FDSCI 305 Exam 2

What is drying?

The use of a natural process for eliminating water from material, e.g., sun drying.

What is dehydration?

The use of artificially controlled conditions for eliminating water from material.

Why is drying done?

For preservation, smaller volume, desired flavor and texture, and lower cost.

What effects can drying have on food quality?

It can change taste, texture, aroma, protein structure, and cause shrinkage.

Does rehydration always restore the original product after drying?

No, rehydration does not always restore the original product due to changes.

What does water activity (aw) measure?

The availability of water for chemical reactions.

How does drying affect water activity in food?

During drying, there is less free water available, resulting in lower water activity.

What water activity (aw) do bacteria need to grow?

Bacteria need aw > 0.91.

What water activity (aw) do molds need to grow?

Molds need aw > 0.65, though some can grow lower depending on the species.

How does drying affect microbiological stability?

Drying increases microbiological stability and shelf life.

What role does water play in chemical reactions?

Water can act as a solvent, reactant, product, or modifier.

What are examples of physical deterioration related to moisture content?

Softening, differential shrinkage, surface wetting, case hardening, and cell collapse.

What is hygroscopic material?

Material that readily absorbs moisture from the air.

What is non-hygroscopic material?

Material that does not readily absorb moisture from the air.

What affects the drying rate of food?

Drying is faster for free water and slower for bound water.

What is the wet basis (wb) of moisture content?

Mass of water divided by total product mass.

What is the dry basis (db) of moisture content?

Mass of water divided by dry solids.

What is a batch dryer?

A dryer that processes small quantities of food at a time.

What is a floor dryer?

A batch dryer where hot air enters through a slotted floor, used for small-scale operations.

What is a freeze dryer?

A dryer that uses low pressure and heating shelves for sublimation, preserving structure well but is expensive.

What is sun drying?

Drying in direct sunlight, which is low cost and requires no fuel.

What is chilling in food preservation?

Temperature reduction without ice formation.

What is freezing in food preservation?

Temperature reduction where ice is formed.

What is the recommended refrigerator temperature?

4°C or below.

What is the recommended freezer temperature?

-18°C or below.

What is freezer burn?

Water loss from the surface of frozen food due to sublimation.

What is blanching?

A mild heat treatment used to deactivate enzyme activity.

What is the purpose of refrigeration in food preservation?

To lower and control the temperature of food to slow or stop detrimental changes.

What is the lag phase in microbial growth?

A phase where no increase in microbial numbers is apparent.

What is the log phase in microbial growth?

A phase where microorganisms grow rapidly.

What is the stationary phase in microbial growth?

A phase where growth no longer occurs.

What is the death phase in microbial growth?

A phase where cells are heat-injured or die.

What is the goal of refrigerated preservation?

To lower and control the temperature of food to slow or stop detrimental changes.

What water activity do bacteria need to grow?

aw > 0.91

What water activity do molds need to grow?

aw > 0.80

What are examples of chemical reactions affected by water?

Enzymatic reactions, Non-enzymatic browning, Lipid Oxidation, Loss of Nutrients and Volatiles, Release of Structural Water.

What is related to moisture content in food products?

Deterioration reactions.

What are some examples of deterioration reactions?

Softening, Differential Shrinkage, Surface Wetting Effects, Case Hardening, Cell Collapse.

What factors influence drying?

Air Temperature, Relative Humidity, Air Velocity, Size and shape of product, Load of wet material per unit area, Nature of material being dried.

What is the difference between free water and bound water in drying?

Free water dries quickly, while bound water dries slowly.

What is the typical drying temperature range for hot air drying?

180-195°F.

What is the definition of moisture content (wb)?

Mass of water divided by the total product mass.

What is the definition of moisture content (db)?

Mass of water divided by the dry solids.

What is a drum dryer?

A dryer where liquid products are distributed in a thin film on a heated drum.

What is a spray dryer?

A dryer that sprays liquid food in a heated chamber to remove water.

What is a fluidized bed dryer?

A dryer that forces air through a perforated plate to dry products.

What are the advantages of microwave drying?

Very short drying time, high production rates, efficient energy usage.

What is the main advantage of sun drying?

Low heating process.

What is osmotic dehydration?

Soaking fresh material in a heavy sugar or salt solution before drying.

What is one challenge in separation technologies in food processing?

Diversity and complexity of food systems.

What is filtration in food processing?

Removal of insoluble particles from a suspension by passing it across a porous material.

What is centrifugation?

A method used to separate components based on density using centrifugal force.

