14- Food processing/preservation

Question 1

What are Food processing/preservation?

Answer 1

• Aims:
– Prevent or delay decomposition by microorganisms (spoilage).
– Destroy pathogens or inhibit their growth
– Prevent or delay self-decomposition by enzymes present in the food.

• Refrigeration and freezing
• Heating (pasteurization)
• Canning
• Reducing water availability
• Irradiation
• Chemicals

Question 2

Explain Refrigeration and freezing

Answer 2

• Aims: slow or inhibit growth of microorganisms.
• At -20°C the aw can reach 0.82. Most microorganisms cannot grow.
• Viable microorganisms will resume growth once the temperature is permissive.
• Freeze/thaw cycles affect the quality of the food (ice crystals).

Question 3

Explain pasteurization (3 methods for milk)

Answer 3

• Aim: reduce the number of microorganisms to delay spoilage and to eliminate
pathogens.

• Dairy products, liquid egg products, alcoholic beverages, fruit juice.

• Three methods for milk:
– Long temperature long time (LTLT): 30 min, 62.8°C, bad taste (ice cream and cheese)

– High temperature short ?me (HTST): 15 sec, 71.7°C (milk for drinking).

– Ultrahigh temperature (UHT): 2 sec, 141°C (long shelf life at room temperature, virtually sterile).

• LTLT or HTST treated milk is equally safe.
• Time and temperature required are affected by the amount of fat, sugar and protein.

Question 4

Explain canning

Answer 4

• Aim: seal the food from the outside world and heat the container to kill most, if not all, of the microorganisms. It creates an anaerobic environment.

• Temperature:
– 100°C for acidic food
– Up to 121°C for low-acid food.

• 12D process: temperature and time of exposure must be sufficient to kill 10’12 spores of Clostridium botulinum.
• Must have a balance between food safety, nutritional value and taste of the food.

Question 5

Explain Water availability

Answer 5

• Aim: prevent microorganisms from growing.

• Drying: meat, fish, fruits, milk
(powdered milk).
– Sun dried
– Hot air drying.
– Freeze-drying (lyophiliza?on) results in lille lost of quality but is expensive.

• Reducing water availability by adding salt or sugar: increases the osmotic strength of the surrounding solution.
• Doesn’t necessarily kill the
microorganisms, inhibits their growth.

Question 6

Explain irradiation

Answer 6

• Aim: reduce contamination of fresh product by pathogen and spoilage organism.

• Dosage can be adjusted to:
– Kill all microorganisms (radappertization)
– Kill specific microorganisms (radicidation)
– Reduce overall contamination (radurization)

• Some concerns among consumers of possible radioactive contamination,
production of toxic or carcinogenic compounds, altered nutritional value,
production of off-flavor.

Question 7

Explain chemicals and other treatments

Answer 7

• Aim: control the growth of microorganisms (usually selected microorganisms).

• Chemicals generally recognized as safe (GRAS).
– Nitrite: prevents outgrowth of C. botulinum.
– Sulfites: wine industry, inhibits wild yeasts.
– Nisin: bacteriocin produced by Lactococcus lactis.

• Bacteriophage preparation (FDA has approved a cocktail of bacteriophages against Listeria monocytogenes).