IMPROVEMENT OF COLD WATER SOLUBILITY OF STARCH EXTRACTED FROM UNDERUTILIZED LEGUMES USING CHEMICAL MODIFICATION

CHAPTER ONE

INTRODUCTION

Legumes  are  the  edible  fruits  or  seeds  of  pod-bearing  plants  belonging  to  the  family

Leguminosae and are widely grown throughout the world (Singh et al., 2004). Legume seeds are of prime importance in human and animal nutrition due to their high protein content (20 – 50%) (Singh et al., 2004) and have historically been utilized mainly as the whole seeds (Saio and Monma, 1993). Recently, the nutritional contents of legumes are being fractionated into their main constituents which are carbohydrate and protein. They contain about 60 % carbohydrates in which starch constitutes the major portion (Sun et al., 1981). Starch is a naturally occurring, biodegradable, cheap, renewable, and abundantly available polysaccharide consisting a large number of glucose units joined by glycosidic bonds (Ashogbon and Akintayo, 2014; Segura- Campos et al., 2015).  It  is naturally produced in granules by green plants as an energy store which serves as a major food source for animals (Naoko, 2014), that is sparingly soluble in cold water or alcohol (Thirumalaivasan et al., 2014).It consists of amylose and amylopectin as its major components.  Amylopectin  consists  of linear chains  of glucose  units  linked  by α-1,4- glycosidic bonds and is highly branched at the α-1,6 positions by small glucose chains while amylose is essentially a linear chain of α-1,4 glucans with limited branching points at the α-1,6 positions (Omeje et al., 2017). Applications of this native starch, had been unsuitable for most industrial processes because of its poor solubility in cold water, tendency to retrograde, low film- forming ability and high viscosity once gelatinized (Shi et al., 2011), Therefore, to enhance the application of native starches in industries and meet the demanding technology, the properties of starch can be modified using chemical modifications improve the physicochemical properties of the starch, and restricted retrogradation (Karim et al., 2011). This can be achieved using alcohol- alkaline method with a variety of other methods such as oxidation, acetylation and acidification (boric acid). All these techniques of starch modification tend to correct one or some of the above mentioned shortcomings,  and  enhance its  application  in  food industry,  as  thickener, binder, stabilizer, texture modifier, gelling and bulking agent and also in non-food industries like pharmaceutical, textile and paper industry to satisfy consumer demands (Waterschoot et al.,

2015). A growing demand for starches for industries has created the need for new sources of this polysaccharide. Currently, the most frequently used starch are obtained from grains (wheat, rice,

maize) and tubers (potatoes, cassava and cocoyam) (Bentancuret al., 2002), which are mainly staple food sources thereby possessing a challenge of food security. This study tends to improve the usefulness of underutilized legumes in starch industries.

1.1 Legumes

The term legume, is derived from the Latin word, legumen (with the same meaning as the English term), which is in turn believed to come from the verb legere “to gather.” English borrowed the term from the French “legume,” which, however, has a wider meaning in the modern language and refers to any kind of vegetable; the English word legume being translated in French by the word legumineuse (Wikipedia, 2009). There are over 13,000 species of plants belonging to this family (Sharma,2013). Some are cultivated as crop plant whose seed are edible (Shakuntala and Shadaksharaswamy, 2001). The legumes used for food are divided into two groups; pulses and oil seeds. Pulses are dried edible seeds of cultivated legumes such as peas, beans and lentils. The second group, the oil seeds, consists of those legumes used primarily for their oil content which may be extracted by pressing or by solvent extraction, the residue being high oil cake. These include the groundnuts and the soybeans (Ihekoronye and Ngoddy, 1985).

1.1.1 Legume seed composition

Legumes contain significant quantities of protein and carbohydrate (Table 1), while fat, ash and fibre are present in relatively small quantities. Some legumes such as pigeon pea, bambara groundnuts, and African yam beans, velvet bean are only consumed in small quantities and have limited utilisation and application. This could be associated with the hard-to-cook defect found in legumes such as cowpea (Akinyele et al. 1986) and Bambara groundnut (Ojimelukwe, 1998). Furthermore, the limited research that has been done on some underulilized legumes may also have contributed to its underutilisation. Thus, focusing on major components of these underutilized legumes, such as starch, may create an opportunity to improve their utilisation, for example, as a source of starch in the food industry.

