Effects Of Rumen Fluid On Fermentation Quality And Degradation Of Sweet Sorghum Straw

With the consumption of fossil fuels and increasing environmental concerns regarding climate change,clean and renewable bioenergy as alternatives have attracted extensive attentions.Due to the high availability and low cost,lignocellulosic biomass has been regarded as a promising feedstock for bioenergy to reduce the dependence on fossil fuel and mitigate the environmental impacts.China is an agricultural country.Among the various lignocellulosic biomass such as crop straw,energy crops and food processing waste,an increasing attention has been paid to sweet sorghum(Sorghum bicolor Moench.),a kind of drought-tolerant C4 energy crop,due to its high sugar and energy content,rapid growth rate and high biomass productivity,early maturity and also strong resistance to saline-alkaline soils.Upon a large scale utilization,however,sweet sorghum is usually harvested in a seasonal manner,which requires appropriate storage to ensure the needs of biofuels are able to supply all the year round.Ensiling is an anaerobic fermentation process and has been proved to be an efficient preservation method for fresh energy crop.During ensiling,water-soluble carbohydrates in the biomass support rapid growth of endogenous aerotolerant lactic acid bacteria(LAB)and are converted into organic acids(primarily lactic acid and acetic acid)causing pH reduction.In order to realize the long-term storage and resource utilization of crop straw,this paper used sweet sorghum straw as test material and used silage principle to conduct solid fermentation.The different treatments as follows:(1)CK: silage with OTU addition of additive;(2)R1: silage with additive at dosage of 1 mL/100 g fresh substrate,(3)R3: silage with additive at dosage of 3 mL/100 g fresh substrate;(4)R5: silage with additive at dosage of 5 mL/100 g fresh substrate;(5)R7: silage with additive at dosage of 7 mL/100 g fresh substrate.The feedstocks were then packed into plastic bucket,sealed tightly and stored at room temperature(20?)for 60 days.For control group,5 mL sterile water was used instead.All treatments were carried in triplicate.After ensiling,fermentation quality,organic components,microbial diversity,structure and enzymolysis saccharification were analyzed to investigate the effects of silage and bioenhanced pretreatment of rumen fluid on sweet sorghum straw.The results were shown in follow:(1)After 30 days and 60 days ensiling,the dose of rumen fluid,ensiling time and their interaction had significant effects on the dry matter(DM),water-soluble carbohydrates(WSC),crude protein(CP)and fiber contents of sweet sorghum.The content of dry matter and water-soluble carbohydrate in five treatments were all lower than fresh sweet sorghum.The DM,WSC,CP and ammonia nitrogen(AN)contents in R1-R7 was all significantly decreased with both the extension of ensiling time and the increase of rumen fluid dosage.(2)The contents of lactic acid and acetic acid and the pH values of the five treatmentgroups were all decreased significantly with the extension of silage time(P<0.05).The contents of LA and AA in R1,R3,R5 and R7 groups were significantly higher than those in CK group.After 60 days ensiling,the LA and AA contents in R7 and R5 were higher than other groups,which attach to 9.42g/kg(R7)and 29.08g/kg(R5),respectively.(3)According to the analysis of dynamic changes of bacterial community,compared with CK and SS,rumen fluid pretreatment significantly increased the relative abundance of Lactobacillus,Ruminococcacceae,Acetobacter and Firmicutes,which decreased the relative abundance of Enterobacter.After 60 days of silage,the Lactobacillus abundance in R7 was highest(98.76%).(4)The analysis of the dynamic changes of fungal community showed that compared with CK and SS,the relative abundance of Pichia was significantly increased with the addition of rumen fluid,while the relative abundance of SchizopHyllum and Penicillium was decreased.(5)Upon ensiling with rumen fluid addition,the surface of fibers became loose,cracked and rough.When both ensiling and rumen fluid were applied to SS,it was found that fibers were disrupted more and became looser,and the surfaces of fibers showed many deep longitudinal cracks,micro-holes and grooves(CK-R7).Fourier transform infrared(FTIR)analysis showed that the characteristic peak strength of lignin changed after gastric juice pretreatment,indicating that the structure of lignin changed to different degrees,making cellulose more easily degraded.(6)Compared with ensiling only(CK),rumen fluid inoculation further enhanced RSY,glucose,cellobiose and xylose yield during 72 h enzymatic hydrolysis.Specifically,the RSY of the R7 silages from 30 and 60 days of ensiling increased by 11 and 19%,respectively,compared with the CK.Meanwhile,the RSY of R7 silages from 30-and 60-day ensiling was also significantly higher than that of other R1-5 silages,reaching 730.3 mg/g and 795.4 mg/g dry solid,respectively.On the other hand,after 60 days ensiling,the glucose and xylose yield in R7 reached the highest,at 492.9 mg/g and 97.5 mg/g,respectively.In a word,the ensiling also had pretreatment effect on the improvement of reducing sugar yield upon enzymatic hydrolysis due to the destruction of lignin-polysaccharide linkages,reduction of crystallinity and increase of porosity.Bioaugmentation with rumen fluid is a promising technology for preservation and pretreatment of sweet sorghum for biofuel production.