeria. 2Department of Chemistry, Federal University Lafia, PMB 146, Lafia, Nasarawa State, Nigeria. 3Department of Chemistry, Nasarawa State University, PMB 1022, Keffi, Nasarawa State, Nigeria. Authors’ contributions This work was carried out in collaboration between all the authors. Author MOA designed the study, performed the statistical analysis and approved the final manuscript. Author HI wrote the first draft of the manuscript and managed the statistical analysis while author BEE carried out the literature searches and proof read the final manuscript. Article Information DOI: 10.9734/BBJ/2016/22581 Editor(s): (1) Mahalingam Govindaraj, ICRISAT, Patancheru, India. Reviewers: (1) Anonymous, Jomo Kenyatta University of Agriculture and Technology, Kenya. (2) Paulo Afonso Granjeiro, Federal University of São João del-Rei, Brazil. (3) Zahrat El-Ola Mahmoud Mohamed, Food Technology Research Institute, Agricultural Research Center, Giza, Egypt. Complete Peer review History: http://sciencedomain.org/review-history/14597 Received 12 th October 2015 Accepted 3rd May 2016 Original Research Article Published 12 th May 2016 ABSTRACT Comparative studies are conducted on the effect of roasting and boiling methods on anti–nutritional properties and in–vitro protein digestibility of bambara groundnut ( Vigna subterranea L.), scarlet runner bean ( Phaseolus coccineus L.) and lima bean ( Phaseolus lunatus L.) which are legume seeds grown in Nigeria. For this purpose some anti–nutritional factors and in–vitro protein digestibility were investigated using standard analytical techniques. Roasting method significantly reduced the anti–nutritional contents while in–vitro protein digestibility values were also decreased by 35.54%, 60.36% and 53.32% for Vigna subterranean , Phaseolus coccineus and Phaseolus lunatus , respectively. Boiling on the other hand significantly decreased the anti–nutritional properties as well as improved the in–vitro protein digestibility by 17.77%, 15.09% and 35.54% for Vigna subterranean , Phaseolus coccineus and Phaseolus lunatus , respectively. Among the two _____________________________________________________________________________________________________ *Corresponding author: E-mail: [email protected]; Aremu et al.; BBJ, 14(1): 1-10, 2016; Article no.BBJ.22581 domestic processing methods, boiling was the most effective in reducing anti–nutritional factors and improving in–vitro protein digestibility. Keywords: Protein digestibility; anti–nutrients; under–utilized legumes. 1. INTRODUCTION Scarlet runner bean (Phaseolus coccineus), a species of family Fabacceae, has been Consumed regularly, legumes contribute to a cultivated in the high parts of Mesoamerica. Its healthy diet, and would help to control metabolic introduction into southern Columbia (Antioquia diseases such as diabetes mellitus [1]. Legumes and Narino) and Europe where it is known as such as bambara groundnut ( Vigna scarlet runner bean and haricot d'Espagne could subterranean ), cowpea ( Vigna unguiculata ), lima have occurred in the seventeenth century before bean ( Phaseolus lunatus ), groundnut ( Arachis reaching other parts of the world such as the hypogeal ), kidney beans ( Phaseolus vulgaris L ) Ethiopian high lands [11]. Like other members of and pigeon pea ( Cajanus cajan ) are consumed the Fabacceae, it possesses climbing stems. Its widely in Nigeria. These legumes are valuable pods are gathered and left to dry in the sun sources of complex carbohydrates, protein and before being beaten and the seeds are stored in dietary fiber; contribute significant amounts of sacks. They are cultivated by peasant farmers vitamins and minerals, and high energy value for home consumption in the middle belt of [2-4]. Protein contents in legume grains range Nigeria. The aesthetic value of the seeds from 17% to 40%, contrasting with 7–13% of prompted their use in recreational activities such cereals, and being equal to the protein contents as traditional marriage in peasant communities of meats (18–25%) [5]. Poor nutritive values of among the Mada and Eggon tribes in Nasarawa the food legumes, due to the presence of some State, Nigeria [12]. antinutritional substances, such as tannins, Lima bean ( Phaseolus lunatus ) is one of the saponins, phytates, flavonoids, alkaloids, most widely cultivated pulse crops both in cyanogenic, glycosides, etc have been reported temperate and subtropical regions. It is adapted [2,6,7]. to highly leach infertile soils of the more humid regions. Lima bean seeds are among the Bambara groundnut is economically