ABSTRACT
The aim of this study was to assess the growth and physiological properties of top and bottom fermenting yeasts from palm wine. 10 randomly selected palm wine samples were collected from different locations within Ikwuano local government area of Abia state. The samples were cultured by streaking and spread plate method, Yeasts were isolated from palm wine and subsequently characterized and identified. Results showed that (two top and two bottom fermenters) were isolated with varying prevalence in palm wine samples. The four isolates were Saccharomyces cerevisiae, Saccharomyces globosus (top fermenters), Saccharomyces carlsbengensis and Saccharomyces uvarum (bottom fermenters). S. cerevisiae was found in all samples while S. globosus and S. carlsbengensis had 80% and 60% respectively with S. uvarum having the least occurrence (40%). The different yeasts have similarities in their growth physiological activities. The isolates show potentials to manage growth stress conditions. S. cerevisiae, had the best temperature tolerance (+ at 420C) while S. uvarum recorded the least growth (+) at 39oC. Some of the isolates demonstrated flocculation ability and were positive in fermentative and assimilation test for glucose and other sugars. Three of the yeast isolates did not grow well at pH 2.0 but rather had just slight growth level (+). S. uvarum did not grow at pH 2.0. At pH 4.0, S. cerevisiae and S. globosus grew profusely (+++), S. carlsbengensis and S. uvarum had moderate growth (++). All the yeasts grew very well at pH 6.0. At ethanol concentration less than 10% (≤ 10% v/v), three of the isolates except S. uvarum recorded slight growth at 16% ethanol concentration. None was able to grow at 19% ethanol concentration. CuSo4 tolerance test recorded moderate growth (++) for each yeast at 1.0g/l copper, slight growth (+) at 2.0g/l and no growth at 3.0g/l. All the yeasts were able to grow at 0.01% - 0.02% of sodium metabisulfite, the isolates recorded low response at 0.03% concentration. Only S. cerevisiae and S. globosus had slight growth at 0.04% but S. carlsbengensis and S. uvarum show no growth at 0.04% and none of the isolates was able to grow at 0.05% Comparatively, sucrose was the most suitable sugar from all the yeasts while S. cerevisiae had the highest CO2 production capacity among with 0.27ml/min. S. uvarum had the least CO2 production rate with 0.16ml/min. The result showed the ability of the yeasts to adapt to various parameters and the level of tolerance was dependent on intensity or concentration of the various parameters.
TABLE OF CONTENTS
Title
Title
page
Certification i
Dedication ii
Acknowledgement iii
Table
of Contents iv
List
of tables vii
List
of Figures viii
Abstract ix
CHAPTER ONE
1.0 Introduction 1
1.1 Aims
and Objectives 2
CHAPTER TWO
2.0 Literature Review 3
2.1 Palm Wine 3
2.1.1 Collection of Palm Wine Sap 3
2.1.2 Health
benefits of Palm Wine 4
2.1.3 Bakery and Preservative Uses of Palm Wine 5
2.1.4 Biochemical Constituents of Palm Wine 5
2.2 Sugar Concentration in Palm Wine 6
2.3 Microbial Communities in Palm Wine 7
2.4.1 History of Yeasts 8
2.4.2 Characteristics
of Yeasts 8
2.4.3 Reproduction in Yeast 8
2.5 Uses
of Yeast 10
2.5.1 Food and Beverage Beer 10
2.5.2 Industrial
Ethanol Production 10
2.6 Yeast
as a Model Organism 10
2.7 Pathogenic Yeasts 11
CHAPTER THREE
3.0 Materials
and Methods 12
3.1 Materials 12
3.1.1 Source
of Material 12
3.1.2 Equipment
and Apparatus 12
3.2 Sample
and Sampling 12
3.2.1 Media Preparation 13
3.3 Isolation of Yeasts from Palm Wine
Samples 13
3.4 Characterization of Yeasts Isolates 14
3.4.1 Microscopy Examination of Yeast Isolates 14
3.4.2 Macroscopic Examination of Yeast Isolates 14
3.5 Viability Test 14
3.6 Glucose Fermentation Test 15
3.7 Biochemical Tests for the Identification
of Yeasts 15
3.7.1 Carbon Assimilation Test 15
3.7.2 Rate of
Co2 Production 16
3.8 Stress
Exclusive Test 16
3.8.1 Temperature
Tolerance Test: 16
3.8.2 Determination
of Ethanol Tolerance 16
3.8.3 Flocculation
Test 17
3.8.4 pH Tolerance 17
3.8.5 Copper
Sulphate (CuSo4)
