Detoxification of a toxid variety of Jatropha curcas using heat and chemical treatments

Eroarome M. Aregheore, K. Becker, H. P. S. Makkar: Detoxification of a toxid variety of Jatropha curcas using heat and chemical treatments, and preliminary nutritional evaluation with rats. In: S. Pac. J. Nat. Sci.. 21, 2003, p. 50 - 56 [Jatropha curcas meal, phorbolester, lectin, food intake, growth rate, PER, TI, rat.].


Makkar, Dr. Harinder P.S., International Atomic Energy Agency, India Field of research: Animal production Host: Prof. Dr. Klaus Becker Universität Hohenheim
E. M. Aregheore, K. Becker, Harinder P.S. Makkar: Detoxification of a toxic variety of Jatropha curcas using heat and chemical treatments, and preliminary nutritional evaluation with rats. In: S. Pac. J. Nat. Sci. 21, 2003, p. 50 - 56 [Jatropha curcar meal, phorbolester, lectin, food intake, growth rate, PER, TI, rat.].

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Products from little researched plants as aquaculture feed ingredients
George Francis1, Harinder P. S. Makkar2 and Klaus Becker1
http://www.fao.org/DOCREP/ARTICLE/AGRIPPA/551_EN.HTM1Department of Animal Nutrition and Aquaculture, Institute for Animal Production in the Tropics and Subtropics, University of Hohenheim (480), D 70593 Stuttgart, Germany.
2 Animal Production and Health Section,
International Atomic Energy Agency, P.O. Box 100,
Wagramerstr. 5, A-1400 Vienna, Austria.
Corresponding author: Prof. Dr. Klaus Becker, Department of Animal Nutrition and Aquaculture, Institute for Animal Production in the Tropics and Subtropics, University of Hohenheim (480), D 70593 Stuttgart, Germany.
Tel. 0049 711 4593158, Fax. 0049 711 4593702, email - kbecker@uni-hohenheim.de
Keywords: Aquaculture feeds, plant-derived ingredients, less researched plants, nutritional quality, antinutritional factors
Abstract
The production of aquaculture feeds is expected to rise from the current level of about 13 million metric tonnes (mmt) to about 30 mmt in 2010. It is estimated that a minimum of 3 mmt of fishmeal equivalent, alternative protein sources will be required in the aquaculture industry yearly by the year 2010. The selection of plant-derived, protein sources for use as animal feeds should take human food security interests into account. It would be highly desirable if products from plants that can grow on degraded soil and require lower external energy subsidies could be used. Four examples of such plants, Jatropha curcas, Moringa oleifera, Sesbania spp. and Mucuna pruriens, are discussed here. These plant species are capable of growing on degraded lands, under stressful environmental conditions, and still sustain a reasonable production of nutrient -rich products with potential as fish feed ingredients. Alongside their potential in the production of feed ingredients, these species can help reclamation of degraded areas. Furthermore, their development may be aided by and profit from the national, international and private funding that is being channelled into wasteland reclamation. In addition to the nutritional quality of these plant products, the presence and detoxification procedures for the various anti-nutrients are also discussed.
Introduction:
As the World's human population continues to expand beyond 6 billion, its reliance on farmed fish production as an important source of protein will also increase (Naylor et al., 2000). Projections of world fishery production in 2010 range between 107 and 144 million tonnes (FAO, 2000). Most of the increase in fish production is expected to come from aquaculture, which is currently the fastest growing food production sector of the world. By the year 2030, aquaculture will dominate fish supplies and more than half of the fish consumed is likely to originate from this sector (FAO, 2000). The projected total production of feeds for aquaculture in the year 2010 range from 25 million metric tonnes (mmt; Tacon and Forster, 2001) to 32.6 mmt (IFOMA, 2000) against an approximate production estimate of about 13 mmt in the year 2000. Requirements for aquaculture feeds are likely to be further increased by an increasing trend towards the intensification of farmed production of omnivorous species in Asian countries, particularly China.
The proportion of global fishmeal production used in fish feeds has increased from 10 to 35 per cent in the last fifteen years (Hardy, 2000). Predictions of fishmeal needs for aquaculture feeds in 2010 are 2.8 mmt, approximately 44 per cent of the ten-year average global fishmeal production of 6.5 mmt. This is in spite of the predicted decrease from current levels of the percentage of fishmeal included in the feed of all, major aquaculture species. Hardy (2000) estimates that this amount of fishmeal would be approximately 1.3 mmt less than that required had there been no decline in fishmeal use in fish feeds. At least this amount of fishmeal equivalent alternative protein sources (to the order of approximately 3 mmt) would be required in the aquaculture industry yearly by the year 2010.
