ABSTRACT
Yoghurt is a nutritionally enriched dairy product consumed by all age groups particularly in summer as well as throughout all year; its microbial quality has always been crucially important to public health. The present study was conducted to assess the microbial quality of ice cream sold in Umuahia metropolis. A total of 5 samples were randomly purchased from fast-food joints, street vendors and hawkers within Umuahia metropolis respectively. It was recorded that the Total heterotrophic count for the yoghurt samples ranged from 5.4x105-8.8x105 (cfu/ml), with a mean count of 7.46±2.06(cfu/ml). The Total Staphylococcal count of the samples ranged from 3.00x105 (cfu/ml) to 7.00x105 (cfu/ml). the highest count 7.00x105 (cfu/ml) was recorded in sample 4 (Y4) while the lowest count 3.00x105 (cfu/ml) was recorded in sample three (Y3). The yoghurt samples had a mean Staphylococcal count of 5.2±2.2(cfu/ml). The Lactobacillus count ranged from 3.8x107-6.7x107 (cfu/ml) yoghurt samples with a mean of 5.06±1.26 (cfu/ml). The highest count 6.7x107 (cfu/ml) was recorded in sample 4 (Y4) while the least count 3.8x107 (cfu/ml) was recorded in sample two (Y2). The E.coli count (cfu/ml) was 1.00x105 (cfu/ml) in two yoghurt samples with a mean count of 0.4±0.6 (cfu/ml). E.coli was detected in only two samples. Salmonella spp. had a count 2.00x105 (cfu/ml) in only one sample, with a mean of 0.4±0.6(cfu/ml). Shigella spp. was only detected in one yoghurt sample and had a count 1.00x105(cfu/ml) with a mean count of (cfu/ml).The Total coliform count ranged from 2.00x105-6.00x105 (cfu/ml) with a mean count of 3.00±1.00 (cfu/ml). The lowest count 2.00x105 [ (cfu/ml)] was recorded in sample five (Y5) while the highest count 6.00x105 [ (cfu/ml)] was recorded in sample 3 (Y3). The fungal count of the yoghurt samples ranged from 1.00x105-3.00x105 (cfu/ml). The least fungal count was recorded in sample Y2. With a mean count of 2.2±1.2(cfu/ml). For the bacteria isolates, Lactobacillus spp, Staphlococcus spp and Bacillus spp.had the highest incidence (5 out of the 5 samples) and percentage occurrence (100%) while Shigella spp., Salmonella spp and Escherichia coli had the least incidence ( 1 out of the 5 samples) and percentage occurrence (20%). For the fungal isolates, Aspergillus spp.had the least incidence (1 out of the 5 samples) and percentage occurrence (20%), while Fusarium spp. had the highest incidence (5 out of the 5 samples) and percentage occurrence (100%). The proximate analysis shows the moisture content, protein, fibre, fat, ash and carbohydrate value of each yoghurt sample expressed as a percentage. Comparing the general counts, the study concluded that the microbial quality of yoghurt sold in Umuahia metropolis differ between samples. The presence of pathogenic organisms in the yoghurt samples should be viewed with concern by the consumers, producers, yoghurt manufacturing industries and the government since food poisoning by Staphylococcus aureus, Bacillus spp., Salmonella spp., and Shigellaspp. is possible through consumption of contaminated yoghurt.
