FDSCI 305 EXAM 2 STUDY

What is separation in food processing?

A process used to separate food components.

What are examples of separation in food processing?

Solid from solid, solid from liquid, liquid from solid, liquid from liquid, and gas from solid or liquid.

Why are separation and concentration technologies important?

They are important unit operations used in food processing to develop new products and recycle water.

What challenges do separation and concentration technologies face?

Diversity and complexity of food systems, lability of components, need for safe technologies, and need for low-energy sustainable processes.

What is filtration?

The removal of insoluble particles from a suspension by passing it across a porous material that retains particles by size.

Where is filtration commonly used?

Edible oil refining, sugar refining, beer production, wine making, and fruit juice processing.

What is centrifugation?

A process that separates particles from suspensions according to size, shape, and density using a spinning mechanism.

What does a sedimenting centrifuge do?

Uses gravitational force to push the denser component to the outer area of the bowl.

What does a filtration centrifuge do?

Uses a porous wall to allow liquid through while barricading solids.

What is pneumatic separation?

An old separation method that uses air to direct lighter material away from heavier desired products.

What principle does pneumatic separation depend on?

Density, mass, and particle behavior in the airstream.

What is mechanical expression?

The extraction of oil or juice from plant materials by compression.

What pretreatments improve oil extraction efficiency?

Dehulling, grinding, and cooking.

What equipment is used for mechanical expression?

Screw press or hydraulic press.

What is crystallization?

A liquid-to-liquid phase separation where solutes form crystals from a supersaturated solution.

What foods or compounds commonly crystallize?

Sugar, lactose, glucose, and salt.

What is supersaturation?

The state where the maximum concentration is reached before crystals begin to form.

What is nucleation?

The process in which solutes bind with existing nuclei to form clusters and start crystal growth.

What is distillation?

The separation of liquids with differing volatility by evaporating the liquid with the lower boiling point.

What is solvent extraction?

Separation of soluble components from insoluble or less soluble components using a suitable solvent.

What is a common solvent in the food industry?

Water.

What are examples of solvent extraction in food?

Specialty oils and coffee or tea extracts.

What are drawbacks of solvent extraction?

Cost, toxicity, reactivity, and environmental effects from use, storage, and disposal.

What is evaporation in food processing?

Removal of partial amounts of liquid, usually water, from food products.

What is commonly used in evaporation systems?

A heat exchanger.

What is supercritical fluid extraction?

An extraction process that uses a supercritical fluid, which behaves like both a liquid and a gas.

What is the most commonly used supercritical fluid in food processing?

Carbon dioxide.

What are the main pressure-driven membrane separations?

Microfiltration, ultrafiltration, nanofiltration, and reverse osmosis.

How does pressure-driven membrane separation relate to pore size?

Operating pressure varies inversely with pore size.

What membrane configurations are common?

Planar or flat sheet, tubular, hollow fiber, and spiral-wound.

What is polarization in membrane systems?

Reversible accumulation of dissolved or suspended species near the membrane surface.

What is fouling in membrane systems?

Irreversible formation of a deposit of retained particles in the membrane pores or on the surface.

What is a common use of microfiltration in dairy processing?

Reducing bacteria in milk and improving shelf life.

What does ultrafiltration remove from whey?

Fat.

What do UF membranes retain in fruit juice processing?

Concentrated pulp and unwanted enzymes.

What is a common RO use in fruit processing?

Concentrating fruit juice to about 25 degrees Brix.

How are membranes used in sugar refining?

For concentration, clarification, and purification.

Why is RO or NF useful in sugar refining?

It is cost-effective compared with evaporation.

How are membranes used in vegetable oil processing?

To remove oxidation products and recover vegetable protein from extracting residues.

How are membranes used in brewing and wine?

MF can recover beer from tank bottoms, improve wine stability, and RO can be used for dealcoholization.

What is electrodialysis?

A membrane-type electrochemical process that uses electric force to separate ionic molecules from non-ionic ones.

What is pervaporation?

A membrane process where the permeate is a low-pressure vapor instead of a liquid.

What are the three steps in pervaporation?

Absorption, diffusion, and evaporation.

What are major sustainability concerns in separation technologies?

Energy and water consumption.

How much energy does food processing in the US use annually?

About $16 billion per year.

How much of that energy is spent on drying and concentration?

About half.

Why are membrane concentration systems attractive?

They do not require a heat-producing unit or phase change and can replace energy-intensive processes.

