Isitua et al. Bioethanol production from cassava (Manihot esculenta) peels pp. 40-45
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e - ISSN: 2602-8360 - Volumen. 2, Nº 2, Junio – Noviembre 2018
INTRODUCTION
Bioethanol is a principal fuel that can be used as
petrol substitute for vehicle. It is a renewable energy
source produced mainly by sugar fermentation
process, although it can also be manufactured
by the chemical process of reacting ethylene with
steam. The main sources of sugar required to
produce ethanol come from fuel or energy crops
like cassava and cassava products, waste straw,
sawdust, etc. (1).
Yeast (Saccharomyces cerevisiae), have been
known to humans for thousands of years as they
have been used in fermentation processes like in
the production of alcoholic beverages (2) and bread
leavening (3). Yeasts metabolize sugar to produce
ethanol and carbon dioxide. The basic carbon and
energy source for yeast culture are sugars (2) (3).
Cassava (Manihot esculenta), also known as
manioc, tapioca or yucca, is one of the most
important food crops in the humid tropics, being
particularly suited to conditions of low nutrients
availability and is able to survive drought (4). It is
the third largest source of carbohydrates for human
consumption in the world, with an estimated annual
world production of 208 million tonnes (5). The
major harvested organ is the tuber, which is actually
swollen root. The nutrient reserve of cassava
is made up of starch. Cassava peels is gotten
during the processing of the cassava tuber and
it is an agricultural waste. Cassava peels contain
starch which when treated with a varying level of
H2SO4 undergoes an abrupt change in the physical
structure of the glycosidic bond linking amylase
and amylopectin. Glycosidic bond are broken to
produce glucose and oligosaccharide residues (4).
In Africa, especially Nigeria, which is one of the
largest centre of cassava production, it is grown on
7.5 million hectares of land and produces about 60
million tonnes per year. Thus, wastes (especially
cassava peels) generated from the processing
of cassava into various products are littered or
dumped in the environment causing pollution. There
is therefore the need for revalorization of cassava
peels waste into useful products. The application of
using cassava peels for ethanol production could
be of great advantage to a country’s economy.
This study therefore determines the possibility of
bioethanol production from cassava peels which
could provide a cheaper bioethanol source; also,
exploit the fermentative ability of Saccharomyces
cerevisiae isolated from palm wine in the production
of the desired bioethanol.
MATERIALS AND METHODS
Collection and processing of cassava peels
Cassava peels were obtained from a cassava
milling factory in Uselu market, Benin City, Edo
State, Nigeria. The peels were washed in clean
water (to remove sand and cyanide content) and
weighed on a laboratory scale. Thereafter, the
peels was allowed to dry naturally (de-watering)
for 4 hours on a clean tray, after which they were
chopped into bits and transferred into a mortar
where they were mashed using a pestle to attain
sufcient size reduction. This was to ensure the
creation of sufcient surface area of the material to
aid the process of fermentation.
Isolation and identication of yeast
(Saccharomyces cerevisiae) from palm wine
Yeast used for this experiment was isolated from
fermented palm wine. One mL of the serially
diluted palm wine sample was plated on sabouraud
dextrose agar supplemented with streptomycin
(0.05 mg/L) using pour plate method and incubated
at 28oC for 48 hours. The yeast colonies that
developed were isolated and puried by spread
plate method on fresh sabouraud dextrose agar
plates. Identication of the yeasts was by the use
of standard morphological and physiological tests
and identication keys described by Barnett et al.
(6) (14).
Preparation of sample for fermentation
100g of the mashed cassava peel was transferred
into two different 1L fermentation asks and 1000mL
of distilled water was added to each of them. The
asks were autoclaved at 121oC for 15 minutes
and allowed to cool. The contents of the asks
were then ltered using a muslin cloth to obtain the
desired cassava medium and again autoclaved and
allowed to cool. For hydrolysis to form sugars, 5mL
of 5% H2SO4 and 5mL of 5% NaOH were added
to each jar and heated to about 50oC. Thereafter,
20mL suspension of the inoculum (yeast) was
introduced aseptically into one of the fermentation
asks which served as the test experiment, while