The need to identify appropriate, new sources of protein is therefore imperative. It is highly desirable that the selected protein sources do not conflict with human food security interests. It is worth mentioning in this context that fish that could form human food are converted into fishmeal for use in animal feeds in countries such as Peru for economic reasons. The importance of the development of non-human-food grade feed resources whose growth can cope with the projected and desired fast growth of the sector has been stressed (Tacon and Forster, 2001). Recent outbreaks of diseases such as BSE in livestock, arguably caused by feeding animal products to animals that do not normally consume them, have cast doubts regarding the suitability of feeding animal-derived proteins to non-carnivorous species. Plants therefore become the preferred sources of protein for these species. There have been a number of efforts in the past decades to test the suitability of a number of plant-derived protein sources for various, popular aquaculture species. Many of these have concentrated on species such as soybean, rapeseed (canola) meal, sunflower seed meal, cottonseed meal, peanut meal, wheat and corn gluten. Most of these plants require environmental and soil conditions and energy subsidies that restrict the scope for increasing their production. With the prospects of increasing direct human demand for nutrients derived from these sources they could not be expected to contribute greatly towards satisfying demands from new sources such as the aquaculture feed industry.
There is, therefore, a need to examine other plants that can grow on degraded soil and require lower external energy subsidies. Alongside their potential in the production of feed ingredients, these species can help reclamation of degraded areas. Furthermore, their development may be aided by the national, international and private funding that is being channelled into wasteland reclamation. According to World Resources Institute (WRI) estimates, there were about 1.2 billion hectares of eroded land (11 per cent of the Earth's vegetated surface) in 1990. Since 1990, an additional 5 to 6 million ha per annum are lost to severe soil degradation, again according to WRI estimates. Conventional, agricultural production would eventually become nonviable in a large proportion of these lands. The International Food Policy Research Institute (IFPRI) data indicate that soil degradation has already significantly lowered the productivity of 16 per cent of farm-land, world-wide. Several, hardy plant species can assist in reclamation of eroded land by increasing the organic matter content of the soil and acting as carbon sinks and dust traps. Alley-cropping with these plants would enable inter-cropping with annuals such as vegetables a few years after initial planting. These multipurpose plants and their products, taking their availability and potential for growth into account, could be considered as protein sources in feeds after adequate treatment. Reclamation of eroded and unproductive land would be an additional benefit. Asia, which accounts for more than 90 per cent of global aquaculture production of global, aquaculture production, is estimated to have 11 per cent wasteland, 15 per cent lightly or moderately degraded and 3 per cent strongly or extremely degraded land according to UN figures. China and India, that together account for about 75 per cent of the total aquaculture production, are listed to beindicated as being severely affected by land degradation. There exist therefore possibilities for regional and local integration of feed ingredient production from wasteland and their use in aquaculture production.
Plants that are capable of resisting adverse soil and climatic conditions often contain high levels of anti-nutritional, toxic principles that keep herbivores at bay. Utilisation of these plants as animal or fish feeds would therefore depend, not only on their nutritional content, but also the presence and level of various toxic principles and methods of detoxification. The purpose of this paper, therefore, is to highlight lesser-utilised and researched plant species capable of growing on degraded lands under stressful environmental conditions and still sustaining a reasonable production of nutrient rich products having potential as fish feed ingredients. The levels of and detoxification procedures for the various anti-nutrients present are also discussed.
Prospective plant species
1. Jatropha curcas
General information
Jatropha curcas (L) or physic nut is a multipurpose and drought-resistant, large shrub or small tree. Although a native of tropical America, it now thrives throughout Africa and Asia. It grows in a number of climatic zones in tropical and sub-tropical regions of the world and can be grown in areas of low rainfall. Jatropha is easy to establish, grows relatively quickly and is hardy. A perceived advantage of Jatropha is its ability to grow on marginal land and to reclaim and restore eroded areas. Various parts of the plant hold potential for use as animal feed, inclusion in medicinal preparations and as a source of honey. If grown on barren lands, Jatropha could add to the removal of carbon from the atmosphere, and the build up of soil carbon.
Seed production ranges from about 0.1 t / ha / year to over 8 t / ha / year (Heller, 1996). The seed yield reaches a peak after about five years of growth. This range in production may be attributable to variation in rainfall and soil nutrient status. The plant takes between four and five years to yield when cultivated on poor soil, with no irrigation and planted in full sunlight but much less time is required under optimal rainfall and soil conditions. Once established, plantations yield for between 30 and 35 years. Jatropha can also be grown as a hedge plant. Henning (1996) estimated seed production of 0.8 - 1.0 kg of seed per square meter from Jatropha hedges in Mali, equivalent to between 2.5 t / ha / year and 3.5 t / ha / year respectively.
