ABSTRACT
In Nigeria and other developing countries, egg is produced all year round and it is a highly perishable product that if not given proper care between the time it is laid, time it is sold and the time it is consumed may deteriorate. The effects of pretreatment methods on some quality indices of stored shell-eggs was studied. Day old deep litter eggs were given the following treatments; hot oil (HOL), cold oil (COL), brine solution (BSN)), brine with antibiotics (BAS), pasteurization (PAU), while un(pre)treated shell-eggs (RTM) served as control. All eggs were stored at room temperature. The stored eggs were analyzed for their; physical, chemical, functional, amino acid, microbial and sensory properties. The results obtained indicated a significant decrease in egg weight among stored eggs (51.0-28.50g). Among the treated samples HOL recorded least decline in egg weight (51.0-50g), COL had highest haugh unit (78.03) at the end of storage. The yolk and albumen pH increased significantly (p < 0.05) from 6.04-7.43 and 8.51-9.21, respectivelyin RTM. COL and HOL retained AA grade all through storage period with RTM and PAU declined to B grade at the end of storage. RTM had lowest moisture content (56.84%), protein (10. 77%), while fat content increased in COL (11.26%) and HOL (11.17%) at end of storage. Result revealed there was a rapid decline in foaming capacity (100.15-50.73%), foaming stability (100.06-51.85%), emulsification capacity (42.20-28.51%), least gelation capacity (4-0) for the RTM at end of storage. COL recorded less decline in these functional properties. Coliform and fungi were not present in samples. The total bacteria count of the shell-eggs were <105 cfu/ml while the RTM recorded moderate growth of total bacteria count 2.10 ×105 at end storage.Cold oil treated eggs (COL) was the most accepted (5.50), followed by hot oil treated eggs (HOL) (4.75). However, the eggs stored under room temperature (control, 1.70) was the least preferred All essential amino acids were present in the shell eggs both at the beginning and at end of storage. PAU recorded highest decrease in total amino acid content (63.61-28.06%). Isoleucine was the most abundant amino acid in all samples while proline was the least. There was an increase in the total amino acid content of COL (19.49-43.98%). COL treatment offered best protective effect against decline of most of the studied quality indicators, next was HOL, and followed by BAS, the least was PAU.
TABLES OF CONTENTS
Title Page
i
Declaration
ii
Certification
iii
Dedication
iv
Acknowledgment
v
Table of Contents
vi
List of Tables
ix
List of Tables
x
Abstract xi
CHAPTER
1: INTRODUCTION
1.1
Background to the Study 1
1.2
Statement of the Problem
3
1.3
Justification
4
1.4
Objectives of the Study 5
1.4.1 Main
objective 5
1.4.2 Specific
objectives 5
CHAPTER 2: LITERATURE REVIEW
2.1 Importance
of Egg 6
2.2 Structure of Eggs and Composition 7
2.2.1 The shell 7
2.2.2 Albumen 8
2.2.3 Yolk 9
2.3 Nutritive Value of Eggs 10
2.3.1 Egg protein and energy 12
2.3.2. Vitamins and minerals 12
2.4 Egg Quality 13
2.4.1 Indicators of egg quality 13
2.4.1.1 Internal quality 13
2.4.1.2 External egg quality 15
2.4.1.1.1 Soundness of the shell 16
2.4.2 Factors
that affect egg quality 16
2.4.2.1 Yolk colour 16
2.4.2.2 Yolk firmness 16
2.4.2.3 Yolk texture 17
2.4.2.4 Albumen consistency 17
2.5 Egg Preservation Techniques 19
2.5.1 Lowering of temperature 19
2.5.2 Shell
coating 19
2.5.3 Pasteurization
of eggs 21
2.5.4 Osmotic
preservation 21
2.6 Grading
of Eggs 22
2.7 Candling 25
2.8 Factors
that affect Egg Quality 26
2.9 Changes
in Eggs during Storage 27
CHAPTER 3: METHODOLOGY
