FUNGI ASSOCIATED WITH THE DETERIORATION OF BAKED PRODUCTS (CAKE AND BREAD)

ABSTRACT

This study was aimed at isolating and identifying some fungi associated with baked food products (cake and bread) of different trademarks. Ten (10) samples of cake and bread were purchased from different retail points in the city of Umuahia. The fungi associated with deteriorated test products were isolated and identified based on their cultural and morphological characteristics. The isolates belonged to five fungal:  Penicillium, Aspergillus, Rhizopus, Mucor, and Cladosporium. Rhizopus stolonifer was isolated from all the deteriorised commercial bread samples while Cladosporium spp had the lowest frequency of occurrence (20.0%). Aspergillus spp had a 60% frequency of occurrence while Penicillium sp and Mucor sp. of 80% and 60% respectively. For the cake samples, Aspergillus sp and Penicillium were the predominant organisms with 80% and 60% occurrence respectively. In this study Rhizopus sp was found to be the most common fungus. The presence of these decay fungi in commercial bread and cakes is a public health hazard as some of them have been known to produce mycotoxins which are injurious to health.

TABLE OF CONTENTS

Title page                                                                                                                                i

Certification                                                                                                                           ii

Dedication                                                                                                                              iii

Acknowledgements                                                                                                                iv

Table of contents                                                                                                                    v

List of tables                                                                                                                           vi

Abstract                                                                                                                                     vii

CHAPTER ONE :INTRODUCTION

1.1       Background Of The Study                                                                                          1

1.2       Aim and objectives                                                                                                     4

CHAPTER TWO : LITERATURE REVIEW

2.1       Environment as contaminants of baked products                                                       5

2.2       Fungal Spoilage of Baked Goods                                                                               6

2.2.1    Mould Growth                                                                                                             9

2.3       Cereals and their contamination with fungi and mycotoxins                                     13

2.4       Spoilage Of Bakery Products                                                                                     14

2.5       Mycotoxins                                                                                                                 15

2.6       Economical Importance Of Bakery Products                                                             16

2.7       Protection against Mould Spoilage                                                                            18

2.7.1    Protective Packaging                                                                                                  19

2.8       Control Of Microbial Growth In Baked Goods                                                          20

CHAPTER THREE:

3.0       Materials And Methods                                                                                              24

3.1       Sample Collection                                                                                                      24

3.2       Culture Media preparation                                                                                         24

3.3       Isolation of microorganisms from the samples                                                          24

3.4       Identification of Fungal Isolates                                                                                 25

CHAPTER FOUR :

4.0       Results                                                                                                                        26

CHAPTER FIVE:

5.0       Discussion and Conclusion                                                                                        31

5.1       Discussion                                                                                                                   31

5.2       Conclusion                                                                                                                  33

References                                                                                                                  34

LIST OF TABLES

Tables

1:         Major causative agents of bread microbial spoilage.                                                 12

2:         Microscopic and Macroscopic Characteristics of the Fungal Isolates.                       27

3:         Fungal Load of the Respective Baked Samples.                                                        28

4:         Rate of Isolation of the Spoilage Fungi in the Bread Sample.                                 29

5:         Rate of Isolation of the Spoilage Fungi in the Cakes sample.                                 30

CHAPTER ONE

1.1       INTRODUCTION

Bread and cake are food products that are universally accepted as a very convenient form of food that has desirability to all humans. It is a good source of nutrients, such as macronutrients and micronutrients that are all essential for human health (Potter and Hotchkiss 2006). Bread and other bakery products are however, subjected to various spoilage problems, including physical, chemical and microbial; the latter is the most serious one particularly bacterial (Bacillus sp.) and mold growth. Various molds involved in spoilage of bread include Rhizopus, Mucor, Penicillium, Eurotium, Aspergillus and Monilia (Saranraj and Geetha 2012). Microbial spoilage of bread and the consequent waste problem still causes large economic losses for both the bakery industry and the consumer (Moore et al., 2008; Moroni et al., 2009).

