MICROBIOLOGY OF RELATED POWDERED MILK SOLD IN UMMUAHIA

ABSTRACT

Five samples of powdered milk collected from retailed shops in the market were analysed for microbial quality. The milks were tested for total aerobic count (TAC), coliform counts and various foodborne pathogens. TACs ranges from 2.98 x 103 to 3.64 x 103 cfu/ml. Escherichia coli were detected in 25% of the samples. Bacillus cereus was confirmed in 27% of the samples. Staphylococcus aureus was detected in 27% of the samples. Lactobacillus was detected in 15.5% of the samples. fumigatus, and mucor sp was observed for the fungi isolates. An apparent relationship between high aerobic count detection of coliforms and presence of food- borne pathogens was observed. These findings suggest that most of the powdered milk sold by retailers may constitute sources of bacterial food poising, consequently public health hazards. The need for improvement and maintenance of good hygienic practices by food handlers in this country is emphasized.

TABLE OF CONTENTS

Title page                                                                                                                                i

Certification                                                                                                                           ii

Dedication                                                                                                                              iii

Acknowledgement                                                                                                                  iv

Table of contents                                                                                                                    v

List of Tables                                                                                                                          ix

Abstract                                                                                                                                 

CHAPTER ONE

1.1  INTRODUCTION                                                                                                         1

1.2 Aims and Objectives                                                                                                        4

CHAPTER TWO

LITERATURE REVIEW

2.1 Milk                                                                                                                                  5

2.2 Factors Affecting Milk Production                                                                                  5

2.3 Breed                                                                                                                                6

2.4 Dry period                                                                                                                         6

2.5 Age and body weight at calving                                                                                       6

2.6 Lactation number                                                                                                              7

2.7 Pregnancy                                                                                                                         7

2.3 Milk Nutrition                                                                                                                  9

2.3.1 Nutritional significance                                                                                                 10

2.4The quality of milk                                                                                                            10

2.5 Types of Milk                                                                                                                   10

2.6 Powdered milk                                                                                                                  11

2.6.1 Salting                                                                                                                            11

2.6.2 Dehydrating                                                                                                                   11

2.6.3 Freezing                                                                                                                         12

2.6.4  Use of Dry milk                                                                                                            12

2.7 Determination of Microbial Quality of Liquid Milk                                                        12

2.8 Milk Fermentation                                                                                                            13

2.9 By Products of Milk                                                                                                         14

2.9.1 Cheese                                                                                                                           14

2.9.2 Ice Cream                                                                                                                      16

2.9.3 Buttermilk (Cultured)                                                                                                    17

2.9.4 Yogurt                                                                                                                            17

2.10 Processing the Powdered Milk                                                                                       18

2.11 Micro Flora of Dried Milks                                                                                            19

 2.12 Contamination of Food                                                                                                  19

2.12.1 Sources of Milk Contamination                                                                                  20

CHAPTER THREE
MATERIALS AND METHODS                                                                                         25
3.1 Collection of Samples                                                                                                      25

3.2. Preparation of Media                                                                                                       25

3.3 Sample Analysis and Identification                                                                                 25

3.4 Viable count                                                                                                                     26 

3.5 Characteristics of Bacterial Isolates                                                                                 26

3.5.1 Gram stain                                                                                                                     26

3.6 Biochemical Test                                                                                                              26

 3.6.1 Oxidase test                                                                                                                  26

3.6.2 Catalase test                                                                                                                   27

3.6.3 Coagulase test                                                                                                                27

3.6.4 Citrate Test                                                                                                                    27

3.6.5 Lysine test                                                                                                                      27

3.6.6 Indole test                                                                                                                      28

3.6.7 Hydrogen sulfide (H₂S)                                                                                                 29

3.6.8 Motility test                                                                                                                   29

3.6.9 Voges Proskauer Test                                                                                                    29

CHAPTER FOUR

CHAPTER FIVE

5.0       DISCUSSION, CONCLUSION AND RECOMMENDATION

5.1 Discussion                                                                                       36

5.2 Conclusion                                                                                    38

5.3 Recommendations                                                                        38

References

LIST OF TABLES

Table 4.1: Morphorlogical and biochemical characteristics of bacterial isolates                        31

Table 4.2: Total Viable Count (cfu/ml)32

Table 4.3: Percentage occurrences of bacterial isolates from powdered milk samples   33

Table 4.4: Total Count                                                                           34

Table 4.5 Fungi Count                                                                          35

CHAPTER ONE

1.1  INTRODUCTION

The world is faced with a problem of food shortage and milk products are considered as a partial solution for this problem in developing countries. But these products are vulnerable to spoilage by certain to human beings. The number and type of microorganisms present in foods are influenced by mans’ factors, that include the general environment for which food was obtained, the microbiological quality of the food in its processed state, the sanitary conditions under which the product was handled and processed and finally the adequacy of subsequent packing. handling and storage conditions in maintaining the flora at low level (Jay.l986).microbial load must kept as loss as possible and the main sources of contamination must he importantly known. Numerous studies have documented that powder milk could contaminated by bacteria. In national institute of public health it was reported that on spray drying of milk artificially contaminated with Bacillus cereus spores (ln’t veld. 1993).

