Composition and Sugar Release of Mixed-Prairie Species After Hydrothermal Treatment and Enzymatic Saccharification

Mixed-prairie species (MPS, containing grass and legume plant species) have been reported to grow well on agriculturally degraded lands with minimal fertilization and low agricultural inputs. Such "species mixtures"  have also been found to exhibit high levels of biodiversity (notably those including legumes) which "benefit from a self-supply of nitrogen, potentially reducing or eliminating the need for nitrogen fertilizer". These features (i.e., thriving on marginal lands, low agricultural inputs) make MPS as good biofuel feedstocks. Cultivation of these bioenergy crops do not compete with agriculturally productive land. The performance of mixed MPS  feedstocks to release ethanol-fermentable sugars (after pretreatment) is not yet well studied.

Scientists from the University of California, Riverside (United States) evaluated the sugar release of some dominant species in an MPS-plot after hydrothermal pretreatment (heating with water at 180^oC) and enzymatic saccharification. Hydrothermal pretreatment "deconstructs" the plant cell walls, exposing the carbohydrate polymers, while enzymatic saccharification breaks-down the carbohydrates into simple sugars for ethanol fermentation. The following plants from an MPS plot were studied: (1) a C3 grass (Poapratensis), (2) a C4 grass (Schizachyrium scoparium), and (3) a legume (Lupinus perennis).

The researchers found that the two grasses "contained higher levels of sugars than did the legume, and also exhibited higher sugar yields as a percentage of the maximum possible from combined pretreatment and enzymatic hydrolysis. They also found that the stems of the two grasses and the legume exhibited higher "recalcitrance" (resistance to plant cell wall deconstruction) compared to other parts of the plant. Thus, plant anatomy was concluded to be an important factor for both glucan digestibility and glucose mass release in the MPS plants studied. The full paper is published in the open access journal, Biotechnology for Biofuels (URL above).