1.1.2 ANTI-NUTRITIONAL FACTORS IN LEGUMES

Notwithstanding the agronomic and nutritional advantages of legumes as cheap protein and carbohydrate sources for many, especially low income persons, legumes have been reported to contain several anti-nutritional factors which include hemaglutinins, neurotoxic factors such as β-

aminopropionitril which cause lethrism. Other anti-nutrients in legumes are hemolytic-fibrile factor, as contained in faba beans, which causes favism, goitrogenic factors and trypsin inhibitors (Okaka, 2005). The anti-nutritional factors are segregated into two major groups based on their responses to heat treatment. One group,includes protease inhibitors, lectins (hemagglutinins), goitrogens and anti-vitamin factors are heat labile, while the other group that include saponins, eastrogens, lysino-alanines, allergens, flatulence inducing factors and phytates are heat stable and need treatments other than heat or other treatments in combination with heat to reduce their negative effects on man and animals ( Okaka, 2005). Some of these anti-nutrients are explained below:

PHYTATES: Phytic acid phosphorus contents the major portion of total phosphorus in several seeds and grains. It accounts for 50–80% of the total phosphorus in different cereals. It was reported by some authors (Schwenke et al., 1989) that phytic acid level has no or very little effect on binding to proteins. The investigation of the possibility of formation of ternary complexes raises difficulties. At alkaline pH values the Ca-phytate is insoluble and forms precipitate. At

very high pH values the phytate is insoluble. From a nutrition point of view, many studies have concentrated on the metal ion chelating property of phytic acid, its binding of zinc and formation of less soluble complexes that reduce zinc availability (Carnovale et al., 1988).

PROTEASE INHIBITORS: All legumes have been found to contain trypsin inhibitors to varying degrees, in addition to chymotrypsin inhibitors. Inhibition of trypsin and chymotrypsin leads to the hypertrophy of pancreas (Enwere, 1998). Conditions of heating- time and temperature, moisture content, and particle size- influence the rate and extent of trypsin inhibitor inactivation (Enwere, 1998).

HEMAGGLUTININS: These are also referred to as lectins. Their occurrence is not limited to legumes alone as they are found in slime molds, fungi, lichens, other flowering plants and

animals such as crustaceans, snails, fish, amphibian eggs and mammalian tissues (Enwere, 1998). Crude raw extract of hemagglutinin agglutinates the red blood cells of human beings and other animals if injected directly to the blood stream. Thus, it impairs the utilization of legumes such as beans, groundnuts, among others (Enwere, 1998). The other set back that has limited the use of legumes in non-traditional food formulations is the objectionable flavour associated with the crops. This set back has been a primary focus of research in a bid to extend the use of some

legumes. The most common off-flavour producing factors are the presence of glucosides- isoflavones, saponins, and sapogenols (Okaka, 2005).

1.1.3 Underutilized legumes

Underutilized legumes in Nigeria can be commonly divided into two classes: The once that can be prepared and eaten, as other known legumes (pigeon pea, bambara groundnuts, and African yam beans) and the once that cannot be eaten, as other legumes but may be used as thickeners, stabilizers or processed into condiments (velvet bean, achi, ofor, Ukpo) or fermented food products (African locust  bean, castor oil seeds) (Enwere, 1998). Overviews of some of the underutilized legumes investigated in this study are described below.