What is pneumatic separation?

A method that uses air pressure to separate food components.

What is mechanical expression?

A method used to extract liquids from solids by applying pressure.

What is a centrifuge used for?

To separate particles from suspensions according to their size, shape, and density.

How does a sedimenting centrifuge work?

It uses gravitational force to push the component with greater density to the outer area of the bowl.

What is the function of a filtration centrifuge?

It uses a porous wall to allow liquids to pass while blocking solids.

What is mechanical expression in food processing?

The extraction of oil or juice from plant materials by compressing pretreated food.

What is crystallization in liquid to liquid phase separation?

The process where solutes bind with existing nuclei to form clusters and initiate crystal growth.

What is distillation?

The separation of liquids with differing volatility through evaporation.

What is solvent extraction?

A method to separate soluble components from insoluble ones using a suitable solvent.

What is evaporation in food processing?

A technique to remove partial amounts of liquid, typically water, from food products.

What is supercritical fluid extraction (SFE)?

A process using supercritical fluids to extract oil from foods by changing pressure.

What are the types of pressure-driven membrane separations?

Microfiltration, ultrafiltration, nanofiltration, and reverse osmosis.

What is polarization in membrane separations?

The reversible accumulation of dissolved or suspended species near the membrane's surface.

What is fouling in membrane separations?

The irreversible formation of deposits of retained particles in the membrane pores or surface.

What are applications of membranes in the dairy industry?

Ultrafiltration of milk, cheese whey, and dairy effluents to reduce bacteria and remove fat.

How does membrane separation benefit sugar refining?

It removes retentate and prepares juice for concentration and crystallization.

What is electrodialysis?

A membrane-type electrochemical process that separates ionic molecules from non-ionic ones using electric force.

What is the purpose of the food cold chain?

To maintain optimal conditions for slowing or preventing changes in food quality.

What happens during the cooling process of refrigeration?

The temperature of food is reduced and maintained during storage, transport, and retailing.

What is the significance of the third temperature threshold in microbiology?

It is the minimum growth temperature for a microorganism.

What occurs during the lag phase of microbial growth?

No increase in microbial numbers is apparent.

What happens during the exponential phase of microbial growth?

Microorganisms grow rapidly at optimum temperatures.

What is generation time in microbiology?

A measure of the time it takes for a microbial population to grow.

What is the concern during food storage regarding temperature?

If foods do not rise above a certain temperature during frozen storage, food safety issues may arise.

What affects vitamin loss in fruits and vegetables?

Storage temperature.

What storage temperature helps maintain vitamin content in fruits and vegetables?

Just above freezing point.

What does humidity control prevent in fruits and vegetables?

Wilting and loss of water-soluble vitamins.

What is the relationship between temperature and quality in food storage?

Lower temperature results in better quality.

What causes in-package frosting in frozen foods?

Water loss from the surface, loose packaging, and temperature fluctuations.

What affects flavor in foods?

Temperature during cooling and storage.

What is necessary to retain desirable sweetness in vegetables?

Prompt cooling.

What is cold shortening in meat?

Occurs when chilling pre-rigor, resulting in tough meat after cooking.

Which type of meat is less prone to cold shortening?

Poultry meat.

What are the symptoms of exposure to temperatures above freezing in fruits and vegetables?

Internal/external browning, superficial spots, failure to ripen, development of off-flavors.

What is blanching used for?

To deactivate enzymes.

What is the temperature range for blanching?

75-95°C (167-203°F).

What types of refrigeration systems are there?

Total loss refrigeration systems and mechanical refrigeration systems.

What is a common total loss refrigerant?

Liquid nitrogen and solid carbon dioxide.

What are the four interlinked components of a mechanical refrigeration system?

Evaporator, compressor, condenser, expansion valve.

What is heat transfer?

The process that exchanges thermal energy from one physical system to another.

What are the four modes of heat transfer?

Conduction, convection, radiation, evaporation/condensation.

What is conduction?

Transfer of energy between objects in physical contact.

What is convection?

Transfer of heat by circulation or movement of hot particles to cooler areas.

What is evaporation in the context of heat transfer?

Transfer of energy required to change a liquid to a vapor.

What are the systems used for chilling and freezing?

Air, contact, immersion/spray, vacuum, scraped surface freezers, high-pressure freezing.

What is a fluidized bed freezer?

An air system where uniform particles are subjected to an upward air stream.

What is wet-air cooling?

Recirculating air over ice-cold water to cool the air.

What are contact systems based on?

Heat transfer by contact between products and metal surfaces.