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Yogurt bought from three producers, in Ilorin Kwara state were taken to the laboratory and examined, different bacteria and fungi were found in all the yogurt tested using conventional methods. The implications of these microorganisms were discussed.







TITLE PAGE                                                                                                  i

CERTIFICATION                                                                                           ii

DEDICATION                                                                                               iii

ACKNOWLEGEMENTS                                                                               iv

TABLE OF CONTENTS                                                                                 v

LIST OF TABLES                                                                                        vi

LIST OF FIGURES                                                                                      vii

ABSTRACT                                                                                               viii



1.0     Introduction and literature review                                                      



2.0     Materials and method

2.1     Sterilization of apparatus

2.2     Collection of samples

2.3     Preparation of culture media

2.3.1 Nutrient agar (NA)

2.3.2 Potato dextrose agar (PDA)

2.4     Preparation serial dilution

2.4.1 Serial dilution for nutrient agar

2.4.2 Serial dilution for potato dextrose agar

2.5     Bacteria examination and isolation

2.6     Fungi examination and isolation

2.7     gram staining

2.8     Catalyses test



3.0     Results

3.1     Colonial morphology and biochemical characteristics of bacteria isolate

3.2     Colonial morphology of fungal isolates

3.3     Description and identification of fungi isolates



4.0     Discussion

4.1     Conclusion

4.2     Recommendation







Table 1:      Colonial morphology and biochemical characteristics of Bacterial isolates

Table 2:      Colonial morphology of fungal isolates









Figure 1:    Flow chart used in production of yogurt

Figure 2:    Rhizopus

Figure 3:    Aspergillus niger

Figure 4:     Saccharonyces









The word “yogurt” is Turkish in origin. Yogurt is a fermented milk product which was apparently brought to turkey by the Mongols Millennia. It is produced by adding a “starter” of active yogurt containing a mixed culture of “lactobacillus bulgaricus (or occasionally L acidophilus a streptococcus thermophilus)”. These produce lactic acid during fermentation of lactose. The lactic acid lower the ph , makes it tart, cause the milk protein to thicken and act as a preservative since pathogenic bacteria cannot grow in acid condition. The partial digestion of the milk when these bacterial ferment milk makes yogurt easily digestible. In addition, these bacterial will help settle GI upset including that which follows oral antibiotics therapy by replenishing non path genetic flora of the gastrointestinal tracts, Saad et al.,(1987).

Also yogurt is a dairy product, (soya milk, nut milk, such as almond milk and coconut milk can also be used) produced by bacteria fermentation of milk, the bacterial used to make yogurt are known as “yogurt culture” . Fermentation of lactose by these bacteria produces lactic acid, which acts on milk protein to give yogurt its texture and its characteristics tong.

Worldwide cow’s milk, the protein of which mainly comprises case in, is most commonly used to make yogurt, but milk from water buffalo, goats, ewes, mares and camel is also used in various part of the world. Dairy yogurt is produce using a culture of lactobacillus deibrueckii subsp bulgaricus and streptococcus thermophilus bacteria. In addition, other lactobacilli and bifid bacteria are also some times during or after culturing yogurt. Some countries require yogurt to contain a certain amount of colony forming units of microorganism. In western culture, the milk is first heated to about 80°c (176°f) to kill any undesirable bacteria and to denature the milk protein so that they set together rather than from curds. In some places, such as part of India, curds are desired component and milk is not pasteurized. The milk is then cooled to about 45°c (112°f). The bacteria culture is added, and the temperature is maintained for 4 to 7 hours to allow fermentation Canganella F., (1998).

Several factors are crucial for successful yogurt making

·        Good sterile technique(i.e. proper sterilization and cooling of the milk, proper cleansing and treatment of glass ware, and keeping out unwanted bacterial). Pasteurized milk still retains some bacterial which can give an off flavor, or prevent the starter from proper acidification. Scalding and cooling the milk ensures good results.

·        Proper incubation temperature; lactobacilli and streptococcus thermophilus and thermophillic bacteria, meaning the prefer elevated temperature for growth. At such temperature (50°c, in this case) pathogenic or purification bacteria are inhibited. However, even these thermophilic bacteria  are killed if exposed  to temperature over 55°c (130°f) and do not growth well below 37°c (98°f) we will incubate at 50°c a temperature on the high side  of its preferred growth temperature (122°f), a temperature which inhibits the growth of pathogenic bacteria. (Note that many call for cooler temperatures than this. We find the results less dependable when incubation temperatures are lower).

·        Protection of the starter from contamination; do not open the starter (either dannon plain yogurt, or 802 starter from the previous yogurt batch) until you are ready to make the next batch.

Yogurt is preserved by its acidity which inhibits the growth of putrefactive or pathogenic bacteria with lids intact, this yogurt will keep at least a month or two in the refrigerator, after that time especially if the refrigerator is on the  “warm” side , a layer of non-pathogenic white mold with a fork, discard and use the yogurt for cooking. Baked good will rise well when yogurt is used, again due to its acidity, use yogurt as part or all of the liquid in cake, waffle pancakes and muffins and countdown on the amount of baking powder. The thickness of yogurt helps to hold up to baking baler, yogurt is an excellent dish by itself but is valuable in it many other uses, Davis J.G., (1975).

There are three main styles of yogurt that vary slightly and how they are made

1.     Balking style or set style yogurt      

The warm cultured milk mixture is poured into containers then incubated without any further stirring. Balkan- style or set style. Yogurt as a characteristic with texture and is excellent for enjoying plain

2. Swiss style or stirred yogurt

The warm cultured milk mixture is incubated in a large Val, cooled and then stirred for a creamy texture, often with fruit or other flavoring added. Swiss-style or set yogurt is often slightly thinner than Balkan style or set yogurt and can be eaten as – is, in cold beverages or incorporated into desert.

