ABSTRACT
This study evaluated and identified various microorganisms associated with baked products in Umuahia metropolis of which five (5) different baked products comprising of Biscuits, Bread, Cakes, Pie and Eggroll were randomly selected for the purpose of the work. From this study a total of fourteen (14) bacteria strains were isolated and identified using morphological characteristics, pigmentation on media, microscopy, biochemical and sugar fermentation methods. This reveals the major bacterial isolates to belong to Salmonella species, Escherichia coli, Staphylococcus aurues, Proteus species and Pseudomonas aeruginosa respectively, while the microscopic and cultural characteristics revealed three (3) fungal strains to belong to Aspergillus niger, and Aspergilus flavus. The total viable microbial counts evaluated in this study varied from one sample to the other. Amongst the five (5) different baked products investigated however within Umuahia metropolis, Pie had the highest viable bacteria count at 9.1x106, followed by Bread (8.4x106), Eggroll (6.9x106), Cakes (5.7x106), while the least viable bacteria count was recorded on Biscuit (3.3x106) in that order. The total viable fungal plate count investigated on the different baked products, reveals Bread as having the highest viable fungi count at (1.7 x106) and Biscuit having the least viable fungi count at (1.2 x106). The contamination rate and percentage distribution accessed on different baked products revealed that Salmonella species and Staphylococcus aureus are the most frequently occurring isolates with a high percentage occurrence of 4(30%) each, followed by Escherichia coli (17.6%), Proreus spp 2(11.8%) and Pseudomonas aeruginosa 1(5.9%) at respectively. However, there were slight variations in the fungi population, with Aspergillus niger 2(11.8%) being most predominant and occurring isolates, followed by Aspergillus flavus 1(5.8%). Therefore, microorganisms are the common genera of molds generally isolated from the fresh baked products during the present investigation. These molds have been known to produce toxins, which are both acutely and chronically toxic in animal and humans.
TABLE OF CONTENTS
Title
Page i
Certification iii
Dedication iv
Acknowledgement v
Table
of Contents vi
List
of Tables vii
Abstract ix
CHAPTER ONE
1.0 Introduction 1
1.1 Aim and Objective 3
CHAPTER TWO
2.0 Literature Review 4
2.1 Economical Importance of Bakery Products 4
2.2 Microbial Spoilage of Bakery Products 6
2.2.1 Bacterial spoilage 7
2.2.2 Yeast spoilage 8
2.2.3 Mold spoilage 8
2.3 Physical Factors Influence the Microbial
Growth 9
2.3.1 Effect of temperature, pH and water activity
9
2.3.2 Effect of salt tolerance 12
2.4 Control of Microbial Growth in Bakery
Products 12
2.4.1 Reformulation to reduce product aw 13
2.4.2 Freezing 13
2.4.3 Preservatives 14
2.5 Effect of Chemical Preservatives 14
2.5.1 Sorbic acid and sorbates 15
2.5.2 Propionic acids and its salts 16
2.6 Effect of Bio-preservatives 18
CHAPTER THREE
3.0 Materials and Methods 21
3.1 Collection of Samples 21
3.2 Sterilization of Materials 21
3.3 Preparation of Culture Media 21
3.4 Inoculation and Isolation 21
3.4.1 Method 21
3.5 Purification of Isolates 22
3.6 Identification of Bacterial Isolates 22
3.7 Gram Staining 22
3.8 Biochemical Test 23
3.8.1 Catalase Test 23
3.8.2 Indole Test 23
3.8.3 Citrate Utilization Test 23
3.8.4 Hydrogen Sulphide (H2S)
Production Test 23
3.8.5 Starch Hydrolysis 24
3.8.6 Motility, Indole, Urease (MIU) 24
3.8.7 Coagulase Test 25
3.8.8 Oxidase Test 25
3.9 Identification of Fungi Isolates 25
3.9.1 Microscopic Features 25
CHAPTER FOUR
4.0 Results 26
CHAPTER FIVE
5.0 Discussion, Conclusion and Recommendation 33
5.1 Discussion 33
5.2 Conclusion 37
5.3 Recommendation 37
References
LIST OF TABLES
S/N
|
TITLE
|
PAGE NO
|
1
|
Mean Microbial Counts on
the Selected Baked Products
|
28
|
2
|
Identification and
Characterization of Bacterial Isolates from the Selected
Baked Products
|
29
|
3
|
Cultural Morphology and
Microscopic Characteristics Fungal Isolates from
the Selected Baked Products
|
30
|
4
|
Percentage Occurrence of
the Various Isolates from the Baked Products
|
35
|
5
|
Distribution of Bacterial
and Fungal Isolates from the Baked Products
|
36
|
CHAPTER ONE
1.0 INTRODUCTION
Bakery
products are the important staple foods in most country and cultures. Bakery
products and cereals are a valuable source of nutrients in our diet providing
us with most of our food calories and approximately half of our protein
requirements. Cereals have been a basic food of man since prehistoric times and
were consumed long before bread making was developed. Variety breads and other
bakery products have increased in sales volume within the past decades. The
nutrients in bakery products are carbohydrates, proteins, lipids, vitamins and
minerals. Bakery industry in India is the largest of the food industries with
an annual turnover of about B 3000 crores. India is the second largest producer
of biscuits after USA. The biscuit industry in India comprises of organized and
unorganized sectors (Guynot et al.,
2004). Breads and biscuits form the major baked foods accounting for over 80
per cent of total bakery products produced in the country. The quantities of
bread and biscuits produced are more or less the same.
