Food Preservation Techniques

• Food preservation treats food to stop or reduce spoilage, nutrient loss, and quality decline.
• It has been practiced since ancient times, primarily by inhibiting microorganism growth, which is the main cause of food decay.
• Food preservation has evolved significantly from primitive to modern methods.

Traditional Food Preservation

• Sundrying reduces moisture in food, preventing bacterial growth and preserving grains like maize, wheat, and beans.
• Smoking preserves foods like meat, fish, and ingredients like tea and malt, which are used for making drinks,.
• Salting, mainly for red meats, dehydrates food via osmosis, inhibiting microorganism growth, and extending shelf life.
• Honey has been used since ancient times for preservation due to its ability to remain unspoiled for long periods.

Understanding Food Spoilage

• Before 1860, spontaneous generation theory explained food changes.
• Pasteur showed that microorganisms in the environment cause ferments, molds, and putrefaction.
• Understanding food spoilage led to the development of new preservation methods.
• Food preservation relies on creating unfavorable conditions for spoilage microorganism growth.

Microbes in Food

• Microbe numbers and types in food are influenced by the food's environment, initial quality, sanitary conditions during handling/processing, and proper packaging/storage.

Principles of Food Preservation

• Preventing or delaying microorganism growth can be achieved through aseptic techniques, filtration, inhibiting growth (freezing, drying, chemicals), or killing microorganisms (heat, irradiation).
• Preventing or delaying self-decomposition involves inactivating inherent enzymes (blanching) or preventing chemical reactions (using antioxidants).
• Preventing damage from insects or animals is done by using suitable chemicals or storing foods in dry, airtight containers.

Inhibition

• Techniques for inhibiting microbial growth in food preservation include avoiding recontamination, inactivation (low/high temperature storage), reducing water activity, decreasing oxygen, increasing carbon dioxide, acidification, fermentation, adding preservatives/antioxidants, controlling pH, freezing, and drying.

Hurdle Technology

• Hurdle technology includes sterilization, pasteurization, irradiation, electrifying, pressure treatment, blanching, cooking, frying, extrusion, light, sound, and magnetic fields.
• Hygienic practices are used in storage and processing such as aseptic processing, HACCP, GMP, ISO 9000, TQM, and risk analysis/management.

Methods of Food Preservation

• Asepsis is the absence of microorganisms; packaging prevents their entry into food.
• Filtration removes microorganisms from liquids like water, fruit juice, beer, and soft drinks by applying pressure through a sterilized filter.
• Anaerobic conditions lack or contain minimal oxygen, preventing bacterial growth by filling containers completely with food and replacing air with nitrogen or carbon dioxide.
• Heat treatment kills microorganisms, with the required intensity based on the target microorganisms and food composition.

Pasteurization

• Pasteurization uses temperatures below 100°C to kill some microorganisms, typically between 65-75°C.
• High Temperature-Short Time (HTST): Food is heated at high temperature for a short time e.g. milk heated to 72°C for 15 seconds.
• Low Temperature-Long Time (LTLH): Food is heated at a lower temperature for longer e.g. milk heated to 62.8°C for 30 minutes.

Boiling and Sterilization

• Boiling at 100°C preserves most fruits and vegetables by destroying inherent enzymes (blanching).
• Sterilization kills all microorganisms at high temperatures or through radiation; time and temperature vary with the food type typically above 100°C.
• Canning uses temperatures over 100°C to kill spoilage organisms and inactivate enzymes, sealing food in sterile airtight containers (tin or glass).

Pasteurization vs. Sterilization

• Pasteurization partially destroys microorganisms at temperatures below 100°C, minimizing damage to flavor, texture, and nutrition, but requires additional preservation methods due to its short shelf life.
• Sterilization completely destroys microorganisms at temperatures above 100°C, ensuring a long shelf life without needing other preservation methods, but can overcook food, causing major changes in texture, flavor, and nutritional quality.

Reasons for Not Sterilizing All Foods

• Many foods are naturally sterile or become contaminated after sterilization.
• Sterilization is expensive, requires sterile processing and packing, and may destroy flavors, vitamins, and texture, making it unsuitable for all foods.

High Temperature Preservation

• This destroys microbes and deactivates enzymes through pasteurization, UHT, canning, and microwaves.
• Pasteurization destroys most disease-causing/spoilage organisms, while allowing some thermoduric and thermophilic organisms to survive.

Pasteurization Methods

• LTLT: 63°C for 30 minutes.
• HTST: 72°C for 15 seconds.

Ultra-High Temperature (UHT)

• UHT sterilizes milk at 140-150°C for 2 seconds.
• It allows storage for up to 8 weeks, but the flavor differs from pasteurized milk.

Canning Process

• The canning method has been around since the 18th century, patented by Nicholas Appert in France in 1810.
• It boils food in a sealed container, killing most sporulating organisms at about 115°C for 15 minutes, enabling long-term storage but changing flavor and nutritional value.
• Low pH and oxygen removal prevent growth, meaning heated canned foods do not have to be sterile.

Microwave Heat Treatments

• Electromagnetic heating uses radio frequencies (1-500 MHz) or microwaves (500 MHz to 10 GHz) to generate internal heat by oscillating molecules.
• These treatments can reduce process times, energy, and water use, but irregular heating can occur.
• Microwaves are used in treating meats like pork to remove parasites.

Irradiation

• Radiant energy heats food, killing microorganisms without marked temperature increases or changes in food nature.
• Gamma rays, x-rays, and ultraviolet radiations are used.
• Irradiation does not make foods radioactive, compromise nutritional quality, or noticeably change taste/texture/appearance.

Purpose of Irradiation

• Prevention of foodborne illness by eliminating organisms like Salmonella and E. coli.
• Preservation by destroying spoilage organisms and extending shelf life.
• Control of insects in imported tropical fruits, reducing the need for harmful pest-control practices.
• Delay of sprouting in vegetables like potatoes, and delaying ripening of fruits to increase longevity.
• Sterilization of foods for immunocompromised patients, stored for years without refrigeration.

Sources of Radiation for Food

• Gamma rays: Emitted from Cobalt 60 or Cesium 137, used to sterilize medical, dental and household products.
• X-rays: Produced by reflecting a high-energy stream of electrons off a target substance into food, also used in medicine and industry.
• Electron beam (e-beam): A stream of high-energy electrons propelled from an accelerator into food, similar to X-rays.

Safety of Irradiated Food

• The FDA, WHO, CDC, and USDA have endorsed the safety of irradiated food through evaluation over more than 30 years.

Microorganism Susceptibility to Radiation

• Gram-positive bacteria are more resistant to radiation than Gram-negative bacteria.
• Sporeformers are more resistant than non-sporeformers.
• The effectiveness of radiation decreases with a larger number of cells; low bioburden is preferable (i.e., wash and package foods in advance)
• Food composition influences the destructive effects; more protein offers more protection to microbes.

Uses of Food Irradiation

• Extends shelf-life of seafood, vegetables, fruits, meats, and spices.
• Kills bacteria, viruses, fungi, protozoa, and insects.
• Prevents sprouting of potatoes and inactivates enzymes, preventing autocatalytic spoilage.