-microorganisms are ubiquitous . They are harmful and also useful for the mankind . Different kind of foods can be prepared by microorganisms .

1. Microorganisms in food
ANJALI SHARMA
M.Sc.
DEPARTMENT OF MICROBIOLOGY
MEERUT INSTITUTE OF ENGINEERING AND TECHNOLOGY

3. WHAT IS FOOD MICROBIOLOGY ?
 “Food microbiology is the discipline that
includes the microbiological aspects of food
spoilage and food-borne diseases and their
effective control and bioprocessing of foods for
human and animal consumption , in addition to
the basic information of microbial physiology ,
metabolism and genetics”.

4. DEFINITIONS …
 SPOILAGE : bad food microbiology
 undesirable changes to food; sour milk,
moldy bread.
 preservatives and refrigeration inhibit the
growth of microorganisms

5.  FERMENTATION : good food microbiology
 food that have been intentionally altered
such as sour cream, cheese,beer.
 any desirable change a microorganism makes
to food.

6.  TOXINS : bad food microbiology
 Toxin [L. Toxicum = poison ] any substance
that is poisonous to other organisms .
 Can induce the disease in the absence of the
toxin – producing organisms .
 E.g. – 1) botulinum toxin causes botulism ,
 2) salmonella toxin causes salmonellosis
.

7. FOOD POISONING : bad food
microbiology
Or food intoxication is a food borne
disease that results from ingestion of
exotoxin secreted by bacterial species
growing on food .
For example : botulism , or
staphylococcal food poisoning .

8. Microorganisms in food .
 There are three main sort of microorganisms
present in the food , they are as follows :-
1. BACTERIA
2. MOLDS
3. YEAST {FUNGI}
 While other can be consideration as parasites ,
protozoan , viruses as well as algae .

9. BACTERIA
 • Rod, spiral, spherical, comma shaped with or
without flagella.
 Covered with endospores that protect them from
changess in temperature.
 They divide every 20 mts.
 Uses: converts ethyl alcohol to acetic acid. This
helps in preparation of vinegar and also idli,
dhokla, curing coffee and cocoa beans.
 Some are used in developing stabilizers for
preparation of jelly and ice creams .
 Diseases caused are sore throat, cholera,
syphilis,typhoid, dysentery and food poisoning.

10. Figure : common bacteria infecting human

11.  Harmful effects

 Spoil food by producing acid .
 Slime or rope as in curd
 Putrefy food products leading to bad odour

12. FUNGI ARE LOWER PLANTS THAT LACK
CHLOROPHYLL .
 YEASTS :

 Unicellular(single cell).
 Grow in foods high jams, bread in sugar and
salts
 Colour less,white in colour.
 Not harmful, mostly useful.
 Like A Phalloides

13.  MOULDS:

 Multi cellular (many cells)
 grow on pickles,cheese.
 red, pink, blue, yellow, black,
 produce toxins like alfa toxins, Parasitic
ringworms.

15. USES OF YEAST :
 Yeast ferments sugar to alcohol and carbon
dioxide.
 It is rich in B complex.
 Yeast grown on industrial waste is used for
making Beer and wine.

16. ALGAE :
 Are both unicellular and multi cellular.
 Usually green in colour( red also) and found in water.
 Usually not pathogenic, but some of them have an
unpleasant odours.
 Uses: important source of agar.Agar is used as a veg
substitute for gelatin in preparation of desserts.
 In water purification and sewage treatment plants. They
are a source of food to the aquatic animals.
 Blue green algae are used as fertilizers.
 Alginic acids and its salt are used in ice cream
preparation to prevent crystallization and give it smooth
texture.
 Also used in preparation of cheese.

18. PARASITES /PROTOZOAN :
 Parasites are micro organisms dependent on living
organisms for thei growth.

 Unicellular and parasitic in nature.
 Used as source of food by aquatic animals.
 Harmful protozoa cause amoebic dysentery and
contaminated water or salad vegetable cause mlalarial
fever.
 Contaminated meat of pigs (uncooked pork) can infect
humans and cause gastrointestinal diseases.
 It causes cysts and also muscularspasms.

21.  Food and nutrients:
 They need protein andcarbohydrates to grow.
 pH level:
 Neutral pH is ideal for their growth .
 Moulds and yeast grow well in acidic medium 4 -4.5
 In general a majority of the microbes will not grow in high pH
levels.
 Foods like pickles have a better keeping quality because of
high pH.
FACTORS RESPONSIBLE FOR THE
GROWTH OF MICROBES :

22.  Moisture:
 water is the main constituent of the living cell.
Salt and sugar are hygroscopic substances. They
bind water, thus making it unavailable to
microbes. Squashes stay longer for the same
reason.

 Temperature:
 temp range of 5- 63 degrees is called danger zone.
Above and below this a number of microbes die.

 Oxygen:
 Moulds and yeast grow best in the presence of
oxygen. Only some bacteria are aerobic

23.  Time:
 Microbes multiply very fast in a very short time
given favourable conditions.

 Osmotic pressure:
 Presence of sugar and salt has an osmotic effect
on the food. Moulds and yeasts grow fast on
pickles and jams also.

 Sunlight and UV rays:
 well lit and well ventilated areas inhibit the
growth of microbes. UV rays sterilize food
partially as their penetrating power is low.