Microbial Contamination of Yoghurt
Chapter One
Objectives of the Study
The main objective of this study is to assess microbial contamination of yoghurt. Specific objectives include;
- To determine the level of the microbial content of yoghurt
- To know the nutritional value of yoghurt.
CHAPTER TWO
LITERATURE REVIEW
PRODUCT DESCRIPTION
Yoghurt is a smooth, fermented milk product that evolved empirically some centuries ago through the growth of thermophilic (heat loving). Lactic acid, bacteria, Streptococcus thermophilus and Lactobacillus bulgaricus which ferment the milks lactose to produce lactic acid. It has a characteristic acidic taste possessing 0.95 -1.5% and PH ranging from 3.7-4.2 with viable and abundant fermenting microorganisms.
PRODUCTION OF YOGHURT
MATERIALS:
In yoghurt preparation the following essential materials are use in processing the product: milk or concentrated skimmed or partly concentrated skimmed milk or milk product and the starter culture Lactobacillus bulgaricus and Streptococcus thermophilus. In. the absence of pure culture one to two spoonful of commercially purchased yoghurt can be used for the inoculation. Also, there are optional ingredients like milk powder, skimmed milk powder, flavour, colours, sugar, wheat, edible casein, preservatives, stabilizers (gelatin, locust bean gum, pectin, starch) etc.
EQUIPMENTS:
They include refrigerator or cooler, boiler or heater, thermometer.
PROCEDURES:
The milk to be fermented is first heated to 70°c for 15 -30 minutes the concentrate or skimmed milk powder is added and the mixture is heated to about 80°c with continuous stirring for 5 minutes so as to kill the microorganisms which are contaminants, lower the redox potential of the mixture and produce factors and condition favourable to the development of the bacteria to be inoculated. Also, the added skimmed milk prior inoculation raises the nutritive value of yoghurt and gives a product of better body and consistency. The product is cooled to about 43°c by dipping in container containing cold water and inoculate with 3% selected strains of actively growing microbial starter (Lactobacillus bulgaricus and Streptococcus thermophilus) or with 1.5% of each culture separately maintain the temperature of 42 -44°c for approximate 5hours until desired degree of acidity is achieved. Then cool rapidly to 8-10°c and refrigerate as you store till the next morning to check for curd formation. The addition of – stabilizers, flavours, colour, sugar, fruit or honey etc may be added before packaging if desired. The final product usually contains some 10 cells per milliliter of each bacteria specie while the’ characteristic flavour is due to the lactic acid and trace amount of ethanol, dimethyl propanol, ethanoic acid and other volatiles products by bacteria fermentation. VARIETIES IN YOGHURT PRESENTATION
Yoghurt has been described as a notoriously balanced food, containing almost the nutrients present in milk but in a more assimilable form. The can be produced from whole or skimmed milk (Ojokoh, 2006). There are large ranges of flavours enhancer available commercially (Anthar, 1996) that can be used in the production of yoghurt and yoghurt is typically categorized as follows:
- SET YOGHURT: This type of yoghurt is incubated and cooled in the final package and is characterized by a firm Jelly-like texture.
- STIRRER YOGHURT: This type of yoghurt is incubated in a tank and the final coagulum is “broken” by stirring prior to cooling and packaging. The texture of stirred yoghurt will be less firm than a yoghurt not stirred which is some what like a very thick cream. There is some slight reformation of the coagulum after the yoghurt has been packed, however this is slight and can not be relied upon.
- DRINKING YOGHURT: This type of yoghurt is very similar to stirred yoghurt, having the coagulum “broken” prior to cooling. In drinking yoghurt,the agitation used to “break” the coagulum is severe. Little care is applied if any reformation of the coagulum will reoccur after packing.
- FROZEN YOGHURT: This is inoculated and incubated in the same manner as stirred yoghurt. However, cooling is achieved by pumping through a whipper/chiller/freezer in a fashion similar to the cream. The texture of the finished product is mainly influenced by the whipper/freezer and the size and distribution of the ice crystals produced.