Nutritional value of the seeds
Jatropha has been investigated mainly as a potential source of oil that has been recognised as an adequate substitute motor fuel. The seed kernel of the plant contains about 60 per cent oil. The seed cake remaining after oil extraction is an excellent source of plant nutrients (Table 1). However the presence of high levels of antinutrients (Table 2) prevents their use in animal feeding. Phorbolesters (phorbol-12-myristate 13-acetate) have been identified as the major toxic principle in Jatropha (Makkar and Becker, 1997a). Varieties of Jatropha plants where phorbolesters are almost absent have been identified in Mexico. These offer promise for inclusion of products from these plants in animal and fish diets. The nutritional composition of the extracted seed meal from the non-toxic variety (from Veracruz, Mexico) appears to be similar or even superior to the toxic variety (from Cape Verde and Mexico) (Table 1). Non-protein nitrogen formed only 7.8 - 9.0 per cent of the total nitrogen in the Jatropha meals suggesting the presence of high levels (~90 per cent) of true protein (Makkar et al., 1998).
The level of essential amino acids of the defatted, kernel meal of the non-toxic variety (see Table 10) are higher than that of FAO reference protein except for lysine (Makkar and Becker, 1999a). A comparison between Jatropha meal and soybean reveals an almost similar pattern for all essential amino acids except lysine and sulphur-amino acids; these are lower and higher respectively in Jatropha meals.
In vitro, digestible organic matter and metabolisable energy of the non-toxic Jatropha seed meal (77.3 per cent and 10.7 MJ/kg DM respectively) were lower than those of soybean meal (87.9 and 13.3 MJ/kg DM respectively), but comparable with those of cottonseed, rapeseed and sunflower meal (Makkar and Becker, 1999a). The pepsin soluble fraction of the total nitrogen has been reported to be 94 - 95 per cent (Aderibigde et al., 1997). The seed meal of the non-toxic Jatropha could thus be regarded as having high potential for use as a feed supplement for fish and monogastrics.
Antinutrients
Even though the Mexican, non-toxic varieties lack the most potent toxin, phorbol esters, other antinutrients such as trypsin inhibitor, lectin and phytate are present in significant amounts (Table 2), and their levels are similar to those in the toxic varieties.
Moist heating of seeds almost completely inactivated trypsin inhibitor activity and decreased lectin activity (Makkar and Becker, 1999a). In addition to reducing heat-labile, antinutritional factors such as trypsin inhibitors and lectins, heat treatment should also increase protein digestibility. Furthermore, moist heating should render the seed cake from the non-toxic variety usable in fish diet. On the other hand, heat treatment followed by aqueous methanol extraction could result in elimination of most of the antinutrients and toxins from the toxic variety. The meal treated in this manner has been found to be innocuous to rats (Makkar and Becker, 1997b).
Fish feeding trials
Carp (Cyprinus carpio) fed diets containing the non-toxic, fat free Jatropha kernel meal (23 per cent by weight of the dietfeed) showed lower body weight gains than fish fed a control diet based on fishmeal. However, a diet containing the same level of Jatropha meal heated for 15 min (at 121°C and 66 per cent moisture) and still containing appreciable amounts of trypsin inhibitors and lectins was found to yield the best performance (243 per cent weight gain compared to 303 per cent observed with the control treatment) among Jatropha containing feeds (Makkar and Becker, 1999b). It is possible that reduction of the amount of inclusion level (to around 15 per cent by weight) in feeds, extraction with water (to remove residual antinutrients and improve acceptability by the fish) and supplementation with lysine containing ingredients may facilitate better utilisation of this ingredient by fish although, more research will be required to confirm these suppositions.
2. Moringa oleifera
General information
Moringa oleifera Lam. or 'horse-radish' tree (so-called because of the taste of a condiment prepared from the roots) or 'drumstick' tree (arising from the shape of the pods), or `never-die-tree' is a multipurpose tree that thrives in both tropical and sub-tropical conditions. It is native to the sub-Himalayan regions of north-west India. This tree is now indigenous to many countries in Africa, Arabia, South East Asia, the Pacific and Caribbean Islands and South America, producing flowers and fruits continuously. Originally considered a tree of hot, semi-arid regions with annual rainfall 250 - 1500 mm, it has also been found to be well adapted to hot, humid, wet conditions with annual rainfall in excess of 3000 mm. Moringa can grow in a variety of soil conditions, from well drained sandy or loamy soils (which the plants prefer) to heavier clay soils. The tree is reported to be tolerant of light frosts and can be established in slightly alkaline soils up to pH 9. Currently, the young leaves and pods are used as vegetables, the oil extracted from kernels for culinary and industrial purposes, the water extract of the kernels as a water purifying agent, the seed cake as fertiliser, and various parts of the tree in traditional medicine (Foidl et al., 2001).
