Introduction
Production of biological fuel ethanol as a convenient and reproducible
energy source to supplement gasoline has been a major focus
in many countries.
In China, sweet potato has been chosen as a
main crop for bioethanol fermentation,
as the country produces
about 85% of the world’s total output of sweet potato (Zhang
et al., 2010).
To produce fuel ethanol, either dried or fresh sweet
potato can be used;
however,
drying fresh sweet potato roots requires
manpower,
energy and time.
Cooked fresh sweet potato
paste has been used in fuel ethanol production at laboratory,
pilot and industrial scales through simultaneous saccharification and
fermentation (SSF) by Saccharomyces cerevisiae (Zhang et al.,
2011).
The main limitation of using cooked sweet potato roots
paste with high solids content is the high viscosity of the paste.
In a study by Lee et al. (2012) co-immobilization of saccharolytic
fungi and S.
cerevisiae was used to produce fuel ethanol from
cooked sweet potato.
After 9–11 days of fermentation the final ethanol
yield was 62% of the theoretical yield but the concentration
was only 4% (v/v) (Lee et al., 2012).
An additional problem of using
cooked sweet potato is the consumption of energy during the cooking
process,
thus greatly reducing the ratio of energy produced (as ethanol) by the cost of energy consumed in cooking (Goyal
et al.,2005).