understanding microbes affecting food

1. Mrs. Vandana Mahajani
FOOD MICROBIOLOGY
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2. What are microbes?
 Tiny micro organisms that cannot be seen with
the naked eye.
 The study of micro organisms is called micro
biology
 The instrument used to study is called
microscope
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3. Classification of microbes
 1. Virus
 2. Bacteria
 3. Fungi
 4. Algae
 5. Parasites
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4. Virus
 Parasitic in nature. They survive on other living beings.
Spherical and rod shaped.
 Most are harmful to humans
 They are not useful to food industry , but are used to
produce antigens to prepare vaccines for polio
 Diseases caused : viral fever, mumps, chicken pox,
sore throat, common cold, polio
 Infection spreads through infected water, contaminated
food and seafood.
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5. Virus
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6. Bacteria
 Rod, spiral, spherical, comma shaped with or without
flagella. Covered with endospores that protect them from
changes 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, dysentry and food poisoning.
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7. Bacteria
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8. Harmful effects
 Spoil food by producing acids
 Slime or rope as in curd
 Putrefy food products leading to bad odour
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9. Fungi are lower plants which lack chlorophyll
 Yeasts Moulds
 Unicellular(single cell) Multi cellular (many cells)
 Grow in foods high grow on pickles,
jams, bread
in sugar and salts cheese
 Colour less red, pink, blue,
yellow, black,
white in colour
 Not harmful, mostly produce toxins
useful. like alfa toxins,
Parasitic
like ringworms.
A.Phalloids
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10. Fungi
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11.  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
 Uses of moulds:
 Used to ripen cheese, give colour and flavour
 Produce life saving antibiotics
 Used to make soy sauce
 And fermented foods like nutri nuggets
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12. 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 odour
 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.
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13. Algae
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14. Parasites are micro organisms dependent on living organisms for their
growth
 Unicellular and parasitic in nature.
 Used as source of food by aquatic animals
 Harmful protozoa's cause amoebic dysentery and
contaminated water or salad vegetable cause
malarial fever.
 Contaminated meat of pigs (uncooked pork) can
infect humans and cause gastro intestinal
diseases. It causes cysts and also muscular
spasms.
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15. Protozoa
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16. Factors responsible for the growth of
microbes
 Food and nutrients: They need protein and
carbohydrates 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.
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17.  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 deg 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
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18.  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.
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