Mold contamination of baked products including cakes and breads can pose a serious health problem when there are species which have the ability to synthesize and actively secrete toxic metabolites. It is known that aflatoxins produced by Aspergillus flavus and A. parasiticus, ochratoxin A produced by Aspergillus ochraceus and some Penicillium spp., and some fusariotoxins produced by Fusarium spp., are strong cytotoxic and carcinogenic agents (Diaz, 2005; Kocić-Tanackov and Dimić, 2012).

Bakery products includes various ingredients such as cereal flour, cocoa powder, sugar, egg, ,edible oil, nuts, dried fruit, spices which regularly contain molds (Levic et al., 2004; Pitt and Hocking, 2009; Kocic-Tanackov and Dimic, 2012). Furthermore, the fine bakery product comprises an intermediate or high moisture baked product having a water activity (aw >0.8), which is sufficient to keep the product mold free when packaged for a storage time of 2 weeks or more at ambient temperature (Samet and Spengler, 2003). Baked products with a relatively neutral pH, high moisture content and water activity such as cakes, muffins, waffles, and tortillas are particularly prone to rapid spoilage from a variety of molds, principally Penicillium and Aspergillus species (Cook and Johnson, 2009).

These microorganisms on cakes can come from the air, contaminated packaging materials and other sources. When water activity is below 0.90 aw, mold appearance is a common type of microbial spoilage. Most molds are more resistant to drying, pH and osmotic pressure than bacteria and their presence always represents a potential risk of spoilage or diseases transmitted by food (Lević et al., 2004; Pitt and Hocking, 2009; Kocić-Tanackov and Dimić, 2012).

Food spoilage is a metabolic process that causes foods to be undesirable or unacceptable for human consumption due to changes in sensory characteristics. Food spoilage is a major issue for the food industry, leading to food waste, substantial economic losses for manufacturers and consumers, and a negative impact on brand names. Among causes, fungal contamination can be encountered at various stages of the food chain (e.g., post-harvest, during processing or storage). Fungal development leads to food sensory defects varying from visual deterioration to noticeable odor, flavor, or texture changes but can also have negative health impacts through mycotoxin production by some molds.

Spoiled foods may be safe to eat if they may not cause illness because there are no pathogens or toxins present but changes in texture, smell, taste, or appearance cause them to be rejected (Smith et al., 2004; Doyle, 2007; Edward, 2007; Montville and Matthews, 2008). A food borne infection involves the ingestion of the microbial pathogens followed by growth in the host, including tissue invasion and release of toxins. Disease caused by consumption of contaminated food always has been a problem around the world and annual expenses spent on improving these conditions. Cake because of ingredients has great potential to be contaminated with many types of microbes. Cakes because of their ingredients are a suitable environment for growth and proliferation of microorganisms and microbial agents transmitted infection or food poisoning to consumers.

When food becomes contaminated with fungi, these fungus leave behind secondary metabolites called mycotoxins that if toxins are received by living things are induced an extreme and harmful effects such as carcinogenesis, malformations, growth retardation, immune suppression and mutagenesis in organisms. Mycotoxins are a group of relatively resistant toxin metabolites that are  produced by fungi and secondary metabolic path ways of fungal cells and cause food contamination and possibly environment (Haidary, 2006; Tajic, 2006; Kazemi et al., 2004; Jafari et al., 2006).

Many industrially produced baked goods emerge from the baking process with a surface that is essentially sterile but post bake handling can quickly lead to fungal surface contamination as a result of exposure to airborne contaminants as well as equipment contact. Following surface contamination, many baked goods are then very vulnerable to surface mold spoilage, the severity of which is linked to factors such as the degree of contamination, the moisture content of the product and the storage conditions (Graham et al., 2006). Mold contamination of cakes and the possibility of mold growth can pose a serious health problem.

1.2       Aims and Objectives

This research study was aimed at:

Determination of the fungal load of baked products (cake and bread)

Isolating and identifying spoilage fungi of cake and bread.

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