The tree is fast growing and high yielding (an estimated 3.0 t seed / ha compared to average yields of sunflower and groundnut of 2.0 and 0.5 t / ha respectively). It can also be planted for forage production under intensive farming conditions. Initial trials in Nicaragua have shown a high biomass production of up to 120 tons dry matter / ha / yr, in eight cuttings after planting 1 million seeds / ha (Makkar and Becker, 1999a). The plant starts bearing pods 6 - 8 months after planting but regular bearing commences after the second year. The tree bears for 30 - 40 years. The drought tolerant nature of the tree makes it particularly suited to those marginal areas where the costs associated with the cultivation and harvesting of other commercial crops are high.
Nutrient composition
The seed kernel contains, on average, 40 per cent by weight of oil, the fatty acid composition of which is similar to that of olive oil and could be used for both culinary and industrial purposes. The seed oil contains 9.3 per cent palmitic, 7.4 per cent stearic, 8.6 per cent behenic, and 65.7 per cent oleic acids among the fatty acids. Myristic and lignoceric acids have also been reported.
In addition to high macronutrient content (Table 3), moringa leaves and pods are also rich in vitamins and minerals. Leaves (100g) contain 440 mg Ca, 70 mg P, 7 mg Fe, 110 mg Cu, 5.1 mg I, 11,300 IU pro-vitamin A, 120 mg vitamin B, 0.8 mg nicotinic acid, 220 mg ascorbic acid, and 7.4 mg tocopherol per 100 g. Per 100 g, the pod is reported to contain 30 mg Ca, 110 mg P, 5.3 mg Fe, 184 IU pro-vitamin A, 0.2 mg niacin, 120 mg ascorbic acid, 310 mg Cu, and 1.8 mg I.
The high true protein content of leaves (23 per cent in DM, Makkar and Becker, 1997c), the high proportion of this protein potentially available in the intestine (Makkar and Becker, 1997c), the presence of adequate levels of essential amino acids (higher than the levels present in the FAO reference protein), and low levels of antinutrients indicate their high nutritional quality. The high pepsin soluble nitrogen (82 - 91 per cent) and the low acid detergent insoluble protein (1 - 2 per cent) values for the meal suggest that most of the protein in the meal is available to most animals (Makkar and Becker, 1997c). The meal is deficient in lysine, leucine, phenylalanine + tyrosine and threonine when compared to the standard FAO protein but the contents of sulphur-containing amino acids in these samples are much higher (see Table 10).
Antinutrients
Moringa leaves are free from antinutrients except for saponins and phenols (Table 4). The concentration of phenol is much below the toxic threshold levels for animals (Makkar and Becker, 1997c) and saponins were inactive as far as haemolytic properties are concerned. In addition to the antinutrients listed in Table 4, alkaloids are also present in kernel meals (root-bark have been found to have two alkaloids, moringine and moringinine; moringinine is known to stimulate cardiac activity, raise blood-pressure, act on sympathetic nerve-endings as well as smooth muscles all over the body, and depress the sympathetic motor fibres of vessels in large doses only).
Glucosinolates, lectins and alkaloids which form the major antinutrient substances in Moringa seed meal could be easily removed by water extraction (Makkar and Becker, 1999a). However, this method has the disadvantage of also removing some soluble nutrients. Solid state fermentation of the seed meal using Rhizopus oligosporus sp. could be considered as this mould has been found to degrade glucosinolates in defatted rapeseed meal (Bau et al., 1994).
Fish feeding trials
There are no studies so far which report utilisation of Moringa leaves or seed meal as fish feed ingredients. Preliminary results from a trial in our lab, where Moringa leaf meal was used in Tilapia nilotica feeds, indicate growth-reducing effects at high levels of inclusion of raw leaf meal. Moringa plant parts have the potential to be a supplier of macro and micronutrients in a fish feed derived from a mixture of plant products.
3. Sesbania spp.
General information
Sesbania sesban (L) Merrill is a short-lived fodder shrub or small tree. This legume can tolerate wide temperature ranges, acidic soils and waterlogging, as well as soil salinity. S. sesban grows rapidly and is useful as fodder and green manure. This species has long been used for feeding livestock and for soil improvement in India and Africa.
Productivity and nutrient composition
Biomass production of Sesbania sesban has been reported to be 4.8 t / ha and N in the above-ground biomass to be 0.1 t / ha (Creamer and Baldwin, 2000). S. aculeata yields in the range of 1 to 1.5 t / ha of seeds (see Hossain and Becker, 2001).
The crude protein contents of Sesbania species (Table 5) are higher than those reported for conventional legumes, such as chickpea, mungbean and cowpea. Sesbania sp. are, however, deficient in essential amino acids except for leucine, tryptophan and histidine (see Table 10). Sesbania sp. are generally a good source of essential fatty acids (Hossain and Becker, 2001).
The organic matter digestibility of Sesbania seeds ranges from 67 - 72 per cent and nitrogen solubility in alkali from 81 - 89 per cent (Hossain and Becker, 2002).
