FOOD*2010: Chapter 8: Food Processing and Preservation
Food Processing: Conversion of raw animal/plant tissue into forms for convenient/practical use
▯Mechanical action, heating, extrusion and other manipulations
Food Preservation: Use of thermal and nonthermal processing techniques to minimize the number of
microorganisms in food, extends shelf life
▯Canning, freezing, dehydration, high pressure, irradiation and additives
Food Processing – From Field & Farms to Consumers
Two reasons for processing:
1) Preserve them so they stay fresh, nutritious, safe
2) Desirable shelf life
One of the prime causes of spoilage is biologically active water (leafy vegetables & red meat)
microbial growth, enzymatic reactions, and chemical changes (i.e. oxidation) occur more rapidly with
high water content & optimal temperature, pH, etc.
By manipulating these factors, you can kill or deactivate microorganisms.
The Unit Operations of Food Processing
Materials Handling: the manger in which raw commodities are harvested/transported.
Separating: isolating part of a raw material from the other parts
Cleaning: Removal of dirt, debris, bacteria. Can also be centrifuged to remove unwanted particles
Liquid foods can be filtered, while solids must be scrubbed or trimmed
Disintegrating: Particle size reduction. E.g. cutting meat (comminution), chopping fruits, etc.
Pumping: Mechanical method of moving foods during processing. Only liquid or semisolid foods
Mixing: Blending ingredients to create a food product. Includes agitating, beating, blending,
emulsifying, homogenization and whipping.
Heat Exchange: Adding/removing heat from food (macro level)
*** Do not confuse with heat transfer which is microlevel (between molecules)
Evaporation: Concentrates solids by removing moisture
Drying: Spray drying for liquids, tunnel drying or vacuum freezedrying for raw food pieces.
Forming: Foods made into specific shapes (cereal, pasta, candy)
Packaging: Protection from contamination, oxygen, moisture, light, etc.
6 Basic Principles of Food Processing
1) Moisture Removal
▯drying/dehydration prevents microbial growth.
Methods include sun drying, drum drying, spray drying (milk, eggs, etc.)
freezedrying (freeze then evaporate moisture with a vaccum)
Microbial activity depends on water activity not just moisture content.
2) Heat Treatment
a) Sterilization: Complete destruction of microorganisms. Requires 121 degrees C for 15 min.
b) Pasteurization: Heating below boiling point in order to destroy known harmful organisms. Will still
have microorganisms so products must be refrigerated still. c) Blanching: Used for fruits/vegetables – inactivates natural food enzymes. Freezing alone cannot
fully deactivate them. E.g. potatoes are blanched before freezing for French fries
d) Canning: Time and temp of heating are determined by TDT (thermal death time) which identifies
the parameters required to kill spores.
3) Low Temp. Treatment
Refrigeration: reducing temp as close to 0 in order to maintain quality and prevent spoilage
Freezing: Solidifies water, which lowers its activity making it unavailable for bacteria.
Direct Expansion Refrigeration pumps gaseous refrigerants through coils, that expands and cools
over the product. Gases that can be used are nitrogen, carbon and ammonia.
IQF Foods (Individual Quick Frozen) frozen using CO2. Very rapid.
4) Acidity Control
Control of pH through use of acidulants (present naturally or added)
High acid foods (pH <4.6) are high in citric, malic or tartaric acid
Do not need to be heated to high temps when canning acidic foods.
5) Traditional Nonthermal Processing
Preservatives, packaging and chemical additives.
Fruits and vegetables respire, so they must have packaging that is permeable to gas (e.g. polyethylene).
High fat foods must have low gas permeability to prevent oxidation
MAP (Modified Atmosphere Packaging) extends shelf life – ideal conditions maintained within
6) Nonthermal Processing Innovations
Includes irradiation, high pressure, and pulses of light/electric fields.
What is Heat Transfer?
▯The manner in which heat is transferred from heat source to food particles in a container. Typically a
result of conduction (direct, via molecular motion) convection (movement of heated fluid from hot to
cold) and radiant energy (heat transferred directly without intervening medium)
Retort Processing is used to heat sealed cans in order to destroy bacteria/spores using conduction and
Steam jets fill a chamber to certain temp, and the heat is transferred to the cans inside.
Steam is injected under pressure so that temps can exceed the boiling point of water.
Cold Point: Last area of the can to heat up. Cold point is the center of the can for conduction, and the
middle/bottom of the can for convection (due to circulation of heat upwards, and cold downwards)