Effects of different nonionic surfactants on in vitro fermentation characteristics of cereal straws.

Abstract

The effects of 3 nonionic surfactants (NIS), including alkyl polyglucoside (APG), sorbitan trioleate (Span85), and polyoxyethylene sorbitan monostearate (Tween80), on in vitro fermentation characteristics of maize stover, rice straw, and wheat straw were examined using an in vitro gas production technique. Four levels each of APG, Span85, and Tween80 [0, 0.02, 0.05, and 0.1% (vol/vol) of incubation solution] were tested in a 4 x 4 x 4 factorial arrangement. The NIS generally increased the in vitro maximal gas production (A), but decreased the lag time of cereal straws. The effects of NIS on the rate of gas production (B) were related to the surfactant type and fermented substrate. The NIS generally increased IVDMD and in vitro OM disappearance (IVOMD) of cereal straws, but responses were dose dependent. The NIS increased total VFA concentration of in vitro fermentation supernatant for maize stover and wheat straw, but decreased total VFA concentration for rice straw. The effects of NIS on the molar proportions of acetate, propionate, and butyrate were dependent on the dose and type of NIS and on fermented substrate. Several interactive effects were noted between or among 3 surfactants (APG, Span85, and Tween80) on in vitro gas production variables, IVD-MD, IVOMD, and VFA for each straw; the optimal combinations of 2 or 3 types of NIS were determined according to the responses of IVDMD and IVOMD to NIS addition. The results of this study suggest that NIS may improve in vitro fermentation of low quality roughages and have potential application as feed additives in ruminant production.

Full text

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Ren
Z. H. Cong, S. X. Tang, Z. L. Tan, Z. H. Sun, C. S. Zhou, X. F. Han, M. Wang and G. P.
cereal straws
Effects of different non-ionic surfactants on in vitro fermentation characteristics of
published online Dec 19, 2008;
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Running head: non-ionic surfactant supplementation

Effects of different non-ionic surfactants on in vitro fermentation characteristics of cereal
straws 1

Z.H. Cong§,†, S.X. Tang§,†, Z.L. Tan§,2, Z.H. Sun§, C.S. Zhou§, X.F. Han§, M. Wang§, and G.P. Ren‡

§ Key Laboratory of Agro-ecological Engineering, Institute of Subtropical Agriculture, The Chinese
Academy of Sciences, Changsha, Hunan 410125, P.R. China
† Graduate University of the Chinese Academy of Sciences, Beijing 100039, P.R. China
‡ Central South University of Forestry and Technology, Changsha, Hunan 410004, P.R. China

1 We express our appreciation to the Chinese Academy of Sciences (No. kscx2-YW-N-022), the
Ministry of Science and Technology of China (2006BAD04A15) and Natural Science Foundation
of Hunan Province (No.05JJ10004) for jointly providing the financial support for this study.
2 Corresponding author: zltan@isa.ac.cn

Published Online First on December 19, 2008 as doi:10.2527/jas.2008-1316
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ABSTRACT: The effects of 3 non-ionic surfactants (NIS), including alkyl polyglucoside (APG),
sorbitan trioleate (Span85), and polyoxyethylene sorbitan monostearate (Tween80), on in vitro
fermentation characteristics of maize stover, rice straw, and wheat straw were examined using an in
vitro gas production technique. Four levels each of APG, Span85, and Tween80 (0, 0.02%, 0.05%,
and 0.1% (vol/vol) of incubation solution) were tested in a 4 × 4 × 4 factorial arrangement. The NIS
generally increased the in vitro maximal gas production (A), but decreased the lag time (LAG) of
cereal straws. The effects of NIS on the rate of gas production (B) were related to the surfactant
type and fermented substrate. The NIS generally increased IVDMD and in vitro OM disappearance
(IVOMD) of cereal straws, but responses were dose dependent. The NIS increased total VFA
concentration of in vitro fermentation supernatant for maize stover and wheat straw, but decreased
total VFA concentration for rice straw. The effects of NIS on the molar proportions of acetate,
propionate, and butyrate were dependent on the dose and type of NIS and on fermented substrate. A
number of interactive effects were noted between or among 3 surfactants (APG, Span85, and
Tween80) on in vitro gas production parameters, IVDMD, IVOMD, and VFA for each straw; the
optimal combinations of 2 or 3 types of NIS were determined according to the responses of
IVDMD and IVOMD to NIS addition. The results of this study suggest that NIS may improve in
vitro fermentation of low quality roughages and have potential application as feed additives in
ruminant production.
Key words: Non-ionic surfactant, Rumen fluid, In vitro gas production, In vitro digestibility, Cereal
straw

