Lecture 14: Preservation Flashcards
What are the ways that food can go bad?
- Oxidation (especially fatty acids and proteins)
- Hydrolysis = loss of texture (especially in milk)
- Loss or migration of moisture (sogging out, drying out)
- Crystallization = retrogradation of starch (honey, jams)
How do low temps preserve foods?
- Refrigeration impedes bacterial growth
- Freezing stops bacterial growth and impedes chemical changes
How do high temps preserve foods?
Kills microorganisms
What does a low water activity mean?
Bacteria (especially pathogens) won’t grow
How can we lower water activity?
- Dry the food (sun dried, beef jerky)
- Add salt (brine)
- Add sugar (jams, jellies, preserves)
Osmosis
Water flows from region of high concentration to region of low concentration
What does pH measure?
Acid content
What is the pH limit for safety?
4.6
What water activity and pH are safer for foods?
High acidity and low water activity
How is salami cured?
Ferment with lactic acid-producing bacteria
What is pickling?
Preservation of foods by adding acid
What are the 2 ways one can pickle foods?
- Fermentation
- Direct addition or infusion of acidity
What is the most common acid for infusions?
Vinegar (acetic acid)
What acids are mosts commonly used for fermentation?
Lactic acid or carbonic acid
What do yeasts do during fermentation?
- Lowers pH
- Removes fermentable carbohydrates
- Makes alcohol
How does smoking foods aid in preservation?
- Drying seals the surface of foods and keeps flies, germs, and maggots away
- Incomplete combustion products have antimicrobial activity
What processes reduce bacterial count in foods?
- Pasteurization
- Filtration
- Irradiation
What are irradiated foods exposed to?
X-rays or gamma rays
How are irradiated foods identified?
- Food must be identified with international symbol (colored green)
- Must also be labeled “Treated with Radiation” or “Treated by Irradiation”
What cause breads and cakes rise?
Production and expansion of CO2 gas produced by yeast or acid plus baking soda
Aseptic packaging
Sterilize product by placing it in a sterile container
What is the measure of water most relevant to food safety?
Water activity
What are the ways in which acid may be added to food?
- Inoculation with lactic acid bacteria
- Addition of vinegar
- Addition of citric acid