Antinutrients
A potent antinutrient in Sesbania sp. in addition to the ones presented in Table 6 are the non-starch polysaccharides (NSP). The seeds contain about 30 - 42 per cent endosperm, 75 per cent of which is made of an NSP, galactomannan (Chandra and Farooqui, 1979).
Soaking overnight in water followed by autoclaving has been shown to be effective in significantly bringing down levels of various antinutrients in Sesbania seed meal (Table 7).
Fish feeding trials
Hossain et al. (2001a, 2002) observed that untreated Sesbania aculeata seed meal could be added to the diets of common carp and Nile tilapia up to a level of 10 per cent without compromising growth. Even after considerably reducing various antinutrients by soaking and soaking + autoclaving (Table 8), growth in carp fed diets containing Sesbania seed meals could not reach levels observed with a fishmeal based diet (Hossain et al., 2001b). The NSP, galactomannan was later found to be the substance primarily responsible for retarding growth in both carp and tilapia (Hossain et al., 2001c and unpublished data). More research is needed as to whether removal of the galactomannan rich endosperm would enable higher inclusion of Sesbania seed meal in fish diets.
4. Mucuna pruriens
General information
The velvet bean (Mucuna pruriens., Fabaceae) is a weed-smothering, nitrogen-fixing herbaceous legume. It is found throughout the tropics, and has potential to help retain and even restore fertility on vast acreage of degraded farmland, including some extremely poor soils and tropical sites with highly adverse environmental conditions. The plant is drought resistant, tolerates acidity in the soil (pH 5 - 6.5) and is a fast grower during the first 4 - 6 months. Cultivation of velvet beans have been encouraged on a large scale by several non-governmental organisations in Africa and South America for reclaiming eroded soils, for use as green manure, and as an inexpensive source of organic fertiliser to build up organic matter.
Production and nutrient composition
Velvet bean has been reported to produce nearly 30 t / ha of fresh leaves and stems per year or about 0.1 t of N / ha per year. Production of green manure and reclamation of eroded soil have been its primary uses so far. In a normal harvest this bean generates around 0.8 to 2 t of seed per hectare making it one of the most productive legumes. Utilisation of these protein rich seeds is a further potential use of this plant. The beans (M. pruriens var. utilis) have been used as food by tribal peoples in the hilly regions of south-west India (Siddhuraju et al., 2000).
The nutrient composition of mucuna presented in Table 8 shows crude protein content to be higher than some commonly cultivated legumes. In vitro protein digestibility is also high (67 - 70 per cent) compared to other legume seeds. The contents of essential amino acids (see Table 10) such as valine, isoleucine, tyrosine, and phenyl alanine, leucine, and lysine were found to be similar to or higher than those of the FAO refernce pattern (Siddhuraju et al., 2000). Sulphur amino acids and tryptophan seem likely to be the limiting factors for inclusion of mucuna beans as a feed ingredient. The seed lipids are rich in unsaturated fatty acids (about 65 per cent) and have very high content of linoleic acid (48 per cent). The high amount of resistant starch (40% of the dry matter; Siddhuraju et al., 2000) may reduce nutritional value.
Antinutrients
Mucuna seeds contain a high level of antinutrients (Table 9). The most important among them are probably NSPs (11 per cent of dry matter) and L-DOPA (4.7 per cent of DM). L-DOPA itself may produce deletereous effects. In addition its degraded products produced during hydrothermal processing (polymeric quinones) may affect protein availability by binding to protein (Siddhuraju and Becker, 2001b). Soaking in CaOH2, rather than in water substantially reduced L-DOPA and total phenol content in mucuna seed meal (Ruíz Sesma, 1999). The resistant starch may become more available after hydrothermal processing.
A number of research projects have investigated the potential of mucuna (different varieties) as a feed for poultry, monogastrics, and ruminants, particularly in Mexico. Studies by Duque Díaz (1993) and Castillo (1996) indicate the suitability of processed Mucuna (12 h soaking followed by 2 h boiling, seed coat removal, sun drying, and grinding) feeds for adult chicken. Ruíz Sesma (1999) found that mucuna flour produced by crushing seed, followed by 24 h soaking in 4 per cent CaOH2, drying at 60ºC, and grinding, could form a pig feed ingredient.
Fish feeding trials
Common carp fed diets containing 13 per cent mucuna seed meal (white variety) showed no significant reduction in growth compared to fish fed a fishmeal based control (Siddhuraju and Becker, 2001b). It was found that hydrothermal treatment did not improve the nutritional quality of mucuna to carp even though it reduced most of the antinutrients (Table 9). The presence of L-DOPA by-products, L-DOPA metabolites and NSPs might have been the reason for the negative effects. Alkaline soaking followed by thermal treatment may improve the nutritional quality of mucuna meal for fish.
