Enzyme Imbalance in Forbs Affects Glucose Yield for Biofuel Production

Old fields, prairies and marginal lands are often the top candidates for growing feedstocks due to several potential benefits such as minimal inputs and high biodiversity. However, species dominant in these landscapes are often forbs, which are herbaceous dicotyledonous plants. Moreover, the potential and obstacles of using forbs as biofuel feedstocks are poorly understood. In the study, the yields of fermentable sugars from four representative forbs were evaluated using corn stover as the baseline. The forbs evaluated were lamb's quarters (Chenopodium album), goldenrod (Solidago canadensis), milkweed (Asclepias syriaca), and Queen Anne's lace or wild carrot (Daucus carota).

 All forbs had lower total glucose content, ranging from 16.2 to 23% on dry weight basis, from all sources compared to corn stover with 39.2%. Yields of glucose as a percentage of total glucose after digestion with commercial enzyme were also lower for all forbs compared to corn stover. Enzyme imbalance was the most probable reason for the low yields from the forbs. Lamb's quarters had enhanced glucose yields after addition of xyloglucanase and α-xylosidase, two enzymes that target glucose-containing polysaccharides abundant in dicotyledonous plants. However, yields were still lower than those from corn stover.

 The utilization of forbs-rich plant communities as biofuel feedstocks must take into account their low glucose content. A new enzyme mixture designed for the different cell wall composition of forbs is essential.