ABSTRACT

Effect of Sacoglottis gabonensis and Aistonia boonei on the fermentation of Raphia palm sap by Saccharomyces cerevisiae was studied. Preliminary studies were carried out to determine the optimal concentration of A. boonei that had a preservative effect on the stored palm sap. Fresh palm sap from Raphia hookeri was treated with different amounts (0-ig/lOOml) of the tree-bark powder of A. boonei. pH, total titratable acidity, rate of CO2production, alcohol production, sugars (sucrose, glucose, fructose) and nitrate assimilation were monitored daily for a 4-day storage period. Statistical analysis indicated 0.50% A. boonei as the optimal concentration needed to preserve palm wine. The effects of optimal concentrations of A. boonei (0.50%) and S. gabonensis (0.625%), on S. Cerevisiae isolated from the palm wine were investigated. The fermentation rate constant K (2.79 x 1ff" mor' sec') for untreated palm wine was higher than the K values for palm wine treated with A. boonei (1.7 x 10 mo1' sec') and S. gabonensis (1.1 x 1O moi sec'). The specific growth rates for yeasts were 0.43, 0.76, 0.88 for control, sample treated with A. boonei and S. gabonensis respectively. Sucrose utilization by yeasts in palm wine was inhibited by exogenous ethanol in the presence of plant products while fructose utilization was enhanced. Glucose utilization was however, not affected in the presence of plant product by exogenous ethanol. Alcohol content (6.38 ± 0.3% v/v) of untreated sample was significantly lower (P<0.05) than the alcohol content (12.11 ± O.2%"/v) of samples treated with S. gabonensis and A. boonei (11.25 ± 0.3% v/v) The two plant products reduced the flocculation and sedimentation abilities as well as invertase activity of the yeast. Sensory evaluation showed that untreated palm wine was generally preferred within the first 48h of storage while palm wine treated with S. gabonensis was preferred after 48h of storage.

TABLE OF CONTENTS

Title Page

Certification ii

Dedication

Acknowledgement v

Table of Contents vi

List of Tables x

List of Figures xi

Abstract Xii

CHAPTER 1

1.0 Introduction 1

CHAPTER 2

2.0 Literature Review 4

2.1 Palm Wine — General Information 4

2.2 Palm Wine Production 5

2.3 Economic Importance of Palm Wine --- 6

2.4 Nutritional Importance of Palm Wine 9

2.5 Microbiology of Palm Wine 10

2.6 Preservation of Palm Wine 13

2.6.1 Progress in Palm Wine Preservation 14

2.7 Synthetic Palm Wine 16

2.8 Importance of Sacchcironiyces to the Food Industry --- 17

2.9 Food Preservation with Plant Materials 19

4.1.6 Nitrate Assimilation 58

4.2 Characterization and Identification of Palm Wine Yeast Isolate 60

4.3 Effect of S. gabonensis and A. boonel on the Fermentation Kinetics of

S. cerevisiae Isolated from Palm Wine 62

4.4 Effect of Plant Products on the Growth Kinetics of S. cerevisiae Isolated

From Palm Wine 64

4.5 Effect of Plant Products on the Flocculation Pattern of S. cerevisiae

Isolated from Palm Wine 64

4.6 Effect of Exogenous Ethanol on Sugar Utilization and Alcohol

Production in Palm Wine 68

4.7 Effect of Plant Products on Alcohol Production and Ethanol Tolerance

of S. cerevisiae Isolated from Palm Wine 70

4.8 Effect of Plant Products on Invertase Activity of S. cerevisiae

Isolated from Palm Wine 73

4.9 Effect of Plant Products on Osmotolerance of S. cerevisiae Isolated

from Palm Wine 75

4.10 Effect of Plant Products on the Sedimentation Rates of S. cervisiae

Isolated from Palm Wine 77

4.11 Effect of Plant Products on Organoleptic Properties of Palm Wine --- 79

CHAPTER 5

5.0 Conclusion and Recommendations --- 82

References 84

Appendices 93