Food Preservation Techniques and Principles

Food Preservation

• Process using physical and/or chemical agents to prevent microbial spoilage, allowing food storage for later use.
• Aim: to prolong storage life.
• Food Classification:
  • Perishable: Deteriorate quickly after harvest (e.g., tomatoes, mangoes, papaya, peaches, plums, meat, fish, poultry). High moisture content, susceptible to spoilage.
  • Semi-perishable: Less moisture content (e.g., beetroot, carrots, peas, green beans, pumpkins, apples, eggs, pasteurized milk, highly smoked fish, pickled vegetables).
  • Non-perishable: Very low moisture content (e.g., mature food grains, cereals, pulses, nuts). Not easily susceptible to spoilage by microorganisms and enzymes.

Food Preservation Principles

• Inhibition Principle (1): Inhibits growth and multiplication of microorganisms. Achieved by these methods:
  • Reducing water activity (e.g., drying, salting)
  • Reducing pH (e.g., fermentation)
  • Using preservatives (e.g., sodium benzoate)
  • Using low temperatures (e.g., chilling, freezing)
  • Smoking (drying and preservative effect)
  • Preservation by inhibition doesn't always destroy organisms.
• Killing Principle (2): Destroys microorganisms. Methods include:
  • Heat treatment (pasteurization, sterilization)
  • Irradiation (gamma rays, cobalt 60)
  • Use of gases (ethylene oxide, ozone)

Food Preservation by Lowering pH

• Lowering pH prevents growth of spoilage and pathogenic bacteria.
• Achieved by adding acids or fermentation.
• Fermentation breaks down carbohydrates under anaerobic conditions into alcohol, lactic acid, and carbon dioxide.

Food Preservation by Lowering Water Activity

• Achieved by adding high salt content (e.g., sodium chloride, sometimes nitrates and nitrites)
• Achieved by adding high sugar content.
• Salting procedures can be: dry cure, pickling, injection cure, or direct salt addition.

Food Preservation by Low Temperatures

• Chilling (0-15°C), common range 4-5°C, slows down or stops microbial growth.
• Freezing (-1°C to -35°C)

Preservatives

• Defined as substances that inhibit, retard, or arrest microbial growth, their enzymes, or their genetic mechanisms.
• Chemical preservatives are added after food processing.
• Divided into two classes: Class 1 (common salt, sugar, dextrose, glucose syrup, vinegar/acetic acid) and Class 2 (benzoic acid, sodium benzoate, methyl and propyl p, nitrites, chlorine, carbon dioxide)

Preservation by Drying

• One of the oldest food preservation methods.
• Essential for preserving cereal grains.
• Sun-drying is the most common method.
• Milk and meats can also be preserved through drying.

Killing Principle (continued)

• Methods include heat treatment (pastuerization and sterilization), radiation (gamma rays etc), and use of gases (ethylene oxide and ozone).

Pasteurization

• Heat treatment of milk (or other liquids) aimed at destroying harmful pathogens without significantly affecting the food's nutritional value.
• Three main methods:
  • Low Temperature Long Time (LTLT) - 63°C for 30 minutes
  • High Temperature Short Time (HTST) - 72°C for 15 seconds
  • Flash Method: 80°C for 1-2 seconds

Sterilization

• Destroys all microorganisms, including spores.
• Achieved using physical or chemical means.
• Can involve heating food at high temperature (100-140°C) or irradiation.

Important Terminology in Heat Preservation

• D-Value: Time required at a given temperature to destroy 90% of the spores or vegetative cells of a specific organism. The higher the temperature, the faster the destruction.

Explore the various methods and principles of food preservation to extend shelf life and maintain quality. This quiz covers classifications of food, including perishable, semi-perishable, and non-perishable items, as well as techniques like drying, salting, and fermentation.