TABLE OF CONTENT
CHAPTER ONE
INTRODUCTION
1.1 PALM WINE
1.2 COMPOSITION OF PALM WINE
1.3 YEAST (saccharomyces cerevisiae)
1.4 BREAD
CHAPTER TWO
LITERATURE REVIEW
2.1 BREAD PRODUCTION
2.2 FUNCTIONS OF THE INGREDIENTS IN BREAD PRODUCITON
2.3 TYPE OF BREAD
2.4 THE PROCEDURES INVOLVED IN BREAD PRODUCTION
2.5 BREAD QUALITY
2.6 PALM WINE (ELAEIS GUINNEENSIS)
2.7 GENERAL CHARACTERISTICS OF
SACCHAROMYCES CEREVISIAE
2.0.71 MORPHOLOGICAL CHARACTERISTICS
2.07.3 CULTURAL CHARACTERISTICS
2.7.4 YEAST CYTOLOGY
2.8 CHARACTERISTICS OF BAKERS’ YEAST
2.9 PURE CULTIVATE ISOLATION AND CULTIVAITON
CHAPTER THREE
MATERIALS AND METHOD
3.1 EQUIPMENTS
3.2 RAW MATERIALS
3.3 SOURCE OF MATERIAL
3.4 PREPARATION OF MEDIUM
3.5 ISOLATION OF YEAST SPECIES DESCRIBED BY
3.6 CHARACTERIZATION AND TEST FOR VIABILITY OF YEAST
3.7 PRODUCTION OF STARTER CULTURE
3.8 PREPARATION OF
YEAST PASTE
3.9 BREAD PRODUCTION
3.10 QUALITY TEST
3.10.1 DOUGH LEAVENING ABILITY
3.10.2 LOAF VOLUME
DETERMINATION
3.101.1
WEIGHT OF LOAF
3.10.4
LOAF SPECIFIC GRAVITY
3.10.5
ORGANOLEPTIC QUALITY TEST
CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 CHARACTERISTICS OF YEAST
ON MALT EXTRACT NUTRIENT MEDIUM
4.2 IDENTIFICATION OF YEAST IDOLATE
4.3 DOUGH LEAVENING ABILITY
4.4 THE VOLUME WEIGHT HEIGHT
AND SPECIFIC VOLUME OF THE SAMPLES
4.5 SENSORY EVALUATION
CHAPTER FIVE
5.0 CONCLUSION AND RECOMMENDATION
5.1 CONCLUSION
5.2 RECOMMENDATION
REFERENCES
CHAPTER ONE
INTRODUCTION
1.1 PALM WINE
Palm wine is a milky alcoholic
beverage produced from the inflorescence of palm tree it is the most widely
used and cherished natural traditional alcoholic beverage especial in the
southern part of Nigeria,
and is the juice of the oil paolm ( Elacis guinneensis) and raffia palm ( Rapia
hooker) ( Ihekoronye and Ngoddy 1985).
A milky juice containing
initially well over 13% sucrose is collected in the calabash which is hung at
the base of the incision of the inflorescence of palm tree soon after leaving
the tree, yeast spares, especially those of Saccharomyces cerevisias infect the
juice and soon start to ferment the fermentable sugar.
Palm wine can be consumed as an
alcoholic beverage. It could be allowed to ferment and subsequently distilled
into gin it could also be used for the leavening of dough for bread making (
Somiari and Udoh 1993).
The use of palm wine and as a
leavening agent for dough is attributed to the presence of a yeast strain
contained in the palm sap. This yeast strain is saccharomyces cerevisiaem
or baking yeast is called in the bakery industry.
Palm wine when fresh, tastes
like ginger bear and can be used as like yeast ( Irvine 1961). Initially, the sap is sweet,
dirty brown in colour. The fermentation process results in the sap becoming
milky white in appearance. This is due to the presence of large number of
fermenting bacteria and yeast.
Fermentation occurs between 36 –
38 hr period during which PH of sap falls from 7.0 –7.2 to < 4. (Jay 1986).
1.2 COMPOSITION
OF PALM WINE
Palm wine has the average
alcoholic content of 2.00 percent to 4. 69 percent. The sugary syrup, which is
dirty brown in colour contains about 10 – 12 % sugar mainly sucrose.
Studies made by faparusi et
al1986 found the following genera of bacteria to be the most predominant in
finished produced Lactobacillus, Micrococcus, Leuconostoc,
Streptococcus and Acetobacter. The predominate yeast found are Saccharomyces
and Candida spp with the
former being the more common.
1.3 YEAST (saccharomyces cerevisiae)
Yeast is a unicellular
micro-organism and fungus type. It makes possible many of the products made by
bakers. This is because various types of bread and certain other bakery precuts
are leavened (raised) by yeast. Many of them produce ethanol and carbon dioxide
as waste products of their metabolism. They are therefore useful in the food
industry for fermentation and aeration.
Yeast usually used in the
temperate region for baking are carefully selected strains of Saccharomyces
cerevisiae. This is a simple chlorophyll – free plant which feeds on
sugar in the batter or dough to produce carbon dioxide (Kotshever 1980). By
enzyme action, it converts fermentable sugars and some of the starch present in
the dough into carbon-dioxide gas and alcohol and provides desirable controlled
fermentation (Sultan 1982).
The discovery of the use of
yeast to leaven bread centuries ago lead to the growth of bakery industry.
