Food Microbiology and Preservation Techniques

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Questions and Answers

Which of the following methods can kill most microbes without affecting spores?

Heating above 100°C

Canning

Heating at 100°C (correct)

Chilling to 6°C

What is the main objective of heating foods during food preparation?

To destroy pathogens and spoilage microorganisms (correct)

To improve texture and taste

To increase the pH level of the food

To enhance the color of the food

Which of the following conditions can lead to microbial spoilage during the canning process?

Under processing or leakage after processing (correct)

Using airtight glass containers

Adding high temperatures during sealing

Using a vacuum for brine addition

Which microorganism is capable of growth at chilling temperatures of around 6°C?

Psychrophiles Signup and view all the answers

What is necessary for the preservation of commercially sterile foods?

Storing in cool, dry places Signup and view all the answers

Which type of radiation is NOT authorized for food irradiation applications?

Ultraviolet light Signup and view all the answers

What is a primary effect of irradiation on fresh meat products?

Changing the color Signup and view all the answers

What limitation affects the development of irradiation technology in the food industry?

Nuclear technology concerns Signup and view all the answers

Which food products are effectively sterilized using cold plasma?

Fruit and vegetables Signup and view all the answers

What is a major challenge associated with cold plasma technology?

Unexplored impacts on food quality Signup and view all the answers

What does supercritical carbon dioxide (sCO2) require to be maintained in a fluid state?

Critical temperature above 31°C Signup and view all the answers

Which mechanism does cold plasma primarily use to inactivate microorganisms?

Reactive oxygen free radicals Signup and view all the answers

What is the primary benefit of using supercritical carbon dioxide (SCCO2) in fruit and vegetable processing?

It inactivates microorganisms and enzymes. Signup and view all the answers

Which of the following compounds can be extracted using supercritical carbon dioxide (SCCO2)?

Carotenoids Signup and view all the answers

What limitation currently affects the commercial use of pulsed light technology?

There is a lack of knowledge about critical factors and mechanisms. Signup and view all the answers

What is the range of pressure used in high hydrostatic pressure processing (HPP)?

300-600 MPa Signup and view all the answers

Which of the following is the primary mechanism of sterilization in high hydrostatic pressure processing?

Irreversible destruction of cellular structure Signup and view all the answers

What is a significant characteristic of pulsed light as a food processing technology?

It consists of short, intense flashes of light. Signup and view all the answers

In high hydrostatic pressure processing, what role does the pressure-transmitting medium play?

It helps to transmit pressure into the food product. Signup and view all the answers

Which statement about supercritical carbon dioxide processing is true?

It can extract bioactive compounds without organic solvents. Signup and view all the answers

What type of irradiation does pulsed light technology use?

Very intense and short flashes of light Signup and view all the answers

What is one of the main benefits of High Hydrostatic Pressure Processing (HPP) in food processing?

It enhances the freshness characteristics of foods. Signup and view all the answers

Which food types are commonly processed using High Hydrostatic Pressure Processing (HPP)?

Seafood, ready-to-eat products, and fruit juices. Signup and view all the answers

What mechanism is primarily involved in microwave and radio frequency heating?

Dipolar and ionic interactions of molecules. Signup and view all the answers

How does microwave and radio frequency heating compare to conventional heating methods?

It offers rapid pasteurization with reduced thermal degradation. Signup and view all the answers

Which of the following is NOT a benefit of using microwave and radio frequency heating?

Enhancement of the flavor profile of all foods. Signup and view all the answers

What does the HPP technology primarily improve in the processing of cheese?

The coagulant activity and yield. Signup and view all the answers

What physical change occurs in food as a result of microwave and radio frequency heating?

Water molecules rotate, generating heat. Signup and view all the answers

In terms of nutritional retention, what is a significant advantage of HPP?

It maintains more bioactive components than thermal processing. Signup and view all the answers

Which characteristic of food is least affected by High Hydrostatic Pressure Processing?

Shelf life after opening. Signup and view all the answers

What is a correct statement regarding the use of microwave and radio frequency in food processing?

