Effect of sodium hydroxide and alkaline hydrogen
peroxide treatment on physical and chemical
characteristics and IVOMD of mustard straw
A.S. Mishra
*, O.H. Chaturvedi, Ananta Khali, R. Prasad,
A. Santra, A.K. Misra, S. Parthasarathy, R.C. Jakhmola
Animal Nutrition Division, Central Sheep and Wool Research Institute, Avikanagar 304 501, IndiaReceived 11 August 1999; received in revised form 23 December 1999; accepted 7 February 2000
Abstract
Mustard straw (MS) was soaked for 6 h in the solutions containing 0% (S0), 1% (S1) or 2% (S2)
sodium hydroxide (NaOH) and 0% (H0) or 1.5% (H1) hydrogen peroxide (H2O2) following a 32
factorial design. The pH of the untreated MS (near neutral) was increased to more than 10 after treatment with NaOH (S1H0and S2H0) or alkaline hydrogen peroxide (AHP; S1H1and S2H1). The
treatment effect on tenacity was not signi®cant. The NDF and ADF contents of MS increased signi®cantly (p<0.01) in the treatment S0H1, whereas these decreased signi®cantly (p<0.01) in the
treatments S2H0and S2H1. However, the change in NDF and ADF was not signi®cant in S0H0, S1H0
and S1H1 treatments. The content of both NDF and ADF decreased linearly (p<0.01) with
increasing level of NaOH in the soaking medium. The effect of various treatments on cellulose content was almost similar to that of NDF and ADF. The acid detergent lignin content of MS increased signi®cantly (p<0.01) in case of S1H0, S0H1and S1H1 but the differences were not
signi®cant among UMS, S0H0, S2H0 and S2H1. The IVOMD content of untreated MS was
162 g kgÿ1DM and it increased signi®cantly (
p<0.01) when straw was soaked in S1H0, S2H0, S1H1
and S2H1, whereas it reduced slightly due to either water (S0H0) or H2O2(S0H1) treatment. With the
increasing level of NaOH, the IVOMD improved signi®cantly (p<0.01). It is concluded that the cell wall constituents and IVOMD of MS were modi®ed by NaOH with or without H2O2in a way that in
vitro organic matter digestibility (IVOMD) of treated MS was 82±112% units higher than untreated MS.#2000 Elsevier Science B.V. All rights reserved.
Keywords: Mustard straw; Sodium hydroxide; Hydrogen peroxide; Physical characteristics; Chemical characteristics; In vitro digestibility
84 (2000) 257±264
*Corresponding author.
E-mail address: anand@cswri.raj.nic.in (A.S. Mishra)
1. Introduction
The livestock in large parts of the world including the South-East-Asian region thrive upon grazing with or without supplementation and often encounter mal/under nutrition during natural calamity like drought. The crop residues, mainly straws, play a major role in this part of the world and even these are in short supply. In India for example, conventional crop residues/dry fodders are de®cit to the tune of ca. 40%. This type of roughages are poor in its nutritional value owing to a low protein content and to a high but poorly digestible cell wall fractions. With changing scenario of Indian agriculture, the area under mustard (Brassica campestris) is increasing and at present ca. 14 million tonnes of mustard straw is being produced annually (Gupta, 1998). However, straw remain unutilized as it is not consumed by ruminants in the raw form owing to its tenacious nature and very low digestibility (Chaturvedi et al., 1998a). If nutritional value of this straw is improved through some process technology then an enormous quantity of roughage will be made available for ruminant livestock. In our laboratory attempts have been made to improve the mustard straw through chemical (Misra et al., 1995; Mishra et al., 1996; Chaturvedi et al., 1999) and biological (Chaturvedi et al., 1998b, 2000) means. Sodium hydroxide (NaOH) treatment is an effective way to valorize straws (Sundstol and Owen, 1984) and NaOH treatment is further pronounced if it is combined with hydrogen peroxide (alkaline hydrogen peroxide treatment; Chaudhry and Miller, 1996; Chaudhry, 1998). In the present experiment, an attempt was made to observe the effect of sodium hydroxide and alkaline hydrogen peroxide (AHP) treatment on physical and chemical characteristics and IVOMD of mustard straw.
