quality dynamics in the processing of underutilized legumes and oilseeds

732

Ramdane Dris PhD. (ed.), ‘’Crops: Growth, Quality and Biotechnology’’, pp. 732-746.All rights reserved © 2005. WFL Publisher, Meri-Rastilan tie 3 C, 00980 Helsinki, Finland.

QUALITY DYNAMICS IN THE PROCESSING OF UNDERUTILIZED LEGUMESAND OILSEEDS

VICTOR N. ENUJIUGHADepartment of Food Science and Technology, Federal University of Technology, P. M. B. 704, Akure, Nigeria.e-mail: [email protected]

1. Introduction

There is a common concern in less-developed areas of the world, and it is so serious that it continually draws the attentionof national governments. This problem is manifested in the widespread prevalence of protein energy malnutrition (PEM),resulting in high mortality and morbidity rates, especially among infants and children in low-income groupings. The majorcause of the problem is the heavy reliance on starchy roots and tubers and protein-deficient cereals as main staples in thedaily diets. It is not uncommon to see an average person in sub-Saharan Africa consuming three stodgy and monotonousstarchy meals in different forms per day. Apart from the insufficient availability of animal protein sources, the plant-baseddiets are highly devoid of needed protein, because the required sources are out of reach of the low-income class. For instance, in Nigeria, most weaning foods sold in the local markets are composed mainly of cereal grains andconventional legumes, especially soybean (Glycine max), which are often in short supply in some regions of the country,thus making them expensive and out of reach of the low-paid population 6. Moreover, since the diets are mainly dependenton cereals for both protein and dietary energy intakes, they do not sufficiently provide the required amino acids, especiallyamong the weaning-age children. For example, cereals and soybean are limiting in lysine and sulfur amino acids, respectively.Legumes generally contain lysine in amounts slightly lower than in beef and milk, but they are known to be generally lowin cysteine and methionine. Composite mixtures are usually advocated for more meaningful nutrient utilization. In the last two decades, research efforts have been channeled towards harnessing the nutrient potentials of bothconventional and unconventional legumes and oilseeds as a way of solving the PEM problem. Terms such as ‘underutilized’,‘under-exploited’, ‘less-common’, ‘lesser-known’ and ‘unconventional’ are frequently used to describe the low distributionor circumstantially limited use of these food crops. Some of these seeds have relatively high protein contents and can beused to increase the protein intake of people through development of new products and fortification of various starchystaples 27. Oilseeds and legumes share one common quality, which is the reasonably high protein content. The proteincontents of most legumes and oilseeds range between 20-40 g kg-1 DM and that contrasts with the low-protein starchystaples in tropical and sub-tropical countries. However, the problem with processing under-exploited legumes and oilseeds is the rigorous, energy-consuming operationsinvolved in the traditional methods, namely, lengthy hydrothermal treatment and soaking and fermentation procedures.These processing operations considerably reduce the levels of anti-nutritional and toxic factors, but at the same timedrastically affect their contents of some important nutrients. The loss of nutrients, especially vitamins and minerals isexpected, although the fermenting microorganisms which are mainly bacteria species tend to contribute to the nutrientcomposition of the respective products. Lower nutrient contents have been observed with the traditional processing ofsome oilseeds 32, 44. In this chapter, the dynamics of nutrient loss and gain during the processing of some of these underutilized andunconventional legumes and oilseeds will be examined. Although there is loss of nutrients during the processing, the loss ofanti-nutritive ant toxic factors greatly enhances nutrient availability and digestibility and, of course, there are other criteriaof quality loss, apart from nutrient content (e.g. colour, texture and flavour), that are important in determining the overallquality of a food product. But to fully appreciate the dynamics of quality changes during the processing of under-exploitedlegumes and oilseeds, their current status and appropriate processing techniques will need to be examined.

2. Status of Underutilized Legumes and Oilseeds

Most available food legumes are at present not fully utilized. Some are less well known; others exist in the forest and arenot yet explored 40. At their different levels of utilization, they are commonly cooked and consumed, either directly assnack or complimentary foods, or fermented and used as condiments in soups and sauces. Cowpea, for instance, is mainlyutilized in the production of bean cake (akara), pudding (moinmoin) and porridge, which are delicacies among target

733 Quality Dynamics in the Processing of Underutilized Legumes and Oilseeds

populations. Pigeon pea, velvet bean, lima bean and sword (or jack) bean are cooked and eaten in form of porridge.Conophor nut is only utilized as a cherished boiled snack that is eaten along with boiled corn. Locust bean, castor bean,mesquite seed and African oil bean are consumed as fermented condiments and seasonings. Bambara nut is used in theproduction of a hard mash that is consumed as snack, or is fermented and used as a condiment in local soups andporridges. Although most of the underutilized oilseeds and legumes contain anti-nutritional factors which could affect mineralavailability 74 and protein utilization by the body 25, as well as some toxic components, these factors are known to beeffectively removed or significantly reduced during the processing of the seeds, especially during hydrothermal treatment,soaking and fermentation 32, 44. The lesser-known under-exploited legumes and oilseeds have recently assumed a new status in developing countries,especially with the focus on sustainable agriculture and nutrient requirements. In Nigeria, for instance, a review of researchpapers presented at the annual conferences of the Nigerian Institute of Food Science and Technology (NIFST) - anumbrella body that covers food production, processing and marketing concerns - within a 4-year period (1999-2002), showthe preponderance of underutilized legumes and oilseeds in contemporary food research works (see Table 1). On theaverage, between 23 and 27 percent of papers are presented each year, focused on lesser-known underutilized legumesand oilseeds. The status of under-exploited legumes and oilseeds could better be explained in terms of their nutrient potentials,current food uses, concentrations of anti-nutritional and toxic factors and functionality in food systems. The most pertinentquestions are: what are the nutrient potentials of the seeds? Do the nutrient contents justify the call for wider exploitation?What are the known and potential impediments to their full utilization? Are there other uses to which they could be applied,especially in other food systems, which may encourage their wider distribution? The answers to these and other questionswill definitely help in ensuring more purposeful research into their exploitation.

