ABSTRACT
This study was to determine the sensory quality of bread produced using different indigenous yeast isolates originating from palm wine in order to offer an insight into the overall quality of the bread. The four yeast types had varied levels of prevalence. Saccharomyces cerevisiae was the predominate yeast species with a 100% occurrence while Saccharomyces uvarium and Saccharomyces carlsbengensis had the least occurrence of 33.3%. The result of the physical properties of the palm wine yeast bread and baker’s yeast bread shows that the baker’s yeast bread had the higher oven rise and value than the palm wine yeast bread while the later had higher weights. There was therefore, variations between the physical characteristics of the palm wine yeast and Baker’s yeast bread. The result of the sensory evaluation of breads produced with palm wine yeasts shows that the most acceptable of the palm wine yeast (6.23) was the bread produced with Saccharomyces globosus. The most preferred color bread (7.43) was the bread produced with Saccharomyces cerevisiae while the least acceptable was the bread produced with Saccharomyces carlsbengensis with a mean score of 7.97 (88.6%) as against 7.67 (85.2%) score of the Bakers yeast bread. The result shows generally that none of the bread samples was unacceptable as all scored above 69% in the acceptability scale. The acceptability of the attributes favoured the commercial yeast bread examples in colour. Thus the use of palm wine yeast to produce bread was successful and the products were acceptable.
TABLE OF CONTENTS
Title page i
Certification ii
Dedication
iii
Acknowledgements
iv
Table of
contents
v
List of
Tables
vii
Abstract
viii
CHAPTER
ONE
1.0 Introduction 1
1.1 Aims and objectives 2
CHAPTER
TWO
2.0 LITERATURE REVIEW
3
2.1 The Bread 4
2.1.1 Bread ingredients
5
2.1.2 Types of
Bread 6
2.1.2.1 Yeast Bread 6
2.1.2.2 Flat Bread
6
2.2 Yeast in Bread making
7
2.3 Loaf
Volume/Cell Structure
10
2.4 Flavour and Aroma 12
2.5 Colour
14
2.6 Shelf Life
15
2.6.1
Staling/Hardness/Firmness
15
2.6.2 Microbial
spoilage 16
2.7
Nutrition
18
CHAPTER
THREE
3.0
MATERIALS AND METHODS 23
3.1 Study Area 23
3.2 Collection of Samples
23
3.3 Sterilization of Materials 24
3.4 Preparation of Culture Media 24
3.5 Isolation of Yeast from the Palm wine
Samples 24
3.6 Purification of Isolates 24
3.7 Identification of the Isolates 24
3.8 Bread Production 25
3.8.1 Formulation of Bread Dough 25
3.8.2 Specific Volume Determination 25
3.8.3 Baking of Bread 25
3.8.4 Physical Properties of the Bread Loaves 25
3.8.5 Sensory Evaluation of the Bread Loaves 26
3.9 Proximate Analysis of the Bread Sample 26
3.9.1 Moisture Content Determination 26
3.9.2 Total Ash Determination 27
3.9.3 Crude Protein Determination
27
3.9.4 Fat Content Determination 28
3.9.5 Crude Fibre Determination 28
3.9.6 Carbohydrate Determination 29
CHAPTER
FOUR
4.0 Results 30
CHAPTER
FIVE
5.0 Discussion
and Conclusion 38
5.1 Discussion
38
5.2 Conclusion
40
References 41
LIST
OF TABLES
Table: 1: Characteristics of Yeast Isolates
Table:
2: Occurrence of Yeast Isolates in Palm Wine at Umudike
Table: 3: Physical Properties of Palm Wine Yeast Bread
Table: 4: Proximate composition of Bread Produced with Palm Wine Yeast
Isolates
Table 5: Sensory
Evaluation
CHAPTER ONE
1.0 INTRODUCTION
Bread is one of the most important staple
food products for the human diet. Yeast fermentation in leavening of dough –
next to beer making is one of the oldest biochemical processes in the world. In
2001 a food consumption survey in Ireland showed that 99% of the participants
had a mean intake of 139 g bread per day, with white breads and rolls covering
78 g/day. These amounts to an average of 50.7 kg bread, respectively 28.47 kg
white bread and rolls per year. However, changing eating patterns and a large
variety of substitute products such as fast food and breakfast cereals have led
to a decrease in bread consumption (Prättälä and Mykkanen, 2001; Siega-Riz and
Carson, 2000).
Carbohydrate containing food products can
furthermore be categorized based on their GI. There are three categories
reaching from products with a low GI (GI< 55; nuts, dairy products, legumes,
pasta), over intermediate GI foods (GI between 55 and 70; certain breads,
muesli) and products with a high GI (GI > 70; white wheat bread, whole meal
barley flour) (Atkinson and Brand-Miller, 2008). Factors affecting
digestibility and therefore also the glycaemic response of bread can come both
from the technological aspects of bread production as well as the used raw
materials (Fardet and Rémésy, 2006). Besides components of the food product,
the technological processing of the breads also has an influence on the GI.
Therefore, Fardet et al., (2006)
recommended a reduction in yeast quantity to increase the density of the
end-product for the production of low-GI breads. Since consumers prefer a soft
and flexible crumb which corresponds to a low hardness (Hager et al., 2012), the focus should
concentrate on changing the chemical characteristics rather than the physical
characteristics of wheat bread. This could be achieved by the application of
different strains of S. cerevisiae.
However the application of different
strains from the species S. cerevisiae can influence all quality
characteristics of bread which are highly important for consumer acceptance.
Not only are the technological and nutritional parameters of the end product,
but also aroma and flavour profile affected by yeast addition. Although a lot
of these flavour and aroma compounds are formed during the baking process, also
fermentation and yeast metabolism play a key role in the unique bread flavour.
Essential contributors to the flavour of fermented foods are alcohols,
aldehydes, esters, ketones and acids originating from the yeast metabolism. The
main pathway responsible for aroma production by yeast is the Ehrlich pathway
(Hazelwood and Dickinson, 2008). In the beverage industry, it is quite common
to use yeast as an important parameter to alter the flavour and aroma profile
of the end product (Pires and Vicente, 2014). However, in bread making only
recently flavour and aroma profiles became more recognized as a quality parameter
(Pico and Gómez, 2015). Therefore, a commercial interest in the field of bread
fermentation to alter flavour and aroma characteristics has arisen in recent
years. Furthermore, a trained panel was used for descriptive sensory analysis
to predict sensory acceptance.
1.1 AIMS AND OBJECTIVES
The
aim of this study was to determine the sensory quality of bread produced using
different indigenous yeast isolates originating from palm wine in order to
offer an insight into the overall quality of the bread.
The
objectives are;
1.
To
isolate and characterize yeasts from palm wine
2. To evaluate the
suitability of selected yeast isolates in the sensory quality of bread produced
To determine the
proximate analysis of the bread samples.
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