2. Materials and methods
2.1. Treatment of straw
The mustard straw (MS) used for the study was obtained from a nearby farm and contained the upper half portion of the plant. It was soaked in solutions containing 0% (S0), 1% (S1) or 2% (S2) sodium hydroxide (NaOH) and 0% (H0) or 1.5% (H1) hydrogen
peroxide (H2O2) for 6 h following a 32 factorial design. Thus, the total number of
treatments remained six Ð S0H0 (water), S1H0(1% NaOH), S2H0 (2% NaOH), S0H1
(1.5% H2O2), S1H1 (1% NaOH1.5% H2O2), S2H1 (2% NaOH1.5% H2O2) Ð and
these were replicated thrice. The solution to straw ratio was kept 3:1 on volume to weight basis. After soaking, the solution was poured out and the treated MS (TMS) was dried at 508C for 2 days and the dried samples of untreated MS (UMS) and TMS were ground to pass through a 1 mm sieve for further analysis.
2.2. Physical characteristics of straw
After treatment, changes in the straw color were observed because these can be used as a crude indicator of uniformity of distribution of either NaOH, H2O2or AHP in the straw.
The pH of residual straws and solutions of alkali or alkaline hydrogen peroxide was
measured using a digital pH meter. Ten grams of straw sample was added with 50 ml distilled water and the slurry was made by manual stirring and then pH of the slurry was measured as pH of the residual straw. The tenacity was measured as `g/tex' using a stelometer (Chaturvedi et al., 1998a). The straw strips were held in jaws and broken by curvilinear displacement on the stelometer. The breaking constant in `kp' units of stelometer was noted down for each strip. The broken straw strip was weighed accurately. The load constant `kp' divided by weight in mg multiplied the stelometer constant 1.4, is a measure of tenacity expressed in `g/tex'.
2.3. Chemical analysis
The dry matter (DM) content was determined by drying the straw in hot air oven at 9558C until a constant weight was achieved. The organic matter (OM) content was determined after ashing the samples in a muf¯e furnace at 6008C for 2 h according to AOAC (1984). The neutral detergent ®bre (NDF), acid detergent ®bre (ADF) and acid detergent lignin (ADL) were estimated following the methods of Goering and Van Soest (1970). The sodium sul®te was omitted because NDF was analysed for lignin after a sequential extraction with neutral and acid detergents. Cellulose and hemicellulose contents were calculated, respectively by subtracting ADL from ADF and ADF form NDF. To analyse in vitro organic matter digestibility (IVOMD) of samples, the method of Tilley and Terry (1963) was followed except that the second stage was avoided because the straw samples have very less amount of protein. The rumen liquor used was obtained from ®stulated rams maintained on a cenchrus (Cenchrus ciliaris) straw based diet (roughage to concentrate ratio, 65:35).
2.4. Statistical analysis
The data were analysed according to Gomez and Gomez (1976). The effect of various treatments on physical and chemical characteristics and IVOMD was statistically ana-lysed using two way analysis of variance, whereas the mean effect of levels of NaOH and H2O2on chemical constituents and IVOMD were analysed in a 32 factorial arrangement.
3. Results and discussion
The chemical composition of mustard straw along with wheat straw, barley straw, paddy straw and sugarcane bagasse is presented in Table 1. From the comparison, it is evident that MS contains the highest amount of cellulose, while the hemicellulose content was lowest. The major limiting factor in MS is its high content of lignin which may possibly act as barrier for microbial breakdown of cellulose in the rumen resulting into low intake.
3.1. Physical characteristics
Physical characteristics Ð pH, colour and tenacity Ð of mustard straw before and after treatment with different combinations of sodium hydroxide and hydrogen peroxide are
presented in Table 2. The pH of the residual solution after soaking the MS was in the range of 12.6±13.1 where the straw was treated with NaOH; with or without H2O2. It
indicates that the pH was in the desired range for effective alkali/AHP treatment. The untreated straw had a nearly neutral pH which increased to more than 10 where it was treated with either alkali or AHP. The changes in colour were also observed due to treatment while the straw treated with different concentration of NaOH acquired brownish colour. The AHP treated straw had golden yellow colour. Tenacity is the mass stress at break and is expressed as g/tex. Tenacity was used to assess the physical characteristics of the straw and it was negatively correlated with IVDMD (Chaturvedi et al., 1998a). There was decrease in tenacity upon treatment with 2% NaOH with or without H2O2and with 1% NaOH1.5% H2O2. However, the tenacity increased when
straw was soaked with water. Although the tenacity decreased with increasing level of NaOH as well as H2O2in soaking medium, the differences were non signi®cant. The
observations with respect to tenacity were similar to our previous study (Chaturvedi et al., 1998a).