It can be used for both pasteurization and sterilization. Signup and view all the answers

What is the primary purpose of using ultrasound in food processing?

To accelerate mass transfer and heat exchange Signup and view all the answers

Which method is NOT a principle of food preservation?

Enhancing chemical reactions for better flavor Signup and view all the answers

What is a common use of ultrasound in food preservation?

Extracting phenolic compounds from vegetables Signup and view all the answers

Which of the following methods focuses on keeping out microorganisms?

Asepsis Signup and view all the answers

What effect does ultrasound have on cell membranes?

It breaks down and dislodges particles Signup and view all the answers

What does the method of drying contribute to food preservation?

Hindering the growth and activity of microorganisms Signup and view all the answers

Which of the following is an example of maintaining anaerobic conditions in food preservation?

Vacuum packaging Signup and view all the answers

What is a primary role of chemical preservatives in food preservation?

To prevent or delay chemical reactions and spoilage Signup and view all the answers

How does irradiation contribute to food preservation?

By killing microorganisms Signup and view all the answers

Which of the following methods prevent damage due to insects and animals?

Packaging Signup and view all the answers

Study Notes

Non-food Processing and Food Preservation

Lecture 10, Imam Abdulrahman Bin Faisal University, Department of Clinical Nutrition, Dr. Mohamed Elsaadany
Covers various methods of food preservation including thermal and non-thermal processing.

Outline

Types of thermal heat processing: Boiling, Blanching, Pasteurisation, Heat sterilization, Evaporation, Distillation, Dehydration, Baking, Roasting, Frying, Infrared, Dielectric, Ohmic, Chilling, Freezing, Freeze drying
Introduction to Non-thermal processing: Traditional methods (pasteurization, sterilization, drying, evaporation) may destroy nutrients, Higher processing temps/times create potentially harmful components. Non-thermal methods developed to increase production rate/profit/quality/shelf life
Types of Non-thermal heat processing: Pulsed electrical field (PEF), Pulsed Ultraviolet, Irradiation, Cold plasma, Super critical carbon dioxide, Pulsed light, High hydrostatic pressure processing (HPP), Radio frequency and microwave, Ultrasound
Principles of Food Preservation: Preventing microbial decomposition, preventing self-decomposition, preventing damage by insects/animals/mechanical causes

Pulsed Electric Field (PEF)

Non-thermal food preservation technology
High voltage electric pulses (20-80 kV/cm) applied to food
Widely used for sterilizing vegetable/fruit juices, milk, liquid egg
Inactivates enzymes, prolongs shelf life, enhances extraction of intracellular compounds (plant oils, polyphenols, pigments) from fruits and vegetables
Improves drying rates of food (potatoes, meat products), accelerates wine aging/chelating reactions
Combined with mild heating, enhances microbial inactivation and extends food shelf-life
Pathogens destroyed through destruction of cell membranes and oxidation of macromolecules

Ultraviolet (UV)

Technique used to inactivate surface microorganisms
Short pulses of intense light (200-280nm) for microseconds
Disinfects water supplies, food contact surfaces
Kills Salmonella on unpackaged/vacuum-sealed chicken, cooked meats, mushrooms
Extends shelf-life of juices, milk, preserves fresh-like qualities of cider compared to thermal processing
Can affect food colour and texture depending on energy dose & lamp distance
DNA mutations due to UV light absorption. Uses often require combining UV irradiation with other methods (PEF, or ultrasound) or packaging or ozone or hydrogen peroxide

Irradiation

Three types of ionizing radiation (gamma rays, X-rays, accelerated electrons)
Mechanism is mainly due to direct/indirect damage to microbial DNA
Largest application is decontamination of spices, herbs, condiments
Used for ready-to-eat meat, fresh mushrooms
Effective sterilization for prolonging shelf life
Can alter color/odour/functional properties of food (e.g., whole wheat flour, rice)
Limited application due to nuclear technology, consumer perception & equipment needs

Cold Plasma

Ionizes gas with neutral molecules, electrons, positive/negative ions
Creates highly reactive species that destroy microorganisms
Uses heating, electricity, lasers for ionization
Effective for inactivating contaminating microbes on meats, poultry, fruits, vegetables
Used for sterilizing cherry tomatoes, strawberries, almonds, and food packaging materials.
Relatively expensive equipment, and impacts on sensory/nutritional properties need more research and understanding.

