FUNGI ASSOCIATED WITH DECAYED CARICA PAPAYA (PAW PAW) IN STORAGE

ABSTRACT

This study evaluated the isolation and characterization of fungi species associated with the spoilage of Pawpaw (Carica papaya) Fruit during storage obtained from National Root Crops Research Institute Umudike, Umuahia Abia State Nigeria and MOUAU farm. A total of Twelve (12) Pawpaw (Carica papaya) fruit samples were selected for the study. The various Pawpaw (Carica papaya) Fruit samples were cultured on Potato Dextrose Agar using a pour plate technique. A total of twenty three (23) fungi were isolated and identified as four (4) different fungi species which included; Aspergillus niger, Penicillium digitatum, Rhizopus stolonifer and Mucor spp. were found in this study to be responsible for Pawpaw (Carica papaya) spoilage. However, there were wide variations in the fungi population, with Aspergillus niger 8(66.7%), and Penicillium digitatum 7(58.3%) being most predominant and occurring fungal isolates, followed by Mucor spp 5(41.7%) and Rhizopus stolonifer 2(25.0%) respectively. All the four organisms isolated were confirmed to be pathogenic on the fruits but in varying degrees. It showed that of all the isolated fungi, Aspergilus niger (32.0mm) was highly pathogenic leading to rapid disintegration of treated fruits in 4-6 days while R. stolonifer (29.0mm) and Penicillium digitatum (24.0mm) were moderately pathogenic, while the least pathogenic was Mucor spp (21.0mm), and caused the least amount of rot on the pawpaw fruits. These fungi are known to be toxigenic or pathogenic to health, therefore their presence in Pawpaw (Carica papaya) must be controlled. This should be achieved through proper washing of the harvested Pawpaw (Carica papaya) fruits, disinfection of transit containers, proper handling of the Pawpaw (Carica papaya) fruits to avoid injuries, adequate hygienic practices by the handlers, provision of good storage facilities and the use of safe food grade fungicides.

TABLE OF CONTENTS

Title Page                                                                                                                                i

Certification                                                                                                                           iii

Dedication                                                                                                                              iv

Acknowledgement                                                                                                                  v

Table of Contents                                                                                                                   vi

List of Tables                                                                                                                          vii

Abstract                                                                                                                                  ix

CHAPTER ONE

Introduction                                                                                                                            1

1.1       Background of Study                                                                                                  1

1.2       Objective of the Study                                                                                                4

CHAPTER TWO

Literature Review                                                                                                                   5

2.1       Brief Description of Pawpaw (Carica Papaya) Fruit                                                5

2.2       Scenario of Food Spoilage Worldwide (e.g. Pawpaw)                                              5

2.3       Food Spoilage Microorganisms                                                                                 8

2.3.1    Yeasts                                                                                                                         9

2.3.2    Molds                                                                                                                          10

2.3.3    Bacteria                                                                                                                      12

2.4       Studies on Fungi Associated With Post Harvest Spoilage of Pawpaw

            (Carica Papaya) Fruit                                                                                                14

2.5       Isolation of Microorganisms Associated With Deterioration of Tomato

            (Lycopersicon Esculentum) and Pawpaw (Carica Papaya) Fruits                                    16

2.6       Control of Rot and Spoilage of Agricultural Products                                               17

2.6.1    Good Agronomic Practices, Field Sanitation and Store Hygiene                            17

2.6.2    Thermal and Physical Control                                                                                    19

2.6.3    Biological Control of Rot Organisms                                                                         21

2.6.4    Chemical Control of Rots and their Causal Agents in Postharvest Produce                       22

CHAPTER THREE

Materials and Methods                                                                                                           25

3.1       Study Area                                                                                                                  25

3.2       Source/Collection of Samples                                                                                    25

3.3       Materials and Media Used                                                                                          25

3.3.1    Sterilization of Materials                                                                                            25

3.4       Processing of Samples                                                                                                26

3.5       Microbiological Studies                                                                                             26

3.5.1    Preparation of sample and inoculation of samples                                                    26

3.6       Isolation of Fungi                                                                                                       26

3.7       Subculturing/Purification and Identification of Test Fungi Pathogens                    26

3.8       Identification of Fungal Isolates                                                                                 27

3.8.1    Wet Preparation                                                                                                          27

3.8.2    Colonial Morphology                                                                                                 27

3.9       Pathogenicity Testing                                                                                                             27

CHAPTER FOUR

Results                                                                                                                                    29

CHAPTER FIVE

Discussion and Conclusion                                                                                                    34

5.1       Discussion                                                                                                                   34

5.2       Conclusion                                                                                                                  37

            References

LIST OF TABLES

CHAPTER ONE

1.1          INTRODUCTION

Pawpaw (Carica papaya) belongs to the family Caricacae constituting of four genera and thirty one species. The genera are: Carica, Farilla, and Cyclicomorpha. The papaya is native to Tropical South America, possibly in the area between Mexico and Central America (Menzel, 2004). It is a widely grown pantropical fruit used for local consumption and assume some importance in trade in Hawaii which is a major producer of fresh fruits while Sri lanka and Tanzania are major producers of pawpaw for the enzyme papain (Umoh, 2008).

The edible portion of papaya is composed mostly of water (86.8%) and carbohydrate principally sugars with little starch (12.18%) which together make up 98.98% of the fruit. The acid content of papaya is very low, this would account for its lack of tartness and its relative high pH value of 5.9.The fruit contain a major enzyme called papain which is proteolytic. Pawpaw has been utilized widely in brewering and pharmaceutical industries (William et al., 2000).

