Agriculture Reference
In-Depth Information
15
96.0
a
94.0
12
b
b
92.0
9
Soft wheat
Waxy wheat
Hard winter wheat
90.0
6
88.0
Waxy
Soft
Hard
3
12
24
36
48
60
72
Fig. 22.5
Ethanol fermentation effi ciency of different wheat
classes.
Fermentation time (h)
Fig. 22.4
Ethanol yield of different wheat classes.
had the highest fermentation effi ciency. Amylo-
pectin might serve as a more effi cient substrate
for α-amylases used in the liquefaction step.
The observed higher effi ciency of ethanol pro-
duction from waxy wheat requires commercial
verifi cation.
Lower temperatures are required to gelatinize
waxy wheat (Graybosch et al., 2000), a necessary
fi rst step in the production of starch-derived
ethanol. When evaluated in a rapid viscoanalyzer,
waxy fl our reached peak viscosity at 80 ºC,
while normal wheat fl our attained this point
at 95 ºC. After cooking to 85 ºC, waxy wheat
starch essentially had lost all of its structure,
making chains readily accessible for digestion by
enzymes employed in the digestion process.
Thus, lower energy input required for gelatiniza-
tion of waxy starch represents another possible
advantage in biofuel production. Waxy wheat
intended for use as a source of biofuel should
likely possess low grain protein content, as
elevated levels of gluten protein might reduce
effi ciency of starch extraction, or render diffi cult
the conversion from maize-based substrates to
wheat-based.
Figure 22.3 is a simplifi ed schematic diagram
of the dry-grind process. The current dry-grind
process is mostly designed for ethanol production
from maize and may not be well tailored for
wheat. Readers are referred to Kelsall and Lyons
(2003) and the references listed in that citation.
Soft and waxy wheat for ethanol production
Potential ethanol yield is directly proportional to
starch content or total fermentable carbohydrates,
especially for dry-grind plants. Unpublished data
(D. Wang) on three wheat classes—soft wheat,
waxy wheat, and hard winter wheat (Fig. 22.4)—
showed that soft wheat had a higher ethanol yield
that was consistent with differences in respective
starch content (68.7%, 60.4%, and 62.4%). Waxy
wheat had higher ethanol yield than hard wheat,
though its starch content was two percentage
points lower. Waxy wheat starch may be more
effi ciently converted into fermentable sugars and
ethanol than soft and hard wild-type wheat (Fig.
22.5), which is in agreement with fermentation
results from other cereal grains (Wu et al., 2007).
Previous research has demonstrated waxy
wheat to be a more effi cient substrate for ethanol
production. Wu et al. (2006) compared fermenta-
tion effi ciency of waxy wheat to that of normal
wheat, maize with varying amylose content, and
waxy and nonwaxy sorghum. After prefermenta-
tion treatment by cooking at 95 ºC, waxy wheat
Feedstock criteria for ethanol production
Feedstock selection may involve different criteria
for the wet-milling process of wheat. Since the
wet-milling co-product, vital wheat gluten, is a
more valuable food ingredient, the protein starch