Commercially
produced and properly handled bread generally lacks sufficient amounts of
moisture to slow growth of any microorganisms except moulds (Guynot et al., 2004). As normal cooking
temperature destroy fungal spores, post-process contamination from airborne
spores and contact with contamination surfaces must be prevented.
Filamentous
fungi involved in spoilage of bread include Rhizopus sp., and Mucor sp.,
Penicillium sp., Eurotium sp., Aspergillus sp. and Monilia
sitophilia (Adams, and
Moss, 2000). One of the most common is Rhizopus stolonifer, often
referred to as the ‘bread mould’. Storage of bread under conditions of low
humidity retards mould growth. In addition to the economic losses associated
with bakery products, another concern is the possibility of mycotoxins
production. Eurotium species are usually the first fungi to colonize
improperly water allowing other species, Aspergillus and Penicillium which
can produce toxins to thrive. Losses of bakery products due to mould spoilage
vary between 1-5 per cent depending on seasons, type of products and methods of
processing.
Members
of the genus Bacillus bring about bacterial spoilage of bread known as
rope. This is of major economic to the baking industry. Ropiness which is the
most important spoilage of bread after moldiness occurs particularly in summer
when the climatic conditions favour growth of bacteria. It is mainly caused by Bacillus
subtilis but Bacillus licheniformis, Bacillus magaterium and Bacillus
cereus have also been associated with ropy bread (Adams, and Moss, 2000). The incidence of wheat bread spoilage
caused by Bacillus has increased during the last few years presumably
because more bread is produced without preservatives and often raw materials
such as bran and seeds are added. Spoilage of bread by rope formation may
constitute a health risk, high numbers of Bacillus subtilis and Bacillus
licheniformis in foods may cause a mild form of food illness. Consumption
of ropy bread has been association with food-borne illness in reports from
Canada and the United Kingdom.
The
stability of bakery products against the attack by fungi is mainly due to
preservatives. Preservatives help to reduce or prevent wastage of food through
spoilage caused by microorganisms. Longer shelf life enables a greater variety
of products to be kept in store and in the home. Sofos and Busta, (1991) reported that
chemical preservatives can control the growth of molds by preventing the
metabolism, by denaturing the protein of the cell, or by causing physical
damage to the cell membrane. Among these preservatives are propionic and sorbic
acid or their salts which have been show to increase the shelf life of bakery
products. Propionic acid and calcium propionate are usually employed at
concentrations of 0.1 and 0.2 per cent respectively. At these levels, moulds
can be inhibited for 2 days or more and the formation of rope can be prevented (Seiler,
1994).
Problems
due to spoilage yeasts in bread usually result from post-baking contamination,
slicing machines, bread coolers, conveyor belts and racks have been identified
as sources. Yeast spoilage is characterized by visible growth on the surface of
products. The most frequent and troublesome yeast is Pichia butonii,
which is known as “chalk mould”. This yeast can multiply rapidly on bread, with
visible growth often apparent some time before mould occurs. Filamentous fungi
are more common than yeast on British breads. Since, filamentous fungi are more
easily recognized than yeast, because they generate the majority of complaints (Seiler,
1994). The stability of bakery products against the attack by fungi is mainly
due to preservatives. Preservatives help to reduce or prevent wastage of food
through spoilage caused by microorganisms. Longer shelf life enables a greater
variety of products to be kept in store and in the home.
1.1 AIM OF STUDY
The
aim of this research work is to evaluate and identify the microorganisms that
are associated with baked products such as bread, meat pie and egg roll.
1.2 SPECIFIC OBJECTIVES
·
To isolate and identify
microorganisms associated with baked products
·
To determine the
contamination rate of the various microorganisms on the baked products
·
To determine the
percentage occurrence of the various isolates from the baked products
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