CHARACTERIZATION OF MICRORGANISMS ASSOCIATED WITH ROTTEN ONION BULBS

ABSTRACT

Vegetables are important protective food and highly beneficial for the maintenance of health and prevention of diseases. This study was aimed at identifying and classifying the microorganisms (bacteria and fungal) associated with rotten onions bulb. With the following objectives which are to isolate the Microorganisms found in rotten onions bulb, identify the Microorganisms in rotten onions bullb. Ten (10) samples of rot onion bulbs used for this study were obtained from onion sellers at popular markets which are Amawon market, Ahiaeke market, and Ndoro market in Ikwuano L.G.A, Umuahia, Abia State. The onions were purchased in batches and brought to the laboratory for Microbiological analysis.  The sample was processed by standard bacteriological method. From the result it shows that bacteria load of rotten onions sample 1.0 x104   to 6.0 x101 while the fungal ranges from 1.5 x103   to 1.5 x101 . The result also shows the bacteria and fungi isolated from rotten onions bulb samples which were identified by morphological characteristics on media, microscopy, biochemical and sugar fermentation methods. These reveals the major bacterial isolates to belong to Bacillus species, Escherichia coli, Proteus spp and Non-haemoltyic streptococcus and fungi isolates are Rhizopus spp, Candida spp and Mucor spp. The result also shows the occurrences of bacteria, Non-hemolytic streptococcus   (41.17%) followed by E. coli (23.52%) has the highest percentage occurrences, while the bacteria isolates with the lowest percentage occurrence are Proteus spp. (17.64%) and Bacillus spp.  (17.64%), fungi isolates Candida spp. (55.55%) has the highest percentage occurrence followed by Mucor spp. (33.33%), while the fungi isolates with the lowest percentage occurrence is found in Rhizopus spp. (11.11%). Rotten onion bulbs harbor a wide range of bacteria and fungi species. The pathogenic microorganisms implicated in the rotten onion bulbs samples are of public health importance.  It was also noted that some of the bacteria and fungi isolates have history of pathogenicity which some fungi involved are to deposit mycotoxins which are inimical to health.

TABLE OF CONTENT

Title page                                                                                                                                i

Certification                                                                                                                           ii

Dedication                                                                                                                              iii

Acknowledgements                                                                                                                iv

Table of contents                                                                                                                    v

Lists of table’s                                                                                                                        viii

Abstract                                                                                                                                  ix

CHAPTER ONE

1.0   Introduction                                                                                                                                         1                                                                                                                                             

1.1 Aim of Study                                                                                                                    3          

1.2 Objectives                                                                                                                                    3

CHAPTER TWO

Literature Review                                                                                                                   4

2.1       Onions                                                                                                                         4

2.2       Species of Onions                                                                                                       5

2.3       Composition of Raw Onions                                                                                      6

2.3.1    Nutrient                                                                                                                       6

2.3.2    Phytochemicals                                                                                                          7

2.4       Spoilage of Vegetables                                                                                               8

2.5 Spoilage Organisms in Vegetables                                                                                   9

2.5.1    Yeasts                                                                                                                         10

2.5.2    Molds                                                                                                                          11

2.5.3    Bacteria                                                                                                          13

2.5.4    Other Bacteria                                                                                                 15

2.6       Factors Affecting Food Spoilage and Shelf Life                                            16

2.6.1    Vegetables                                                                                                      17

2.7       Control of Spoilage Microorganisms                                                             18

CHAPTER THREE

3.0   Material and Methods                                                                                         20

3.0.1 Study Area                                                                                                         20

3.1 Methods                                                                                                                20

3.1.2 Sample Collection                                                                                             20

3.1.3 Sterilization of Glass Wares                                                                              21

3.1.4 Media Preparation                                                                                             21

3.1.5 Microbiological Serial Dilution                                                                        21

3.2       Isolation of Bacteria and Fungi                                                                      21

3.3.2    Inoculation and Incubation                                                                             21

3.4         Microbial Colony Count                                                                                       22

3.5       Identification of Fungi                                                                                    22

3.5.1      Macroscopy and Colonial Identification                                                             22

3.5.2    Microscopy                                                                                                     22

3. 6      Gram Reaction                                                                                               23

3.6.1      Characterization of Bacteria (Biochemical Tests)                                         23

3.5.1.1    Motility Test                                                                                                                             23

3.6.1.2    Catalase Test                                                                                                                             24

3.6.1.3    Indole Test                                                                                                                               24

3.6.1.4 Citrate Utilization Test                                                                                   24

3.6.1.5 Methyl Red (MR)

3.6.1.6 Coagulase Test (Slide Test)                                                                              25

3.6.1.7 Voges- Proskauer (VP) Test                                                                                                    25

3.6.1.8 Sugar Fermentation Test                                                                                                            25

CHAPTER FOUR

4.0. Results                                                                                                                              27

CHAPTER FIVE

5.0. Discussion, Conclusion and Recommendation                                                               38

5.1. Discussion                                                                                                                        38