2.1. Nutrient potentials

The nutrient potentials of most known underutilized and unconventional legumes and oilseeds have been studied byvarious workers 13, 24, 25, 27, 34, 51, 62, 70. Ezeagu et al. 34 studied the nutrient composition of nine species of wild gathered plantseeds in comparison with soybean grown in Nigeria and concluded that these less familiar wild seed plants should not beignored. Badifu 12 reviewed the food potential of some unconventional oilseeds grown in Nigeria and observed that theirexploitation could contribute immensely in solving the hunger and starvation problem in the country. All the studies on thenutrient status of these seeds point to their increased exploitation as a potential solution to the dietary imbalance experiencedby the diverse populations in the third world. The nutrient potentials of some underutilized legumes and oilseeds are presented in Tables 2 and 3. As earlier notedprotein content ranges between 20 and 40% dry weight for most of these seeds. They constitute a potential source ofedible protein, containing the 20 essential amino acids and essential fatty acids that make up more than 80% of fatty acidsin the oil 2, 39. The amino acids profiles for some of these seeds are comparable to the FAO reference protein, althoughsome are limiting in the sulfur amino acids (cysteine and methionine). The profiles of fatty acids in the oils and thephysico-chemical properties of oil extracts in these seeds reveal a high degree of unsaturation 23, 65. The principal fattyacids are linoleic, linolenic and oleic acids. Arachidonic acid is found in trace amounts. It has been reported that linoleic,α-linolenic and docosahexaenoic acids are essential to the well being, growth and development of children, especiallybreast-fed infants during the first six months 41. This underscores the great potential of most of the underutilized cropseeds as weaning food ingredients. The mineral composition of some of the known underutilized legumes and oilseeds reveals high phosphorus contents23,25,

27. This is reflected in Table 3, and also confirms the observation of Nwokolo 59 that phosphorus was high in some tropicalgrains and oilseeds. Balogun and Fetuga 13 linked the low sodium levels of some legume seeds to the subnormal

Year Total no. of papers Papers on the legumes % of total

/oilseeds

1999 112 27 24.11

2000 134 37 27.61

2001 122 32 26.23

2002 107 25 23.36

Table 1. Trend of research efforts towards underutilized legumes and oilseeds in Nigeria.

Victor N. Enujiugha 734

concentrations of sodium in tropical crops, which are a reflection of the low sodium contents of the soils. The largeamount of potassium relative to sodium in some legume seeds could be a disadvantage to hypertensive patients becauseof mineral imbalance. However, according to an earlier report 29, K/Na ratio of >1 is desirable since an average humandiet is low in potassium and high in sodium. The low iron content could be augmented by other dietary sources to meet theiron needs of the body. Vitamins of the B-group are abundant in most lesser-known legumes and oilseeds. Achinewhu and Riley 4 reported thepresence of significant quantities of thiamin, riboflavin and niacin in Citrullus vulgaris and Pentaclethra macrophylla.Biotin and other growth factors are also found in some of the seeds.

2.2. Current food uses

The cultivated underutilized legumes and oilseeds are found useful in many local dishes. Some are used as main meals,others as fermented condiments and sauces, yet others as snacks and in-between-meal complimentary foods and appetizers.For example, the most common cowpea-based food product in West Africa is akara, a deep-fat fried product made fromwhipped cowpea paste 54. There has been the production of milk and beancurds from some of these seeds after soy milk soy tofu, respectively.Lee and Beuchat 47 produced excellent milk from peanut without the typical green, beany flavor and undesirable texture.They gave the most satisfactory conditions for preparing peanut milk as consisting of soaking peanuts in 0.5% NaHCO3,cooking for 10 min. and homogenizing the extract at 4000 psi. There are equally great prospects for the production ofmilk from African oil bean seed, cowpea and conophor nut. Attempts have also been made to produce beancurds fromwinged bean 42, mungbean, cowpea and peanuts 55, as substitutes for soybean curds (tofu). It was found that satisfactorycurds could be formed from legume sources other than soybean only after the partial removal of starch (in mungbean andcowpea) or oil (in peanuts). The use of unconventional protein sources in weaning food formulation is not new. Agbede and Aletor 6 used leafprotein concentrates and reported excellent responses from some weaning rats. Proll et al. 70 examined the nutritionalquality in rats of some wild-gathered leguminous crop seeds and reported that the rats responded well to some of theseeds. Currently, legume seeds and defatted oilseed flours are used as protein supplements in the local cereal-basedweaning foods with some remarkable results. The most popular traditional corn-based weaning food in West Africa, ogior akamu, has been prepared from corn/legume mixtures at up to 70:30 (corn : legume) substitution levels, withoutnegatively affecting the pasting and textural properties. Some underutilized legumes and oilseeds have been used in composite flour formulation for bread and biscuit making.Okaka and Isieh 63 developed a cowpea-wheat biscuit product which compared well with wheat-only biscuits. There hasalso been the development of conophor nut-based biscuit-like snack food 5. McConnell et al. 53 showed that acceptablebread can be made from faba beans at 5-15% replacement level of wheat flour. Rooney et al. 72 compared the bakingproperties of some oilseed flours with satisfactory baking performance. The advantage of composite flour technology isthe resultant improvement in the nutritional status of the target population.

Table 2. Approximate nutrient contents in some underutilized legumes and oilseeds (% dry wt.).

