Food Spoilage

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

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

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

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)

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.

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.

FATTY ACIDS -------- ALDEHYDES

Food Preservation

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: 23x24 = 272 Slowdown of growth due to: Exhaustion of available food supply in growth medium Autosterilization

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.

Unfavourable growth conditions extend the generation time Starting with one cell: Gen. Time # after 10 hrs 30 min 1.000.000 cells 60 min 1.000 cells 120 min 32 cells Killing/destroying/sterilizing : Make the microorganisms loose their viability (ability to grow and multiply) through some operation

Main Food Presevation Methods