Spoilage in pawpaw can also be referred to as rot or decay. Spoilt pawpaw fruits is characterized by excess softening, mycelia growth, loss of moisture unpleasant odour, shrinkage and total drying up of water in the fruits (Franzier and Westhoff, 2001).The spoilage may be caused by microorganisms, insects and rodents attack, physical injury such as bruising and freezing as well as chemical breakdown of the fruit may also lead to deterioration in quality of the fruit.

The occurrence of spoilage in fruits by microorganisms depends on the types of organisms present and whether the fruit under its existing condition of storage can support the growth of any or all of them. Only certain species out of all the organisms present in a fruit will be able to thrive well and spoil it. Spoilage by microorganisms may be influenced by some qualities such as water content, pH value, temperature, texture and nutrient composition of the fruit (Lloyd, 2003). The edible portion of papaya is composed mostly of water (86.8%), carbohydrates (10.82 g/100g), fat (0.26g/100g), protein (0.47 g/100g), vitamins and trace metals. Traditionally, juice from the papaya fruit and root has been used as medicinal and dietary supplements (Aravind et al., 2013).

It has been known that fruits constitute commercially and nutritionally important indispensable food commodity. Fruits play a vital role in human nutrition by supplying the necessary growth factors such as vitamins and essential minerals in human daily diet and that can help to keep a good and normal health. Fruits are widely distributed in nature. One of the limiting factors that influence the fruits economic value is the relatively short shelf-life period caused by pathogens attacked. It is estimated that about 20-25% of the harvested fruits are decayed by pathogens during post-harvest handling even in developed countries (Droby, 2006). In developing countries, postharvest losses are often more severe due to inadequate storage and transportation facilities. Fungal fruits infection may occur during the growing season, harvesting, handling, transport and post-harvest storage and marketing conditions, or after purchasing by the nutrients element and their low pH values make them particularly desirable to fungal decayed (Singh and Sharma, 2007).

Generally, spoiling fungi are considered toxigenic or pathogenic. Toxigenic fungi have been isolated from spoiling fruits. During refrigeration some moulds may produce mycotoxins (Tournas and Stack, 2001). Pathogenic fungi, on the other hand, could cause infections or allergies (Monso, 2004). Aspergillus spp. are known to produce several toxic metabolites, such as malformins, naphthopyrones (Pitt and Hocking, 1997) and they can produce Ochratoxins (OTA), a mycotoxin which is a very important toxin worldwide because of the hazard it poses to human and animal health (Petzinger and Weidenbach, 2002) thus extra care should be taken during personnel handling of these fruits; such as harvesting, cleaning, sorting, packaging, transport and storage.

In developing countries, postharvest losses are often more severe due to inadequate storage and transportation facilities. Fungal fruits infection may occur during the growing season, harvesting, handling, transport and post-harvest storage and marketing conditions, or after purchasing by the consumer. Fruits contain high levels of sugars and nutrients element and their low pH values make them particularly desirable to fungal decayed (Singh and Sharma, 2007). Studies by Li-Cohen and Bruhn, (2002) had shown that fungi can survive and/or grow on fresh produce and that the nutrient content (carbohydrate, protein and fat) of fresh produce support pathogens.

Spoilage microorganisms can be introduced to the crop on the seed itself, during crop growth in the field, during harvesting and postharvest handling, or during storage and distribution (Barth et al., 2009). Those same types of soil-borne spoilage microbes that occur on produce are the same spoilage microorganisms that are present on harvesting equipment, on handling equipment in the packinghouse, in the storage facility, and on food contact surfaces throughout the distribution chain (Barth et al., 2009). Therefore, early intervention measures during crop development and harvesting through the use of good agricultural practices (GAP) will provide dramatic reductions in yield loss due to spoilage at all subsequent steps in the food-to-fork continuum (Barth et al., 2009).

The post-harvest loss of pawpaw fruits has been a very serious problem to farmers, as more than 40% of their harvest maybe list because of spoilage. It is estimated that in the tropics each year between 25% and 40% of stored agricultural products are lost because of inadequate farm and village-level storage (Okigbo, et al., 2015). The principal species of microorganism associated with pawpaw rot in Nigeria are; Aspergillus flavus, Penicillium digitatum, Botryodiplodia theobromae and Erwinia carotovora (Agu et al., 2015). These fungi are believed to be pathogenic to various pawpaw fruit, causing rot of several parts of Southern Nigeria (Onuegbu, 2009). Fungi spoil the pawpaw by colonizing it by depolymerizing certain specific cell wall polymers such as proto-protein, the cementing substance of the produce. This study was to evaluate various Pawpaw (Carica papaya) fruits obtained from different source for the presence of rot fungi (Aspergillus niger, Penicillium digitatum, Rhizopus stolonifer and Mucor spp) and to ascertain its pathogenic potentials when inoculated into a healthy Pawpaw (Carica papaya) fruit. These organisms have been noted to diseases to human which their presence Pawpaw (Carica papaya) fruit can be controlled. This could be achieved through proper washing of the harvested Pawpaw (Carica papaya) fruits, disinfection of transit containers, proper handling of the Pawpaw (Carica papaya) fruits.

1.2       AIMS AND OBJECTIVES OF THE STUDY

·       To determine the fungal agent responsible for the spoilage of Pawpaw fruit

·       To characterize various fungi species associated with Pawpaw fruit spoilage

·       To determine the pathogenicity of the isolated fungi from Pawpaw fruit

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