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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVING ALFALFA AND OTHER FORAGE CROPS FOR BIOENERGY, LIVESTOCK PRODUCTION, AND ENVIRONMENTAL PROTECTION Title: Comparison of cell wall polysaccharide hydrolysis by a dilute acid/enzymatic saccharification process and rumen microorganisms

Authors
item Jung, Hans Joachim
item Bernardo, Rex -

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 14, 2011
Publication Date: June 15, 2011
Citation: Jung, H.G., Bernardo, R. 2011. Comparison of cell wall polysaccharide hydrolysis by a dilute acid/enzymatic saccharification process and rumen microorganisms. BioEnergy Research. Available: http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s12155-011-9131-9.

Interpretive Summary: A commercial cellulosic bioenergy industry will require biomass crops with improved conversion potential and industry must be able to price biomass lots for their potential to yield biofuel. Because the actual industrial conversion process is too complex to use for routine testing of biomass, assays must be developed that mimic the conversion process. Because microorganisms in the rumen of cows can breakdown cellulose, laboratory assays based on this process have been proposed as a test for biomass conversion potential. This project compared the extent to which rumen microorganisms breakdown cellulose and other plant cell wall polysaccharides in corn stover with breakdown by a laboratory assay based on the industrial dilute acid pretreatment and enzyme conversion process. The rumen assay actually broke down more cellulose than the conversion assay, but most other polysaccharides were broken down more effectively by the conversion assay. The degree of agreement between the two assays was limited for ranking the potential biofuel yield of corn stover samples. The rumen assay may have some limited use for breeding improved biomass crops; however, pricing biomass will require greater predictive accuracy than the rumen assay can provide. These results will be of interest to biomass crop breeders and economists concerned with tools for pricing biomass.

Technical Abstract: Evaluation of biomass crops for breeding or pricing purposes requires an assay that predicts performance of biomass in the bioenergy conversion process. Cell wall polysaccharide hydrolysis by dilute sulfuric acid pretreatment at 121 degrees C followed by cellulase hydrolysis for 72 h (CONV) and in vitro rumen microflora incubation for 72 h (RUMEN) were compared for a set of maize stover samples with a wide range in cell wall composition. Residual polysaccharides were analyzed for sugar components and extent of hydrolysis calculated. Cell wall polysaccharide hydrolysis was different for all sugar components between the CONV and RUMEN assays. The CONV assay hydrolyzed xylose, arabinose, galactose, and uronic acid containing polysaccharides to a greater degree than did the RUMEN assay, whereas the RUMEN assay was more effective at hydrolyzing glucose and mannose polysaccharides. Greater hydrolysis of hemicellulosic components by CONV can be attributed to the acid hydrolysis mechanism of the CONV assay for non-cellulosic polysaccharides whereas the RUMEN assay was dependent on enzymatic hydrolysis. Although CONV and RUMEN hydrolysis were correlated for most polysaccharide components, the greatest correlation was only r = 0.70 (glucose). Linear correlations and multiple regressions indicated that polysaccharide hydrolysis by the RUMEN assay was negatively associated with lignin concentration and ferulate ether cross linking as expected. Corresponding correlations and regressions for CONV were less consistent and occasionally positive. Use of rumen microbial hydrolysis to characterize biomass performance in a conversion process may have some limited usefulness for genetic evaluations, but such assays would be unreliable for biomass pricing.

Last Modified: 11/26/2014