TABLE OF CONTENTS
Title page i
Certification ii
Dedication iii
Acknowledgement iv
Table
of Contents v
List
of Tables viii
List
of Figures ix
Abstract x
CHAPTER ONE
1.1
Introduction 1
1.2
Nutritional and health benefits of yoghurt 3
1.3
Aims and objectives of the study 4
CHAPTER TWO:
LITERATURE REVIEW
2.1
Definition of yoghurt 5
2.2
History of yoghurt 5
2.3
Types/varieties/classification of yoghurt 6
2.4 Probiotics and their health defects 7
2.5 Nutritive values of yoghurt 14
2.6 Yoghurt ingredients 15
2.6.1
Milk fat 15
2.6.2
Milk solids non-fat 16
2.6.3
Sugar and sweetening agents 17
2.6.4
Stabilizing agents 17
2.6.5
Coloring materials 18
2.6.6
Flavoring materials 19
2.7 Factors affecting the production of
yoghurt 20
2.7.1
Milk standardization 20
2.7.2
Homogenization 20
2.7.3
Heat treatment 21
2.7.4
Inoculation and fermentation 21
2.7.5
Cooling 22
2.7.6
Blending 22
2.7.7
Pasteurization 23
2.7.8
Packaging 24
2.7.9
Storage and distribution 25
2.8 Potential microbiological hazards
associated with yoghurt 27
2.9 Major diseases transmitted through
yoghurt 28
2.10
Microbiology of yoghurt ingredients
29
CHAPTER THREE: MATERIALS AND METHODS
3.1 Study
Area 31
3.2 Sample
Collection 31
3.3 Sterilization
of Materials 31
3.4 Media
used and their Preparation 32
3.5 Microbiological
Analysis of Samples 32
3.5.1 Serial
dilution 32
3.5.2 Isolation
and enumeration 32
3.5.3 Detection
of Salmonella spp. 33
3.6 Characterization
and Identification of the Bacterial Isolates 34
3.6.1 Purification
and storage of the isolates 34
3.6.2 Colonial
morphology 34
3.6.3 Motility
test 34
3.6.4 Gram
staining 35
3.6.5
Biochemical tests 36
3.6.5.1 Catalase test 36
3.6.5.2 Coagulase
test 36
3.6.5.3 Indole test 36
3.6.5.4 Voges
Proskauer test 37
3.6.5.5 Citrate utilization test 37
3.6.5.6 Oxidase test 37
3.6.5.7 Sugar fermentation test 38
3.7 Identification and Characterization of
the Fungal Isolates 38
3.8
Proximate composition and mineral analyses 39
3.8.1
Determination of moisture content 39
3.8.2
Determination of crude protein content 39
3.8.3
Determination of ash content 40
3.8.4
Determination of energy value of yoghurt 40
3.8.5
Determination of total solids (dry matter) 42
3.8.6
Determination of titratable acidity
42
3.8.7 Determination of ether extract 43
3.8.8
Determination of crude fibre 43
CHAPTER FOUR: RESULTS
4.1 Results 44
CHAPTER FIVE: DISCUSSION, RECOMMENDATIONS AND CONCLUSION
5.1 Discussion 54
5.2 Conclusion 57
5.3 Recommendations 58
References 61
Appendix 69
LIST OF TABLES
Table Title Page
4.1
Total heterotrophic count of the yoghurt samples 46
4.2
Bacterial count of the yoghurt samples sold in Umuahia metropolis 47
4.3
Cultural, morphological and biochemical characteristics of the bacterial
Isolates 48
4.4
Total fungal count of the yoghurt samples 50
4.5
Cultural and morphological characteristics of the fungal isolates 51
4.6
Yoghurt samples, microorganisms isolated, Total incidence and percentage
of occurrence of the isolates 52
4.7
Proximate analysis and result 53
LIST OF FIGURES
Figure Title Page
2.1 Yoghurt processing 26
CHAPTER
ONE
INTRODUCTION
1.1
INTRODUCTION
Yoghurt is a fermented milk product
of creamy texture that can be prepared from milk of many species but mostly
made from cow milk. It is rich in protein, calcium and vitamins and
tremendously popular all over Nigeria and the world at large. Yoghurt is made
by the controlled thermoduric fermentation of pasteurized non-fat or low fat
milk carried out at 45°c (Prescott et al; 2005)
Yoghurt is produced by the
fermentation of milk by lactobaccillus bulgaricus and streptococcus
thermophilus. These organisms produce organic acids and other flavor
components and can grow in such numbers that a gram of yoghurt regularly
contains 100 million bacteria.
The natural yoghurt is characterized
by a smooth and viscous gel-like texture and has a delicate walnutty flavour
(Fuquay et al., 2011). In fact, the fermentation of lactose by lactic
acid bacteria results in the production of lactic acid, carbondioxide, acetic
acid, diacetyl, and acetaldehyde and several other components giving a characteristic
flavour to yoghurt (Tamime and Robinson, 2004). However very careful processing
is required for the production of safe and good quality yoghurt. In fact, even
a little contamination may deteriorate the quality of yoghurt and may have very
negative effect on the consumers’ health. (Tamime and Robinson, 2004).