Supercritical Carbon Dioxide (SCCO2)

Specialized fluid state of carbon dioxide at/above its critical temperature/pressure
Valuable for processing/preservation of fruit & vegetables
Inactivates microorganisms and enzymes in fruit/vegetable products (juices, purees, smoothies)
Effective/green technology for extracting bioactive compounds (carotenoids, flavonoids, phenols) from fruit/vegetables without organic solvents

Pulsed Light

Surface irradiation system, not penetration system
Intense/short flashes of light (UV-NIR) from Xenon lamps
Primarily effective for surfaces/thin films
Approved by FDA for surface microorganism control but has limited market penetration due to knowledge gaps regarding critical factors/inactivation mechanisms

High Hydrostatic Pressure Processing (HPP)

Treats food under high pressure (300-600 MPa) to inactivate microbes
Food packaged in flexible containers, inserted into a high-pressure chamber filled with a pressure-transmitting medium (usually water)
Effective inactivation depends on pressure, holding time, & resistance of microorganisms/food matrix.
Main mechanism: irreversible destruction of cellular structure (cell membranes, cell walls)
Application in seafood processing, cooked products, meat/poultry products, ready-to-eat foods, plant-based foods, juices
Minimises thermal degradation, results in fresher foods with better appearance, texture, nutrition

Radio Frequency and Microwave

Electromagnetic waves of certain frequencies generate heat in a material
Dipolar interaction: polar molecules (e.g., water) rotate in the alternating electromagnetic field, generating heat
Ionic interaction: ionic compounds (e.g., dissolved salts) accelerate and collide with other molecules, generating heat
Pasteurization/sterilization preferred over conventional heating due to speed
Benefits: approach benefits of high-temperature short-time processing while reducing thermal degradation of components; systems can be turned on/off easily and more energy efficient

Ultrasound

Mechanical waves exceeding the threshold of human hearing (20 kHz)
Used for degassing, defoaming, filtration, emulsification
Food preservation/extraction of active ingredients
Promoting protein hydrolysis, accelerating mass transfer, heat exchange in food processing
Preservation of vegetables, fruits, juices
Extraction of phenolic compounds, pigments, prebiotic oligosaccharides
Sounds result in intracellular cavitation; breaks down/dislodges particles, destroying cell membranes

Principles of Food Preservation

Asepsis: Keeping out microorganisms
Removal of microorganisms: Filtration; centrifugation
Maintenance of anaerobic condition: Evacuate/fill with N2/CO2
Use of high/low temperatures: Heat treatment (Pasteurization, above 100°C, canning)
Drying & Smoking: Reduce water content
Chemical preservatives: Prevent spoilage, oxidation
Radiation: Ionising radiation (gamma rays, x-rays)

Chemical Preservatives

Additives preventing food deterioration
Includes:
- Interfering with cell membranes
- Inactivating enzymes, genetic mechanisms
- Antioxidants, acidity neutralisers, stabilisers, firming agents, coatings, preventing water loss
- Propionates
- Benzoates
- Sorbates
- Acetates (dehydroacetic acid, acetic acid)
- Sulfur dioxide & sulfites (sulfurous acid)
- Ethylene & propylene oxide

Other Preservative Methods

Filtration: Removing microorganisms from food
Radiation: Ionizing radiation for food preservation (gamma rays, x-rays)

Antibiotics

Some antibiotics used to extend storage time for specific food types (meat, fish, poultry).
Some problems: species variability in antibiotic susceptibility, adaptation/resistance development.

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Description

Test your knowledge on the various methods of food preservation and the effects of different treatments on microorganisms. This quiz covers topics such as irradiation, supercritical carbon dioxide, and cold plasma technology. Determine how these methods influence food safety and spoilage.