Table 1
Chemical composition (g kgÿ1DM) of some course roughages as compared to mustard straw
Attributes Wheat
Crude protien 33 43 51 34 45
NDF 798 809 720 701 810
ADF 518 513 485 443 687
Hemicellulose 280 296 235 258 123
Cellulose 376 413 319 403 486
Lignin 96 98 97 33 145
Gross energy (Mcal/kg) 3.7 4.4 NDe 2.8 5.0
aChaturvedi and Tiwari (1997).
Physical characteristics and pH of untreated (UMS) and treated mustard straw (TMS)
Attributes UMS TMS SEM Tenacity (g/tex) 1.07 1.30 1.03 0.91 0.83 0.82 0.81 0.200
aMeans bearing similar letters do not differ signi®cantly (p<0.01).
3.2. Chemical characteristics and IVOMD
The chemical composition and IVOMD of untreated mustard straw (UMS) and those treated with different combinations of NaOH and H2O2are depicted in Table 3. The NDF
content of UMS was 832 g kgÿ1DM and it increased to 852 and 899 in S0H0and S0H1,
respectively, whereas NDF content decreased signi®cantly (p<0.01) in the treatments where MS was soaked in solution containing either 2% NaOH (S2H0) or 2%
NaOH1.5% H2O2 (S2H1). The change in NDF, however, was negligible in S1H0and
S1H1. In our earlier study, the adverse effects of water on cell wall constituents (CWC)
were observed (Chaturvedi et al., 1999) and the decrease in NDF content of straw caused by NaOH and AHP treatment was probably due to solubilization of hemicellulose (Chaudhry, 1998). The content of NDF decreased linearly (p<0.01) with increasing level of NaOH in the soaking medium (Table 4). The ADF content of MS decreased by 12.2 and 7.7% units when it was treated with solutions containing 2% NaOH (S2H0) or 2%
NaOH1.5% H2O2(S2H1), respectively, indicating no additive effect of AHP on ADF
content. With increasing level of NaOH, the content of ADF decreased linearly (p<0.01). Table 3
Chemical composition (g kgÿ1DM) and IVOMD of untreated (UMS) and treated mustard straw (TMS)
Attributes UMS TMS SEM
S0H0 S1H0 S2H0 S0H1 S1H1 S2H1
OM 941 ba 973 c 898 a 890 a 975 c 936 b 896 a 3.5
NDF 832 c 852 c 817 bc 759 a 899 d 849 c 778 ab 9.6
ADF 781 c 793 c 752 bc 686 a 855 d 757 bc 721 ab 11.0
Hemicellulose 52 58 65 74 44 92 57 9.5
Cellulose 645 c 653 c 584 b 531 a 692 d 600 b 571 b 7.8
ADL 133 a 152 ab 163 b 151 ab 163 b 157 b 149 ab 4.5
IVOMD 162 a 154 a 241 b 261 b 138 a 291 b 360 c 11.1
aMeans bearing similar letters do not differ signi®cantly (p<0.01).
Table 4
Effect of soaking medium on chemical composition (g kgÿ1DM) and IVOMD of MS
Attributes Levels of NaOH SEM Levels of H2O2 SEM Interaction
S0 S1 S2 H0 H1
OM 974 ca 917 b 893 a 2.7 921 a 936 b 2.2 **b
NDF 875 c 833 b 768 a 7.2 809 a 842 b 5.9 NSc
ADF 824 c 754 b 703 a 7.6 744 a 777 b 6.2 NS
Hemicellulose 51 79 65 7.0 66 65 5.7 NS
Cellulose 672 c 592 b 550 a 5.3 589 a 621 b 4.3 NS
ADL 157 160 150 3.5 155 156 2.8 NS
IVOMD 146 a 266 b 310 c 8.0 219 a 263 b 6.5 **
aMeans bearing similar letters do not differ signi®cantly (p<0.01). bp<0.01.
cNot signi®cant.