Legume/oilseed Crude protein Oil content Crude fibre Ash Carbohydrate Reference

Phaseolus vulgaris 17.75 1.13 - 4.79 76.33 Barampama and Simard 14

Tetracarpidium conophorum 29.09 48.90 6.34 3.09 12.58 Enujiugha 24

Pentaclethra macrophylla 33.42 50.15 7.64 4.02 4.77 Enujiugha and Olagundoye 32

Citrullus vulgaris 31.41 43.93 6.62 4.79 3.96 Enujiugha and Ayodele-Oni 27

Parkia biglobosa 29.06 26.19 6.71 2.50 15.47 Enujiugha and Ayodele-Oni 27

Sphenostylis stenocarpa 20.67 5.81 - 3.87 60.09 Oshodi et al. 68

Mung bean 23.56 0.37 1.10 3.00 59.92 Del Rosario and Flores 19

Lathyrus sativus 23.60 1.30 5.00 2.90 63.50 Chavan et al. 17

Table 3. Mineral contents of some less-common legumes and oilseeds (mg 10-2 g-1 dry wt.).

Na K Ca Mg P Zn Fe Cu Reference

Phaseolus vulgaris - 554 66.6 43.8 496 7.51 6.88 1.01 Barampama and Simard 14

Tetracarpidium conophorum 4.00 590 42.06 57.37 465.95 6.84 1.55 1.56 Enujiugha 24

Pentaclethra macrophylla 40 91 30 30 112 40 30 - Enujiugha and Olagundoye 32

Parkia biglobosa 29.0 400.0 150.0 212.0 285.0 3.0 12.0 - Enujiugha and Ayodele-Oni 27

Sphenostylis stenocarpa 5.38 6.19 8.35 12.07 218 6.92 5.11 5.85 Oshodi et al. 68

Lathyrus sativus 60.5 1098 156 150.0 482 6.7 9.7 2.4 Chavan et al. 17


Oilseeds and legumes are usually fermented and used as condiments and seasonings in local soups and sauces. This isthe most popular traditional form in which these seeds are consumed. Others like conophor nut are cooked and eaten ascomplimentary and lunch-time snacks. Condiments are important additions to meals in the third world because of theirsavoury flavours, apart from their nutrient potentials.

2.3. Anti-nutritional and toxic factors

Food legumes are known to contain several anti-nutritional factors such as protease inhibitors (especially trypsin inhibitors),lectins or haemagglutinins, flatulence factors, phytates and polyphenols, among others. The presence and concentration ofthese anti-nutritional factors depend upon the legume type 76. Numerous studies have indicated that these anti-nutrientscan be eliminated or reduced significantly by processing techniques such as thermal heating (e.g. infrared heating, extrusioncooking, irradiation, steam treatment and pelleting), milling, soaking, germination, fermentation, cooking and proteinextraction29, 32, 82. Table 4 shows a general survey of some anti-nutritive and toxic factors in selected under-exploited legumes andoilseeds. These factors occur in significant concentrations in the seeds. Legumes are particularly rich sources of phytateswhich could reduce significantly the overall availability of certain minerals found in them. Forbes and Erdman 38 noted thatthe anti-nutritional nature of phytin lies in its ability to chelate certain mineral elements, especially Ca, Mg, Fe and Zn,thereby rendering them metabolically unavailable, and leading to the subsequent development of oesteomalacia whencertain legumes are fed to growing animals. Tannins are powerful protein-binders. The poor palatability generally associatedwith high tannin diets is ascribed to its astringent property which is a consequence of its ability to bind to proteins of salivaand mucosal membranes. Oxalates bind to proteins and divalent minerals making them unavailable. The high contents ofanti-nutritional factors in the seeds may not pose any problem if they are to undergo combined process of cooking, soakingand fermentation.

Marconi et al. 49 reported haemagglutinating activity of 240 HA and trypsin inhibitor activity of 985 TIU mg-1 in Vignaunguiculata. There has also been a report of haemagglutinating activity in Pentaclethra macrophylla at a level of 4 HUmg-1 25. These concentrations could be said to be on the high side, and the seeds may not be utilizable without rigorousprocedures to reduce significantly the levels of these factors. Barampama and Simard 14 reported high levels of lectins andtrypsin inhibitor activity in common beans. Table 5 shows the contents of flatus-forming oligosaccharides in some underutilized legume seeds. Oligosaccharidesconsist of more than half of total sugar contents of the legumes studied. The α-galactosides are known to constitute themajor portion of sugars in legume seeds and have been reported to be involved in flatus formation 36. The raffinose familyof oligosaccharides (raffinose, stachyose and verbascose) is well known to produce flatus in humans and animals. Owingto the absence of α–galactosidase enzyme capable of hydrolyzing the α-1-6-galactosidic linkage in the gastro-intestinaltract, these oligosaccharides accumulate in the small intestine and undergo anaerobic fermentation by bacteria. Therefore,to utilise legumes as a more acceptable source of inexpensive proteins, it is desirable to reduce the level of of componentsproducing flatulence. Attempts that have been made to reduce the content of raffinose oligosaccharides in legumesinclude dehulling, soaking, cooking, gamma irradiation, germination and fermentation 8, 43, 58, 79.

Tannins Phytates Oxalates

Phaseolus vulgaris 8.02 16.75 -

Tetracarpidium conophorum 0.12 2.15 3.6

Pentaclethra macrophylla 0.79 4.10 1.7

Ricinus communis 0.11 0.89 6.5

Citrullus vulgaris 0.11 1.77 1.8

Parkia biglobosa 0.15 0.84 2.8

Table 4. Anti-nutritional factors in some underutilized legumes and oilseeds (mg g-1 dry wt.) 14, 27.


