Enzymatic saccharification of milled timothy (Phleum pratense L.) and alfalfa (Medicago sativa L.)

Size reduction is an essential step in the conversion of lignocellulosic crops to fuel, feed and other products. Many pre-treatments may then be used to fractionate such materials and/or prepare them for conversion to other substances. In order to evaluate the energy efficiency of some pretreatments, including more extensive mechanical reduction, it is important to know what would be the yields from the preliminary shredding and milling. Furthermore, most rural communities are already equipped with the infrastructures necessary for milling, and it is possible that further investment in specialized mills could lead to a simpler route to production of fermentation products and co-products. This study reports saccharification yields of timothy (Phleum pratense L.) at two stages of maturity, and of alfalfa (Medicago sativa L.) at one stage of maturity. The hydrolysate from the late-season timothy was fermented with Saccharomyces cerevisiae. Multifect Cellulase 300 and Spezyme CP, both supplied by GEN-ENCOR International, were used to hydrolyze the ground material. Saccharification of cellulose was 7 times greater than that of hemicellulose, and was dependent on the relative carbohydrate content, plant maturity and on the extent of size reduction. The quantity of reducing sugars in the hydrolysate exhibited a strong fluctuating component that could be related to adsorption/desorption phenomena. The extent of saccharification was influenced by the rate of addition of enzyme to the biomass. Total saccharifications with enzyme activities of 5 FPU g−1 were as high as 51.4% in the case of timothy. The timothy hydrolysate was fermented to at least 88% of theoretical yield, with addition of nutrients, and to at least 80% without addition of nutrients.