5.2. Conclusion                                                                                                                       39

5.3. Recommendation                                                                                                             40

Reference                                                                                                                                        41

LIST OF TABLES

TABLE                              TITLE                                                   PAGE

4.1.                      The sources of samples                             29

4.2                        The percentage occurrence of the bacteria isolates                              30

4.3                       The percentage occurrence of the fungal isolates                                                 31

4.4.                        Morphological and biochemical characteristics of bacterial isolates       32

4.5                         Morphological characteristics of fungal isolates    33       

4.6                        Distribution of bacteria isolates from rotten onion sample       34          

4.7                       Distribution of bacteria isolates from rotten onion sample            35

4.8.                       Bacterial load                                                        36

4.9                        Fungal load                                                        37

CHAPTER ONE

1.1       INTRODUCTION

Generally, vegetables are considered as the leafy outgrowth of plants or plants shoot used food. These include those plants or plant part used in making soup or served as an integral part of main meal (Yusuf et al., 2004). Vegetables can also be regarded as the edible component of plants, such components includes leaves, stalk, roots, tubers, bulbs, flowers and seed (ICMSF, 1998). Vegetables are important protective food and highly beneficial for the maintenance of health and prevention of diseases. They contain valuable food ingredients, which are essential for the proper function of the body. Pathogenic bacteria contribute to a worldwide crop loss of roughly 10-15% annually (FAO 2005; Strange and Scott 2005). Plant pathogenic bacteria affect innumerable and valuable agriculture crops, causing hundreds of millions of dollars in damage each year. Pathogenic bacteria affecting plant health are a major and chronic threat to food production and ecosystem stability worldwide (Ste’phane et al., 2005; Abd-Alla and Bashandy 2008; Abd-Alla et al., 2010).

Onions belongs to the Allium genus and have been used as an herbal remedy for a wide range of ailments, due to their association with many pharmacological effects (Lanzotti, 2006; Yin and Cheng, 2008). Biological effects attributed to onions have been commonly ascribed to the volatile sulfur-containing compounds, such as thiosulfinates, mainly responsible for the characteristic taste, aroma and lachrymatory effects (Krest and Keusgen, 2002). These compounds are formed from cysteine sulfoxide precursors and the effect of the enzyme alliinase, which is released from cell vacuoles when tissues are damaged (Ioku et al., 2001). However, these volatile products are highly unstable and recently, attention has been focused on the effects of phenolic compounds, such as flavonoids, which are more stable (Fossen et al., 2008). Onion is known for being a good natural source of flavonoids mainly represented by the flavonols - quercetin and kaempferol, which are present as their glycosides (Viuda and Fernández, 2008). Protection of food from pathogens and spoilage organisms has been traditionally achieved by chemical methods, but during recent years there has been an increase in consumer interest in developing Onion, which contain a low level or are free of chemical preservatives (Xu and Lee, 2001). The emergence of pathogens, which are resistant to classical preservatives, has also created an urgent necessity to find alternative antimicrobial agents (Grohs and Kunz, 2000). In consequence, the food industry is interested in developing natural components for the partial replacement of synthetic antimicrobials (Navas et al., 2006). Onions can be considered as a good source of natural additives to retard food deterioration (Uzeh et al., 2009). Numerous benefits have been attributed to onions including prevention of cancer and cardiovascular disorders, reduction in the blood levels of cholesterol, reduction in osteoporosis (Adebajo and Diyaolu, 2003). Reduction in stomach ulcers, inhibition of the proliferation of cultured ovarian, breast and colon cancer cells, inhibition of platelets-mediated thrombosis, prevention of inflammatory processes associated with asthma, treatment of fever, common cold, cough, sore throat and its use as an antimicrobial agent (Tyson  and Fullerton, 2004).

Onions are packed locally in baskets and jute bags. These packaging materials come from palm, bamboo and fibrous jute trees. However, these materials provide no barriers of dust, and can easily be crushed which might lead to damage of the onions. During storage, some losses occur due to sprouting, drying and rotting (Muhammed et al., 2004). Bulb rots are a common cause of onion loss during storage. They are caused by microorganisms particularly fungi. The black mould disease caused by Aspergillus niger is a limiting factor in onion production worldwide (Raju and Naik, 2006). Aspergillus niger has been reported to survive between onion crops as a soil saprophyte in or on bulbs in field or storage and is ubiquitous in nature. The fungus invades bulbs of onions in field or storage whenever they find injured tissues by producing various enzymes or toxins (Samuel and Ifeanyi, 2015). Association of Aspergillus niger with onion seeds produced in hot climates and their transmission from soil and naturally-contaminated seeds to onion seedlings cause 30-80% loss or spoilage of onion bulbs (Federal Republic of Nigeria, 2006).

1.2         OBJECTIVES THE STUDY

The aim of the present study is to evaluate the spectrum of Microorganism associated with rotten onions bulbs

Specific Objectives include to;

1.     To isolate and identify the Microorganisms responsible for causing onions spoilage

2.     To determine the microbial load associated with spoilage

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