1. Food Spoilage

2. Average storage lives of certain foods at 200C
Meat, fish, poultry, leafy vegetables : 1-2 days
Fruits : 1-7 days
Root crops : 7-20 days
Dried fruits, dried meats, seeds : up to 1 yr

3. Major causes of food spoilage
Growth and activities of microorgansms; bacteria, yeasts and moulds
Activities of inherent food enzymes
Insects, parazites and rodents
Temperature effects; high or low
Moisture or dryness
Oxgen
Light

4. Sources of microbial infection
In green plants and fruits surface flora is important. Contamination from inner tissues is very limited
Animals may contaminate foods by their surface, respiratory tract and gastrointestinal tract flora
Sewage may contaminate foods with human pathogens
Soil is the largest source of microorganisms
Water. Natural flora and microorganisms transferred from soil, animals and sewage
Air contains suspended solids and moisture droplets as carriers of many microorganisms

5. Effects of Insects, Parasites and Rodents
Parts of food eaten
Damage caused on the food which opens it to microbial infection
Contamination of food with filth (dirty matter)

6. Effects of Temperature
Heat: Deterioration reactions are faster. Protein denaturation, breaking of emulsions, drying out, destruction of vitamins, flavor compounds.
Cold: Loss of texture, cracking of skins, breaking of membranes. Freezing denatures some proteins, breaks emulsions, breaks cell membranes, inherent enzymes released.

7. Effects of moisture and dryness
Moisture: Surface moisture causes surface defects, provides a favourable growth environment for microorganisms
Dryness: Causes food to loose its water. Loss of texture and flavor.

8. FATTY ACIDS -------- ALDEHYDES

9. Food Preservation

10. Growth of microorganisms in foods
Bacteria reproduce by cell fission.
Time between each division is called the generation time. If generation time is 20min.,
N (# of cells) after x hrs = 2 (# of divisions) = 23x
In one day N will be: x24 = 272
Slowdown of growth due to:
Exhaustion of available food supply in growth
medium
Autosterilization

12. How to keep concentration of viable microorganisms low
Have as few spoilage organisms as possible initially (reduce contamination – use clean raw materials)
Avoid addition of actively growing organisms to the food (keeping good manufacturing practices and hygienic conditions during production)
Create unfavourable conditions for microbial growth in the food (aw, T, O2, pH, inhibitors)
Destroy organisms by heating or irradiation.

13. Unfavourable growth conditions extend the generation time
Starting with one cell:
Gen. Time # after 10 hrs
30 min cells
60 min cells
120 min cells
Killing/destroying/sterilizing : Make the microorganisms loose their viability (ability to grow and multiply) through some operation

14. Main Food Presevation Methods