Study performed in New Zealand for sample of milk powder revealed that it’s contaminated by Bacillus licheniformis and Bacillus subtilis (Ronimus et al.. 2006). Milk powder is made by removing water from liquid milk. Removing water is necessary to reduce water activity for the prevention of microorganism growth. Dry milk is used to produce such products as yogurt, cheese; ice cream and whey powder. There are a multitude of products derived from dried milk. Moreover, the advantages of dry milk over liquid milk are better keeping quality, less storage space and low shipping costs. Powdered infant formula (PIF) is readily available, as either a supplement to or replacement for breast milk. PIF is heat-treated during processing but. Unlike liquid formula products, it is not subjected to sufficient treatment to make the final packaged product commercially sterile. While PIF may not be commercially sterile, its production is undertaken using rigorous hygienic precautions coupled with monitoring of the process environment and finished product by the manufacturer. These activities assist in reducing the microbial load of PIF Salmonella and Cronobacter sakazakii (formerly classified as Enterohacter sakazakii) have been identified as the organisms of greatest concern with PIF (FAO/WHO. 2004 & 2006). To date, no cases of illness in infants linked to the consumption of infant formula have been reported in Australia. Salmonella is a well-known food borne human pathogen. Overseas. at least six reported outbreaks of salmonellosis involving approximately 250 infants were associated with PIF between 1985 and 2009(Appendix I). Most of the outbreaks involved unusual Salmonella serotvpes. hich assisted in outbreak investigations. It has been suggested that outbreaks and sporadic cases of salmonellosis due to PIF are likely to he under-reported (FAO/ WHO. 2006). (sakazakii is an opportunistic pathogen emerging as a public health concern. Considerable progress has been made in understanding the ecology of this organism, but there is still little known about its pathogenesis and virulence factors. Infections from C. sakazakii have been reported as both sporadic cases and outbreaks. The primary manifestations of C. sakazakii infection in infants include meningitis sand bacteraemia, which tend to vary with age.

Reported fatality rates of C. sakazakii infections in infants vary considerably with rates as high as 50% reported in at least one outbreak (Appendix 1). In addition, a portion of surviving infants has permanent disabilities such as retardation and other neurological conditions. In some of these outbreaks and cases, PIF was established as the source of the infections. In many, the exact source could not he determined. Ten studies determining the microbiological quality of commercial powdered infant formula were identified by a literature search. C. sakazakii was detected in seven of the studies with prevalence rates ranging from 0.5% to 25% (Appendix 2). Three of’ the studies also performed quantitative tests and C. sakazakii was detected at levels from 0.36 cfu/100g up to 66 cfu/100g (Muytjens et al.. 1988:Nazarowec-White & Farber. 1997; Zink. 2003). Salmonella was tested in five surveys and %as not detected in any of the formula tested (Estuningsih et al. 2006: Iversen & Forsythe. 2004: Muytjens et al. 1988: Thompson. 2010).To date. there is limited public information in Australia on the microbiological quality of powdered infant formula. One PIE sample from Australia tested positive for C. sakazakii in the survey reported by Muytjens et al. (1988) at the level of 0.36 cfu/100g. However, no data was provided on the number of samples actually taken from Australia in that survey and it is likely that this result does not reflect recent changes in the production of PIF that are likely to influence the microbiological quality of PIF.

The most recent survey conducted by the South Australian Government did not find any pathogens in the twenty samples tested (Thompson. 2010). In 2008, a suspected case of food borne illness initially linked to infant formula took place in South Australia. Further investigation found that the illness was not actually due to the product. but due to poor of hygiene and improper handling of reconstituted infant formula. The incident, however, highlighted the lack of available data on microbiological quality of infant formula in Australia. Thus, a survey was conducted to gather information on the microbiological quality of’ these products sold in NSW. The information collected on the microbiological quality of powdered infant formula will supplement the communication message on the safe handling of powdered infant formula that was developed for consumers and caregivers and is available on the NSW Food Authority website. Milk and dairy products form a significant part of the human diet. They are rich sources of nutrients such as proteins, fats, vitamins and minerals: ironically. It is because of this that these products are susceptible to rapid microbial growth. In some instances, this microbial growth may be beneficial, while in others it is undesirable. Dairy products are vulnerable to spoilage or contamination with pathogens or microbial toxins: therefore, the microbiology of these products is of key interest to those in the dairy industry. Food spoilage is an enormous economic problem worldwide. Through microbial activity alone, approximately one-fourth of the world’s food supply is lost. Milk is a highly nutritious food that serves as an excellent growth medium for a wide range of microorganisms. The microbiological quality of milk and dairy products is influenced by the initial flora of’ raw milk, the processing conditions, and post—heat treatment contamination. Undesirable microbes that can cause spoilage of dairy products include Gram-negative psychrotrophs, coliforms, lactic acid bacteria, yeasts, and molds. In addition, various bacteria of public health concern such as Salmonella spp., Lisieria monocytogenes, Camphylobacter jejuni, Yersinia enterocolitica,

pathogenic strains of Escherichia coli and enterotoxigenic strains of Staphylococcus aureus may also he found in milk and dairy products. For this reason, increased emphasis should he placed on the microbiological examination of milk and dairy foods. Microbiological analyses are critical for the assessment of quality and a safety, conformation with standards and specifications, and regulatory compliance.

 
1.2 AIMS AND OBJECTIVES

To evaluate the microbial load of powdered milk

To determine the presence of microbial pathogens in powdered milk samples

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