Bioconversion of peanut husk with white rot fungi: Pleurotus ostreatus and Pleurotus pulmonarius

A Akinfemi

Nasarawa State University, Keffi,Faculty of Agriculture, Department of Animal Science, PMB 135, Shabu-Lafia, Nigeria
akinjournal2000@yahoo.com

Abstract

This study was carried out for 21 days to determine the impact of treating peanut (Arachis hypogea) husk, an economically important cash crop in Nigeria with white rot fungi: Pleurotus ostreatus and Pleurotus pulmonarius, and the resulting impact on the chemical composition and in vitro digestibility.

Solid state fermentation improved the crude protein (CP) from 7.39% (control, UM) to 9.29% for Pleurotus ostreatus (POT) and 16.10% for Pleurotus pulmonarius (PPT). On the contrary, fungal treatment depleted the crude fiber (CF) from 26.2% in UM to 16.9% for POT and 18.7% for PPT. In a similar trend, the fungal treatment increased significantly (p<0.05) the neutral detergent fiber and acid detergent fiber . Wide variations were also observed in the mineral contents of the substrates under study with higher value obtained in all the major minerals with the exception of sodium. However, copper (Cu) was observed to be higher in the treated substrates compared with the untreated. Fungal treatment increased the iron (Fe) content of POT. The fermentation of the insoluble fraction (b) increased consistently from 34.33mL in the control to 50.67mL for POT and 53.33mL. Faster rates of gas production were also observed in the treated peanut husk compared with the untreated. Gas volume was significantly higher at all incubation period in the fungal treated substrates. The estimated metabolisable energy (ME), organic matter digestibility (OMD) and short chain fatty acid (SCFA) also increased with fungal treatment.

The results of this study indicate that fungal treatment of peanut husk have the potential to be used as feed supplements for ruminants especially during the dry season when feedstuffs are lacking and the only available feedstuffs are crop residues.

Keywords: in vitro digestibility, mineral content, peanut husk, solid state fermentation, white rot fungi

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 Nigeria, it is a common practice to feed livestock with fibrous feedstuffs. These fibrous feedstuffs or agricultural wastes are low in nutritive value. Preston and Leng (1987) reported that these feed resources have generally been directed to ruminant production due to the high level of the cell wall fraction. A very important class of non-conventional feedstuff in Nigeria is peanut husk. Peanut (Arachis hypogea) is a cash crop especially in the northern part of Nigeria where a huge of tonnage of it is produced annually. From the production, processing and consumption of groundnut, there are a great variety of reminders especially the husks, which create increasing problems of elimination. It is a common practice in Nigeria either to feed the agricultural wastes to the animals, burn or left on the farm to rot. Burning has received global condemnation in the recent past and therefore the need for bioconversion. One of the strategies to utilize agricultural wastes and by products is to grow edible fungi such as edible mushrooms that will not only reduce the fibre but also help in obtaining protein rich substrates. Edible mushrooms are able to bio-convert a wide variety of lignocellulosic materials due to the secretion of extracellular enzymes (Buswell et al 1996; Rajarathman et al 1998).

The objectives of this study was to determine the changes in the nutritive value of bio converted groundnut husk using the in vitro gas production techniques

Materials and methods  

Sample collection

Dried samples of peanut husk and were collected from the Teaching and Research Farm, Nasarawa State University, Keffi, 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 in triplicate.

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 21days 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 1988) 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) 1998 package.

Result and discussion  

Alteration in the chemical and mineral composition

Shown in Table 1 is the result of the chemical composition of the treated and untreated peanut nut shells.

Shown in Table 2 is the result of the mineral composition of the treated and untreated peanut nut shells.

There were significant differences (p<0.05) in the results obtained for chemical composition in the treated and untreated substrates. The CP content ranged from 7.39 to 16.10%, CF ranged from 16.92 to 26.15% while NDF ranged from 62.94 to 69.41%, ADF ranged from 43.93 to 51.08% while ADL ranged from 15.31 to 28.61% cellulose and hemicellulose ranged from 15.36 to 35.77% and 13.35 to 19.67% respectively. CP increased has been reported to be associated with increased fungal biomass (Chen et al 1995). The increase of CP content in the treated substrates could also be due to the capture of access nitrogen by aerobic fermentation (El-Shafie et al 2007). This agrees with the findings of El-Marakby (2003); El-Ashry et al 2002, Akinfemi et al 2009a and Akinfemi et al 2009b. The decrease of CF may be related to the utilization of carbohydrates by the fungus as an energy source for mycelia growth. This is consistent with the findings of Akinfemi et al (2008a) and Akinfemi et al (2009b). The decrease in the values of neutral detergent fiber (hemicellulose, cellulose and lignin) and acid detergent fiber (lignin and cellulose) could be indicative of the degradation of the cell wall component of the substrates produced by the extracellular enzymes of the fungi used. Edible mushrooms (Pleurotus sajor caju and P. pulmunarium) are able to bioconvert a wide variety of lignocellulose materials due to the secretion of extracellular enzymes (Buswell et al 1996 and Rajarathman et al 1998). The lowest decrease in value obtained for hemicellulose in Pleurotus ostreatus treated substrates (POT) may be due mainly to the extensive utilization the hemicellulose as energy source for the fungus. On the contrary, the highest cellulose content recorded for fungi treated substrates will provide more glucose for ruminant animals since the gut of the animal is well equipped with microbes that can convert the cellulose to glucose (Belewu and Belewu, 2005). The mineral contents of the substrates under study with the exception of potassium differed significantly. Higher mineral contents were observed in all the major and minor minerals of the control except  copper. The major minerals except phosphorus, sodium and potassium were within the range values previously reported (McDowell 1995). The values are adequate to meet the requirement for growth, reproduction and milk in west African dwarf sheep and grass (Babayemi  2006). The calcium and phosphorus ratios were not within the approved 1:1 to 2:1 range recommended (McDowell 1995). Iron, copper, zinc and manganese contents in the present study were extremely deficient in all the fungal treated substrates. This therefore implies that the feed will require fortification with minerals either in form of salt lick or diet inclusions.

