L 10 Food Preservation Techniques

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Questions and Answers

What is the primary effect of freezing food at low temperatures?

It significantly increases the number of viable microorganisms.

It sterilizes the food completely.

It reduces the number of viable microorganisms but does not sterilize. (correct)

It causes food to spoil faster.

Which type of drying method can effectively maintain the color and vitamin content of food?

Treatment with SO2 before drying (correct)

Freeze drying

Sun drying

Spray drying

What water activity level (Aw) is considered most unlikely for spoilage to occur in dried foods over a period of up to 2 years?

Aw of 0.65 (correct)

Aw of 0.80

Aw of 0.70

Aw of 0.75

How does fast freezing differ from slow freezing in terms of ice crystal formation and food quality?

Fast freezing creates smaller ice crystals and preserves food quality better than slow freezing. Signup and view all the answers

Which treatment before drying significantly reduces the number of microorganisms by using heat?

Blanching or scalding the food Signup and view all the answers

What is the main purpose of using supercritical carbon dioxide (SCCO2) in food processing?

To inactivate microorganisms and enzymes Signup and view all the answers

Which bioactive compounds can be extracted using supercritical carbon dioxide?

Carotenoids, flavonoids, and phenols Signup and view all the answers

What is a significant limitation of pulsed light technology in food processing?

Lack of knowledge regarding its inactivation mechanisms Signup and view all the answers

At what pressure range is high hydrostatic pressure processing (HPP) typically conducted?

300-600 MPa Signup and view all the answers

How do flexible containers facilitate the high hydrostatic pressure processing of foods?

They allow for uniform pressure distribution Signup and view all the answers

What is the primary mechanism of microbial inactivation during high hydrostatic pressure processing?

Destruction of cellular structures Signup and view all the answers

What kind of light does pulsed light technology utilize for irradiating surfaces?

Intense short flashes of light with varying wavelengths Signup and view all the answers

Which of the following is a reason for pulsed light technology not being widely adopted in food processing?

Inadequate knowledge of critical factors and mechanisms Signup and view all the answers

What type of medium is used in the high-pressure chamber during HPP?

Water Signup and view all the answers

What is the primary principle behind Pulsed Electric Field (PEF) technology?

Discharge of high voltage electric pulses into food Signup and view all the answers

Which of the following food items can benefit from PEF technology?

Vegetable and fruit juices Signup and view all the answers

What effect does PEF have on enzymes in the food industry?

It inactivates enzymes to prolong shelf life Signup and view all the answers

What is the main advantage of combining PEF with mild heating?

It enhances microbial inactivation and extends shelf life Signup and view all the answers

In the context of UV light technology, what is its primary application?

Inactivating surface microorganisms Signup and view all the answers

How does UV light primarily exert its germicidal properties?

Through absorption of UV light leading to DNA mutations Signup and view all the answers

What potential effect can pulsed UV light have on food products?

It can alter the color and texture of food Signup and view all the answers

What frequency defines ultrasound, which is beyond human hearing?

20 kHz Signup and view all the answers

Which method is NOT used to prevent microbial decomposition in food preservation?

Aging Signup and view all the answers

Which of the following is a method to extract active ingredients from food using ultrasound?

Degassing Signup and view all the answers

What is one of the mechanisms by which ultrasound affects food processing?

Generating intracellular cavitation Signup and view all the answers

Which principle does NOT contribute to food preservation?

Enhancing evaporation Signup and view all the answers

What is the purpose of using asepsis in food preparation?

To keep out microorganisms Signup and view all the answers

Which method of food preservation does NOT involve temperature control?

Irradiation Signup and view all the answers

What type of reaction is targeted when preventing oxidation in food preservation?

Chemical Signup and view all the answers

Which is an effective way of preventing damage from insects in food preservation?

High temperatures Signup and view all the answers

What is a common property of the natural protection found in food?

It shields against microorganisms Signup and view all the answers

What is the primary objective of heating foods during preparation?

To destroy undesirable enzymes and microorganisms Signup and view all the answers

Which method involves heating foods above 100°C to destroy spoilage and pathogenic microorganisms?

Steam pressure processing Signup and view all the answers

What is a characteristic of chilling temperatures in food preservation?

They can prevent growth of most food poisoning microorganisms. Signup and view all the answers

What is the risk involved in the canning process?

Microbial spoilage can occur due to under processing or leakage. Signup and view all the answers

What happens to thermophilic spores if commercially sterile foods are not stored properly?

They sprout and grow significantly. Signup and view all the answers

Which of the following is a method employed at about 100°C to preserve acid foods?

Boiling Signup and view all the answers

What is the effect of low temperatures on chemical reactions in food?

They reduce the activity of microorganisms. Signup and view all the answers

Which microorganisms can grow at chilling temperatures?

Psychrotrophs Signup and view all the answers

What is an effect of heating food at ultra-high temperatures?

It can kill spoilage organisms quickly. Signup and view all the answers

What is a common part of the canning process?

Vacuuming the headspace before sealing Signup and view all the answers

Study Notes

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.

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Description

This quiz explores various methods of food preservation, including both thermal and non-thermal processes. Learn about techniques aimed at preventing microbial and self-decomposition of food, as well as damage from pests. Test your understanding of heat processing and preservation methods.