INTRODUCTION
Agricultural by-products such as cereal straws are carbohydrate-rich residues representing a
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large potential source of dietary energy for ruminants. It has been well recognized that maize stover,
rice straw, and wheat straw have poor nutritional value because of their low nitrogen and high fiber
content (Tang et al., 2006, 2008), and the greater fiber makes mature plant materials less digestible
(Chesson, 1984; Tan et al., 1995). Great efforts have recently been made to improve forage
utilization by increasing the degradability of fibrous materials through chemical (Vadiveloo, 2000),
physical (Hai et al., 1998), and biological (Yamada et al., 2000) treatment. The partial breakdown of
the rigid cell wall structure of forage results in the greater accessibility of fiber-degrading bacteria
and their associated enzymes to forage plants. Furthermore, the addition of exogenous supplements
(fibrolytic enzymes and yeast culture) can improve in vitro fermentation of low quality cereal
straws (Tang et al., 2008).
Non-ionic surfactants (NIS) are known to stimulate the release of enzymes from a range of
aerobic microbes (Hung et al., 1988; Yazdi et al., 1990; Long and Knapp, 1991). In recent years,
some experiments have been conducted to test whether NIS had a similar effect on the activity of
anaerobic microbes in the rumen. Polyoxyethylene sorbitan monostearate (Tween80), a type of NIS,
has been proven to increase cellulase activity and stability (McAllister et al., 2000; Lee and Ha,
2003; Lee et al., 2003), numbers of viable bacteria (Kim et al., 1982; Lee et al., 2003; Lee et al.,
2004), microbial growth rate (Lee et al., 2003), and degradation of forage substrates (Goto et al.,
2003a) in the rumen. In addition, Lee et al. (2004) reported that SOLFA-850 (Span85, sorbitan
trioleate, a type of NIS) increased the enzyme activities of protease, amylase, carboxymethyl
cellulase (CMCase), and xylanase in the rumen contents, the in situ degradation rate of rice straw,
the concentrations of VFA and NH3-N in the rumen fluid, and the growth rate of ruminal anaerobic
microorganisms. Although the above mentioned 2 types of NIS have different structure and physical
or chemical properties, both of them have the ability to stimulate the activity of ruminal microbes.
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Alkyl polyglucoside (APG) is another type of NIS, and it is derived from a reaction of cornstarch
glucose and a natural fatty alcohol (decyl polyglucose). Its structure and physical and chemical
properties differ from Tween80 or Span85; few studies have been conducted to investigate its effect
on ruminal fermentation. Therefore, the objective of this experiment was to assess the effect of
direct addition of NIS, including APG, Span85, and Tween80, on in vitro fermentation
characteristics of maize stover, rice straw, and wheat straw, using an in vitro gas production
technique, to determine optimal ratios of the 3 types of NIS.

MATERIALS AND METHODS
This experiment was approved by the Animal Care Committee, Institute of Subtropical
Agriculture (ISA), the Chinese Academy of Sciences, Changsha, China.

Straw Preparation
The experiment was conducted at the experimental farm of ISA in southern China (28°12′N and
113°5′E; altitude 38 m). After wheat (Triticum aestivum var. Weimai 8), rice (Oryza sativa var.
Jinyou 207), and maize (Zea mays var. Linao 1) grains were harvested on May 21, July 25, and July
27, 2005, respectively, 2 kg each of mature maize stover, rice straw, and wheat straw were randomly
collected and chopped to a length of 2 cm, then approximately 500 g of each straw was oven-dried
at 60oC for 48 h and ground through a 1-mm screen (DF-2, Changsha Instrument Factory, Changsha,
China) for chemical analysis and in vitro fermentation.

Experimental Design
Experiments were conducted to measure in vitro gas production characteristics of maize stover,
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