Complete Lecture on Microbiology of Food and Positive and Negative role of microorganisms

1. Environmental
Microbiology
Lecture 22

2. • Microbiology of soil
• Aquatic microbiology
• Microbiology of domestic water
and wastewater
• Microbiology of foods
Environmental Microbiology

3. MICROBIOLOGY OF FOOD
Food supply basically consist of
Plant
Animals
Or products derived from them
Food supply can contain microorganisms
in interaction with food
Microorganisms use food supply as
A source of nutrients

4. Food microbiology is
“the study of the microorganisms that inhabit, create,
or contaminate food”
MICROBIOLOGY OF FOOD

5. Food microbiology
includes the study of microorganisms
causing food spoilage
causing diseases especially
if food is improperly cooked or stored
used to produce fermented foods such as
cheese,
yogurt,
bread,
beer,
and wine etc.
MICROBIOLOGY OF FOOD

6. Importance of microorganisms in food

7. Food Spoilage/deterioration

8. Food Bioprocessing/Fermented foods

9. Inner tissues of plant and animals are sterile
Surfaces of raw vegetables, fruit, meat, are contaminated
• FOOD CONTAMINATION
“Growth of undesirable microorganisms in food”
There are certain factors for contamination
 Microbial population of environment from which food is taken
 Condition of raw material/ product
 Method of handling
 Time & condition of storage
Microbial flora of fresh foods

11. Freshly dressed eviscerated (contents/gut removed) poultry have
a bacterial flora on their surface (skin) originated from
 live birds,
 the manipulations during killing,
 defeathering
 and evisceration
Pseudomonas as major contaminants
Bacteria and molds may enter the egg
through cracks in the shells
or penetrate when “bloom’’ (thin protein coat) covering the shell deteriorates
Microbial flora of poultry

12. Carcass of healthy animal slaughtered for meat, refrigerated, have
only nominal surface contamination
Common species of bacteria occurring on fresh meat are:
Pseudomonads
Staphylococci
Micrococci
Enterococci
Coliforms
Microbial flora of meat

13. susceptible to infection by bacteria, fungi and viruses
Microbial invasion can occur at any stage of development
Post-harvest handling can also contribute to contamination
Acidic pH of fruit ranging from 2.3 (for lemons) to 5.0 (for bananas)
restricts bacterial growth but not fungal ones
Slightly higher pH range of vegetables ranging from 5.0 to 7.0 makes
more susceptible to bacteria
Microbial flora of fruit and vegetables

14. Cause food to become inedible due to changes in
color,
flavor,
odor,
appearance
or texture
Most of the food material is good source of bacterial growth because it contains
proteins
carbohydrates
and vitamins
Sometimes food is contaminated when it is processed or preserved
Some microbes discolor foods as a result of pigment production
Slimes may be developed by microbes capable of synthesizing certain
polysaccharides
Microbial spoilage of food

15. • Microbes will effect in different ways to spoil food.
Putrefaction:
“Proteolytic microorganisms have the enzyme proteases that degrade
the protein food in amino acids, amines, ammonia and hydrogen
sulfide”
Microbial spoilage of food

16. Fermentation:
“Carbohydrate – fermenting microorganisms convert carbohydrate food
into acid, alcohols and gases (CO2 , CH4)”
Caused by yeast and bacteria
Gives bubbles and sour odor
Microbial spoilage of food

17. Rancidity:
• Lipolytic microorganisms (having lipases) convert fatty acids (lipids
and fats) into fatty acids and glycerol
Microbial spoilage of food

18. Milk is an excellent bacteriological medium
Sterile skimmed milk is used routinely as a culture medium
Fresh whole milk contains
protein (casein),
carbohydrate (lactose)
and fat
 that can be degraded by microorganisms
Degradation of these substrates impart undesirable characteristics to milk
Some can also synthesize compounds like pigments and slimes
Microbial Spoilage of fresh milk

19. Species of Clostridium and Bacillus are main contributor in canning industry due to
heat resistance,
sporeforming characteristics
Three most important types of microbiological
spoilage of commercially canned foods are:
Flat sour spoilage (Flat sour bacteria produce lactic acid and acids from bacillus)
Thermophilic anaerobe (TA) spoilage (Clostridium thermosaccharolyticum, causes spoilage
and the can swells and may burst due to production of CO2 and H2)
Putrefaction (spoilage by proteolytic bacteria)
Microbial Spoilage of canned food

20. Fermented foods are best example of beneficial microbial flora of food
Fermented foods are
“foods and beverages that have undergone controlled microbial
growth and fermentation”
Fermentation is
“an anaerobic process in which microorganisms like yeast and bacteria
break down food components (e.g. sugars such as glucose) into other
products (e.g. organic acids, gases or alcohol)”
Beneficial Microbes of food/Bioprocessing

21. Examples of fermented foods
Cheese Yogurt Kafir Kamis
made by fermenting raw
unpasteurized mare's
milk over the course of
hours or days, by stirring
fermented milk drink like
a thin yogurt made from
kefir grains, a mesophilic
symbiotic culture
dairy product, derived from
milk, produced by coagulation of
the milk protein casein having
diff flavors, textures and forms

22. Pickel Sauerkraut Sausage
Examples of fermented foods
fermented cabbage dish
meat product usually
made from ground meat,
along with salt, spices
and other flavorings

23. Single Cell Proteins (SCP) are defined as
“Microorganisms such as bacteria, yeast, mold, algae are produced in
massive quantities on industrial wastes or byproducts and yield a large
cell crop that is rich in protein (single-cell protein) because microbes
have almost 70-80% protein”
Microbes as foods-Single Cell Protein

24. High yield of protein
1000 lb of yeast would produce several tons of protein in one day
Algae grown in ponds can produce 20 tons (dry weight) of protein per acre per year
Microbial cells have high protein content (Pseudomonas-69%, yeast 40-50%)
Proteins of microorganisms contain all the essential amino acids
Some microorganisms, particularly yeasts, have a high vitamin contents
Medium for growth of microorganisms may contain industrial wastes or by-
products e.g., liquid paraffins (hydrocarbons) from oil refineries
Characteristics of Single Cell Proteins

25. Concentrated supplement of beneficial live friendly bacterial culture
Taken orally to improve our health
Improve digestion system
Promote body’s natural immunity
• Examples
Baby milk-Lactobacillus acidophilus, bifidus bacteria
Yogurt rich with probiotics-Lactobacillus bulgaricus,
Streptococcus thermophilus
Blue cheese-Panicillium roqueforti
Example of Single Cell Proteins-Probiotics

27. references
 https://www.wikilectures.eu/w/Micro-
organisms_in_Foods
 https://en.wikipedia.org/wiki/List_of_microorga
nisms_used_in_food_and_beverage_preparation
 Prescott, M. L., Microbiology, 5th Edition, ISBN:
0-07-282905-2, The McGraw−Hill Companies,
2002.
 Pelczar Jr.; Chan, E.C.S.; Krieg, M.R. Microbiology,
McGraw Hill, London. 1986.