AN EVALUATION OF THE EFFECT OF CONTROLLED FERMENTATION USING ASPERGILLUS NIGER AND TRICHODERMA HARZIANUM ON NUTRIENT COMPOSITION OF PRE-TREATED BENGAL INDIGO (INDIGOFERA ARRECTA) SEEDS
The genus Indigofera Linn. is a large genus of about 700 species of flowering plants belonging to the sub-family Papilionoideae in the family Fabaceae / Leguminosae. They occur throughout the tropical and subtropical regions of the world. Burkill (1995) recognized 60 species while Soladoye and Lewis (2003) recorded 60 species in Nigeria with over 60% abundance in the Northern region of the country with 27 species distributed across the South Western area of the country. Indigofera in Greek means indigo dye which is famous for the natural blue colors obtained from the leaflets and branches of this herb. The most important of the species are Indigofera arrecta and Indigofera tinctoria.
Indigofera spp. display excellent adaptation to a range of environments, and possess diverse morphological and agronomic attributes, significant to their use as forage and cover crops (Hassen et al., 2006). Some of these species, Indigofera tinctoria and Indigofera suffruticosa are used to produced indigo dyes while some have medicinal values such as Indigofera articulata used for the treatment of toothache, Indigofera oblongifolia, Indigofera suffruticosa and Indigofera aspalathoides are used as anti–inflammatories for treatment of insect stings, snake bites and swellings (Shahjahan et al., 2005); and Indigofera arrecta extract is used to relieve ulcer pain.
The stem of Indigofera tinctoria is chewed to cure cough and decoction of leaves is used to cure chest pains, epilepsy, nervous disorders, asthma, bronchitis, fever and complaints of stomach, liver, kidney and spleen- especially in Cameroon (Takawira-Nyenya and Cardon, 2005). The twine paste cures dislocation. Also the warm leaves dismiss bruises (Ibe and Nwufo, 2005). Phytochemical investigation of Indigofera species shows that they are rich in organic and fatty acids, flavonoids such as carotenoids and coumarins (Yinusa et al., 2007).
Indigofera arrecta is readily found in abundance in the locality of Samaru- Zaria, Kaduna State and the young leaves are eaten as vegetable. In the northern part of the country among the Hausa, it is called ―Ba-ba‖, in the south-west among the Yoruba, it is known as ―Elu-aja‖ and in eastern part of the country among the Igbos, it is known as ―Uri‖. Indigofera arrecta seeds contain several anti-nutritional factors which limit their consumption and affect the digestibility and bioavailability of nutrients. Seeds are well known rich sources of minerals but the bioavailability of these minerals is usually low due to the presence of antinutrients and enzyme inhibitors (Valencia et al., 1999). These antinutrients and enzyme inhibitors interfere with absorption of nutrients from foodstuff thus affecting their metabolism. The seed of Indigofera arrecta is known for its hardness which is due to the presence of a hard seed coat which is the seed‘s primary defense against adverse environmental conditions. Seed hardness is the effect of two components: hardness of the seed coat and hardness of the seed interior. Hardness is related to seed coat (testa) impermeability and also to cotyledon impermeability. In the testa it may involve lignins as well as tannins, whereas in cotyledons it may be primarily lignification as cotyledons have low concentrations of phenolic compounds. Some anti-nutritional factors such as trypsin and cysteine inhibitors and lectins are heat-labile compounds and their negative effects are, therefore, markedly reduced by cooking (Boufassa,et al., 1986; Akinyele, 1989), while tannins and phytic acid are heat-stable compounds that retain negative effects on mineral and protein bioavailability after cooking (Ogun et al., 1989).
All necessary experimental steps employed in producing fermentable substrates are referred to in a single term as pretreatment. Pretreatment strategies have generally been categorized into biological, physical and chemical processes, or a combination of these approaches.Pretreatments change the structure of cell walls and polymers by disrupting intermolecular forces holding them together, allowing greater access by enzymes and water. Phenolic compounds in the seed coat contribute to seed hardness and inhibition of microorganism growth hence the need for pretreatment in order to increase the accessibility to enzyme hydrolysis or fermentation.
The presence of lignin also impedes enzymatic hydrolysis, as enzymes bind onto the surface of lignin and hence do not act on the cellulose chains (Palonen et al., 2004). Biodegradability can be enhanced by pretreatment of lignocellulolytic materials, including acid or alkali treatment, ammonia and urea, physical grinding and milling, fungal degradation and steam explosion, and combined alkali and heat treatment (Galbe and Zacchi, 2007). Gharpuray et al.(1983) examined several of these pretreatment options individually and in combination, and found that those treatments which enhanced specific surface area were most effective at increasing enzymatic hydrolysis.
Fermentation has always been an important part of human lives with exclusive benefits as food. It can produce vital nutrients or eliminate antinutrients. Several experiments have demonstrated that fermentation of legumes enhances their nutritive value (Zamora et al., 1979; Akpapunam and Achinwehu, 1985), reduces some anti-nutritional endogenous compounds such as phytic acid (Kozlowska et al., 1996), and exerts beneficial effects on protein digestibility and biological value of legumes.
Trichoderma spp. and Aspergillus spp. are good secretors of lignocellulolytic enzymes(Archer and Peberdy, 1997). They are producers of tannase (Dapiya et al., 2010) and phytase (Aseri et al., 2009, Newkirk et al., 2001) which are two enzymes capable of degrading tannin and phytic acid respectively. The incubation of substrate with Trichoderma harzianum and Aspergillus niger markedly reduce the phytate and tannin in Jatropha curcas seeds(Balewuet al.,2011). Efforts have been focused on how to combine pretreatment and solid state fermentation to maximize productivity and to make the overall process economically efficient.
This study is aimed at evaluating the effect of pretreatment on nutrient composition of Indigofera arrecta seeds using controlled fermentation by Aspergillus niger and Trichoderma harzianum in mono and co-culture.