2.4. Functionality in food systems

Functionality as applied to food ingredients is defined as any property on which the utility of those foods depends. Afunctional food may be defined as a food having health promoting benefits and/or disease preventing properties over andabove its usual nutritional value 77. Functional foods encompass a broad range of products, ranging from foods generatedaround a particular functional ingredient (e.g. stanol-enriched margarines), through to staple everyday foods fortified witha nutrient that would not normally be present to any great extent (e.g. folic acid fortified bread or breakfast cereals).Although some ingredients are nutraceutic, functional foods are categorized as foods and not medicines. The absorptionor adsorption of water and fat, emulsification, colour, viscosity and formation of gels are important characteristics ofconcentrated proteins. These physico-chemical properties are somehow related. For example, hydration is related toother functional properties such as solubility, emulsification, viscosity and gelation. Water and fat retention are basicfunctional properties of proteins which determine the quality (juiciness, texture, binding of structure, appearance andmouth feel) and yield of finished meat products 48. Of course, the functional properties of a compound cannot be attributedto only the protein portion; other components such as carbohydrates and lipids can also exert some level of influence. Extensive studies have been carried out on the functional characteristics of protein isolates, concentrates and defattedflours of a great number of under-exploited legumes and oilseeds. Reports of previous studies on functional propertiesinclude those of pigeon pea 67, mung bean 18, conophor nut 23, faba bean 16, African yam bean 68, jack bean 35, African oilbean 29 and winged bean 57. The protein concentrates and isolates from these and other such seeds have been suggestedas excellent complementary ingredients and potential functional foods. For example, Akubor and Badifu 9 have averredthat African breadfruit kernel flour could be used as a protein supplement in the human diet and as a functional ingredientin formulated foods such as cookies. Some local techniques are currently used in the functional utilization of lesser-known oilseeds. They are cooked, dried,ground to powder and added to soups as thickeners. The fermented forms are also dried and ground into powders asthickeners. Some seeds are found useful as meat extenders. There are also stories about the consumption of some ofthese seeds contributing to longevity.

3. Avenues for Quality Evaluation

In the processing of underutilized and unconventional legumes and oilseeds, the criteria for quality evaluation must bewell-defined for us to be able to appreciate the avenues for measuring quality loss. If quality is to be explained in terms ofnutrient digestibility and bioavailability via reduction in levels of anti-nutritional and toxic factors, some processing stepsand postharvest conditions which are considered detrimental for certain nutrients may be employed as long as the constituentnutrients are made more available to the body. If on the other hand, quality loss is to be evaluated in terms of reduction inlevels of essential nutrients then some steps which bring out the edibility of these seeds may actually be disallowed orside-tracked. However, it is appropriate to state that the dynamics of quality change in the processing of these seeds mustbe viewed in terms of both reduction in levels of anti-nutritional factors and enhancement of concentrations of essentialnutrients. In a study of nutrient changes during the fermentation of African oil bean seeds using the traditional technique, it wasfound that although the process brought about remarkable improvement in protein quality, it also caused increased unsaturationof the seed oil 23, and this could obviously predispose the product to rancidity and development of off-flavours during shelfstorage. Nevertheless, the overall assessment of the quality of product points to fermentation as bringing about enhancementof seed quality. This implies that total quality is important in assessing these seeds, than examining a particular attribute.In other words, no single parameter is sufficient in describing quality loss; the whole process must be weighed in order toqualify the overall status of the seed or seed product.

Legumes Total sugars Sucrose Raffinose Stachyose Verbascose % of total

Faba bean 5.98 1.37 0.52 1.41 1.85 63.2

Lentil 5.13 1.14 0.45 1.65 0.62 53.0

Common bean 4.90 1.25 0.45 1.80 0.25 51.0

Cowpea 6.05 1.51 0.77 3.00 0.30 67.3

Table 5. Oligosaccharides and total sugar contents of some dry legume seeds (% dry weight) 1.


The avenues for quality evaluation in the processing of underutilized legumes and oil seeds will be considered in termsof postharvest storage conditions, processing techniques and conditions, and shelf-life of products, especially duringtransportation and distribution. Quality loss can be evaluated effectively by assessing the process based on these conditions.

3.1. Postharvest storage conditions

The postharvest storage conditions are important in determining the level and reduction of loss in quality of seeds generally.What happens during postharvest storage affects the subsequent processing and the final product quality, especially in thecase of oilseeds. Most of the problems of storage are tied to the action of enzymes and activities of microorganisms andpests that cash in on the poor storage conditions. It has been reported that lipases are active in the dormant (or ungerminated)seeds of peanut 75, castor bean 66 and African oil bean 33. In these seeds the enzyme is apparently inactive in vivo buthighly active in vitro. In other words, as long as the seed is in the intact state, the enzyme will remain inactive, but anyslight change in the seed or storage conditions will probably initiate activity. Results show that most oilseeds deterioratewith storage 33. The storage conditions in the developing countries are inadequate to preserve nutrients in farm produce prior toprocessing and use. The application of controlled and modified atmospheres in storage is not known or, where known, isnot practiced. It could be said that the major quality losses are encountered during postharvest storage. Factors involvedin final losses have been outlined to include crop variety, climate, poor harvesting techniques and consequent moulddamage 78. It seems however, that more emphasis is laid on quantitative losses than on qualitative losses. As a result,most processed foods in the third world would have started suffering quality depreciation right from the storage stage. The major problems encountered during storage are insect and mould attacks. For instance the growth of Aspergillusflavus with attendant aflatoxin production has been a major source of worry in peanut storage prior to processing. Otherstriking examples are Bruchide attack on cowpeas and seed borers’ action on African oil bean seeds. The impact ofinsect attack on legumes and oilseeds is felt in the lower protein content of infected seeds and reduced functionality of theseed product.