The effect of treatment combinations on hemicellulose content was not signi®cant. Although AHP treatment reduced the hemicellulose content signi®cantly in wheat straw (Amjed et al., 1992; Chaudhry, 1998), these were not observed in the present experiment, probably, because of the lower concentration of hemicellulose in MS than that of wheat straw. The effect of different treatments on the cellulose content was similar to that of NDF and ADF. Among the TMS, ADL content was lowest in S2H1which was similar to
that of UMS. Thus, the treated straw had a higher amount of ADL than that of UMS, however, the mean effect of NaOH and H2O2on ADL was non-signi®cant (p>0.05). The
lack of effect of NaOH and AHP in reducing ADL was also reported by Chaudhry and Miller (1996) and Chaudhry (1998). However, it was contrary to those reported by Gould (1985) and Kerley et al. (1987), where pronounced decreases in lignin from straws treated with AHP were observed. Soaking of wheat straw in AHP at pH 11.5 released ca. 15± 50% of the lignin as water soluble products (Gould, 1984; Chaudhry and Miller, 1994). Alkali treatment, however, does not reduce or destroy the phenolics; it breaks speci®c lignin carbohydrate complexes (Chesson, 1986). Results of one of our earlier studies also indicated that NaOH or AHP treatment of MS saponi®ed polyphenolic acids due to which the quantity of saponi®able groups reduced in the treated straw (Chaturvedi et al., unpublished data). The changes in cellulose content of MS brought about by different treatments were more pronounced where MS was soaked in NaOH (S1H0and S2H0) or
AHP (S1H1and S2H1) solutions.
Mustard straw is of poor nature with respect to IVOMD (162 g kgÿ1 DM) which reduced slightly due to either water (S0H0) or H2O2 (S0H1) treatment. Signi®cant
(p<0.01) increase in IVOMD, however, was observed when straw was soaked in S1H0,
S2H0and S1H1. The highest IVOMD was observed in MS when it was soaked in S2H1.
Alkali treatment causes swelling and changes in the crystalline structure of cellulose (Guggolz et al., 1971; Klopfenstein, 1978) and makes it susceptible to ruminal microbial degradation. Further, the crosslinks between phenolic groups on lignin and a polymer of xylan (hemicellulose) and cellulose are broken by NaOH through saponi®cation (Tarkow and Feist, 1969). The IVOMD content of MS increased by 122.8, 80.0, 61.3 and 49.1% units in S2H1, S1H1, S2H0and S1H0, respectively. Improvement in IVDMD has also been
seen in our previous study when straw was soaked in NaOH solution. An increased potential degradability was observed in wheat straw through 1% AHP treatment (Bhargava et al., 1989). A lower in sacco ®bre disappearance was observed when wheat straw treated with AHP in a 3.5:1 liquid and substrate ratio resulting in no loss of ADL, was not washed after treatment compared with treated straw when it was either washed (Lewis et al., 1987) or allowed to dry in the sun (Meeske et al., 1993).
The IVOMD content increased signi®cantly (p<0.01) with the increasing level of NaOH. Mean effect of NaOH treatment on IVOMD was highly signi®cant (p<0.01) as it increased IVOMD by 82 and 112% units at NaOH concentration of 1 and 2%, respectively.
3.3. Relationship among cell wall constituents, tenacity and IVOMD
As expected, the correlation of NDF, ADF and cellulose with IVOMD were highly negative (Table 5). In spite of lesser variations caused by sodium hydroxide or AHP
treatment in NDF, ADF and cellulose content, the NaOH and AHP treatments could improve the IVOMD of MS signi®cantly. Negative correlation between CWC and IVDMD has also been found by Gupta (1998) and it is presumed that more cross-links between CWC and phenolic groups on lignin resulted in an increase in crystallinity, thereby hindering the swelling and digestion of ®bre.
From the results obtained it is concluded that the cell wall constituents and IVOMD of MS were modi®ed by NaOH with or without H2O2in a way that in vitro organic matter
digestibility (IVOMD) of treated MS was 82±112% units higher than that of untreated MS. Bene®cial effects of H2O2were observed on IVOMD of straw.
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Table 5
Correlation among cell wall constituents, tenacity and IVOMD
Attributes NDF ADF HC Cellulose ADL Tenacity IVOMD
NDF 1.00
ADF 0.93*** 1.00
Hemicellulose ÿ0.14 ÿ0.50* 1.00
Cellulose 0.86*** 0.96*** ÿ0.55* 1.00
ADL 0.35 0.22 0.22 ÿ0.01 1.00
Tenacity ÿ0.02 0.07 ÿ0.24 0.20 ÿ0.17 1.00
IVOMD ÿ0.64** 0.72*** 0.42 ÿ0.76*** 0.06 ÿ0.35 1.00
*p<0.05; **p<0.01; ***p<0.001.
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