3.1
Materials
28
3.1.1 Sources of raw materials 28
3.2
Sample Preparation and Treatments 28
3.2.1
Hot oil (pre) treatment 28
3.2.2 Cold oil (pre) treatment 29
3.2.3 Hot water (pre) treatment 29
3.2.4 Brine solution (pre) treatment 29
3.2.4 Brine with antibiotics (pre) treatment 29
3.3 Analysis 31
3.3.1 Physical property analysis 31
3.3.1.1 Egg weight loss 31
3.3.1.2 Albumen height 31
3.3.1.3 Haugh unit 31
3.3.1.4 Yolk index 32
3.3.1.5 pH of the egg albumen/egg yolk 32
3.3.2 Proximate composition analysis 33
3..3.2.1
Determination of moisture content 33
3.3.2.2 Determination of crude protein 33
3.3.2.3 Ash content determination 34
3.3.2.4 Fat content determination 35
3.3.2.5 Estimation of carbohydrate 35
3.3.3 Functional properties analysis 35
3
3.3.1 Foaming capacity and foaming
stability 35
3.3.3.2 Emulsification capacity 36
3.3.3.3 Gelation capacity 36
3.3.4 Microbial analysis 37
3.3.4.1 Total aerobic bacterial count 37
3.3.5 Sensory analysis of boiled eggs 37
3.3.6 Amino acid profile 38
3.3.7 Preparation of sample by hydrolysis 38
3.3.8 Determination 38
3.3.9 Experimental design
41
3.3.10 Statistical analysis 41
CHAPTER 4: RESULTS AND
DISCUSSION
4.1 Egg
Weights of Pretreated Stored Shell Eggs 42
4.2 Yolk
Index of Pretreated Stored Shell Eggs 44
4.3 Yolk
Height of Pretreated Stored Shell Eggs 47
4.4 Albumen
Height of Pretreated Stored Shell Eggs 49
4.5 Yolk
Width of Pretreated Stored Shell Eggs 51
4.6 Haugh
Unit of Pretreated Stored Shell Eggs 53
4.7 Yolk
pH of Pretreated Stored Shell Eggs 56
4.8
Albumen pH of Pretreated Stored Shell Eggs 58
4.9 Effect
of Pretreatment Methods on Proximate Composition in Stored Shell Eggs 60
4.10 Functional
Properties of Pretreated Stored Shell Eggs 67
4.11 Effect
of Pretreatment Methods on Foam Stability (%) in Stored Shell Eggs 69
4.12 Effect
of Pretreatment Methods on Emulsification Capacity in Stored Shell Eggs 72
4.13 Effect
of Pretreatment Methods on Least Gelation Capacity in Stored Shell Eggs 74
4.14 Effect
of Pretreatment Methods on Microbial Properties in Stored Shell Eggs 76
4.15 Effect
of Pretreatment Methods on Amino Acid Profile in Stored Shell Eggs 79
4.16 Effect
of Pretreatment Methods on Sensory Properties in Stored Shell Eggs 84
CHAPTER 5: CONCLUSION AND
RECOMMENDATIONS
5.1 Conclusion 88
5.2 Recommendations 89
References 90
Appendix
107
LIST OF TABLES
2.1
Nutritive value of chicken eggs per
100g 11
2.2
Grading of eggs 24
3.1 Experimental treatment/design 30
3.2 Wavelength for amino acids 40
4.1
Egg weight (g) loss of stored shell
eggs 42
4.2
Effect of pretreatment methods on
yolk index of stored shell eggs 44
4.3
Effect of pretreatment methods on
yolk height of stored shell eggs 47
4.4
Effect of pretreatment methods on
albumen height of stored shell eggs 49
4.5
Effect of pretreatment methods on
yolk width of stored shell eggs 51
4.6
Effect of pretreatment methods on
haugh unit of stored shell eggs 53
4.7
Effect of pretreatment methods on
yolk pH of stored shell eggs 56
4.8
Effect of pretreatment methods on
albumen pH of stored shell eggs 58
4.9 Effect of pretreatment methods on
proximate composition of stored shell eggs 60
4.10 Effect of pretreatment methods on foaming
capacity of stored shell eggs 67
4.11 Effect of pretreatment methods on foaming
stability of stored shell eggs 69
4.12 Effect of pretreatment methods on
emulsification capacity of stored shell eggs 72
4.13 Effect of pretreatment methods on least
gelation capacity of stored shell eggs 74
4.14 Effect of pretreatment methods on microbial
properties of stored shell eggs 76
4.15 Effect of pretreatment methods on amino
acid profile of stored shell eggs 80