3.2. Processing conditions

It is widely believed that once the processing conditions are altered the product quality is not expected to be the same.This alteration could come in the form of change in raw material or ingredient formulation, or change in process schedule.Again, some aspects of processing conditions could significantly cause reduction in quality. Heat treatment, especiallyhydrothermal treatment, for instance, affects the vitamin content of most legumes during processing. A condition couldalso be favourable to the preservation of one component, while contributing to the destruction or loss of another keycomponent. An example is the decortication of cowpeas during processing. Akinjayeju and Enude 7 observed that when the seedcoat of cowpea was milled along with the cotyledons, there was little effect on most of the physico-chemical andrheological properties of the flours, or on the moinmoin prepared from the flours. Obviously, the yield of flour obtainedfrom a given quantity of seeds will increase when the seed coats are included in the flour and the flour will contain mostof the nutrients present in the seed coat, especially minerals. The seed coat may also provide fibre to the diet, which aidsdigestion. In addition, the time-consuming seed coat removal operation could be eliminated. However, it is known thatdecortication brings about significant reduction in the levels of flatus-forming oligosaccharides in cowpea. Therefore, ifthe overall benefits of decortication are weighed against the disadvantages, one may still advocate the step during theprocessing. An important step in the processing of underutilized legumes and oilseeds is hydrothermal treatment because of thehigh content of anti-nutritive and toxic factors, some of which are destroyed via moist heat. Some of the seeds like pigeonpea, Bambara groundnut and hard-to-cook common beans require long hours of boiling to bring them to a consistency softenough for human consumption. This lengthy heat treatment causes the removal or destruction of B-group vitamins andother water soluble and heat-labile components of the seeds. The leaching of protein into processing water during cookinghas been reported 44. Dry heat particularly during roasting of some of the oilseeds is expected to cause nutrient losses.Roasting has been linked to the undesirable concentration of anti-nutritional factors 32, 24. Fermentation as a processing step has been found to contribute positively to the nutritional quality of food products 23.The growth and activities of microorganisms lead to increased nutrient digestibility and hydrolysis of macromolecules.


Bacillus species are associated with the fermentation of most of the underutilized legumes 28, and they have beenreported to be responsible for the breakdown of polysaccharides, peptides and triglycerides into simpler utilizable componentsthrough the action of enzymes 28. Achinewhu 3 reported that fermentation considerably decreased or eliminated sucroseand flatus-forming oligosaccharides in the oil bean seed.

3.3. Transportation and distribution of products

A major concern in food processing is the state of the food product at the point of consumption. This is the reason forextensive shelf-life studies carried out on processed foods. Nutrient losses that are recorded during post-processingstorage can be quite significant. As earlier pointed out, most underutilized oilseeds contain highly unsaturated fatty acidsthat constitute more than 80% of total fatty acids in the oil. Unfortunately, there is no record of anti-oxidants being usedduring the processing of these seeds in the local areas where they are extensively consumed. Oxidation of the oils duringstorage would definitely constitute a great avenue for nutrient loss. Apart from the loss in nutrients there are bound to beoff-flavours and off-colours, the development of which lowers the market value and desirability of such products. Shelf-life studies of a roasted oilseed product over an 8-weeks period showed increased peroxidation of the oil 21. Inview of the fact that there are serious transportation problems in the developing countries, one can better appreciate thecolossal loss in product quality experienced in those areas. That is why the drive for sustainable development in the thirdworld emphasizes efficient transportation and product distribution systems. Since most of the oilseed products are in thefermented form, it is known that the organisms continue to act until the final point of use. This of course makes theproduct susceptible to spoilage and loss in quality, especially because the fermentations are still at the wild uncontrolledstage. The fermented product of oil bean seed, for instance, has a very short shelf-life and gets bad within two weeks ofproduction. In most cases the stock is not exhausted within that period, and they continue to sell until stock is sold out. Thequality loss in such cases can be quite significant. Some conditions during transportation and distribution of products could initiate chemical changes in the food product.Such conditions include heat and high relative humidity. Most of the legume-based products are in moist form and suchconditions are not conducive for their transportation. The cowpea products, akara and moinmoin, for instance, are highlysusceptible to both oxidative and hydrolytic reactions which lead to serious off-flavours.

4. Appropriate Processing Techniques

4.1. Cooking

Cooking is one of the most common processing techniques used for legume seeds. During the cooking of legume seeds,two simultaneous processes occur inside and outside the cotyledon cells. Gelatinization of intracellular starch anddenaturation of proteins are accompanied by softening of the seeds as a result of plasticization or partial solubilization ofthe middle lamella, which leads to separation of individual cotyledon cells. Legume seeds require a relatively long cookingtime, ranging from 1 to 6 h. The cooking time depends primarily on the softness of the cooked seeds, using thumbpressure. As the cooking process depends on water imbibition and rate of heat transfer the size, composition and structure oflegume seeds have a large influence on the cooking time. Therefore, any preliminary processing that causes changes inthe characteristics of the legume affects the cooking properties. For example, dehulling or abrading modifies the compositionand structure of the seed because of the different distribution of seed components and differences in structure within thecotyledon 46. In a study on chickpeas and wrinkled and smooth peas, it was observed that the hardness of the seedsdecreased continuously during cooking for up to 110 min., while the gelatinization of the legume starch was completedafter cooking for 70 min. 45. Retrogradation of starch in the legume seeds occurred relatively quickly during cooking andwas promoted by extended cooking. Onigbinde and Onobun 64 observed that intensity of browning increased significantly (p<0.05) in cowpea (Vignaunguiculata) after boiling. In the light of the fact that the most popular method of preparing cowpea for human consumptionis by boiling in excess water until it becomes soft to touch, cooking time has been reduced among Nigerian consumers bythe addition of potash or natron. Potash helps to soften the cotyledons and at the same time raise the potassium level inthe seed product. Cooking has also been found to greatly reduce the content of flatus-forming oligosaccharides in legumeseeds. The soaking of seeds in tap water or sodium bicarbonate solution for 12 h, followed by cooking, caused losses of


sucrose, raffinose, stachyose and verbascose to the extent of 45.6-64.2, 78.8-100, 43.3-62.8 and 41.9-60%; respectively1. All the legume seeds that are processed via fermentation have cooking as a major processing step. During cooking andsoaking/washing of the seed cotyledon during fermentation, many potential toxins and anti-nutritive factors, such asprotease inhibitors (especially trypsin inhibitors), phytates, tannins, haemagglutinins and alkaloids are destroyed orsignificantly reduced. Kingsley 44 observed that trypsin inhibitor activity of raw African oil bean seeds decreased duringcooking by 98% while subsequent fermentation increased the activity of the cooked sample by 1%. Some aids are usually used or added when cooking legumes in order to reduce the cooking time and improve on thecooking characteristics. Bueno et al. 15 used sodium bicarbonate, trisodium phosphate and ammonium carbonate ascooking aids for kidney beans, as combined inorganic salts at a concentration of 0.5% each. No thought is cast on theimpacts of such additions on the overall quality of product, especially with regard to nutritional status.