Yeasts are major cause of spoilage of
yoghurts and fermented milks in which the low pH provides a selective
environment for their growth
Yoghurts produced under conditions of
good manufacturing practices (GMP) should contain no more than 10 yeast cells
and should have a shelf life of 3-4 weeks at 5°C. However, yoghurts having
initial counts of >100 cfu/ml tend to spoil quickly. Contamination by moulds
during production and distribution is directly connected to technological
problems, economic losses and health aspects. It is mainly caused by the
decomposition of products, deterioration of organoleptic properties and health
risk due to the potential production of mycotoxins or allergic conidia,
ascospores, and mycelia fragments(Yabaya and Idris, 2012) .
Coliforms are routinely used as
indicator of the quality of the milk and milk products as some members of
coliforms are responsible for the development of objectionable taints in milk
and its products rendering them of inferior quality or even unmarketable
(Yabaya and Idris, 2012).
Due to the negligence of the various
monitoring agencies in Nigeria to supervise the hygienic practices of the
various yoghurt companies that have been registered under them, many of them
have relaxed in their sanitary routine leading to contamination of the
products.
The high and easily assimilable
nutritive value of yoghurt provides a suitable environment for microbial
contamination, proliferation and spoilage. Cases of food infections and
intoxication have been attributed to poor and inadequate sanitary conditions
observed in processing of many locally made foods (Beel, 1994;2002).
Since the era of industrialization in
Nigeria, many of her citizens have enrolled in several businesses, one of which
is yoghurt production. And because of thebusiness profit, many unqualified and
uncertified people – whose products lack NAFDAC (National Agency for Food and
Drug Administration Control) registration number - have moved into it for the
sole purpose of making money; caring less about the health implications of not
following good manufacturing practices on the consumers of yoghurt. This has
consequently led to the emergence of substandard and contaminated yoghurt.
1.2 NUTRITIONAL AND HEALTH BENEFITS OF
YOGHURT
Milk and milk products such as
yoghurt are good sources of some minerals. They are the best dietary source of
calcium and have a calcium-to-phosphorus ratio that is conducive for optimal
skeletal growth. The presence and amount of vitamin D in these products give
them excellent calcium bioavailability (Katz, 2001).
Yoghurt is also nutritionally rich in
protein and the B-vitamins (riboflavin, vitamin B6 and vitamin B12). People who
are moderately lactose-intolerant can enjoy yoghurt without ill effects due to
the conversion of lactose to lactic acid during the fermentation of the product
(Robinson 2004).
Many researchers have reported the
use of cultured dairy products including yoghurts in the treatment of several
ailments and disorders. It has been suggested that such products may have
hypocholesterolemic effect (Katz, 2001).
This can be used for the treatment of
gastrointestinal infection, and potential prevention of colon cancer. (Robinson
2004).
In addition, cultured dairy products
have been successfully employed in the treatment of antibiotic associated
colitis (Robinson 2004).
Normally all fermented milk products
have nutritional values corresponding to the composition of the milk from which
they are made even though small differences in the concentration of chemical
constituents could be present due to the manufacturing and fermentation
processes as well as the effects of some ingredients used.
The main differences that may occur
are:
i.
a considerable formation
of lactic acid and a consequent decrease of lactose;
ii.
an increased content of
free molecules such as small peptides, amino acids and fatty acids (Gambelli et
al., 2001).
Slight increases in mineral
composition may be due to leaching from some metal equipment and the type or source
of water used for production. It is important that the final product maintains
the desirable content of important minerals such as calcium and phosphorous,
while limiting contamination by other minerals. Apart from the final product
having a nutritional value similar to that of the milk base, the Codex
Alimentarius recommends standard permissible levels for some important
nutrients. For instance a minimum of 2.7% (w/w) protein and a maximum of 15%
(w/wfats are generally required for yoghurts (Codex Standard 243-2003). Whole
milk yoghurts have been found to contain up to 5.7% (w/w) protein and 3.0%
(w/w) fat while fat free yoghurt contains 5.4% (w/w) and 0.2% (w/w) protein and
fat respectively. Drinking yoghurts have also been reported to have protein
content up to 3.1% (w/w) and only traces of fat (The Dairy Council, 2008).
1.3 AIMS
AND OBJECTIVES
·
The specific objectives
of this work are: To determine the nutritional qualities of different brands of
yoghurt prepared and sold by producers
identified in Abia state.
·
To isolate, characterize and identify the microbial consortium
constituting the microbial load of different yoghurt samples sold in Umuahia metropolis.
·
To assess the microbial quality of yoghurt offered for public
consumption in Umuahia metropolis and its potential to pose risk to public
health.
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