| Livestock Research for Rural Development 30 (12) 2018 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
This study examined the bioconversion of rice stubble fermented with different Pleurotus species: Pleurotus ostreatus (POT) , Pleurotus sajor-caju (PSC) and Pleurotus eous (PE). The rice stubble was inoculated with the fungi and incubated in the dark at 30°C and 75% relative humidity for a period of 25 (POT), 30 ((PE) and 35 days (PSC).
Fermentation decreased the NDF, ADF and ADL fractions of the stubble and increased the in vitro gas production, estimated organic matter digestibility and crude protein content.
Key word: gas production, rice straw, white-rot fungi
The waste-products from agriculture such as rice straw, maize stove, oil palm fronds, and sugarcane bagasse, are abundantly available in many tropical countries (Wan Zahari et al 2003); however, they are high in fiber and low in protein with resultant low nutritive value for ruminants (Karunanandaa et al 1995). The problems of farmers who raise ruminants in the dry season are the shortage of fresh grasses. Rice straw and stubble are potential alternatives. Currently, there is wide use of mechanical equipment for rice harvesting, which means that more rice straw and rice stubble are left in the field.
The use of white-rot fungi (Pleurotus species) could increase the digestibility of rice straw and rice stubble helping to break down the lignin bonds that reduce the availability of the cellulose and hemicellulose in the straw. The aim of this study was therefore to examine the bioconversion of rice straw by fermenting it with different Pleurotus species:Pleurotus ostreatus (POT), Pleutus sajor-caju (PSC) and Pleurotus eous (PE).
Three white-rot fungi (P. sajor-caju, P. eous and P. ostreatus) were purchased from a commercial company.
Dried samples of rice stubble were collected from paddy fields after harvesting in Nakhon Ratchasima province, Thailand.
Glass bottles (120ml) were thoroughly washed and dried for 24 h at 100°C. The dried chopped rice stubble (25g) was weighed into each bottle and 70 ml of distilled water added. The bottles were covered with aluminum foil and sterilized in the autoclave at 121°C for 15 minutes. Each treatment was applied in triplicate.
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| Photo 1. Substrate preparation |
Each bottle was inoculated at the center of the substrate with 2% of spawn (Jafari et al 2007) and covered immediately and kept in the dark cupboard in the laboratory at 30°C and 75% relative humidity (RH). After 25 days for POT, 30 days for PE and 35 days for PSC, the substrates were harvested by autoclaving to terminate the mycelia growth, then oven-drying to constant weight prior to chemical analysis and in vitro incubation.
Nitrogen content was determined by the standard Kjeldhal method according to AOAC (1995). NDF, ADF and ADL were assessed using the methods of Van Soest et al (1991).
The in vitro incubation was done according to Menke and Steingass (1988). Syringes were filled with 200 mg of substrate, 20 ml of buffer solution and 5 ml of rumen fluid (obtained by stomach tube from four Anglo-Nubian goats) with incubation at 39oC. Gas production was recorded at 2, 4, 6, 9, 12, 16, 24, 36, 48, 60, 72 and 96h. The gas production data were fitted to the model of Ørskov and McDonald (1979):
p = a + b (1-exp -c t)
Where:
p represents gas volume (ml) at time t,
a the gas produced from soluble fraction (ml),
b the gas produced from insoluble but fermentable fraction (ml),
(a+b) the potential gas production (ml), and
c the rate constant of gas production during incubation (ml h-1).
The data were analyzed as a Complete Randomized Design (CRD) using the general linear model in the ANOVA program of the SAS software.
Fungal treatments decreased the concentrations of NDF, ADF and ADL and increased the crude protein in the substrates (Table 1). The increase in crude protein may have been an effect of increased fungal biomass (Chen et al, 2015). It may also be due to secretion of certain extracellular proteinaceous enzymes into the waste during their breakdown and subsequent metabolism (Akinfemi et al 2010). It may also be due to the capture of nitrogen from the air during fermentation (Sallam et al 2007).
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Table 1. Proximate composition and cell wall content (% in DM) of rice stubble incubated with Pleurotus spp |
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|
Control |
POT |
PSC |
PE |
SEM |
p |
|
|
OM |
84.9 |
83.6 |
82.9 |
82.3 |
0.36 |
0.22 |
|
CP |
2.50b |
3.33a |
3.42a |
3.21a |
0.03 |
0.002 |
|
EE |
0.90 |
0.94 |
0.90 |
0.94 |
0.05 |
0.98 |
|
NDF |
77.9a |
66.9b |
65.6b |
64.3b |
0.47 |
0.001 |
|
ADF |
58.0a |
51.5b |
49.6b |
50.5b |
0.61 |
0.02 |
|
ADL |
4.90a |
3.98b |
2.86c |
3.15c |
0.09 |
0.01 |
|
abc
Row means with different superscripts differ at p<0.05.
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This result confirms numerous studies that reported that white-rot fungi are capable of degrading lignin without affecting much the cellulose and hemicellulose components of the cell wall (Mahesh and Mohini 2013), thus causing the decayed residue to turn white. The concept of preferential delignification of lignocelluloses materials by white-rot fungi has been applied to increase the nutritional value of forages (Jalc 2002). Zadražil et al (1995) described how white-rot fungi attack unaltered lignin polymers causing cleavage of interlignol bonds and aromatic ring cleavage, which ultimately results in an increase in in vitro digestibility.
In the in vitro incubation, gas production was increased by all Pleurotus spp (Table 2). This is consistent with a previous report that in vitro gas production of cowpea husks was increased by treatment with Pleurotus spp and could be due to the depletion in the lignin content (Kinfemi et al 2009).
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Table 2. In vitro gas production characteristics and estimated organic matter digestibility OMD) |
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|
TRT |
Control |
POT |
PSC |
PE |
SEM |
p-value |
|
a |
2.29c |
9.29a |
5.47b |
6.58b |
0.347 |
0.002 |
|
b |
62.2c |
71.1b |
77.5a |
71.3b |
0.691 |
0.001 |
|
c |
0.04 |
0.04 |
0.04 |
0.04 |
0.001 |
0.21 |
|
a+b |
64.5b |
80.3a |
83.0a |
78.0a |
0.925 |
0.002 |
|
OMD, % |
52.0b |
65.3a |
67.1a |
61.4a |
0.281 |
0.0001 |
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abc, Means within a row with common superscript do not differ at p>0.05 POT = Pleurotus Ostreatus, PSC= Pleurotus Sajor-caju, PE= Pleurotus Eous, c = gas production rate, a = gas production (ml) from quickly soluble fraction, b gas = gas production (ml) from insoluble fraction, (a + b) = potential gas production |
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Gas production from rice straw increased with incubation time (Figure 1) and was higher when the straw was incubated with the white rot fungi.
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| Figure 1. In vitro gas production of rice stubble fermented by three Pleurotus fungi |
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Received 24 October 2018; Accepted 14 November 2018; Published 2 December 2018