Bakers used brewers yeast till about 80 –1000 years ago due to its performance
in the bakery which was low and variable. The isolation of a special yeast
strain which possessed the desired characteristic needed, brought about
revolutionary changes in the bakery industry. This strain is known as saccharomyces
cerevisiae or otherwise “ bakers” yeast in the form of cakes of
compressed fresh yeast cell, with moisture content of about 70%.
NUTRITION AND GENERATION
Since the yeast cell is a living
organism, it has numerous nutritional needs and it is only if these are met
that it will grow vigorously and produce a large quantity of carbon dioxide.
Food and moisture are needed for this growth.
Saccharomyces cerevisiae
differs from other yeast species. It
has more aerobic growth habit, maximum yielding capability stability during storage.
It is usually derived from special selection of fast growing (short generation
time) naturally occurring yeast strains ( Oyawoye and Bassey 1997) .
The plant grow best at the
temkperature between 80 – 900 cooler temperatures retards their
growth and a temperature as high as 1110 F kills the plant within an
hour 1400 F destroy them within 5 minutes.
IMPORTANCE OF
BAKERS YEAST
This principle involved in dough
leavening is based on the utilization of the carbohydrate by the ‘bakers’ yeas
to give out carbon dioxide entrapped in the dough. As the yeast multiply in the
dough, fermenting at room temperature. More and more carbon-dioxide is produced
and the dough expanse because of the pressure of gas. This yeast activity is
destroyed during baking at the temperature of 1400 F.
Bakers
yeast is useful chiefly in three different ways.
1.
TESTURE FORMATION: They produce carbon dioxides gas,
which leavens or raises the dough, giving the bread the desired loose porous
texture.
2.
INCREASE OF DOUGH VOLUME: The use of bakers yest as a
leavening agent help to achieve great great increase in volume and make a wide
variety of baked products. This means that it is no longer a necessity to rely
on egg white foam to encompass enough air
1
FLAVOUR PRODUCTION: Bakers yeast is reported to
contribute to the flavour of bread and other yeast leavened products. During
dough fermentation, many secondary metabolites such as ketones, higher
alcohols, organic acids, aldehydes, and
esters are produced by the yeast. Some of these alcohols escape during baking.
Others react with one another and with other compounds found in the dough to
form a new and more complex flavour compounds. The resultant flavour diffuses
into the crumb of baked bread ( Graw – hill 1971).
1.4 BREAD
Bread is food produced by mixing
flour with water and yeast and baking in an oven ( Hornby 1995). In some cases,
other ingredients such as eggs, butter, milk and sugar are added basically to
augment its nutritional value. Like all other foods produced from cereals,
bread is eaten primarily as a cheap source of energy. It contains valuable
amount of protein, iron and vitamins flour is the basic ingredient in the
production of bakery goods. This is because of its gluten. The unique properties
of wheat protein, glademin and can prdice bread dough of the strength and
elasticity required to produce low density of bread of desired texture and
flavour (Ihekoronye and Ngoddy 1985). The elasticity of gluten retains the gas
and supports the structure of the loaf.
The dough is made by mixing
together the flour, water, yeast, salt and other additions ingredients. Dough
raising is the act of producing carbon dioxide in the dough. This is a results
of yeast cell saccharomyces cerevisiae incorporated into the
dough, and this helps in the puffing up of the dough during the process of
bread making.
Bread is baked at the
temperature of 2500 - 2600 for a period of 30 –50
minutes. During baking, the mixtures (dough) are expanded by air, steam or
carbon dioxide. The proteins present (gluten) coagulates and the starch takes
on water and sets (gelatinizes). The coagulated proteins and gelatinized
starches give baked product their structure and colour ( Kotschevar and Lunderg
1970).
Bread production is of vital importance
as its is a product which is not liable to seasonal fluctuation and can be made
from varieties of flour.
In this work,
palm wine was selected as a medium for the isolation of saccharomyces
cerevisiae for the production of bakers yeast. This is due to ability of
the yeast cells present in the palm sap to produce alcohol ( ethanol) and
carbon dioxide form the fermentable sugar in the palm juice.
Past work showed that other
yeast strains are present in which wine apart from saccharomyces cerevisiae
which have the desired characteristics of the bakers yeast. These other
strains are generally referred to as “ wild yeast” ( Frazier and Hoff 1988).
The presence of this “ Wild
yeast “ as well as mold and bacterial flora limits the direct use of palm wine
for bread production. Those loaves produced with 90% palm wine dreg developed
sour – taste and pronounced palm wine flavour and were unacceptable after 3days
thereby limiting leavening , for this reason, Saccharomyces cerevisiae, which
occur naturally in palm wine and have the desirable characteristics to the
bakers yeast is isolated, propagated and used as pure culture for dough
fermentation.
Somiari, and Udoh (1993) worked
on the isolation of yeast from palm wine using malt extract agar ( MEA DIFCO)
for the leavening of the dough.
1.4.1 AIMS AND
OBJECCTIVES
1.
To isolate the yeast saccharomyces cerevisiae from palm
wine for the production of bakers yeast whose performance can compete
favourably with commercial bakers yeast in bread production.
2.
To embark on bread production with locally sourced
yeast rather than commercial bakers’ yeast.
3.
To determine the optimum proofing temperature for the
isolated yeast during bread production
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