Gas production characteristics and volume

Table 3 presents the gas volume and gas production characteristics.

The fermentation of the insoluble but degradable fraction (b) mL increased significantly from 34mL in the control to 53.33mL in the Pluerotus pulmonarius treated substrate (PPT). It can be seen from the result obtained in this study that fermentation of the insoluble fraction in the fungal treated was higher compared with the untreated, possibly a reflection of the depletion of lignin contents (Chumpuwadee et al 2005). The high fermentation of the insoluble fraction (b) observed in the treated substrates may also be possibly influenced by the carbohydrate fraction readily available to the microbial population (Chumpuwadee et al 2005). Deaville and Givens (2001) have also reported that kinetics of gas production could be affected by the carbohydrate fraction.

The fast rates of gas production (c) were observed in the treated substrates, possibly influenced by the soluble carbohydrate fraction readily available to the microbial population (Chumpuwadee et al 2007)

Gas volume at different hours of incubation showed a wide variation. The result showed that cumulative gas volume at 24, 48, 72 and 96h were significantly (p<0.05) higher in fungal treated substrates compared with the untreated. Cell content (NDF and ADF) has been reported to have a negative correlation with gas production at all incubation time and estimated parameter (Sallam et al 2007b). The reduction in the value of NDF and ADF of the fungal treated substrates tend to increase the microbial activity through increasing through the favourable environmental conditions as incubation time progress. This is consistent with De Boever et al (2005) who reported that gas production was negatively related with NDF content and positively with starch. Also the lower levels of ADL in the treated substrates increased the amount of gas produced. One of the main reasons for this low degradability is the presence of lignin which protects carbohydrate form attack by rumen microbes (Sallam et al 2007b). However, since gas production on incubation of feed in buffered rumen fluid is associated with feed fermentation and carbohydrate fractions. Low gas production from the control could be related to low feeding value of this feed. Sommart et al (2000) suggested that gas volume is a good parameter from which to predict digestibility, fermentation end product and microbial protein synthesis of the substrate by rumen microbes in the in vitro system. Gas volume has also been shown to have close relationship with feed intake (Blümmel and Becker 1997) and growth rate (Blümmel and Ørskov 1993)

Estimated metabolisable energy (ME), short chain fatty acid (SCFA) and organic matter digestibility (OMD) of treated and untreated peanut husk

The result of the ME, SCFA, and OMD are shown in Table 4.

The estimated ME increased from 5.15MJ/kgDM to 8.61 MJ/kgDM, The values estimated for ME in this study for the fungal treated substrates are higher than those estimated for broken rice, soybean hull, rice bran and peanut hull (Chumpuwadee et al 2007); rice straw, linseed straw and date stone (Sallam et al 2007b), fungal treated maize cob (Akinfemi et al 2009b) and fungal treated maize straw (Akinfemi et al 2009a). The in vitro gas production value of several classes of feed (Getachew et al 1999; Getachew et al 2002; Aiple et al 1996). Krishnamoorthy et al (1995) also suggested that in vitro gas production technique should be considered for estimating ME in tropical feedstuffs, because other method requires time, cost and is time consuming. Wide variations were observed in the values estimated for (SCFA).Incubation of feedstuffs with buffered rumen in vitro, the carbohydrates are fermented to short chain fatty acid (SCFA), gases mainlyCO₂ and CH₄ and microbial cells. Getachew et al (2002) reported a close association between SCFA and in vitro which, use of this relationship between SCFA and gas production to estimate the SCFA production from gas volumes, which is an indication of energy availability to the animal (Sallam et al 2007b).

The estimated OMD increased from 39.12% in the control to 63.19%. Higher OMD were observed in the treated substrates. The higher OMD observed in the fungal treated substrates may be because the major carbohydrates of the treated feedstuff are starch which is fermented by amylolytic bacteria and protozoa (Kotarski et al 1992). This result implies that the microbes in the rumen and animal have high nutrient uptake (Chumpuwadee et al 2007). The lower CF content in the treated substrates probably resulted in their higher OMD since high NDF and ADL contents in feedstuffs result in lower fibre degradation (Van Soest  1988).

In general, the tropical forages and concentrates feedstuffs have large proportion of lignified cell walls with low fermentation rates and digestibility, leading to low digestibility rates as limited intake (Ibrahim et al 1995; Hindrichsen et al 2001). Methane production (|Figure 1) was highest in the control.

Methane production has negative effect on the animal on the one hand as it is an energy loss to the animal and on the other hand when it accumulates in rumen, it results in bloat (Babayemi 2006). Miller reported that the reduction in methane production could be due to conversion of CO₂ and H₂ to acetate instead of CH₄. This process mainly occurs when roughages diet containing high proportion of sugars and protein is fed (Leedle and Greeming 1988). Also the deposition of CH₄ production in fungal treated substrate is probably due to indirect effect via fiber digestion (Sallam et al 2008b). 
 

Conclusion  

• Peanut husk has shown to be good substrate when treated with white rot fungi in the solid state fermentation through biotechnological approach which leads to an effective and economic way to utilize this otherwise unused residue and improve the economy of the peanut industry.
   

Acknowledgements 

The author is grateful to Dr O A  Adu, of the Department of Animal Production and Health, Federal University of Technology, Akure, Nigeria, for his advice and provision of materials needed for the successful implementation of this project.
 

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Received 15 September 2009; Accepted 10 January 2010; Published 1 March 2010

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