EFFECTS OF CHEMICAL PRESERVATIVES ON THE SHELF LIFE AND MICROBIAL LOAD OF COCOA PULP JUICE

 ABSTRACT

The effect of chemical preservatives on the shelf life and microbial load of cocoa pulp juice was studied. Cocoa pulp juice was produced and treated with three preservatives, sodium benzoate, potassium sorbate and citric acid and then stored at room temperature alongside an untreated control. Quality parameters of the drink were monitored during the 14 day storage period. Obtained results show that the pH, Total Soluble Solids and sugar contents decreased during storage while Total Titratable Acidity (TTA) increased. The pH decreased in the control sample from 6.23 to 3.13, while the TTA increased from 0.29 to 2.33. The sugar was reduced from 8.82 to 0.00 while the total solids reduced from 21.17 to 17.47. The changes which occured in the sodium benzoate treated juice was from 6.20 to 3.50 in PH, from 0.32 to 2.02 in TTA, from 8.41 to 0.62 in sugar content. The result obtained from those treated with potassium sorbate ranges from 6.20 to 3.33 in PH, from 0.32 to 2.10 in TTA, from 21.28 to 16.99 in TS and from 8.52 to 0.52 in sugar content. The microbial load also increased with time. The fungi Load increased from 4.33cfu/ml to 8.00cfu/ml while the bacteria load increased from 66.0 cfu/ml to 191.33 cfu/ml in the control. The increase in the sodium benzoate treated juice was from 65.67 cfu/ml to 152.00 cfu/ml (bacteria) and from 3.67cfu/ml to 13.00 cfu/ml (fungi). Similar values were recorded for the potassium sorbate and citric acid preservatives. The values of the treated juice samples were lower than the control and was considered to be as a result of their potency as preservatives. Comparatively, the citric acid and the sodium benzoate preservatives performed better than the potassium sorbate preservatives. 

TABLE OF CONTENTS

Title page                                                                                                                                i

Certification                                                                                                                           ii

Dedication                                                                                                                              iii

Acknowledgment                                                                                                                   iv

Table of Contents                                                                                                                   v

List of Tables                                                                                                                          vii

Abstract                                                                                                                                  viii

CHAPTER ONE

1.0           INTRODUCTION                                                                                                      1

1.1           Aim                                                                                                                             3

CHAPTER TWO

2.0           LITERATURE REVIEW                                                                                           4

2.1           Historical Background of Cocoa                                                                                4

2.2           Historical Exploitation of Cocoa Industry                                                                  11

2.3           Cocoa Production in Nigeria and Farming Method                                                   12

2.4           Harvesting of Cocoa Pod                                                                                            12

2.5           Cocoa Pulp Juice                                                                                                        13

2.6           Nutritional Composition of Cocoa Pulp Juice                                                           15

2.7           Effects of Microorganism on Cocoa Pulp Juice                                                         16

2.8           Microbial Spoilage of Fruit Juice                                                                               16

2.9           Preservatives                                                                                                               18

2.9.1    Sodium Benzoate                                                                                                       19

2.9.2    Potassium Sorbate                                                                                                      20

2.9.3    Citric Acid                                                                                                                  21

CHAPTER THREE

3.0           Materials and methods                                                                                                23       

3.1       Source of raw materials                                                                                              23       

3.2       Sample preparation                                                                                                     23       

3.3       Treatment with preservatives                                                                                     23

3.4       Physicochemical Analysis                                                                                          24

3.4.1    Determination of hydrogen ion concentration (_PH)                                                    24

3.4.2    Determination of Total Titratable Acidity                                                                 24

3.4.3    Determination of Total Soluble Solids (Brix)                                                                        25

3.5       Microbiological Analysis                                                                                           25

3.6       Sensory Evaluation                                                                                                     26

3.7       Statistical Analysis                                                                                                     27

CHAPTER FOUR

4.0       Result                                                                                                                          28

CHAPTER FIVE

5.0       Discussion, conclusion and recommendation                                                            34

5.1       Discussion                                                                                                                   34

5.2       Conclusion                                                                                                                  35

5.3       Recommendation                                                                                                       36

References                                                                                                                  37

LIST OF TABLES

Table 1: Bacteria Load of test samples from day 0 to day 14                                               28

Table 2: Fungi load of test samples from day 0 to day 14                                                    30

Table 3: Changes in quality parameter cocoa pulp juice during storage                                    32

CHAPTER ONE

1.0       INTRODUCTION

Cocoa (Theobroma cacao L) is a major cash crop of tropical world, including Nigeria, belonging to the family Sterculiaceae with two main varieties; Criolla, Forastero and Trinitario; a hybrid of the two main varieties dominating the world cocoa trade . The cultivars exhibit differences in the appearance of pods, yields of beans, flavour characteristics and in resistance to pests and disease (Afoakwa, 2010).