Tolerance Test 17
3.8.6 Sodium
Metabisulfite Tolerance Test 17
CHAPTER FOUR
4.0 Results 19
CHAPTER FIVE
5.0 Discussion,
Conclusion and Recommendation 35
5.1 Discussion 35
5.2 Conclusion 39
5.3 Recommendation 39
REFERENCES 40
APPENDIX 44
LIST OF TABLES
Table Title Page
1
Characterization of Yeast
isolates. 22
2
Carbon Assimilation by the yeast isolate. 26
3
Effect of temperature on
growth of yeast isolates. 27
4
pH tolerance test on yeast isolates. 28
5
Ethanol tolerance test on
yeast isolates. 29
6
Sodium metabisulfite tolerance
test. 30
7
Copper sulphate (cuso4)
tolerance test on the yeast isolates. 31
8
Flocculation test. 32
9
Rate of Co2 Production
by palm wine yeasts during
fermentation of
different sugars. 32
LIST OF FIGURES
Figure Title Page
1
Occurrence
of Yeast Isolates in Palm Wine 24
3 Sugar fermentation result 24
CHAPTER ONE
1.0 INTRODUCTION
Palm
wine is the collective name for a group of alcoholic beverages produced by the
natural fermentation of the sap obtained from various tropical plants of the
Palmae family (Okafor, 2014), Palm wine is obtained from the fermentation by
indigenous microbes. The major sources of Palm wine in Nigeria are
Elaeisguineensis and Raphia palm (Okafor, 2014).
It
is produced and consumed in very large quantities in the South Eastern Nigeria.
Palm wine is a nutritionally rich medium for the growth of many organisms among
which is yeast species. Different species of yeast can be found in palm wine.
Yeast population, among other organisms, have been found to vary in palm wine
depending on the source. The yeasts quantitatively convert the sugars in the
palm wine into alcohol. Hence, the physicochemical condition of palm wine is a
function of the metabolic activities of the inherent yeasts in palm wine.
The
characteristics of palm wine is so unique that it has generated research
interest (Nwachukwu et al., 2006,
2008; Naknean, 2010) to investigate the practical applications and industrial
utilization.
The wine is an excellent substrate
for microbial growth and fermentation starts soon after the sap is collected
and within an hour or two become reasonably high in alcohol (up to 4%), if
allowed continue fermentation for more than a day, it starts turning into
vinegar. Palm wine yeast have been found to possess good sedimentation
properties for high products recovery. Saccharomycess
species have been isolated from Palm wine and used for Bio-ethanol products
(Agu et al., 2015).
Some special strains of
fermenting yeast have been selected, these strains fall into two groups known
as top and bottom yeast. Top yeast as so called because during fermentation
they are swept to the vat by the rapid evolution of carbon dioxide. They are
vigorous fermenters acting best at relatively high temperature and produce high
alcoholic palm wine. In contrast the bottom yeast as so called because of the
slower rate of carbon dioxide evolution that allow them settle to the bottom of
the vat during fermentation. They are slow fermenters, they act best at low
temperature and produce highly low alcoholic contents.
Palm wine is a cheap source of yeast
that can augment for the more expensive commercial yeast. Utilizing palm wine
yeasts for industrial processes requires a comprehensive knowledge of their
technological properties. The production
of Palm wine yeast can then be scaled up from which starters can be obtained
for various industrial applications. The yeast isolates from Palm wine are also
used in baking, single cell protein production etc. (ogbonna, 2014) used palm
wine isolates of Saccharomycess
cerevisiae to produce artificial palm wine and beer respectively.
1.1 AIMS AND OBJECTIVES
To
study the growth and physiological properties of top and bottom fermenting
yeasts from Palm wine.
The objectives are;
i.
To isolate top and bottom
strains of fermenting yeasts from Palm wine.
ii.
To determine the varying
physiological/physiochemical parameters during the fermentation period.
iii.
To quantify the yeast
bioactivity during fermentation period.
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