Use of white rot-fungi in upgrading maize straw and, the resulting impact on chemical composition and in-vitro digestibility

A Akinfemi, O A Adu* and O A Adebiyi**

Nasarawa State University, Keffi, Faculty of Agriculture, Department of Animal Science, Shabu-Lafia, Nigeria
akinfemiabayomi2003@yahoo.com
* Animal Physiology Laboratory, Department of Animal Science, University of Ibadan, Ibadan, Nigeria
** Department of Animal Science, University of Ibadan, Nigeria

Abstract

Studies were carried out for 40 days on the conversion of maize straw into value added ruminant feed using two white-rot fungi: Pleurotus sajor caju and Pleurotus pulmonarius in a solid state fermentation. The chemical composition and in- vitro digestibility of the resulting substrate were determined.

The results of the study showed that the crude protein (CP) increased from 7.37% for the control (UM) to 9.66% for the Pleurotus pulmonarius degraded maize straw (PPM) and  Pleurotus sajor caju degraded maize straw (PSM). The ether extracts (EE) and ash contents also follow the same trend. On the contrary, Crude Fiber fractions (Neutral detergent fiber (NDF), Acid detergent fiber (ADF),acid detergent lignin (ADL), cellulose and hemicellulose) decreased significantly (p<0.05) during the period of solid state fermentation. The estimated short chain fatty acid (SCFA) and metabolisable energy (ME) were not significantly different (p>0.05).Organic matter digestibility (OMD) were enhanced by the fungi used compared with the untreated straw. Gas volume also follows the same trend while the rate of gas production constant (c) was highest in UM and PSM.

This study shows that the fungal treatment of maize straw enhanced the chemical composition and in -vitro digestibility.

Key words: fermentation, fungi, Pleurotus sajor caju, Pleurotus pulmonarius, ruminant

Introduction

Agricultural wastes are the most abundant ones present on earth comprising 50% of all biomass with an estimated annual production of 50 billion tons (Smith et al 1983).  In the developing countries, inclusion of fibrous feed in the diet of ruminant animals is a common practice. The animals are fed with materials left in the field after harvesting the target crops. These fibrous materials are low in protein, vitamins and mineral, and high in crude fibre. A common example of agricultural waste is maize residue. Maize residues were estimated to be about 4.11 million tonnes in 1989, consisting mainly of straw, husk, skins and trimmings, cobs and bran. These residues which are often either burned or plough into the soil account for almost 25% of the total energy suitable for ruminant livestock (Adebowale 1988). They form the principal feed in small scale farming system during dry seasons. A successful exploitation of agricultural waste will not only improve environmental sanitation but also provides economically utilizable products (Fasidi et al 1996). The inadequate utilisation of lignocelluloses is due to lignin which surrounds and protects the cellulose from enzyme hydrolysis, for example, in plant residues having more than 10% lignin content (Teferedegne 2000). By suitable biological treatments through fermentation, maize Straw can be converted into value added ruminant feed.

Although, the gas production from the in vitro fermentation is a nutritional waste, it remains one of the reliable means to measure quality of feeds (Fievez et al 2005).Therefore, the gas production technique should be considered for use in nutritive evaluation in developing countries (Chumpawade et al 2007 ) because  it is economical, highly reproducible and easy method of obtaining a dynamic descriptions of nutritive value of feedstuffs, while at the same time allowing more samples to be analysed (Herrero et al 1996).          

This study was undertaken to assess the nutritive value of edible mushroom (Pleurotus sajor caju and Pleurotus pulmonarius) degraded maize Stover through the analysis of their chemical composition as well as their in vitro digestibility and gas production potential.

Materials and methods 

Sample collection

Dried samples of maize residues (maize straw) and were collected from the Teaching and Research Farm, University of Ibadan, Ibadan, Nigeria. The materials were milled and oven-treated at 65⁰C until a constant weight was obtained for any dry matter determination.

The fungus

The sporophores of Pleurotus pulmonarius and Pleurotus sajor caju growing in the wild were collected from Ibadan University botanical garden. These were tissue cultured to obtain fungal mycelia (Jonathan and Fasidi 2001).The pure culture obtained was maintained on plate of potato dextrose agar (PDA).