4.2. Roasting

The purpose of roasting is to promote flavour and texture changes that ultimately increase the overall palatability of theproduct. Roasting involves a number of physico-chemical changes, including heat exchange, chemical reactions anddrying. Heat is transferred to the product through the roasting medium. Heat absorbed by the product initiates severalchemical reactions, the control of which is critical for optimizing flavour, colour and texture. Free amino acids andmonosaccharides are essential flavour precursors for the development of unique flavours during roasting and they giverise to pyrazine compounds via Maillard sugar-amine-type reactions. During roasting, food is exposed to circulating hot air and heated by convective heat transfer. In the roasting ofhazelnuts, Saklar et al. 73 observed that air temperature was always the most important independent variable affectingquality characteristics, significantly. Non-enzymatic reactions during the roasting were very important and they impartedthe characteristic roasted flavour and colour to the product. Hazelnuts contain 66.7% oil and 5.02% moisture. Roastinghas also been applied to conophor nut 24 but it increased the concentration of anti-nutritional factors, especially tanninsand phytates. The process also lowered the functional ability of the oilseed as a food gel. Roasting has been applied to African oil bean seeds (the traditional form of processing is fermentation to give acondiment and local snack) as a post-fermentation step 21 and as an alternative processing technique to fermentation 32,with quite remarkable nutritional and storage advantages, over the fermented commercially-available product. The twoapproaches to roasting are presented on Fig. 1. The preparatory stages during roasting are important and must result insignificant reduction in anti-nutritive and toxic factors. Otherwise, these undesirable components will be concentratedleading to their increased presence on a dry weight basis.

Figure 1. The steps in roasting of African oil bean seeds 21, 32.

Prepared seedslices

Drying 1000C, 90 min Soaking in 5% brine 400C,2h

Roasting 2000C, 90 min Fermentation 350C, 72h

Drying 600C, 8h

Roasted product Roasting 1500C,30min


4.3. Fermentation

In the developing countries, fermentation has been effectively employed in the utilization of hitherto unknown wild forestseeds that contain substantial quantities of nutrients but with significant concentrations of toxic and anti-nutritive factors26.Most of these seeds are not edible in the raw form because of the presence of astringent and toxic components. However,the process of fermentation which involves hydrothermal treatment, washing, soaking and microbial breakdown of complexconstituents, has made it possible for the nutrient potentials of these seeds to be harnessed. Uzogara et al. 81 reported thatsome of the benefits of fermentation include increased shelf-life, removal of toxins, improvement in texture, taste andflavour, as well as increased nutritional value. Steinkraus 80 enumerated five major roles played by fermentation in food processing as (i) enrichment of human dietthrough development of a wide diversity of flavours, aromas and textures in food, (ii) preservation of substantial amountsof food through alkaline fermentations among others, (iii) enrichment of food substances biologically with vitamins, proteins,essential amino acids and essential fatty acids, (iv) detoxification during food fermentation processing and (v) a decreasein cooking times and fuel requirements. Table 6 shows the effect of fermentation on some vitamin B components of seedsof Citrullus vulgaris and Pentaclethra macrophylla. Fermentation enhanced the concentration of these vitamins in theseeds.

Some of the major products of legume fermentation in the third world include iru and dawadawa from African locustbean seed 11, 60, ugba or ukpaka from African oil bean seed 23, 52, ogiri from castor bean seed 10, okpeye from mesquiteseed (Prosopis africana) and variants of the above products from some wild-gathered seeds. The fermentation isusually the solid-substrate type, with some in form of seed mash (e.g. ogiri) and others in form of seed slices (e.g. ugba)or even whole cotyledons (e.g. iru). Oilseeds are widely recognized as excellent bases for food condiments, and this widerecognition borders on their high nutrient potentials and savoury flavours. Dawadawa, for example, constitutes more than5% of the daily protein intake among the Hausas of Nigeria 11.

5. The Major Quality Changes

The changes in quality during the processing of underutilized legumes and oilseeds could be positive and/or negative,depending on the final use to which the products are put. There are nutrient losses, reduction in anti-nutritional and toxicfactors, and flavour and colour changes. There is also the impact of water quality in the processing and quality of the finalproduct. The major focus, however, is on the nutrient losses. The overall quality is important to justify the call for the useof these seeds as supplements and functional ingredients.

5.1. Nutrient losses

The processing of underutilized legumes and oilseeds results in significant nutrient losses because of the rigorous heattreatment required to make them truly edible for use by the human body. Nutrient losses have been recorded throughleaching into processing water, destruction by heat or acid/alkaline environments and degradation by enzyme action.Kingsley 44 reported the leaching of proteins into the cooking liquor during the cooking stage in the production of ugbafrom African oil bean seeds. It is known that proteins generally leach out into processing water. Significant reductions in nutrient contents have been observed with processing of particular underutilized oilseeds. Forexample, crude protein content of African oil bean seed decreased with roasting from 334.18 g kg-1 DM in the raw seedto 269.42 g kg-1 DM in the roasted product 32. The same process reduced ash content (which is an indication of mineralcomposition) from 40.24 g kg-1 DM to 15.77 g kg-1 DM. In the fermentation of Pentaclethra seeds, oil content was

Concentration (mg 10-2 g-1 dry wt.)