Table 1: The proximate composition of some of the underutilized legumes

Legume                                         Moisture   content          Crude   protein         Crude   Fats          Ash   Crude   fiber            Total   carbohydrates   Pigeon pea 67.40   7.0   0.60   1.3   3.50   20.20 Unripe dried 10.10   19.2   1.50   3.8   8.10   65.40 African yam bean seed 6.40   21.8   1.30   2.2   4.70   63.60   Bambara groundnut   9.70     16.0     5.90     2.1     ND     33.09   Deuterium microcarpium   6.14     13.52     13.81     2.20     ND     64.26 MucunaFlagellipes 5.84   20.11   9.64   3.14   ND   61.10     Brachystegiaeurycoma       6.49                   10.47               8.48              2.68          ND                   71.94

Source: (Mbaeyi, 2005)

1.1.2.1 Sphenostylis stenocarpa

Sphenostylis stenocarpa (Ijiriji) is an underutilized legumes that belongs to the family of Fabaceae,    sub-family    Papilionoideae,    tribe    Phaseoleae,    sub-tribe    Phaseolinae,    and genus Sphenostylis (Porter, 1992). It is one of the most important tuberous legumes and the most economically  important  among  the  seven  species  of Sphenostylis.  Sphenostylis  stenocarpa commonly originated within the tropical regions of Africa: Chad and Ethiopia (Northeast tropical Africa); Kenya, Tanzania and Uganda (East tropical Africa); Burundi, Central African Republic and Democratic Republic of Congo (West-Central tropical Africa); Côte d‟Ivoire, Ghana, Guinea, Mali, Niger, Nigeria, and Togo (West tropical Africa); Angola, Malawi, Zambia, and Zimbabwe (South tropical Africa) (GRIN, 2009). The crop has twining vigorous vines, which could be green or pigmented red. The vines twine clockwise around the stakes or climb other supports to a height of

are admirable and attractive ornamentals. Pods are usually linear, housing about 20 seeds. These vary in size, shape, colour, colour pattern.  AYB has different names in different countries; Ijiriji, Ukpodudu and Asama in Igbo, Nsama in Ibibio, Ewa in Itsekiri, Sese in Yoruba, Girigiri in Hausa, Yam bean in English, Raya and Norouko in Sudan, Diegemtenguere in Mali, Haricotigname and Pommedetere du mossi in France (Onyechi and Nwachi, 2009). Past research efforts had revealed that the flour of African yam bean is composed mainly of 18-25% protein and 58-63% carbohydrate, starch being the major carbohydrate reserve (Adeyeye, 1997).

1.1.2.2 Brachystegia eurycoma

Brachystegia  eurycoma(Achi)is  an  underutilized  dicotyledonous  legume  that  belongs  to  the family Caesalpiniaceae. It is commonly cultivated in the swaps or rain forests and well-drained soil of South-Eastern Nigeria and Western Cameroun. It is a huge tree which has twisted and spreading branches with a bark that often exudes a buttery gum (Giami et al., 1997). Its flowers spring forth between April and May and the fruits ripen between September and January. The fruits occur as broad leathery dark purplish brown pods containing four to six brown shiny flat disk-like brown seeds with a hard hull (Igwe et al., 2013). Brachystegia eurycoma is called Achi in Igbo, Ekalado or Eku in Yoruba, Okweri in Edo, Akpakpa or Taura in Hausa, Apaupan in Ijaw, and Odukpa in Ibibio (Bafor et el., 2017).

Figure 2: The Brachystegia eurycoma seeds and fruits sample used in this study

1.1.2.3 Deuterium microcarpum

Detarium  microcarpum(Ofor) is  an  underutilized  African tree  that is  commonly  left  when  a farmland is left uncultivated. It belongs to the family of Fabaceae and is popularly known as sweet detar, sweet dattock or tallow (Abdalbasit et al., 2011; Contu, 2012). In Nigeria it is known by Ibos as ‘ofor’, by Yorubas as ‘ogbogbo’ and by Hausas as ‘taura’.  It grows naturally in the drier regions of West and Central Africa which includes Nigeria, Ghana etc. It is a small tree or shrub growing up to 15 m tall but can reach 25 m in moist areas. In terms of growth rate, the shoots of the trunk can reach a height of 1.5-2 m in 1 to 2 years and are much more vigorous than seedlings which on average grow to 0.6 m after 3 years and may reach 1.5 m in 4 years. It flowers during the rainy season (July to September/November), but the main flowering period only las

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