ABSTRACT
Sweet potato tubers (peeled) were examined for ethanol production and biomass. The sweet potato tubers were grinded and hydrolyzed/Saccharified enzymatically using Trichoderma viride which resulted to a sugar yield of 7.20% brix and was optimized to 21.05% for fermentation to occur. Saccharomyces cerevisiae from palm wine was used to ferment the hydrolysate to produce alcohol. During the fermentation process, records showed that the specific gravity, pH and sugar content reduced. The sugar reduced from 21.05% to 2.13%, the specific gravity reduced from 1.160g/cmᶟ to 1.020g/cmᶟ and the pH reduced from 6.50 to 2.67. The acidity increased from 0.57% to 2.95% and the alcohol content increased from 1.60% to 10.20% v/v. The produced biomass which started as 0.48% after 24hr of fermentation increased and accumulated to 2.03g/l. An assessment of the produced alcohol showed that it had a boiling point of 78.83ᴼC, a specific gravity of 0.791g/cmᶟ and a pH of 3.53. The total alcohol yield was11.86% v/v. The result of the experiment showed that sweet potato is a potential substrate for alcohol production and biomass used as single cell proteins.
TABLE OF CONTENTS
Pages
Title i
Certification
ii
Dedication iii
Acknowledgements
iv
Table of contents v-vii
List of tables viii
List of figures ix
Abstract
x
Chapter One
1.0 Introduction
1
1.2 Aim 4
1.3 Objectives
4
Chapter Two
2.0
Literature
Review
5
2.1 Sweet potato
5
2.2 Nutritional
Value
5
2.3 Saccharomyces cerevisiae (palm wine
yeast)
6
2.4 History of
yeasts
8
2.5 Growth and
Nutrition of yeast
8
2.6 Nutritional
Supplements
9
2.7 Alcohol
Tolerance
9
2.8 Biomass
10
2.9 Fermentation
10
Chapter Three
3.0 Materials and
Methods
12
3.1 Materials
12
3.2 Methods 12
3.3 Production of sweet
potato flour
12
3.4 Production of palm wine yeast
12
3.5 Media
Preparation
13
3.6 Preparation of Crude Enzyme
Extract
13
3.7 Saccharification of
sweet potato flour
13
3.8 Determination of sugar content of
saccharified direct potato flour
14
3.9 Optimization of
sugar content
14
3.10 Fermentation for
Biomass and Alcohol production 15
3.11 Determination of
pH
15
3.12 Determination of
Temperature
16
3.13 Determination of
Total Solid
16
3.14 Determination of
Specific Gravity
16
3.15 Determination of
Titratable Acidity (TTA)
17
3.16 Measurement of
Biomass
17
3.17 Determination of
Ethanol Contents
18
Chapter Four
4.0 Results
19
Chapter Five
5.0
Discussion,
Conclusion and Recommendation 31
5.1 Discussion
31
5.2 Conclusion
33
5.3
Recommendation
33
References 34
Appendix
LIST OF TABLES
Tables
Title Pages
1 Quality characteristics of
sweet potato flour hydrolysate used 21
for alcohol production.
2 Changes in quality
characteristics of fermenting sweet potato flour must 22
during the production of ethanol and biomass.
3 Quality characteristics of
produced alcohol.
23
LIST OF FIGURES
Figures
Title pages
1 Changes in pH during
fermentation period.
24
2 Changes in Temperature
during fermentation period. 25
3 Titratable acidity
during fermentation.
26
4 Changes in specific
gravity during fermentation period. 27
5 Changes in sugar content during
fermentation period. 28
6 Alcohol content during
fermentation period
29
7 Concentration of Biomass
during fermentation period. 30
CHAPTER ONE
INTRODUCTION
There
is a considerable interest in developing bio renewable alternatives to substitute
fossil fuels such as bioethanol as transportation fuel. Bioethanol contributes
a diminish petroleum dependency, generates new development opportunities in the
agricultural and agro industrial sectors and is of environmental benefits. The main
feedstock for bioethanol production is the sugarcane and corn grain.
Sweet
potato (Ipomoea batatas) has been
considered a promising substrata for alcohol fermentation since it has a higher
starch field per unit land cultivated than grains (Duvernay, et al.
2013, Lee, et al. 2012; Srichuwong, et al. 2009; Ziska, et al. 2009). Industrial sweet potatoes are not intended for use as
food crop. They are bred to increase its starch content, significantly reducing
its attractiveness as a food crop when compared to other conventional food
cultivars (visual aspect, color, taste). Therefore, they offer potentially
greater fermentable sugar yields from a sweet potato crop for industrial
conversion processes and the opportunity to increase planted acreage even on
marginal lands beyond what is in place for food. It has been reported that some
industrial sweet potatoes breeding lines developed could produce ethanol yield
of 4500-6500L/ha compared to 2800-3800L/ha for corn (Duvernay, et al. 2013; Ziska, et al. 2009).
