| Wheat straw is an abundant biomass resource.The cellulose and hemicellulose contained in wheat straw can be digested and absorbed by ruminants.However,the complex physical and chemical structure of wheat straw prevents microbial digestion or enzymatic saccharification.Therefore,pretreatment is a necessary to improve the digestibility of wheat straw.As an environmentally friendly physical and chemical method,steam explosion can improve the digestibility of biomass through various mechanisms including reducing particle size,breaking the degree of polymerization and crystallinity of cellulose,hydrolyzing some hemicellulose,and increasing porosity.In the paper,we studied the effects of steamexploded wheat straw on rumen fermentation,sugar yield and microbial structure.The results showed that steam explosion could enhance the digestibility and fermentation of wheat straw as forage for cattle.1.Optimization of steam explosion pretreated wheat straw using response surface methodologyThe study choosing the steam pressure(1.5 Mpa-2.5 Mpa),moisture content(10%-50%)and treatment time(90 s-210 s)as the independent variables,the VFA production in the in vitro rumen fermentation was the response value,and then established the regression model and fitted.The results as following:(1)the treatment time had a significant effect on the VFA production(P<0.05),and the VFA production gradually increased with the treatment time;(2)The optimal condition for steam explosion pretreatment by response surface methodology were steam pressure 2.30 Mpa,moisture content 36.46% and treatment time 90 s.Under this condition,the VFA production in the in vitro rumen fermentation could reach the maximum.2.Effect of steam explosion on sugar production and microbial structure of wheat strawWheat straw was steam exploded by the optimized conditions of experiment 1.We analyzed the effect of steam explosion on the fermentation parameters of wheat straw,the sugar production and microbial structure.The results showed that:(1)Under the optimal steam explosion conditions,steam explosion pretreatment significantly increased the VFA concentration and its components of wheat straw in vitro fermentation,and significantly reduced the value of acetate/propionate(P<0.01);(2)Steam explosion significantly increased the content of fructose,xylose,arabinose,maltose and cellobiose in vitro fermentation;(3)At the phylum level,steam explosion significantly increased the relative abundance of phylum Firmicutes(P<0.01),and had little effect on the relative abundance of the phylum Bacteroidetes(P > 0.05);at the genus level,significantly increased the relative abundance of Saccharofermentans and Butyrivibrio(P<0.01),significantly reduced the relative abundance of Succiniclasticum and Selenomonas(P<0.01),steam explosion had little effect on the relative abundance of the Prevotella and Ruminococcus(P > 0.05).3.Effect of steam explosion on rumen degradationThe untreated and steam-exploded wheat straws were incubated for 2 h,6 h,12 h,24 h,48 h,and 72 h by the nylon bags in the rumen.The results were following:(1)The NDF degradation of steam-exploded wheat straw at 24 h and 48 h was significantly higher than that of untreated wheat stalks(P <0.05),and the NDF degradation rate of steam-exploded wheat straw at 72 h was significantly higher than that of untreated wheat stalks(P <0.01),and the degradation rate increased by 28.78%.Steam explosion also significantly increased the effective degradation rate of wheat straw(P <0.05).(2)The ADF degradation rate of steam-exploded wheat straw at 24 h and 48 h was significantly higher than that of untreated wheat straw(P <0.05),and the ADF degradation rate at 72 h was significantly higher(P <0.01),and the degradation rate increased by 18.02%.Steam explosion does not have significantly effect on the effective degradation rate of wheat straw(P >0.05).In conclusion,steam explosion may be a useful pretreatment of wheat straw to improve its nutritional value as forage for ruminants. |
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