Limitations to the use of plant derived ingredients in fish feed
Acceptability
Plant ingredients, particularly those containing high levels of antinutrients have been found to have a bitter taste which could result in lack of acceptability of the feed. Soaking in water followed by drying has been shown to increase acceptance, and also rid the plant material of several toxic compounds. The disadvantage is that some soluble nutrients are also lost.
Nutrient inadequacy
Plant-derived proteins are conventionally deficient in amino acids such as lysine, methionine, cysteine and tryptophan. The amino acid composition of the various plants dealt with here, and some of their products are listed in Table 10. It can be seen that jatropha and moringa products have higher levels of one of the most commonly deficient amino acids (methionine) compared to soybean meal (among the most highly regarded plant protein sources). It should be mentioned here that soybeans have undergone considerable species betterment through breeding over the last several years and grow on highly enriched soil whereas the plants mentioned here have not and they grow on poor soils. There is thus scope for improving the genetic character and biological value of these plants through agronomic interventions. Synthetic amino acid supplementation have been effective in partially compensating for lower dietary levels in large stomached fish such as trout (Mambrini et al., 1999), whereas it is much less effective in the case of stomachless fish such as common carp (Becker, 1984; Murai, 1985). This group of fish happen to be the most important culture species, particularly in Asia. Plant products such as those obtained from jatropha and moringa that are rich in commonly deficient amino acids such as methionine could be used as a source of these amino acids in carp species.
The definitive amino acid requirements of fish are difficult to obtain. In most of the research papers, amino acid requirements are calculated from amino acid dose to growth response regressions. Many fish are known to use synthetic amino acids sub-optimally (see NRC, 1993 for references), and the requirement of individual amino acids depend on other factors such as digestibility of protein, and presence and availability of other amino acids (Lovell, 1998). The essential amino acid requirements presented in Table 11 are based on NRC recommendations (NRC, 1993). It can be seen that requirements for essential amino acids differ from species to species. There is therefore need to formulate diets keeping in mind the requirement of the fish species concerned. Since fishmeal has a superior quality as far as essential amino acid content is concerned, its complete elimination from feeds might adversely affect growth in most fish. A judicious mixture of different plant derived materials along with a minimal amount of fishmeal would seem to be the best choice in feed formulation to ensure nutrient adequacy and ready acceptance by the fish.
Antinutrients
As described in previous sections, most of the abovementioned plant-based nutrient sources contain high levels of various antinutrients. The most important among the antinutrients in plant-based material are glucosinolates, phytates, protease inhibitors, non-starch polysaccharides (NSP), saponins, tannins, lectins, and gossypols. Others such as phytoestrogens, alkaloids, cyanogens, mimosine, cyclopropenoid fatty acids, canavanine, antivitamins, and phorbol esters could also prove deleterious. From the fish feeding trials described above it is evident that common culture species do tolerate many of these antinutrients at inclusion levels of up to 15 per cent of plant-derived materials. The effects of antinutrients on finfish have been reviewed in Francis et al. (2001a). Hydrothermal treatment and soaking with water is efficient in removing high levels of antinutrients such as glucosinolates, protease inhibitors, lectins, tannins and saponins (see tables 7 and 9). Supplementing high phytate diets with the enzyme phytase have been found to increase availability of dietary phosphorous to various fish species (see Hardy, 2000). NSPs present in the diets could be neutralised to a certain extent by addition of enzymes such as glycanase (Hardy, 2000). Gamma-ray irradiation also holds some promise in neutralising the negative effects of certain antinutrients e. g. NSPs and saponins (Siddhuraju et al., 2002)
Some of the secondary plant compounds may even have beneficial effects when present in diets of fish in small amounts. For example, saponins have been found to promote growth in common carp and tilapia when present in the diets at 150 mg kg-1 (Francis et al., 2001b, 2002). Saponins might increase the digestibility of carbohydrate-rich foods because of their detergent-like activity, which reduces viscosity and thus prevents the normal obstructing action of such foods against movement of digesta in the intestine (the NSPs exert their antinutrient action by forming viscous clumps in the intestine, which obstruct the digestive process). Cyclical, short-term offers of trypsin inhibitors along with the diet have been shown to increase protein digestibility and growth performance in carp (Becker K., unpublished). Interactions among various antinutrients in a particular feed source may also have effects on their potency. Saponin-tannin, tannin-lectin and tannin-cyanogen interactions may reduce their individual toxic effects (see review by Francis et al., 2001a). These interactions may also result in effects that are more detrimental than those of individual antinutrients. More insights into the nutritional, physiological and ecological effects of antinutrients on fish need to be accumulated through studies using purified individual antinutrients and their mixtures in proportions similar to those in alternative nutritional sources in fish feeds. Such studies would provide data useful for designing optimum inclusion levels of plant-derived materials in aquaculture diets. Research should also be directed at: i) treatment methods that would neutralise the negative effects of the antinutritional factors and/or bring them down to harmless levels without affecting availability of other nutrients, ii) economic analysis in terms of cost:benefit ratio of incorporating the treated meal in fish diet, on which the use of these unconventional feed resources will be based, iii) exploitation of other lesser-known and lesser-researched seeds in fish diets, a collated information on some of these seeds is available in Makkar and Becker (1999a).