Melon seed African oil bean seed

Component

Raw Fermented Raw Fermented

Thiamin 0.08 0.23 1.1 2.2

Riboflavin 0.12 0.22 0.11 0.3

Niacin 3.2 3.2 2.0 3.2

Table 6. Effect of fermentation on the thiamin, riboflavin and niacin contents of melon seed and African oil bean seed 4.


reduced to 36.3% dry wt. from 41.4% 23. Comparatively, some processing conditions tend to exert more severe nutrientlosses than others. For instance, roasting conophor nuts significantly lowered the functionality of the see protein comparedto cooking 24. There are also quite significant losses in the B-complex vitamins. There are losses of thiamin, riboflavin andbiotin during the processing of these seeds.

5.2. Reduction in levels of anti-nutritional and toxic factors

The nutritive quality or digestibility of plant proteins is affected by the presence of anti-nutritional factors such as proteaseinhibitors, especially trypsin and chymotrypsin inhibitors, α-amylase inhibitors, pherolic compounds and phytates. Proteaseinhibitors may inhibit growth, reduce digestibility and cause pancreatic hypertrophy. Phytate, a common constituent ofplant tissues, has been shown to have an inhibitory action against a proteolytic enzyme. Tannins are known to impairutilization of proteins in human and animal diets by binding with protein. Growth retardation has been observed in animalsfed diets containing tannins. Gossypol, a polyphenolic compound, is a constituent of cotton seeds and is toxic to monogastricanimals. Also some factors appear to be the dominant anti-nutrients in certain seeds. In a study of wild and cultivated accessionsof cowpea (Vigna unguiculata L. Walp.) with regard to levels of trypsin and chymotrypsin inhibitors and lectins, it wasfound that the anti-nutritional factor content in cowpea is to be explained principally by trypsin inhibitors, while lectins arenot present in great quantities 49. Table 7 shows the impact of fermentation on the levels of some anti-nutritive factors in African oil bean seed. Therewas significant reduction in the levels of those factors in the respective research works. Fermentation involves preparatorystages of cooking, size reduction, soaking and washing. These processing steps contribute to the significant reduction inthe levels of the seed alkaloids and phenolic compounds. Roasting also has been shown to reduce the levels of anti-nutritional factors if it is done after the preparatory stages of cooking and soaking 32.

5.3. Colour changes and role of enzymes

The changes in colour are an integral part of food processing, but the change could be desirable or undesirable. Oneundesirable change is enzymatic browning. Browning during storage and processing is a significant problem in the foodindustry and is believed to be one of the main causes of quality loss during postharvest handling 56. Browning is awidespread phenomenon that causes loss of quality and is of major economic importance. It can cause deleteriouschanges in the appearance and organoleptic properties of the food product, resulting in reduced consumer acceptanceand economic value. Polyphenol oxidase in the presence of oxygen catalyzes the oxidation of phenolic substances to quinones. Thesequinones spontaneously polymerize to form a brown pigment. Polyphenol oxidase has been studied in the broad bean andthe field bean 37, 69 as well as in some other legumes. Enzymatic browning is a major problem in African oil bean seedprocessing. The desirable light-brown colour of the fermented product is most often replaced by a dark brown andsometimes blackish pigment. This undesirable browning is usually experienced during the natural inoculation stage. In thetraditional fermentation, prepared seed slices (cooked and soaked) are spread on matted surfaces for upwards of 16 h toprovide enough inoculum for the subsequent fermentation 32. By the time fermentation sets in, the colour would havechanged. During roasting of oilseeds and legumes such as African oil bean seed and conophor nut, Maillard reactions take placebetween the sugar and amino ends giving rise to furfurals and other pyrazine derivatives, as well as some other flavourants.

Table 7. Impacts of fermentation on some anti-nutritive factors in African oil bean seeds.

Enujiugha and Olagundoye 32 a* Kingsley 4 b*

Anti-nutritive factor Raw Fermented Raw Fermented

__________________________________ _______________________________

Tannins 0.81 0.29 9.50 4.10

Phytin 2.48 1.47 11.20 2.70

Phytate phosphorus 0.70 0.41 3.20 0.80 a Three days fermentation (results expressed as g 10-2g-1DM)

b Five days fermentation (results expressed as g kg-1 DM)


Brown colour develops during the process and is desirable in the product. On the other hand anthocyanidins are colourpigments which are abundant in fruits, vegetables and legume seeds. During processing the application of heat (moist ordry) brings about their degradation and off-colour development. Some undesirable colours are also imparted, if the product is fermented, by wild microbial contaminants. An exampleis the reported greenish colour in fermented African oil bean seed product imparted by the action of Pseudomonaschlororaphis 52.

5.4. Impacts of water quality

Most food-related hazards have been traced to the contamination of water used in production or preparation of suchfoods prior to consumption. Usually water used in food production and preparation should be of drinking water standard.In this regard, studies have shown that drinking water supplies in most developing countries are polluted at the treatmentsites and along distribution systems at points of abstraction or use by consumers 30, 71. This means that improper watertreatment and post-treatment contamination have both contributed to the contamination of foods via water use. Manywater treatment plants designed for and constructed in many third world countries have inherent operational problems.These include problems of sedimentation tanks which cannot be drained, sand filters which are prone to flooding andwhich produce inconsistent effluent quality, non-functioning chlorinators and non-provision, or inadequate provision, oflaboratory facilities 61. The implication of this is that treated water drawn from taps even within the premises of mosttreatment plants in developing countries are not entirely devoid of contamination. The quality of water used in processing a particular food material definitely affects the quality of the final product.Water as a part of the food external and internal environments could be modified (or treated) or channeled in such a waythat its interaction with other food components would produce positive nutritional changes. As it is not possible to excludethe environment from food production, it is nonetheless pertinent that the interaction of food with the environment shouldnot jeopardize human health via quality loss 22. There is no gain saying the fact that the quality of water used in processinga particular food has direct bearing on the quality and safety of the final product. Heavy metal presence in food processing water presents a special problem because of the implications for humanhealth. Tropical waters (both surface and ground waters) are known for the high heavy metal load. Iron content is high inground waters and lead poisoning has occurred in some cases. That of lead is particularly noteworthy, because a changein pH of 1 unit could result in an increase of lead by a factor of 2.1 in the blood of an exposed organism 31. The processing techniques of most underutilized legumes and oilseeds are still at the traditional household level. Morerecently some small-scale cottage industrial concerns are beginning to adapt the local appropriate technologies. Theadequacy of water quality is not the concern of this level of processing; especially in the third world. Therefore, qualityloss via water use during processing is expected.