Sweet
potato has several agronomic characteristics that determine its wide adaptation
to marginal lands such as drought resistant, high multiplication rate and low
degeneration of the propagation material, short growth cycle, low illness
incidence and plagues, cover rapidly the soil and therefore protect it from the
erosive rain and controlling the weed problem (Ann, et al. 2011; Duvernay, et al.
2013; Vilaro, et al. 2009). Previous
transformation of the raw material into chips or flour (powder) can be done in
order to facilitate its transport and/or plant conservation. An effective
ethanol production process is one where the amount of water added is minimal
since more energy will be required to remove it at the end of the process if
the final ethanol concentration is low (Ann, et al. 2011; Shaibani, et al.
2011). High ethanol concentration can be reached in the fermentable sugar
concentration in the case of ethanol production from root and tuber crops, it
implies the use of a very high gravity (VHG) medium with high solid content and
high viscosity. The high viscous nature causes several handling difficulties
during process, and may lead to incomplete hydrolysis of starch to fermentable
sugars (Shanavas, et al. 2011; Walker,
et al. 2002; Yatanabe, et al. 2010; Zhang, et al. 2011).
Fresh
sweet potato contains high water content. The drying process of this material
is an aspect to be studied to optimize its transport, storing and processing.
The use of flour of sweet potato would allow working with higher sugar
concentration during the fermentation than fresh sweet potato without the
addition of water. In this case, it should assess the energy saving of
manipulating lesser amount of material, the handling of high viscous material,
the extra cost of drying and the effect of drying on the performance of the
process (Conversion of starch of fermentable sugars) (Moorthy, 2002).
The
conventional process for bioethanol production from starch based materials
includes the conversion of starch into fermentable sugars which generally takes
place in two enzymatic steps: Liquefaction using thermal-stable, alpha amylase
and saccharification by addition of amyloglucosidase (AMG). Most studies of
starch hydrolysis use enzymes, temperature conditions and reaction times which
have been done for grains, such as corn. The starch of sweet potatoes is
considered more complex than cereal starches, making it more challenging to
hydrolyze into fermentable sugars. Besides, the digestibility of starch by
enzymes vaines among different cultivars (Duvernay, et al. 2013; Moorthy, 2002; Srichuwong, et al. 2005) yet there is still a need to establish a more defined
biologically based approach to sweet potato starch conversion and evaluate the
enzymes and processing conditions suitable for effective fermentable sugar
production (Duvernay, et al. 2013).
The sweet potatoes used in the article has biomass yields of 10t/ha (dry
basis), higher value than cultivated varieties for human consumption which
presented an average yield of up to 4.2t/ha.
Sweet
potato roots are bulky and perishable unless cured. This limits the distance
over which sweet potato can be transported economically. It was established
that in cases where countries are capable of generating surplus, it tends to be
relatively localized but dispersed and this leads to lack of market integration
and limits market size (Yang, et al. 2011).
Moreover, production is highly seasonal in most countries leading to market
variation in the quantity and quality of roots in markets and associated price
swings.
Sweet
potato consumption has been adjudged to decline as incomes rise- a change often
linked with urbanization, partly because of the lacks of post-harvest
processing or storage (FAOSTAT,2008; Centro internacional de ia papa, 2009).
The latter can lengthen the period for which sweet potato can be marketed but
may also be relevant for subsistence oriented households to increase the period
over which sweet potato can be consumed, particularly where there is a market
dry season. A sensible approach to achieve the goal of sweet potato product
development would be to increase the nutritional content of this highly
consumed crop.
Sweet
potato is one of the crops selected by the U.S National Aeronautics and Space
Administration (NASA) to be grown in a controlled ecological life support
system as a primary food source. Recent studies show that sweet potato contains
such functional components as polyphenols, anthocyanins and dietry fiber, which
are important for human health. Sweet potato tops (leaves and stems) contain
additional nutritional components in much higher concentrations than in many
other commercial vegetables. Sweet potato leaves are cooked as a vegetable in
many parts of the world. They are rich in vitamin B, β-carotene, iron, calcium,
zinc and protein, and the crop is more tolerant of disease, pests and high
moisture than many other leafy vegetables grown in the tropics. Because sweet
potato tops can be harvested several times a year, their annual yield is much
higher than many other green vegetable.
Currently,
there is a growing interest for ecological sustainable bio-fuels all over the
world. In Nigeria, simultaneous saccharification and fermentation of
lignocelluloses to alcohol as substrate was reported by (Xang and Zhao 2011).
1.2 AIM
The
aim of this research is to utilize sweet potato (Ipomoea batatas) as biomass for alcohol production using Trichoderma viride and Saccharomyces cerevisiae.
1.3 OBJECTIVES
Ø To
saccharify sweet potato (cellulose) using Trichoderma
viride.
Ø To
generate biomass and ethanol using Saccharomyces
cerevisiae.
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