In conclusion, addition of any of the abovementioned plants/ plant products mentioned above beyond levels of 10-15 per cent replacement of fishmeal in the diet can be attempted only after adequate treatment of the material to reduce toxin levels and increase acceptability. More work toward techniques that would increase their nutritional value could prove to be profitable in many ways, although a cost-benefit analysis is called for in each instance.
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Table 1. Chemical composition of extracted meal (% dry matter) of the toxic and non-toxic varieties of Jatropha curcas

Toxic variety
Non-toxic variety
Crude protein
56.4
63.8
Lipid
1.5
1.0
Ash
9.6
9.8
Gross energy (MJ/kg)
18.2
18.0
Neutral Detergent Fibre
9.0
9.1
Source: Makkar et al. 1998
Table 2. Important antinutrients in seed meal of toxic and non toxic variety of Jatropha curcas
Component
Toxic variety
Non-toxic variety
Phorbolesters (mg/g kernel)
2.79
0.11
Total phenols (% tannic acid equivalent)
0.36
0.22
Tannins (% tannic acid equivalent)
0.04
0.02
Phytates (% dry matter))
9.40
8.90
Saponins (% diosgenin equivalent)
2.60
3.40
Trypsin inhibitor (mg trypsin inhibited per g sample)
21.3
26.5
Lectins (1/mg of meal that produced haemagglutination per ml of assay medium)
102
51
All data are on dry matter basis,
Source: Makkar et al. 1998
Table 3. Chemical composition of Moringa oleifera parts (% dry matter)
Substance
Leaves
kernels
Fat free kernel meal
Crude protein
26.4
36.7
61.4
Lipid
ND
41.7
ND
Ash
8.87
3.8
5.65
Neutral detergent fibre
1.51
4.8
8.2
Gross energy (MJ/kg)
19.35
26.7
19.4
Source: Makkar and Becker 1997c.
Table 4. Important antinutrient factors present in Moringa oleifera parts
Substance
Leaves
Kernels
Fat free kernel meal
Total phenols (% tannic acid equivalent)
4.4
0.02
0.04
Tannins (% tannic acid equivalent)
1.2
ND
ND
Saponins (% diosgenin equivalent)
8.1
1.1
1.4
Phytate (% dry matter)
2.1
2.6
4.1
Lectins (1/mg of meal that produced haemagglutination per ml of assay medium)
ND
Variable (15/66.5/250)
Variable (15/66.5/500)
Cyanogenic glycosides (%)
ND
0.5
1.3
Glucosinolates (mmol/g)
ND
46.4
65.5
ND - not detected
Source: Makkar and Becker 1997c.
Table 5. Proximate composition of different Sesbania seeds (% of dry matter)
Seeds
Crude protein
Lipid
Ash
Crude fibre
Nitrogen Free Extract
Gross energy (kJ g-1)
S. aculeata
33.1
6.0
3.9
10.9
46.1
20.0
S. rostrata
32.0
4.7
4.0
11.8
47.4
19.2
S. sesban (ILRI no. 10865D)
32.3
5.0
2.7
15.5
44.6
19.8
S. sesban (ILRI no. 15019D)
29.1
6.0
3.3
15.8
45.8
20.0
Source Hossain and Becker, 2001
Table 6. Antinutrients present in seed meals of Sesbania species
Component
Sesbania aculeata
Sesbania rostrata
Sesbania sesban (1)
Sesbania sesban (2)
Total phenols (% tannic acid equivalent)
3.08
2.96
4.85
5.95
Tannins (% tannic acid equivalent)
2.25
1.99
1.97
2.02
Phytates (% dry matter)
2.16
1.89
2.35
2.37
Saponins (% diosgenin equivalent)
0.52
0.50
1.46
1.26
Trypsin inhibitor (mg trypsin inhibited per g sample)
5.25
5.64
14.01
13.70
Lectins (1/mg of meal that produced haemagglutination per ml of assay medium)
10.20
20.5
20.5
20.5
All data on DM basis
Source - Hossain and Becker, 2001; S. sesban (1) - ILRI no. 10865D, S. sesban (2) - ILRI no. 15019D
Table 7. Antinutrients present in raw and treated Sesbania aculeata seed meal
component
Raw meal
Soaked meal