4.16 Effect of pretreatment methods on sensory
properties of stored shell eggs 84
LIST OF FIGURES
2.1: Structures of egg 7
2.2:Grading of eggs 25
CHAPTER
1
INTRODUCTION
1.1 BACKGROUND TO THE STUDY
It has been reported by different authors that eggs
are considered to be highly nutritious containing high levels of vitamins and
minerals as well as protein. Protein from animal sources plays a significant
role in providing sufficient and balanced nourishment to human health
(Dudusola, 2009). Eggs as food, provides a means through which the animal
protein needs of humans can be met; they have various applications and uses
(Scott and Silversides, 2001).
Egg protein is said to be of high biological value. This
is because it is rich in all the amino acids required by the human body.
Moreover, egg protein can to a great extent complement other sources of food
protein that are obviously lower in biological value. This it does by providing
the amino acids that are lacking in such foods (Okiki and Ahmed, 2017). In
addition to being nutritious, egg also offers a variety of functional
properties like; whipping, foaming, gelling and emulsifying (Chang and Chen,
2000).
A whole egg has three main parts; the shell, egg white
(albumen) and the yolk. The egg shell is separated from the egg white by the
shell membrane, also the yolk is separated from the egg white by the vitelline
membrane (Okiki and Ahmed, 2017). An intact vitelline membrane prevents the
content of the egg white and yolk from mixing together thus preventing egg
molting. Storing shell eggs at room temperature causes the vitelline membrane
to weaken; this causes the yolk and egg white to become thinner and watery and
this continues to occur as the egg ages (Jacob et al., 2000). When an egg is newly laid, the yolk is usually round
and firm, but as the egg age increases, the yolk absorbs water from the albumen
thus it increases in its size, stretches and then the vitelline membrane is
weakened. This produces a flattened egg yolk (Gramenidis, 2006).
Egg quality can be said to comprise those
characteristics of an egg which affects its acceptability and use to consumers
(Dudosola, 2009). The quality characteristics that are important to
acceptability of shell eggs by consumers includes; freshness, egg weight and
sensory properties. The interior characteristics that include chemical
composition, Haugh unit, yolk diameter and others are of importance in various
foodindustry because the demand of good quality shell eggs and egg products
like egg powder, frozen egg and yolk oil is on the increase (Scott and
Silversides, 2001).
There is the decrease of egg quality due to high
temperature conditions during storage and this adversely affects the food
sector. Since egg provides means through which animal protein needs are met and
also its various applications in the food industry (Scoot and Silversides,
2001). Spoilage that occurs during egg storage has been documented to be as a
result of entrance of microorganisms through the semipermeable pores of egg
shell, as well as escape of carbon dioxide and evaporation of moisture among
others (Okiki and Ahmed, 2017).
To retard the deteriorative changes in the internal
quality of eggs, various shell treatments like coating with vegetable oil and
mineral oils, pasteurization, water glass and lime sealing has been suggested
(Olamide et al., 2016; Ndife et al.,
2020). Edible films and coatings play an important role in the food
industries because they have versatile properties. Surface coatings of eggs are
likely to increase the egg shell strength and shelf life leading to reduction
of egg spoilage (Biladeau and Keener, 2009).
