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.
TABLE OF CONTENTS
OF TABLES vi
OF FIGURES vii
and literature review
Materials and method
Sterilization of apparatus
Collection of samples
Preparation of culture media
Nutrient agar (NA)
Potato dextrose agar (PDA)
Preparation serial dilution
Serial dilution for nutrient agar
Serial dilution for potato dextrose agar
Bacteria examination and isolation
Fungi examination and isolation
Colonial morphology and biochemical
characteristics of bacteria isolate
Colonial morphology of fungal isolates
Description and identification of
1: Colonial morphology and
biochemical characteristics of Bacterial isolates
morphology of fungal isolates
chart used in production of yogurt
1.1 INTRODUCTION AND
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
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
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.
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
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.,
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
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
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
2. Pasteurize milk.
4. Cool milk.
5. Inoculate with starter cultures.
8. Add flavors and fruit.
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
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.
The blend is homogenize (2000 to 2500psi) to mix all ingredients
thoroughly and improve yogurt consistency.
The milk is cooled to 108°f (42°c) to bring the yogurt to the ideal
growth temperature for the starter culture.
with starter cultures
The starter cultures are mixed into
the cooled milk.
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.
The yogurt is cooled to 7°c to stop the fermentation process.
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
The yogurt is pumped from the
fermentation vat and packages as desired
FIG 1: FLOW CHART USED IN PRODUCTION OF YOGURT,
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
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.