Cocoa beans are mostly processed into chocolate and cocoa products such as cocoa liquor, cocoa butter, cocoa cake and raw cocoa powder. Cocoa powder is essentially used in flavouring biscuits, cakes, ice cream, drinks and other dairy products, in the manufacturing of coatings for confections and frozen desserts (Afoakwa 2007).

Cocoa pulp juice could be used in industrial processes for beverages manufacture such as pineapple, orange and many tropical fruit juices if its production is supported and improved in the on-going processing of cocoa. In addition, cocoa bean juice can be used in alcohol and non-alcoholic drinks due to its high sugar contents (Redgwel, 2003).

Cocoa pulp is reported to be rich in fermentable sugar such as glucose, fructose and sucrose and has low pH of 3.0 to 3.5, mainly because of the presence of citric acid (Guehi, 2007) making it a rich medium for microbial growth. This makes cocoa pulp exudates an interesting by- product of cocoa production and has led to its utilization as a potential raw material for development of soft drink to enhance the importance of cocoa as a source of income for farmers (Afoakwa,2007).

The primary colonizers of cocoa are yeasts, followed by lactic acid bacteria (LAB), acetic acid bacteria (AAB) and Bacillus species. During the early and mid-phase of the spontaneous fermentation of raw cocoa beans yeasts produce ethanol from carbohydrates and assimilate citric acid under anaerobic and low pH conditions and cause depectinization of the pulp, consequently the pulp liquefies and the juice drain off allowing air to diffuse into the heap (Schwan, 2004). As air diffuses into the heap, microaerophilic LAB, citrate-fermenting, acid-tolerant and ethanol-tolerant Lactobacillus plantarum and Lactobacillus fermentum strains dominate this phase (Afoakwa, 2000).

Different kinds of preservatives are used to prevent bio deterioration of food products. In the food industry, sodium benzoate, potassium sorbate and sodium nitrite are often used as preservatives (Mahindru, 2000). Sodium benzoate is a preservative that is widely used in the food industry. European Commission limits for benzoic acid and sodium benzoate are 0.015 to 0.5%, potassium sorbate is used to conserve cheeses, cakes and syrups. The effective concentration is 0.2% (EC, 1995).

The inhibitory effect of preservatives varies, depending on the concentration and type of preservative, pH of the medium and the species of microorganism (Frazier, 2002). Inhibition of growth and activity of microorganisms can be achieved by lowering pH of the medium or by increasing the concentration of preservatives (Restaino, 1981). The low pH value of soft drinks and fruit juices, pH 2.5 to 3.8 inhibits most bacteria, but leaves yeasts unaffected.

A number of factors have an interrelated impact on the growth of cocoa plant. This factor ranges from weather element of rainfall, temperature, sunlight and humidity to others such as soil nutrient status, pest and diseases, farmers planting practices and so on. It was observed that the higher the temperature ( maximum of 320^oc ), the higher the yield, while the lower the relative humidity, the better yield. Cocoa is known to produce well with minimal but sustained water availability throughout the year ( Restaino, 1981). Meanwhile, yearly variation in the yield of cocoa is affected more by rainfall than any other climatic factors. Cocoa prefrs calm conditions and persistent moderate wind can cause a severe damage to the yield. Being a very picky (i.e. selective plant), cocoa reacts badly to any incidence of extreme weather (Battey, 2002)

            1.1           AIMS AND OBJECTIVES

The main aim of this study is to determine the effect of some chemical preservatives on the shelf life and microbial load of cocoa pulp juice.

            Specific Objectives Includes:

·       To produce cocoa pulp juice

·       To determine the efficiency of citric acid, potassium sorbate and sodium benzoate as preservatives in cocoa pulp juice

·       To evaluate the microbial load and physicochemical analysis of the sample

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