MICROBIOLOGICAL ASSESSMENT OF STREET VENDED BAKED FOODS

ABSTRACT

This study was aimed at assessing the microbiological quality of selected baked snacks within Umuahia. The samples were processed in the ten-fold serial dilution technique and appropriate inoculum (0.1ml) plated out into Nutrient Agar, MacConkey agar, Mannitol salt agar, Salmonella Shigella agar and potato dextrose agar(PDA) using pour plate techniques. This revealed the major bacterial isolates to be Salmonella species, Escherichia coli, Staphylococcus aureus, Klebsiella species and Bacillus species, while the microscopic and cultural characteristics revealed three (3) fungal strains belonging to Fusarium oxysporum, Rhizopus stolonifer and Mucor species. The total viable microbial counts evaluated in this study varied from one sample to the other. Amongst the four (4) different baked products investigated however within Umuahia, Doughnut had the highest viable bacteria count of 8.40x105cfu/g, followed by Eggroll (7.92x105cfu/g), while the least viable bacteria count was recorded on meat pie (1.08x105cfu/g). The total viable fungal plate count investigated on the different baked products, reveals meat pie obtained from Ubakala Market as having the highest viable fungi count of 4.70x105cfu/g and Fish Roll obtained from Ishi-gate having the least viable fungi count with (­­1.36x105cfu/g). The contamination rate and percentage distribution on the different baked products revealed that Escherichia coli had the highest percentage occurrence on the baked products at 61(21.9%), followed by Klebsiella species(12.9%), Staphylococcus aureus 35(12.5%) while the least was recorded for Salmonella species at17(6.1%). However, there were slight variations in the fungi population, with Mucor species 26(9.3%) being most predominant and occurring isolates, followed by Rhizopus Stolonifer 8(8.6%). Therefore, the need of the hour is to control the microbial growth in baked products by using preservatives from natural sources.

TABLE OF CONTENTS

Title page                                                                                                                                i

Certification                                                                                                                           iii

Dedication                                                                                                                              iv

Acknowledgements                                                                                                                v

Table of contents                                                                                                                    vi

Lists of Table                                                                                                                          viii

Abstract                                                                                                                                  ix

CHAPTER ONE

1.0       Introduction                                                                                                                1

1.1       Aim of Study                                                                                                              3

CHAPTER TWO

2.0       Literature Review                                                                                                       4

2.1       Economical Importance of Baked Products                                                               4

2.2       Microbial Spoilage of Baked Products                                                                       6

2.2.1    Bacterial Spoilage                                                                                                       7

2.2.2    Yeast Spoilage                                                                                                            8

2.3       Fungal Species Associated With Spoilage of Bakery Products                                    9

2.3.1    Penicilliumspp                                                                                                            9

2.3.2    Mucorspp                                                                                                                    10

2.4       Physical Factors that Influence the Microbial Growth in Baked Foods              10

2.4.1    Effect of Temperature, pH and Water Activity                                                          10

2.4.2    Effect of Salt Tolerance                                                                                             13

2.5       Control of Microbial Growth in Baked Products                                                       13

2.4.1    Reformulation to reduce product aw                                                                          13

2.5.2    Freezing                                                                                                                      14

2.5.3    Preservatives                                                                                                               14

2.6       Effect of Chemical Preservatives                                                                               15

2.6.1    Sorbic Acid and Sorbates                                                                                           16

2.6.2    Propionic Acids and its Salts                                                                                      17

2.7       Effect of Bio preservatives                                                                                          19

CHAPTER THREE

3.0       Materials and Methods                                                                                               21

3.1       Sample Collection                                                                                                      21

3.2       Sterilization of Materials                                                                                            21

3.3       Normal Saline Preparation                                                                                         21

3.4       Media Preparation for Isolation of Microorganisms                                                  21

3.5       Enumeration and Isolation of Bacteria                                                                       22

3.6       Characterization and Identification of Isolates                                                           22

3.7       Cultural Characteristics                                                                                              22

3.7.1    Microscopy Examination                                                                                           23

3.7.2    Biochemical Tests                                                                                                      23

3.8       Isolate Purification                                                                                                     25

3.9       Identification of Fungal Isolates                                                                                 26

3.9.1    Wet Preparation                                                                                                          26

3.9.2    Colonial Morphology                                                                                                 26

CHAPTER FOUR

4.0       Results                                                                                                                        27

CHAPTER FIVE

5.0       Discussion, Conclusion and Recommendation                                                          35

5.1       Discussion                                                                                                                   35

5.2       Conclusion                                                                                                                  39

5.3       Recommendation                                                                                                       39

            References

LIST OF TABLES

CHAPTER ONE

1.0       INTRODUCTION

Baked products are the important staple foods in most country and cultures. Baked 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 of breads and other baked products have increased in sales volume within the past decades. The nutrients in baked products are carbohydrates, proteins, lipids, vitamins and minerals. 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 baked 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 reduces the 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, 2010). 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 baked products, another concern is the possibility of mycotoxins production. Eurotium species are usually the first fungi to colonize water allowing other species, such as Aspergillus and Penicillium which can produce toxins to thrive. Losses of baked products due to mould spoilage vary between 1-5 per cent depending on seasons, type of products and methods of processing (Guynot et al., 2015).

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 (Guynot et al., 2015). 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, 2010). 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 (Abellana et al., 2011).

The stability of baked 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, (2011) 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 baked 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, 2004).

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, 2004).

1.1       AIM OF STUDY

The aim of this research work is to assess the microbiological quality of baked food such as doughnut, fish roll and meat pie sold in Umuahia.

1.1.1    Specific Objectives

·       To determine the microbial load of the baked foods

·       To isolate and identify bacterial and fungal species associated with baked foods

·       To determine the percentage occurrence and distribution of the various microorganisms on the baked foods.

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