MICROBIAL QUALITY OF POWDERED SOY MILK SOLD IN ABA

ABSTRACT

The present study was conducted to assess the microbial quality of powdered soymilk samples sold in Aba, Abia state. A total of 10 samples were randomly purchased from local markets within the metropolis. The study samples were differentiated into two categories, branded and unbranded powdered soymilk samples. The branded soymilk samples were labeled TE, BC, and UCD to reflect their brand names while the unbranded samples were labeled N1 to N4 .The total viable count of the soymilk samples ranged from 2.0×105-8.7×105 (cfu/g) with a branded powdered soymilk sample (TE2) giving the lowest count, while the highest count was recorded in an unbranded sample (N2). The Total coliform count ranged from 4.5×104-9.0×104 (cfu/g), with a branded sample (UCD2) giving the lowest count while the highest count was recorded in an unbranded powdered soymilk (N2). The total fungal count ranged from 1.1×104 in a branded sample (TE1) to 3.3×104 (cfu/g) in an unbranded sample (N1). The isolates were four (4) bacteria (Staphylococcus aureus, Bacillus spp., Streptococcus spp., and E. coli) and two moulds (Aspergillus spp. and Penicillium spp.). Bacillus spp. recorded the highest incidence (8) and percentage occurrence (80%) while Aspergillus spp. and E. coli recorded the least incidence (4) and percentage occurrence (40%). Comparing the general counts, the study suggested the need for implementing regulatory measures like good manufacturing and management practices, hygienic distribution and retail storage practices for ensuring microbiological safety of powdered soymilk offered for public consumption in Aba, since both the branded and unbranded powdered soy milk samples gave results above the acceptable limits.

TABLE OF CONTENTS

Title page                                                                                                                                i

Certification                                                                                                                            ii

Dedication                                                                                                                              iii

Acknowledgement                                                                                                                  iv

Table of Contents                                                                                                                   v

List of Tables                                                                                                                          x

List of Figures                                                                                                                         xi

Abstract                                                                                                                                   xii

CHAPTER ONE

INTRODUCTION

1.1       INTRODUCTION                                                                                                      1

1.2       AIMS AND OBJECTIVES                                                                                        3

CHAPTER TWO

LITERATURE REVIEW 

2.1       SOYBEAN                                                                                                                 4

2.1.1    ORIGIN OF SOYMILK                                                                                             4

2.1.2    AGRONOMIC CHARACTERISTICS                                                                      4

2.1.3    COMPOSITION OF SOYBEAN                                                                               5

2.2       SOYMILK                                                                                                                  7

2.2.1    DEFINITION OF SOYMILK                                                                                                7

2.2.2    HISTORY OF SOYMILK                                                                                          8

2.2.3    COMPOSITION OF SOY MILK                                                                               8

2.2.3.1 CHEMICAL COMPOSITION OF SOY MILK                                                         8

2.2.3.2 PHYTOCHEMICALS IN SOY MILK                                                                      10

2.2.4    CLASSIFICATION OF SOY MILK                                                                          12

2.2.5    SOYMILK PREPARATION METHODS                                                                 12

2.2.6    NUTRIONAL VALUES OF SOY MILK                                                                  18

2.2.6.1 SOYMILK INTAKE AND HEART DISEASE                                                         18

2.2.6.2 SOYMILK AND MENOPAUSE                                                                               19

2.2.6.3 SOYMILK INTAKE AND BONE HEALTH                                                            20

2.2.6.4 SOYMILK INTAKE AND BREAST HEALTH                                                       21

2.2.7    MAJOR CONCERNS ABOUT SOY SUPPLEMENTS                                           22        AND HEALTH PRODUCTS

2.2.8    MICROORGANISMS ASSOCIATED WITH SPOILAGE OF MILK              22                    AND MILK PRODUCTS

2.2.8.1 PSYCHROTROPHS                                                                                                     22

2.2.8.2 COLIFORMS                                                                                                                23     

2.2.8.3 LACTIC ACID BACTERIA                                                                                         23

2.2.8.4 FUNGI                                                                                                                            24   

2.2.8.5 SPORE-FORMING BACTERIA                                                                                   25

2.2.8.6  OTHER MICROOGANISMS                                                                                       26   

2.2.9    PRESERVATION AND STORAGE OF MILK AND PRODUCTS                   26   

CHAPTER THREE

MATERIALS AND METHODS

3.1       SOYMILK SAMPLES                                                                                                  28

3.2       STERILIZATION OF MATERIALS                                                                             28

3.3       MEDIA USED AND THEIR PREPARATION                                                             28

3.4       MICROBIOLOGICALANALYSIS OF SAMPLES                                                      29

3.4.1    SERIAL DILUTION                                                                                                       29

3.4.2    ISOLATION AND ENUMERATION                                                                             29

3.5       CHARACTERIZATION AND IDENTIFICATION                                                             OF THE BACTERIAL ISOLATES                                                                           30

3.5.1    PURIFICATION AND STORAGE OF THE ISOLATES                                         30

3.5.2    COLONIAL MORPHOLOGY                                                                                   30      

3.5.3    GRAM STAINING                                                                                                      30

3.5.4    BIOCHEMICAL TESTS                                                                                             31

3.5.4.1 CATALASE TEST                                                                                                        31    

3.5.4.2 COAGULASE TEST                                                                                                    32

3.5.4.3 INDOLE TEST                                                                                                               32

3.5.4.4 METHYL RED TEST                                                                                                     32

3.5.4.5 VOGES PROSKAUER TEST                                                                                         33

3.5.4.6 CITRATE UTILIZATION TEST                                                                                    33 

3.5.4.7 OXIDASE TEST                                                                                                               34