Soaked and Autoclaved meal
Total phenols (% tannic acid equivalent)
3.08
1.36
1.30
Tannins (% tannic acid equivalent)
2.25
1.15
0.99
Phytates (% dry matter))
2.16
1.64
1.16
Saponins (% diosgenin equivalent)
0.52
0.44
0.29
Trypsin inhibitor (mg trypsin inhibited per g sample)
5.25
4.77
1.02
Lectins (1/mg of meal that produced haemagglutination per ml of assay medium)
10.20
10.20
ND
All data are on DM basis
Source Hossain et al., 2001b
Table 8. Chemical composition of different Mucuna pruriens var. utilis seeds (% of dry matter)
Mucuna seeds
Crude protein
Lipid
Ash
Crude fibre
NFEa
Gross energy (kJ g-1)
White variety
29.8
4.5
3.4
8.8
53.3
19.4
Black variety
24.3
4.9
3.9
9.0
57.9
19.6
a Nitrogen free extract
Source: Siddhuraju and Becker, 2000
Table 9. Antinutrients present in raw and treated Mucuna pruriens var. utilis (white variety)
Component
Raw meal
Soaked and Autoclaved meal
Alkali soaked and autoclaved
Total phenols (% tannic acid equivalent)
5.54
2.56
2.06
Tannins (% tannic acid equivalent)
0.37
0.20
NA
Phytates (% dry matter))
0.90
0.48
0.49
Saponins (% diosgenin equivalent)
1.15
0.51
NA
L-DOPA
4.70
1.85
1.62
Trypsin inhibitor (mg trypsin inhibited per g sample)
13.8
0.55
1.07
Chymotrypsin inhibitor (chymotrypsin inhibitor unit per mg sample)
10.97
ND
ND
Phytohaemagglutinating activity (phytohaemagglutinating unit per mg sample)
0.2
ND
ND
All values on DM basis
L-DOPA - 3, 4-dihydroxyphenylalanine
ND - not detectable
NA - not available
Source: Siddhuraju and Becker, 2001a
Table 10. Composition of important amino acids of seeds/parts (g / 16gN) compared with fishmeal and soybean meal
Aminoacids
Fish meala
Soybean mealb
Jatropha seed mealc
Moringa leavesd
Moringa kernel meald#
Sesbania aculeatab
Sesbania sesbanb
Mucuna seedsa
Methionine
3.12
1.22
1.76
1.98
1.90
1.03
0.96
0.83
Cystine
1.19
1.70
1.58
1.35
4.22
0.70
0.75
1.13
Valine
5.84
4.59
5.30
5.68
3.47
3.00
2.71
4.17
Isoleucine
4.70
4.62
4.85
4.50
3.05
3.06
2.56
4.07
Leucine
8.09
7.72
7.50
8.70
5.27
5.36
4.56
5.87
Phenylalanine
4.03
4.84
4.89
6.18
3.97
3.55
2.99
4.17
Tyrosine
3.01
3.39
3.78
3.87
1.50
2.73
2.14
3.97
Histidine
2.10
2.50
3.08
2.99
2.27
8.58
12.5
3.07
Lysine
7.38
6.08
3.40
5.60
1.47
4.55
4.20
5.67
Arginine
7.18
7.13
12.9
6.23
11.6
8.58
6.01
5.30
Threonine
4.52
3.76
3.59
4.66
2.25
2.45
2.38
2.83
Tryptophan
1.13
1.24
1.31*
2.10
NA
1.36
2.38
0.83
a,Adapted from Siddhuraju and Becker, 2001b
btaken from Hossain and Becker, 2001
cTaken from Makkar and Becker, 1999a; *value of toxic variety, other values of non toxic seeds
d From Makkar and Becker 1997c, # after oil extraction
Table 11. Essential amino acid requirement of some culture fish (% of diet)
Aminoacids
Common carp
Nile tilapia
Rainbow trout
Pacific salmon
Channel catfish
Methionine + cystine
0.94
0.90
1.0
1.36
0.64
Valine
1.10
0.28
1.2
1.09
0.84
Isoleucine
0.76
0.87
0.9
0.75
0.73
Leucine
1.00
0.95
1.4
1.33
0.98
Phenylalanine + tyrosine
1.98
1.55
1.8
1.73
1.40
Histidine
0.64
0.48
0.7
0.61
0.42
Lysine
1.74
1.43
1.8
1.70
1.43
Arginine
1.31
1.18
1.5
2.04
1.20
Threonine
1.19
1.05
0.8
0.75
0.56
Tryptophan
0.24
0.28
0.2
0.17
0.14
Protein, crude (digestible) present
35 (30.5)
32 (28)
38 (34)
38 (34)
32 (28)
After NRC 1993, these requirements have been determined with highly purified ingredients in which the nutrients are highly digestible, therefore the values presented represent near 100% bioavailability.