Sodium chloride is the most important ingredient used
to process eggs. With respect to preservation, sodium chloride plays a role in
reducing the growth of pathogens and organisms that cause spoilage, thereby
extending shelf life. Adding salt to foods causes microbial cells to undergo
osmotic shock because of intracellular water loss; thus, their growth is
retarded or microbial death ensues (Davidson, 2001). Sodium chloride is not
only beneficial for egg preservation, but it also modifies egg characteristics.
During the salting process, sodium chloride gradually diffuses into the egg
white and yolk through the pores and membrane of the shell using either the
brining or coating method (Chen et al.,
1999).
Pasteurization which is a heat treatment, involves the
immersion of eggs for a short time in boiling water to coagulate the thin
albumen immediately beneath the shell membrane. The coagulation that occurs is
known as cauterization and it helps extend the shelf life of shell-eggs by
preventing the escape of carbon dioxide and evaporation of moisture and others
(Owolabi et al., 2016).
1.2 STATEMENT OF PROBLEM
Egg
production is on the increase every day. As it stands, Nigeria is the largest producer
of poultry eggs in Africa. The Food and Agriculture Organization (FAO) reported
that Nigeria produces 784,000 metric tonnes of Africa’s total poultry egg of
951,000 metric tonnes (FAO, 2012).
In Nigeria and other developing countries, egg is
produced all year round; both during hot and cold seasons. Egg is a highly
perishable product and if not given proper care between the time it is laid,
time it is sold and the time it is consumed may deteriorate. Because of the
above reason, egg producers and processors are faced with the problems and
challenges of egg preservation especially during the hot season when there is
increase in temperature. This is the period when lots of spoilage is
experienced that leads to the deterioration in the quality of eggs (Dauda et al., 2006).
According to experts, the use of refrigeration as
preservative means is considered the best, but is expensive and thus not
suitable in Nigeria and other developing countries because of erratic power
supply. There is therefore, the need to explore alternative methods of
shell-egg preservation that can result in preservation of the quality indices of
the eggs, thereby making them available at reduced cost.
1.3 JUSTIFICATION
Pre-treatment
has been identified to be a means of curbing shell egg spoilage and it is based
on the following principle; reducing microbial growth, closing the shell pores
of eggs to reduce the escape of gases and evaporation of moisture (Nongtaodum et al., 2013). To retard the
deteriorative changes in the internal quality of eggs, various shell treatments
like coating with vegetable oil and mineral oils, pasteurization, water glass
and lime sealing has been suggested.
Hence this work will employ; edible oil coating,
brining and pasteurization as pretreatment methods for shell-egg storage, with
the view to selectthe most effective. This will profer solution to the
challenges of shell egg storage especially with the prevailing unreliable power
supply. All the pretreatment methods does not require electricity and are thus
cost effective.
1.4 Objectives of the Study
1.4.1 Main objective
The current study was aimed at evaluating the effect
of different pretreatment methods (Oil treatment (hot oil and cold oil) and
pasteurization (hot water), brining and antibiotics) on some quality indices of
stored shell-eggs.
1.4.2
Specific objectives
The specific objectives of this study
were;
1.
Pretreat eggs using
different pretreatment techniques.
2.
Store pretreated egg samples
in ambient temperature.
3.
Evaluate the effect of
pretreatment methods on the physical properties of stored shell-eggs.
4.
Evaluate the effect of
pretreatment methods on the proximate composition and functional properties of
stored shell-eggs.
5.
Determine the effect of
pretreatment methods on the amino acid profile of stored shell-eggs.
6.
Evaluate the effect of
pretreatment methods on the microbial load of stored shell-eggs.
7.
Evaluate the effect of
different pretreatment methods on the sensory properties of stored shell-eggs.
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