Food Preservation Methods

 FOOD PRESERVATION

GENERAL PRINCIPLES OF FOOD PRESERVATION

Method	Key Concept	Mechanism	Examples
Asepsis	Prevent entry of microbes	Hygiene, packaging, sealed containers, sterilized equipment	Milk packaging, cheese making
Removal of Microorganisms	Reduce microbial load	Filtration, centrifugation, washing, trimming	Filtered juices, beer, milk clarification
Anaerobic Conditions	Absence of oxygen prevents aerobic microbe growth	Vacuum packing, CO₂/N₂ flushing, oil layer	Canned foods, pickles, vacuum-packed meat

HIGH TEMPERATURE PRESERVATION

Method	Temperature / Condition	Effect on Microbes	Used In
Pasteurization	Low-Temperature, Long-Time (or Hold Pasteurization): 63°C – 30 min/ High-Temperature, Short-Time (or Flash Pasteurization): 72°C – 15 sec	Kills pathogens, not spores	Milk, juices
Sterilization	>100°C (121°C for canned foods)	Kills vegetative cells + spores	Canned foods, baby foods
Blanching	Mild heating at 80–100°C	Inactivates enzymes, reduces surface microbes	Vegetables before freezing
12D Concept	Based on Clostridium botulinum spore destruction	Ensures can safety	Commercial canning

LOW TEMPERATURE PRESERVATION

Type	Temperature	Effect on Microbes	Advantages	Examples
Refrigeration	0–7°C	Slows growth of bacteria	Preserves freshness	Dairy, meat, fruits
Freezing	-18°C or below	Microbes dormant, water becomes ice	Long shelf life	Frozen meats, vegetables
Quick Freezing	Rapid freezing	Prevents large ice crystal formation	Better food quality	Frozen peas, seafood

DRYING/DEHYDRATION

Method	Process	Effect	Examples
Sun Drying	Sunlight removes water	Slows microbial growth	Grains, chillies
Hot Air/Tray Drying	Heated air removes moisture	Shelf-stable dry foods	Milk powder, fruits
Freeze Drying (Lyophilization)	Freezing + vacuum drying	Best nutrient retention	Coffee, instant foods
Spray Drying	Liquid → powder by hot air	Fast, efficient	Milk powder, egg powder

PRESERVATION BY CHEMICAL ADDITIVES

Preservative	Type	Action	Foods Used In
Sodium Benzoate	Chemical	Inhibits yeasts & molds	Juices, soft drinks
Sorbic Acid	Anti-mold	Prevents mold growth	Cheese, bakery items
Nitrites/Nitrates	Antibotulinal	Prevent C. botulinum	Cured meats, sausages
Sulfur Dioxide	Antioxidant + antimicrobial	Prevents browning & spoilage	Dry fruits, wine
Acetic/Lactic Acid	Organic acids	Lowers pH	Pickles, fermented foods

PRESERVATION BY RADIATION

Type	Source	Penetration	Use
UV Radiation	Ultraviolet light	Low penetration	Surface sterilization
Gamma Irradiation	Cobalt-60	High penetration	Spices, meat, potatoes
Electron Beam (E-beam)	Accelerated electrons	Medium penetration	Packaged meats
Microwave Heating	Microwave energy	Rapid heating	Ready-to-eat meals

PRESERVATION BY FERMENTATION

Microorganisms	Product formed	Action	Examples
Lactic Acid Bacteria	Lactic acid	Lowers pH, inhibits pathogens	Curd, cheese, sauerkraut
Yeasts	Alcohol + CO₂	Inhibits microbes	Wine, bread
Mixed cultures	Acids + flavor compounds	Improves shelf life	Idli, dosa batter, pickles

MODIFIED ATMOSPHERE PACKAGING (MAP)

Feature	Mechanism	Advantage	Used In
Replace air with CO₂/N₂	Reduces oxygen	Slows oxidation & microbial growth	Meat, bakery products, vegetables

NATURAL INHIBITORS IN FOODS

Food	Natural Inhibitor	Prevents
Eggs	Lysozyme, Avidin	Bacteria
Cranberries	Benzoic acid	Yeasts & molds
Mustard	Allyl-isothiocyanate	Spoilage bacteria
Milk	Lactenin	Coliforms