Degradation of maize straw by Pleurotus pulmonarius and Pleurotus sajor caju

Preparation of substrate

The jam bottles used for this study were thoroughly washed, dried for 10 min. at 100^oC. 25.00g of the dried milled substrate were weighed into each jam bottle and 70ml distilled water were added. The bottle was immediately covered with aluminium foil and sterilized in the autoclave at 121^oC for 15 min. Each treatment was triplicates.

Inoculation

Each bottle was inoculated at the centre of the substrate with 2, 10.00mm mycelia disc and covered immediately. They were kept in the dark cupboard in the laboratory at 30⁰C and 100% RH. After 40days of inoculation, the experimental bottles were harvested by autoclaving again to terminate the mycelia growth. Samples of the biodegraded samples were oven dried to constant weight for chemical analysis and in vitro digestibility.

In vitro gas production

Rumen fluid was obtained from three West African Dwarf female goat through suction tube before the morning feed. The animals were fed with 40% concentrate feed (40% corn, 10% wheat offal, 10% palm kernel cake, 20% groundnut cake, 5% soybean meal, 10% brewers grain, 1% common salt, 3.75% oyster shell and 0.25% fishmeal) and 60% Guinea grass. Incubation was carried out according to (Menke and Steingass 1998) in 120ml calibrated syringes in three batches at 39⁰C. To 200mg sample in the syringe was added 30ml inoculum contained cheese cloth strained rumen liquor and buffer (9.8g  NaHCO₃ + 2.77g Na₂HPO₄ + 0.57g KCL + 0.47g NaCL + 0.12g MgSO₄. 7H₂0 + 0.16g CaCI₂ . 2H₂0 in a ratio (1:4 v/v) under continuous flushing with CO_2.  The gas production was measured at 3, 6, 9, 12, 15, 18, 21 and 24h. After 24 hours of incubation, 4ml of NaOH (10M) was introduced to estimate the amount of methane produced (Fievez et al 2005). The average volume of gas produced from the blanks was deducted from the volume of gas produced per sample. The volume of gas production characteristics were estimated using the equation Y = a + b (1 – e^ct) described by Ǿrskov and McDonald 1979, where Y = volume of gas produced at time‘t’, a = intercept (gas produced from the soluble fraction), b = gas production from the insoluble fraction, (a+b) = final gas produced, c = gas production rate constant for the insoluble fraction (b), t = incubation time. The post incubation parameters such as metabolizable energy (ME, MJ/Kg DM), organic matter digestibility (OMD %) and short chain fatty acids (SCFA) were estimated at 24h post gas collection according to Menke and Steingas (1988).

ME = 2.20 + 0.136* Gv + 0.057* CP + 0.0029*CF;

OMD = 14.88 + 0.88Gv + 0.45CP +0.651XA;

SCFA = 0.0239*Gv – 0.0601;

Where Gv, CP, CF and XA are net gas production (ml/200mg, DM) at 24 h incubation time crude protein, crude fibre and ash of the incubated sample respectively.

Chemical composition

DM was determined by oven drying the milled samples to a constant weight at 105⁰C for 8 hours. Crude protein was determined as Kjadhal nitrogen x 6.25. Ether extracts and ash were determined according to (AOAC 1995) method. Neutral detergent fibre (NDF), Acid detergent fibre (ADF) and Acid detergent lignin (ADL) was determined using the method described by Van Soest et al (1991).Hemicellulose was calculated as the difference between NDF and ADF while cellulose is the difference between ADF and ADL.

Statistical analysis

Data obtained were subjected to analysis of variance (ANOVA) and mean separation was by Duncan multiple range tests using Statistical Analysis System (SAS) 1999 package.

Results and discussion 

Proximate composition and crude fibre fractions

The results of the proximate composition of fungal treated maize straw is  shown in Table 1.

