Biomass Feedstock Storage for Quantity and Quality Preservation - Engineering and Science of Biomass Feedstock Production and Provision - page 179

Fig. 7.7 Percent conversion of cellulose to glucose, during hydrolysis, in the presence of
lower-lignin and higher-lignin content

particle size was reduced based on images from scanning electron micrographs
(SEM) of raw and cooked corn slurry samples before and after sonication. About
five times more glucose can theoretically be released from the sonicated samples
relative to the control. An ultrasonic unit with a power output of 2.2 kW and a fre-
quency of 20 kHz was used, and its energy efficiency was calculated based on the
calorific content of the sugar (glucose) released from the treatment samples.

7.5.3 Harvest Time as a Method for Minimizing Lignin Content

Plant age decreases the percent of plant dry matter that can be degraded. Chaves et al.
[ 41 ] empirically modeled the rate at which an increase in the age of ryegrass shoots
decreased plant fiber digestibility. Even though for ethanol production purposes it is
the free sugar and lignin content that is relevant, plant fiber digestibility is an indirect
measure of the biomass's resistance to degradation, which is relevant when breaking
down plant cellulose to sugars. In Chaves et al. [ 41 ], the fraction of dry matter disap-
pearing per hour upon incubation in a liquid-permeable bag in a cow's rumen
decreased from 0.11 to 0.03 as the plant shoot aged by about 80 days. As plant shoots
aged, plants gained in fiber content and lost in nutrients. According to Chaves et al.
[ 41 ] neutral detergent fibers (fibers that would be accessible to amylase if there was
no pretreatment with acid) are correlated to plant age as follows ( R 2 = 0.80):

Neutral rgent fiber content det =

( ) + ( )

2

486 016 . - . shoot age in days 0 033 . shoot age in days (7.3)