- CONCENTRATED YOGHURT: This type is inoculated and fermented in the same way as stirred yoghurt, following the “breaking” of the coagulum. The yoghurt is concentrated by boiling off some of the water. This is often done under vacuum to reduce the yoghurt often lead to protein being totally denatured and producing rough and gritty texture. This is called strained yoghurt due to the fact that the liquid that is released from the coagulum upon heating used to be “strained” off in a manner similar to making of soft cheese.
CHAPTER THREE
MATERIALS AND METHOD
MATERIALS
The media used in this work include Nutrient agar, MacConkey agar, Peptone water, Petri dish, autoclave, inoculating wire loop, forcep, Bunsen burner, Conical flask, Antibiotic discs, Weighing balance, Test tube rack, plastic pipette, wire loop, Microscope, Incubator, beakers, glass slide, sterile cotton wool, test tube rack,universal container. The composition of the media, their method of production is presented in the appendix.
SAMPLE COLLECTION
Six different brands of bottle packaged yoghurt were bought from hawkers and beverage stores in Enugu Urban. Two samples of each brand were used and the brands were designated A, B, C, D, E, F, giving a total of 12 yoghurt samples. The samples were brought to the laboratory and analyses within 6hours of collection.
ANALYSIS OF SAMPLE
Each sample was serially diluted using sterile distilled water as diluents (Prescott et al.,2002).9ml of distilled water was measured out into test tubes, using separate sterile pipettes, 1ml of yoghurt sample was measured out into the first test tube properly mixed. using a different sterile pipette, 1ml from the first test tube was pipette into the second test tube already containing 9ml of distilled water, this continued following the same procedure till the last dilution(ie the last test tube).using the pour plate method 1ml each of each sample unit from the test tubes was pipetted into the sterile Petri dishes(using separate sterile pipettes per sample) with their duplicates, then into each Petri dish the prepared MacConkey agar was poured aseptically and mixed by movement of the plate while flat on the bench. This was also carried out on Nutrient agar media was used. The plates were incubated at 37°c for the 24hr.
CHAPTER FOUR
RESULT
The physicochemical properties of bacteria isolated from the yoghurt samples are shown in Table 3. The bacteria isolated include Klebsiella sp. Streptococcus sp, Escherichia coli, Bacillus sp, Staphylococcus aureus, Pseudomonas sp, Enterobacter sp and Proteus sp. The antibiotic resistance patterns of the isolates are presented in Table 5. The isolates showed varied antibiotic resistance pattern. The isolates were resistant against many of the antibiotics tested.
CHAPTER FIVE
DISCUSSION/CONCLUSION
The result showed that many of the Yoghurt samples were contaminated by microorganisms that have public health implications. The isolates especially the potentially pathogenic ones showed resistance againstmany of the antibiotics tested (Table 5). Staphylococcus showed resistance against Drovid, Amoxil, Septrin and Clindamycin and were slightly sensitive to cephalexin, ciprofloxacin but sensitive to Ampiclox and Norfloxcin.
Pseudomonas was also resistance to many of the antibiotics tested. Some of the antibiotic patterns reported in this work were also reported by Enabulele and Orikpete (2009). Their isolates however showed higher resistance pattern probably because they were isolated from clinical patients. The sensitivity pattern shown by Escherichia coli in this work is similar to that reported by Njoku (2009).
Conclusively, evaluated milk products clearly pose some yet undefined risks. This is of clinical significance in immuno suppressed people who may consume these product6. These groups of people should be conscious when consuming milk products as they may” ingest isolates resistant to some broad spectrum antibiotics. This is because the concentration of bacteria isolated from locally produced yoghurt in the area sample differs from one local’ producer to the other, and lack of standardization makes it hard to be sure of the quality of their products. The relatively high level of resistance to antimicrobial agents constitutes a major threat to public health as it may spread bacterial resistance among the populace who come in contact with such milk products. Since the analysis of the work carried out assessed local producers in Enugu City, it is important that the food monitoring bodies provides a standard for the local producers in order to reduce the risk that their products might pose to consumers
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