What is drying?

The use of a natural process for eliminating water from material, such as sun drying.

What is dehydration?

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

Why dry foods?

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

What food quality effects can drying cause?

Taste, texture, aroma, protein denaturation, and shrinkage.

Why may rehydration not fully restore a dried product?

Because drying can cause irreversible structural and chemical changes.

What is water activity?

A measure of the availability of water to take part in chemical reactions.

What happens to aw during drying?

It decreases because less free water is available.

Why does drying improve microbial stability?

Most microorganisms grow best in high-aw environments.

What aw do bacteria generally need?

Above about 0.91.

What aw do molds generally need?

Above about 0.65.

How does drying affect shelf life?

It increases shelf life by lowering microbial activity.

What does chemical stability mean in dried foods?

Resistance to reactions such as enzymatic activity, browning, oxidation, and nutrient loss.

What does physical deterioration in dried foods relate to?

Moisture content rather than water activity.

What is hygroscopic?

Readily absorbs moisture from the air.

What is non-hygroscopic?

Does not readily absorb moisture from the air.

Why is free water easier to remove than bound water?

Free water is removed more readily by capillary diffusion.

Why does drying below 10 to 15 percent moisture take more time and money?

Because the remaining water is mostly bound water.

What factors influence drying rate?

Air temperature, relative humidity, air velocity, product size and shape, load of wet material, and the nature of the material.

What product properties affect drying?

Initial moisture content, thermal properties, and porous nature.

What is hot air drying?

Most food dryers use heated air passed across a product to remove moisture.

What does relative humidity represent in drying?

The water activity of the air.

If air relative humidity is greater than food aw, what happens?

The food absorbs moisture from the air.

What are the two moisture content bases?

Wet basis and dry basis.

What is wet basis moisture content?

Mass of water divided by total product mass.

What is dry basis moisture content?

Mass of water divided by dry solids.

How is surface moisture removed during drying?

By evaporation due to a vapor pressure difference between surface moisture and the air.

What is a floor or compartment dryer?

A batch dryer where hot air comes in through a slotted floor below the product.

What products are commonly dried in a floor dryer?

Apple slices, hops, and occasionally potatoes.

What is a bin dryer?

A mobile batch dryer made with metal or wooden boxes.

What are bin dryers used for?

Semi-dried products such as soybean and final drying of vegetables.

What moisture reduction is mentioned for bin drying vegetables?

From about 10 to 15 percent down to 3 to 6 percent.

What is a cabinet or tray dryer?

A chamber where hot air circulates and product is placed on trays.

What is a cabinet dryer used for?

Laboratory or small commercial drying, especially fruits and vegetables.

What temperature and time are used for cabinet drying?

About 180 to 195°F for 15 to 28 hours.

What is an advantage of cabinet drying?

Low building cost.

What is freeze drying?

Drying by sublimation using heating shelves under lower air pressure.

What is sublimation in freeze drying?

Direct conversion from ice to vapor.

What is a major advantage of freeze drying?

The product structure is preserved better.

What is a major disadvantage of freeze drying?

It is expensive.

What foods are often freeze dried?

High-quality products including starter cultures and coffee.

What is a drum dryer?

A continuous dryer where liquid product is spread in a thin film on a steam-heated drum and scraped off.

What temperature is used in drum drying?

About 250 to 300°F.

What is the drum speed range?

About 6 to 24 revolutions per minute.

What products use drum drying?

Whey, mashed potato flakes, apple sauce, and cereals.

What are advantages of drum drying?

Easy to operate, only small area needed, easy to fit into operations, and fast drying time of about 1 to 2 minutes.

What are disadvantages of drum drying?

Lower product quality, flavor and color problems, and nutritional loss.

What is a spray dryer?

A continuous dryer where liquid food is sprayed into a heated chamber through a nozzle or spinning disc.

What products are spray dried?

Milk, fruit juices, coffee, flavor materials, some baby foods, and soup mixes.

What are advantages of spray drying?

Very short drying time, good retention of flavor, color, and nutritive value, and good for heat-sensitive products.

What is a disadvantage of spray drying?

The product must be a solution, paste, or slurry and may need preconcentration.

What is a fluidized bed dryer?

A dryer that forces air through a perforated plate so the product behaves like a fluid.

What temperature is used in a fluidized bed dryer?

About 300 to 350°F.

What moisture reduction is typical in a fluidized bed dryer?

From about 11 to 12 percent to 3 to 5 percent.