L 10 Food Preservation Techniques

Non-food Processing and Food Preservation

• The lecture covers food preservation methods, including thermal and non-thermal processes.
• Food preservation techniques aim at preventing microbial decomposition and self-decomposition of food, as well as damage from insects, animals and other factors.
• Methods for achieving microbial decomposition include asepsis, removal of microorganisms, maintenance of anaerobic conditions, use of high and low temperatures, drying, smoking, use of chemical preservatives, irradiation, and mechanical destruction of microorganisms.

Types of Thermal Heat Processing

• Heat processing methods use steam or water (boiling, blanching, pasteurization, heat sterilization, evaporation, and distillation), hot air (dehydration, baking, roasting), hot oils (frying).
• Heat processing can use direct and radiated energy (infrared, dielectric, ohmic).
• Processing by removal of heat includes chilling, freezing, and freeze drying.

Non-thermal Processing: An Introduction

• Traditional food technologies, like pasteurization and sterilization, may destroy essential nutrients (vitamins, polyphenols) to maintain food safety.
• Non-thermal methods aim to prolong shelf life and preserve quality without affecting these essential nutrients.
• Non-thermal methods have increased production rates and profit margins for the food industry.

Non-thermal Processing Methods

• Pulsed electrical field (PEF)
• Pulsed ultraviolet method
• Irradiation method
• Cold plasma
• Supercritical carbon dioxide
• Pulsed light
• High hydrostatic pressure processing
• Radio frequency and microwave
• Ultrasound

Pulsed Electrical Field (PEF)

• PEF uses high-voltage electric pulses to inactivate enzymes and extend shelf life.
• Applications include vegetable and fruit juices, milk, and liquid eggs.
• PEF enhances extraction of intracellular compounds (plant oil, polyphenols, pigments).
• It improves drying rates for foods like potatoes and meat, and accelerates wine ageing reactions.
• Combined with mild heating, enhances microbial inactivation.
• Destroy pathogens by destroying cell membranes, and oxidation of macromolecules.

Ultraviolet (UV)

• Pulsed UV light inactivates surface microorganisms.
• Used for disinfecting water supplies and food contact surfaces.
• Effective against Salmonella on unpackaged and vacuum-packaged foods.
• Extends shelf life without major alteration to food quality in foods like juices and milk

Irradiation

• Authorized ionizing radiation (gamma rays, X-rays, accelerated electrons) applied to food.
• Mechanism involves direct/indirect damage to microbial nucleic acids (DNA).
• Important application for decontamination of spices, herbs, and condiments.
• Useful for ready-to-eat meat, and fresh mushrooms, extending their shelf life.

Cold Plasma

• Ionization of gas generates reactive species that kill microorganisms.
• Used to sterilize cherry tomatoes, strawberries, almonds, and food packaging materials.
• Relatively complex equipment needed but is effective on fruits, vegetables and meats.

Supercritical Carbon Dioxide (SCCO2)

• Supercritical fluid state of carbon dioxide at or above its critical temperature and pressure.
• Effective for inactivation of microorganisms and enzymes in fruit and vegetable products (juices, purees, smoothies).
• Green Technology for extracting bioactive compounds (carotenoids, flavonoids, phenols.) from fruits and vegetables.
• Doesn't use organic solvents, which is eco-friendly.

Pulsed Light

• Surface irradiation, not penetration.
• Short intense light pulses in UV to NIR range from Xenon lamps.
• Effective for surface microorganism control.
• Food safety and extended shelf life.

High Hydrostatic Pressure Processing (HPP)

• High pressure treatment (300-600 MPa) in flexible containers submerged in pressurized water.
• Achieves microbial inactivation.
• Irreversible destruction of cellular structures (cell membranes, cell walls)
• Useful in seafood processing, cooked meat and poultry products, ready-to-eat products
• Preserves desirable characteristics like appearance, texture and nutrition.

Radio Frequency and Microwave

• Electromagnetic waves to generate heat in materials.
• Dipolar interaction: Water molecules rotate in the alternating electric field, producing heat.
• Ionic interaction: Ions collide with other molecules, also generating heat.
• Used for pasteurization and sterilization due to the rapid heating that occurs.

Ultrasound

• Mechanical waves above the human hearing threshold.
• Used to increase mass transfer, degassing, defoaming, filtration, emulsification, protein hydrolysis in food preservation and extraction.
• Creates intracellular cavitation, destroying cell membranes which inhibits microbial growth.
• Used for preserving fruits, vegetables and their juices.

Principles of Food Preservation

• Prevention of microbial decomposition: Keeping out/removing microorganisms (asepsis, filtration), or hindering/killing their growth (drying, anaerobic conditions, lowering the temperature, heat or radiation).
• Prevention of self-decomposition: Preventing/inactivating food enzymes, and mitigating chemical reactions.
• Prevention of damage: Protecting against insects, animals, mechanical damage.

Methods of Food Preservation

• Asepsis
• Removal of microorganisms
• Maintenance of anaerobic conditions
• Use of high and low temperatures, Drying, Smoking
• Use of chemical preservatives
• Irradiation
• Mechanical destruction of microorganisms, Combinations of methods

Chemical Preservatives

• Substances to prevent food deterioration.
• Inhibit microbial activity by interfering with cell membranes, enzymes, or genetic mechanisms.
• Used as antioxidants, acidity neutralizers, stabilizers, firming agents, coatings, and to prevent water loss.
• Common types include propionates, benzoates, sorbates, acetates (e.g., dehydroacetic acid, acetic acid), nitrites/nitrates, sulfur dioxide/sulfites, and ethylene propylene oxide (used for fumigation).

Other Preservative Methods

• Filtration is used to remove microorganisms like in juices, soft drinks, water.
• Radiation (gamma and X-rays) sterilises food, often a cheaper and potentially more effective method than thermal treatments, but may have limitations related to public perception.
• Antibiotics are used for extending the storage life of raw food.