important leguminous plants that are under–utilised in because it is an inexpensive source of high Nigeria. It is a potential supplement or even a quality protein. It is highly valued among the substitute for the expensive soy meal and Eastern and Northern states of Nigeria [8]. groundnut meal which constitute the major Bambara nut is processed into consumable food portion of conventional protein sources used in and taken in various forms as source of protein composite livestock feeds. The shift from this to Nigerians. Bambara nut ( Vigna subterranea ) is plant to other legumes such as soybean and a novel legume of African origin grown mainly by groundnut was not unconnected with its subsistence female farmers intercropped with extended cooking period resulting into the major commodities such as maize, millet, wastage of scarce and expensive fuel [13]. Also sorghum, cassava, yam, peanut and cowpea [9]. lima bean seeds contain anti–nutritional factors The bambara groundnut is one of the most such as hydrogen cyanide, phytic acids, adaptable of all plants and tolerates harsh saponin, oxalate, tannin, trypsin inhibitor and conditions better than most crops. It is ideally haemagglutinin activity [14]. These anti– suited for hot, dry regions where growing other nutritional factors have been observed to inhibit pulses is risky. It yields on poor soils in areas of absorption of nutrients and their subsequent low rainfall and does not yield well in times of utilisation and assimilation by animals. Besides, heavy rainfall. The cultivars had distinct colour they cause some level of damages to some differences ranging from cream through brown, organs such as liver, kidney and spleen [15]. maroon to black, with variations in the seed sizes and seed coat thicknesses [10].`The seeds can The presence of anti–nutritional factors such as be consumed in different forms either in the trypsin inhibitors and chemotryosin inhibitors in immature green state or matured form. But at legumes affects the digestibility of legume maturity, the seeds become very hard and protein [16]. Other anti–nutritional factors such therefore require boiling before any specific as tannins, phytates, anthocyannins and preparation can be carried out. hemaglutinins impart bitter or unacceptable taste 2 Aremu et al.; BBJ, 14(1): 1-10, 2016; Article no.BBJ.22581 to the legumes, prevent protein digestibility and undertaken to explore the effect of two domestic decrease the absorption of divalent metal ions processing methods (roasting and boiling) on such as F 2+ , Zn 2+ in the intestine. This is anti–nutrients and protein quality of three under– achieved by complexing with these metals and utilized legume seeds grown in Nigeria. then making them unavailable for absorption. Many approaches have been adopted to address 2. MATERIALS AND METHODS problems associated with legumes in food/feed. 2.1 Sample Collection Anti–nutritional factors are a chemical compounds synthesized in natural food and / or About 3 kg each of fresh samples of bambara feedstuffs by the normal metabolism of species groundnut and scarlet runner bean seeds used and by different mechanisms which exerts effect for this study were purchased from a local market contrary to optimum nutrition [17]. Such chemical in Garaku, Nasarawa State, Nigeria while 3 kg of compounds, are frequently, but not exclusively lima bean seeds were obtained from a Farmer in associated with foods and feeding stuffs of plant Owo local government area of Ondo State, origin. These anti–nutritional factors are also Nigeria. All the purchased seeds were taken to known as ‘secondary metabolites’ in plants and the laboratory and each sample was stored in a they have been shown to be highly biologically sealed plastic container at room temperature active. These secondary metabolites are prior treatment. secondary compound produced as side products of processes leading to the synthesis of primary 2.2 Sample Preparation metabolites. One major factor limiting the wider food utilization of many tropical plants is the 2.2.1 Raw seeds ubiquitous occurrence in them of a diverse range About 500 g each of the raw seeds of bambara of natural compounds capable of precipitating groundnut, scarlet runner bean and lima bean deleterious effects in man, and animals were soaked in ordinary water at room compound which act to reduce nutrient utilization temperature and manually dehulled and dehulled and/or food intake are often referred to as anti– seeds were dried in an oven at a temperature of nutritional factors [18]. Antinutrients