title: Winter rye as a bioenergy feedstock: impact of crop maturity on composition, biological solubilization and potential revenue.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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 than 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%.
  
  
  CONCLUSIONS
  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. 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.
authors: Thayer School of Engineering at the Dartmouth College, 14 Engineering Drive, Hanover, NH 03755 USA ; DOE BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA.
authors: Xiongjun
authors: X
authors: Shao
authors: Penn State University, 225 Agricultural Engineering Building, University Park, PA 16802 USA.
authors: Kay
authors: K
authors: DiMarco
authors: Penn State University, 225 Agricultural Engineering Building, University Park, PA 16802 USA.
authors: Tom L
authors: TL
authors: Richard
authors: Thayer School of Engineering at the Dartmouth College, 14 Engineering Drive, Hanover, NH 03755 USA ; DOE BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA ; Enchi Corporation, Lebanon, NH 03766 USA.
authors: Lee R
authors: LR
authors: Lynd
keywords: Biological solubilization; Boot stage; Carbohydrate solubilization; Clostridium thermocellum; Consolidated bioprocessing; Growth stage; Harvest maturity; Lignocellulosic biomass; Protein recovery; SSCF; Secale cereale L; Unpretreated; Winter rye