3.5.4.8 SUGAR FERMENTATION TEST                                                                                  34

3.6       IDENTIFICATION AND CHARACTERIZATION OF                                                       THE FUNGAL ISOLATES                                                                                              34

CHAPTER FOUR

RESULTS                                                                                                                                     36

4.1       RESULTS                                                                                                                   36

CHAPTER FIVE

DISCUSSION, CONCLUSION AND RECOMMENDATIONS

5.1       DISCUSSION                                                                                                              42

5.2       CONCLUSION                                                                                                             45

5.3       RECOMMENDATIONS                                                                                            45

REFERENCE                                                                                                                           47

LIST OF TABLES

Table Title                                                                   Page

 2.1                  Average chemical composition of soybean seed (dry weight basis)               6

2.2                   Composition of soymilk, cow’s milk and human breast milk                 9

2.3                  Processes used for the extension of the shelflife of soymilk                                    16

4.1                   Total viable count and total coliform count of the powdered                                                             soymilk samples                                                                                             37

4.2                   Cultural, morphological and biochemical characteristics of the                   38                                bacterial isolates

 4.3                  Total fungal count of the powdered soy milk samples                                    39       

 4.4                  Cultural and morphological characteristics of the fungal isolates            40

4.5                  Ice cream samples, microorganisms isolated, Total incidence and                                                  percentage occurrence of the isolates                                                            41

LIST OF FIGURES

Figure        Title                                                                Page

2.1   Methods of soymilk production                                       15      

CHAPTER ONE

INTRODUCTION

1.1 INTRODUCTION

Soybean (Glycinemax(L)Merrill) is a member of the family Leguminosae, sub-family Pailionacae(Hermann, 1962). It is an annual plant of varying heights. The number of pods and seeds are strongly influenced by environmental factors (Smith, 1972). It is prone to fungal infection on farm and after harvest. Nasir (2003) observed that fungicides reduced in vitro growth of fungi isolated from soybean seeds. The oldest written reference to soymilk surfaced from China in a poem titled “Ode to Tofu” by Su Ping at about A.D. 1500 (William and Akiko, 2000).

Soymilk was first referred to in the United States by Trimble in 1896 and the first commercial soymilk in the U.S was produced by J.A Chard soy products in the New York (Gavin and Wettstein, 1990).

Soymilk which is a liquid extract of whole soybean, is rich in water soluble proteins, carbohydrates and oils. So, its benefits when compared to cow milk include cost effectiveness and larger quantity production. Soymilk can be produced by traditional method, whole bean method, defatted method or extruder method (Harrigan and McCane, 1976). It is lactose-free unlike dairy milk and can be taken by lactose intolerant people (Poskitt, 1993; Samona, 1993; Nsofor et al., 1997). It is also non-allergic and can be easily produced with low level technology and serve as good nutrient for vegetarian diet (Samona, 1993; Varnam and Sutherland, 1994). Soybeans have been included in diverse food sauce like Koji (Nester et al., 2004). That is also why it was referred to as the nature’s perfect food as cow milk and human milk (Kon, 1972;Mita and Stemkrain, 1975; ITTA, 1989).

Despite these arrays of benefits derivable from soymilk it can easily be a route for transmitting food borne bacterial pathogens identified with food poisoning, gastroenteritis and enteric fever. These pathogens can be harbored in unhygienically prepared soymilk. Some potential pathogenic contaminants in dairy food cause mycetoma in humans (Cheesbrough, 2000). Aspergillus flavus is involved in allergic aspergillosis (Pulmonary aspergillosis) and also produces aflatoxin that is highly carcinogenic (Prescott et al., 2005).

The basic cause of malnutrition (protein-energy malnutrition and micronutrient malnutrition) is poverty. The poor strata in developing countries such as Nigeria have a lack of purchasing power and spend a large percentage of their income on staple food. Animal products and fruits that are important source of micronutrients are often more expensive and unaffordable; therefore it can be expected that singular deficiencies to be common in these settings (Richard and Martins, 2008). Although reduced energy intake remains a problem in many settings, suboptimal intakes of several micronutrients are more widespread and may be present even when energy needs are met.

Recently, the composition of soymilk has greatly increased for reasons which include poverty alleviation and because it is recommended for people that cannot tolerate lactose since it does not contain lactose. It is continuously being used as a substitute to cow milk in most remote areas in Nigeria and indeed Africa. This may also be because it has some other known advantages over cow milk for  example it has a beneficial effect in the prevention of protein malnutrition in infants and growing young children as well as in the prevention of Osteoporosis and kidney diseases (Messina, 1995).

The nutritious nature of soymilk however, makes it pronetomicrobial attack if not properly processed and storedasthe nutrients it contains are also required for thegrowthof most spoilage organisms. A large number ofmicroorganismssuch as mesophilic aerobic bacteria,coliforms,yeasts and moulds are known to beresponsiblefor the spoilage of soymilk, producing undesirable changes in the milk (Osuntongun andAboaba,2004). In Nigeria and most West Africancountries, powdered soymilk is produced mostly at home under notveryhygienic conditions and is thus prone tocontaminationand spoilage by the microflora of the rawmaterialsand utensils. The metabolic products of theseorganismsas well as their presence in soy milk, posehealth hazards to the consumers, hence the necessity of this present study.

1.1  AIMS AND OBJECTIVES OF THE STUDY

i.             To isolate, characterize and identify the microorganisms constituting the microbial load of different powdered soymilk samples sold in Aba.

ii.           To evaluate the microbial quality of powdered soymilk sold in Abaand its potential to pose risk to public health.

iii.          To compare the microbial load between branded and unbranded powdered soymilk samples.

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