Effect of the Growth Period on Bioethanol Production from the Branches of Woody Crops Cultivated in Short-rotation Coppices

Woody crops cultivated in short-rotation coppices are attractive sources of lignocellulosic materials for bioethanol production, since they are some of the most abundant renewable resources. In this study, we evaluated the effects of the growth period on bioethanol production using short-rotation woody crops (Populus nigra ${\times}$ Populus maxiwiczii, Populus euramericana, Populus alba ${\times}$ Populus glandulosa, and Salix alba). The carbohydrate contents of 3-year-old and 12-year-old short-rotation woody crop branches were 62.1-68.5% and 64.0-67.1%, respectively. The chemical compositions of 3-year-old and 12-year-old short-rotation woody crop branches did not vary significantly depending upon the growth period. However, the 3-year-old short-rotation woody crop branches (glucose conversion: 26-40%) were hydrolyzed more easily than their 12-year-old counterparts (glucose conversion: 19-24%). Furthermore, following the fermentation of enzymatic hydrolysates from the crop branch samples (by Saccharomyces cerevisiae KCTC 7296) to ethanol, the ethanol concentration of short rotation coppice woody crops was found to be higher in the 3-year-old branch samples (~ 0.18 g/g dry matter) than in the 12-year-old branch samples (~ 0.14 g/g dry matter). These results suggest that immature wood (3-year-old branches) from short-rotation woody crops could be a promising feedstock for bioethanol production.