3. Greek-style yogurt

A very thick yogurt that is either made from milk that had same of water removed or by straining whey from plain yogurt to make it thicker and creamer. Greek-style yogurt tends to hold up better when heated than regular yogurt, making it perfect for cooking, it is also referred to as Mediterranean or Mediterranean-style yogurt and is often used for dips such as Tz atziki. A Balkan style as 6% m.f or more make and excellent substitute for Greek style yogurt.


Nutrient in yogurt.

Yogurt as with all dairy products in naturally contains many nutrients essential to growth development and maintenance of human body. Numerous different types and flavors of yogurt are now available and market is continually growing. Yogurt can be given to children as part of a weaning, included in packed lunches in the cooking of sweets and savory dishes or just as a quick nutritious snacks. As with milk, yogurt as been associated with many health benefit and provides and important and popular addition to the diet, Alexopoulos C.J., (1996).

Ingredient used in yogurt production

The main ingredients in yogurt is milk, the type of milk used depends on the type of yogurt-whole milk for full fat yogurt. Low fat milk for low fat yogurt, and skim milk for nonfat yogurt. Other dairy ingredients are allowed in yogurt to adjust the composition, such as cream to adjust the fat content, and nonfat dry milk to adjust the solids content. The solids content of yogurts often adjusted above the 8.25% minimum to provide a better body and texture to the finished yogurt.

Stabilizers may also be used in yogurt to improve the body and texture by increasing firmness, preventing separation of the whey (syneresis), and helping to keep the fruit uniformly mixed in the yogurt are alginates (carrageen), gelatins, gums(locust bean, guar), pectin’s and starch.

Sweeteners, flavors and fruit preparations are used in yogurt to provide variety to the customers.


General yogurt processing steps:

1.       Adjust milk composition and blend ingredients.

2.       Pasteurize milk.

3.       Homogenize.

4.       Cool milk.

5.       Inoculate with starter cultures.

6.       Hold.

7.       Cool.

8.       Add flavors and fruit.

9.       Packages.


1.           Adjust milk composition and blend ingredients.

Milk composition may be adjusted to achieve the desired fat and solids contents. Often dry milk is added to increase the amount of whey protein to provide desirable textures. Ingredients such as stabilizers are added at this time.


2.     Pasteurize milk.

The milk mixture is pasteurized at 185°f(85°c) for 30 minutes. a high heat treatment is used to denature the whey(serum)is allows the proteins to form a mere stable gel which events separation of the water drying storage. The high heat treatment also further reduces the number of spoilage organisms in the milk to provide a better environment for the starter culture to grow. Yogurt is pasteurized before the starter cultures are added to ensure that the cultures remain active in the yogurt after fermentation to act as probiotics; if the yogurt is pasteurized after fermentation the cultures will be inactivated.


3.     Homogenize

The blend is homogenize (2000 to 2500psi) to mix all ingredients thoroughly and improve yogurt consistency.


4.     Cool milk

The milk is cooled to 108°f (42°c) to bring the yogurt to the ideal growth temperature for the starter culture.


5.     Inoculate with starter cultures

The starter cultures are mixed into the cooled milk.


6.     Hold

The milk is held at 108°f (42°c) until GPH 4.5 is reached. This allows the fermentation to progress to form a soft gel and the characteristics flavor of yogurt. This process can take several hours.


7.     Cool

The yogurt is cooled to 7°c to stop the fermentation process.


8.     Add fruit and flavors

Fruit and flavors are added at different steps depending on the type of yogurt. For set style yogurt the fruit is added in the bottom of the cup and then the inoculate yogurt is poured on top and the yogurt is fermented in the cup. For Swiss style yogurt the fruit is blended with the cooled yogurt prior to packaging.


9. Packages.

The yogurt is pumped from the fermentation vat and packages as desired


France (1992) reported that Acidophilus prevent Candida virginities. Thirteen women recurrent Candida virginities consumed ounces of yogurt daily for 6 months and no yogurt for an additional 6 months(control period).The yogurt used contained greater than 100,000,000 colony forming unit/ml of L. acidophilus. The mean number of virginal Candida infection per 6 months was 0.38 during the yogurt and 2.54 during the non-yogurt period (85% reduction with yogurt; (P<0.001). The prevalence of asymptomatic Candida colonization of the vagina or rectum was 74% lower during the yogurt period than during the control period (P=0.001).

Nursing center for American journal of primary health care (2009),reported that yogurt have many vital healthy benefit, by eating yogurt you are adding good bacterial to your gut. These bacterial helps to breakdown foods, and allow your body to absorb more nutrition. Adding fermented yogurt to diet as shown to help aid digestion, and build a strong immune system and everything from multiple sclerosis, and colitis, to constipation and asthma. This is where yogurt feta it good health reputation.

Hahai (2009)reported that a new type of yogurt prevent gastrointestinal distress; A new yogurt, containing urea’s antibodies, as been shown to prevent helicobacter pylori from binding to stomach walls and causing infection such as gastritis and stomach ulcers. This yogurt is made using vaccine-making technology urea injected into chickens allowed their immune system to produce an antibody to increase called igy-urease. The antibody is then harvested from chickens eggs and made into yogurt containing lactobacillus acidophilus, Bifid bacterium and egg yolk igy-urease. This yogurt is particularly  significant in developing countries where standard of care treatment like antacid and antibiotics are either unavailable or unaffordable it is currently available in Japan, Korea, and Tawan, Fleet G.,(1990).

The aim of this project work, is to make the public know different types of microorganism that take part in yogurt production and to put the mind of the public at rest that not all microorganism are harmful to humans.

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