5.5. Flavour changes

The term flavour is a compound word consisting of aroma and taste. However, it could be used to refer to either aromaor taste separately. If a processed product has an unacceptable taste and unpleasant smell, its value will obviouslydepreciate. This implies that to the average consumer, the major quality loss is immediately observed and measured interms of flavour depreciation. Legumes generally possess beany flavour which makes them objectionable in food systems,especially where they are used as functional ingredients. This has been a major limitation in the production of milk andpasta products from the seeds. Additionally, most underutilized oilseeds have astringent tastes when improperly processed,as a result of the presence of saponins, alkaloids and polyphenols. Astringency and beany flavour have concertedlylimited the use of the less-common crop seeds to the rural environments. On the other hand, some processing operations have immensely contributed to flavour enhancement in legume-basedproducts. For example, subjecting fermented African oil bean seed product to roasting in a kiln has produced a highlyflavourful bread spread which was overwhelmingly rate high by a panel of 50 judges 21. African oil bean seed in thefermented form is used as a meat analogue in local dishes to replace scarce animal protein in parts of West Africa 52. Thisis because of its pleasant meaty flavour, which seems to be more pronounced with roasting. There are cases of off-flavour development in the processing of oilseeds. Most of these seeds are high in theircontentsof unsaturated fatty acids. Oxidative and hydrolytic rancidity reactions could be major problems during shelf storage.


6. Current Efforts at Reducing Quality Losses

Attempts are made in different parts of the world to reduce loss in quality during processing of legume seeds. In thecooking of beans, for example, the cooking water is not drained off if the end product is porridge. Even if the cookedseeds are to be used otherwise, the cooking liquor (or bean broth) is added to fortify the nutrients in the product, thusminimizing loss. However, studies have shown that when beans are consumed together with the cooking liquor, theirdigestibility is lower than when they are consumed alone, a fact which may be accounted for by the amount of tannins inthe broth 20. For some other situations, processing steps have been adjusted to minimize loss. In the traditional processingof cowpea into moinmoin, for instance, there is inevitable loss of protein through leaching into the cooking water due tothe nature of process involved. This waste channel has been blocked through the use of steam instead of boiling water. Enzymatic browning has been effectively curbed in legume processing. Several methods have been developed toinhibit browning during processing using chemical additives 50. However, the problem with some of these additives is thatthey are oxidized irreversibly and they do not meet the shelf-life requirements without special packaging which may notbe affordable in a third world situation. The traditional processing of legumes and oilseeds includes some form of boiling.To shorten cooking time and increase effectiveness, potash or natron is commonly added. This helps to soften the seedconsistency faster and at the same time prevents browning. Enzymatic browning may be delayed or eliminated byremoving the reactants such as oxygen and phenolic compounds or by using polyphenol oxidase inhibitors. Germination has been applied to legume seeds prior to processing to reduce quality losses. Germination brings aboutdecrease of phytic acid (through the action of endogenous phytase) and degradation of trypsin inhibitor activity in theseeds. It also results in increase in the relative content of both essential and non-essential amino acids. Past studies haveshown that germinating the seeds prior to processing could increase the digestibility of the seed nutrients as well as thefunctionality of the seed proteins 29. Germination has been linked to degradation of sucrose and raffinose family ofoligosaccharides in cowpea, and the removal of toxic alkaloids in African oil bean seeds. Process optimization goes a long way in reducing losses in quality during processing generally. The processing of mostunderutilized legumes and oilseeds is still at the traditional household level with attendant problems of variability andirreproducibility. Products obtained from the same processor using the same steps and seed varieties have shown unexplainedwide gap in nutrient content. The introduction of starters in the local fermentation encourages optimization 52. Thepractice of spreading prepared seeds for natural inoculation could be discouraged in the rural areas if the starters aremade commercially available. The only problem is that many of the advancement in upgrading the traditional processingare still at the laboratory stages. Quality losses are reduced during processing through the careful treatment of the processing water and hygienichandling of processing equipment. Groundwaters, especially boreholes, are encouraged in the third world environmentbecause of their relative purity. Apart from the fact that tropical groundwaters are high in iron, the chances of microbialcontamination and lead poisoning are greatly minimized.

7. Conclusions

The dynamics of quality changes in the processing of underutilized legumes and oilseeds have been highlighted in thischapter. Emphasis has been laid on the loss of nutrients, flavours and colours, and the reduction of anti-nutritional andtoxic factors. The processing techniques and procedures are effective in reducing anti-nutritional factors, while at thesame time contributing to significant nutrient losses. However, there are efforts currently being made to reduce nutrientlosses. Quality plays a very important role when entrepreneurs are looking for new opportunities. It relates to the product andprocess characteristics, and the product and process quality are influenced by the availability and reliability of equipment,information services, training and organization. In the processing of underutilized legumes and oilseeds, no sophisticationin equipment or process is encountered, and there is no reproducibility in product qualities.

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quality dynamics in the processing of underutilized legumes and oilseeds

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