Title: Winter rye as a bioenergy feedstock: impact of crop maturity on composition, biological solubilization and potential revenue

Abstract

We report that winter annual crops such as winter rye (Secale cereale L) can produce biomass feedstock on seasonally fallow land that continues to provide high-value food and feed from summer annuals such as corn and soybeans. As energy double crops, winter grasses are likely to be harvested while still immature and thus structurally different from the fully senesced plant material typically used for biofuels. This study investigates the dynamic trends in biomass yield, composition, and biological solubilization over the course of a spring harvest season. The water soluble fraction decreased with increasing maturity while total carbohydrate content stayed roughly constant at about 65%. The protein mass fraction decreased with increasing maturity, but was counterbalanced by increasing harvest yield resulting in similar total protein across harvest dates. Winter rye was ground and autoclaved then fermented at 15 g/L total solids by either (1) Clostridium thermocellum or (2) simultaneous saccharification and cofermentation (SSCF) using commercial cellulases (CTec2 and HTec2) and a xylose-fermenting Saccharomyces cerevisiae strain. Solubilization of total carbohydrate dropped significantly as winter rye matured for both C. thermocellum (from approximately 80% to approximately 50%) and SSCF (from approximately 60% to approximately 30%). C. thermocellum achieved total solubilization 33% higher thanmore » that of SSCF for the earliest harvest date and 50% higher for the latest harvest date. Potential revenue from protein and bioethanol was stable over a range of different harvest dates, with most of the revenue due to ethanol. In a crop rotation with soybean, recovery of the soluble protein from winter rye could increase per hectare protein production by 20 to 35%. Double-cropping winter rye can produce significant biomass for biofuel production and feed protein as coproduct without competing with the main summer crop. During a 24-day harvest window, the total carbohydrate content remained relatively constant while the early-harvest yielded much higher carbohydrate solubilization for both C. thermocellum fermentation and SSCF. C. thermocellum fermentation achieved higher carbohydrate solubilization than SSCF across all growth stages tested. In conclusion, although winter rye’s yield, composition, and biological reactivity change rapidly in the spring, it offers a substantial and stable income across the harvest season and thus flexibility for the farmer.« less

Authors:

Shao, Xiongjun ^[1]; DiMarco, Kay ^[2]; Richard, Tom L. ^[2]; Lynd, Lee R. ^[3]

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+ Show Author Affiliations

1. Dartmouth College, Hanover, NH (United States). Thayer School of Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. Pennsylvania State Univ., University Park, PA (United States)
3. Dartmouth College, Hanover, NH (United States). Thayer School of Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Enchi Corporation, Lebanon, NH (United States)

Publication Date:

Fri Feb 27 00:00:00 EST 2015

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1259861

Grant/Contract Number:  

AC05-00OR22725; 2012-68005-19703

Resource Type:

Accepted Manuscript

Journal Name:

Biotechnology for Biofuels

Additional Journal Information:

Journal Volume: 8; Journal Issue: 1; Journal ID: ISSN 1754-6834

Publisher:

BioMed Central

Country of Publication:

United States

Language:

English

Subject:

60 APPLIED LIFE SCIENCES; Winter rye; Secale cereale L; Unpretreated; Lignocellulosic biomass; Growth stage; Boot stage; Harvest maturity; Biological solubilization; Carbohydrate solubilization; Protein recovery; Consolidated bioprocessing; SSCF; Clostridium thermocellum