The result shows a significant (p<0.05) increase in the crude protein (CP) contents of the treated straw compared to the untreated while the crude fibre (CF) and the crude fibre fractions decreased significantly (p<0.05).The increase in CP may have been a result of the fungal biomass (Chen et al 1995).This agrees with the findings of Akinyele and Akinyosoye (2005). Zadrazil 1993 and, Belewu and Okhawere (1998) reported that the colonization of wastes by fungi results in increase in their nutritional values. The decreased in CF values obtained for the fungal treated straw may have been the result of the fungi ability to produce extracellular enzymes cable of reducing the fibre contents. This observation is in tune with the reports of Akinfemi et al (2008a) and Akinfemi et al (2008b). The value for CF as observed in this study is also comparable with the findings of Belewu and Belewu (2005) and this makes it nutritionally good for the ruminant animals. There were also to 3.20% which represents the crude fat. This could mean additional energy available to the ruminant animal. This agrees with consistently significant (p<0.05) increases in the ether extract (EE) and ash contents of the fungi treated straw. The EE values ranged from 1.57% the findings of Akinyele and Akinyosoye (2005) but disagree with the report of Belewu and Belewu (2005). Ash contents increase from 8.78% to 9.79%.This is similar to the increase from 8.54% to 9.79% obtained by Akinyele and Akinyosoye (2005) when he treated corn cobs with Volvariella volvacea. The improved ash contents indicate increase in mineral contents. The two fungi used decreased NDF concentrations mainly due to the extensive utilization of hemicellulose, Chen et al (1995). Likewise, cellulose and hemicellulose were significantly (p<0.05) decreased by the fungi used. The may have been the results of the fungi utilization of the cellulose and hemicellulose as its source of energy. The extent of lignin degradation by the two fungi used may be related to their ability to produce lignin degrading enzymes, such as lignin peroxidase and manganese peroxidase (Nerude et al 1995). The extensive degradation of cellulose and hemicellulose (Table 1) by the fungi most likely contributed to the increased  ME (Table 2).

Estimated short chain fatty acid (SCFA), organic matter digestibility (OMD), methane (CH₄) and metabolisable energy (ME)

Shown in table 2  are the estimated short chain fatty acid (SCFA), organic matter digestibility (OMD), metabolisable energy (ME) and methane production (CH₄).The results obtained shows no significant difference in the in SCFA. Fievez et al (2005) observed that SCFA is an indication of energy content. Hoffman et al (2003) further corroborate this when he stated that SCFA is an end product of carbohydrate fermentation and this contributes to the energy supply for the host animal. The length of the fermentation period could have contributed to the values obtained in the treated straw. OMD were significantly (p<0.05) higher in the treated straw. This is expected because of improved CP and reduced CF contents (Table 1).ME was also not significantly (p<0.05) different. Methane was significantly reduced in the fungi treated maize straw, (Figure 1).

Methane production indicates energy loss to the animal and many tropical feedstuffs have been implicated to increase methanogenesis (Babayemi et al (2004), Babayemi and Bamikole (2006) as an integrated part of carbohydrate metabolism (Demeyer and Van Nevel 1975).

Gas production characteristics       

Table 3 shows the result of in vitro gas production characteristics.

The values obtained for volume of gas produced at time t (y ml), gas production rate constant for the insoluble fraction (c), and gas production from the insoluble fraction (b) were significantly (p<0.05) higher in the control (UM) compared with fungi treated straw. This may be due to the length of fermentation period, as it can be seen from the graph of the in vitro gas production pattern shown in fig. 1, more of dry matter fermentation were still possible beyond 24 hours, more so is the extent of biodegradation and physiological behaviour of the fungi used are other likely reasons that may be responsible for this. However, the result obtained in this study is comparable to that obtained by (Chumpawade et al 2007). The final gas produced (a + b) ml and the volume of gas produced, y ml were observed to be highest in PPM. This may be due to strain differences in the fungi used. 

Gas volume

Shown in table 4 are the results of the in vitro gas production over a period of 24hours.

The cumulative gas production was highest in PSM (27.67%) followed closely by PPM (26.33%) with the least from UM (20.67%). The variations observed in the total gas production may be due to many factors such as the content of the fermentable carbohydrate and available nitrogen in them (Aregheore 2000). Sommart et al (2000) suggested that gas volume is a good parameter from which you predict digestibility, fermentation end-product and microbial protein synthesis of the substrate by rumen microbes in the in vitro system. The gas production is basically the result of the fermentation of carbohydrates into acetate, propionate and butyrate (Getachew et al 1999). Gas volume has also shown to have close relationship with feed intake (Blummel and Becker 1997) and growth rate (Blummel and Ǿrskov 1993).  

Conclusions 

• The fungi treated and untreated maize straw shows variation in the chemical composition and in vitro digestibility.

  
  

• The result of this study shows that treatment of maize straw improves it CP and CF contents.

  
  

• This suggests that fungal treated maize may form part of the diet of ruminant animals.

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Received 8 April 2009; Accepted 22 June 2009; Published 1 October 2009

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