FS 161 : Lesson 10 (Dehydration)

maximize

Air velocity can affect dehydration because you want to ( minimize / maximize ) the velocity of heated air moving around food particles to heat the food most rapidly/efficiently.

60-80; velocity; low; shrinkage; dense

Air/tray drying involves trays/racks & heated air (___-___°C) at a set _____, with a ( low / high ) percent rehydration. It can result in food _____ & a(n) _____ product.

fast; inexpensive; more; poor/moderate; case hardening (ex: pasta, vegetables, fruit, spices)

Air/tray drying is a ( slow / fast ), ( expensive / inexpensive ) method with ( less / more ) control than sun drying. It has _____/_____ rehydration properties & can result in _____ _____.

water vapor (ex: apple... when dried, its surface is coated with sugars/acids/salts, its shape is distorted due to cell shrinkage, & water solubles migrate to the surface)

As dehydration occurs, food shrinks & _____ _____ is released.

1; decreases; heat-sensitive

Atmospheric pressure & vacuum can affect dehydration because water boils at 100°C at ___ atm (or 760 mm Hg), but at a lower pressure, boiling point ( increases / decreases ). This is especially important for _____-_____ products.

slows down (see sketch of graph on p72)

Case hardening ( speeds up / slows down ) dehydration rate.

denaturation; polysaccharides; water-binding capacity

Chemical changes during dehydration can include _____ of proteins & aggregation/clustering of _____ (due to loss of _____-_____ _____).

Maillard browning; flavor

Chemical changes during dehydration can include color (particularly _____ _____) & _____ changes due to reactions.

water-soluble; volatiles

Chemical changes during dehydration can include the loss of _____-_____ components (ex: vitamins) or _____ (ex: flavor compounds).

0.3; 0.2 to 0.3

Chemical reactions, such as Maillard browning, need a water activity ≥ ___ to occur; a water activity from ___ to ___ prevents many of them.

freeze-dried

Chuño, a _____-_____ potato product, is made during June & July, during which the temperatures reach about -5°C at elevations greater than 3,800 meters.

shrinkage; case; chemical; method

Dehydration can cause cell/tissue _____, _____ hardening, & _____ changes. However, not all foods show these changes; it depends on the _____ of drying.

higher; Maillard browning

Dehydration causes a ( lower / higher ) solute concentration, which can cause _____ _____.

1

Dried foods are stable for ___+ years at room temperature.

lower; lower; preservation

Dried foods have a ( lower / higher ) weight & a ( lower / higher ) shipping cost, as well as increased _____.

increased; less

Dried foods have a(n) ( increased / decreased ) amount of product per container & take up ( less / more ) space per container.

indirectly; pressed; squeezed

Drum drying involves heating the inside of a drum ( directly / indirectly ) so that is gets very hot; moist raw materials are _____ between two drums so that the liquid is _____/evaporated out.

more; lower; about equal to; flaked or powdered

Drum drying is ( less / more ) efficient than just hot air, there is ( lower / higher ) nutrient loss, the cost is ( less than / about equal to / greater than ) air drying, and it produces a(n) _____ or _____ product.

0.2 to 0.6

Dry foods have a water activity that ranges from ___ to ___.

vacuum chamber (at 0.3 atm); sublimation; nitrogen; 9 to 24

During freeze-drying, the food is frozen (at around -30°C), then placed on trays in a(n) _____ _____ under low heat; this is when the frozen water crystals evaporate via _____. Next, the food is _____-sealed. This process takes about ___ to ___ hours, and upon rehydration, the product is restored.

less

Faster processes yield ( less / more ) nutrient loss.

1-5(%); heat

Foods are dried to a final moisture content of ___-___%, and _____ is added to evaporate water.

radiant

Heat for freeze-drying comes from _____ heaters.

tropical or temperate

High-sugar food products usually include _____ or _____ fruit products.

moist; dry

In fluidized bed drying, ( dry / moist ) granules go in one side, and ( dry / moist ) granules go out the other side.

frozen

In order to be freeze-dried, food must be in the _____ state.

0.8 to 0.9

Intermediate-moisture foods have a water activity that ranges from ___ to ___.

mold inhibitors

Intermediate-moisture foods use _____ _____ as preservatives.

osmosis

Meat curing is a(n) _____ process.

water

Microbial growth & chemical reactions can occur only when enough _____ is present in food.

are not (they resume growth upon rehydration)

Microorganisms ( are / are not ) killed upon dehydration.

0.6

Mold needs a water activity ≥ ___ to grow.

0.93; 0.6

Most microorganisms need a water activity ≥ ___ to grow; a water activity < ___ prevents growth.

liquid (ex: powdered skim milk, instant coffee, tea, eggs)

Spray drying can only be used for what kind of product?

fast; good; low; more

Spray drying is ( slow / fast ), there is ( poor / good ) control/efficiency & ( low / high ) nutrient loss, and it is ( less / more ) expensive than drum/air drying.

faster

Surface area can affect dehydration because a smaller piece of food yields a ( slower / faster ) moisture loss rate.

higher

Temperature can affect dehydration because a higher temperature yields a ( lower / higher ) dehydration rate.

more; moisture content

The humidity of the drying air can affect dehydration because drier air absorbs ( less / more ) moisture, and the percent rehydration of drying air indicates the final _____ _____ of the food.

0.83; 0.88

The pathogen Staphylococcus aureus needs a water activity ≥ ___ to grow & ≥ ___ for toxin production.

sulfites (and/or) blanching

To prevent or reduce enzymatic browning, you can use _____ and/or _____.

does not

Water activity ( does / does not ) equal moisture content.

0.96

Water activity limit optima for microorganisms are all > ___.

sublime

Water can _____ (i.e. it can turn from ice to vapor... there is no transition through the liquid state).

freeze-drying (lyophilization)

What drying method provides the best nutrient quality & product quality upon rehydration and is easy to control, but is the most expensive?

dehydration

What is the oldest & most widely-used preservative method?

oxidative

With dehydration, the potential for _____ rancidity of fats increases.

fluidized bed; porous

_____ _____ drying involves hot air going through a _____ plate to dry food; moist air goes out the top.

sun; slow; high; inexpensive (ex: fruits, vegetables, fish)

_____ drying occurs in dry, warm climates; it is very ( slow / fast ), there is no control, there is often invasion by insects/microorganisms/etc., & there is ( low / high ) nutrient loss, but it is ( expensive / inexpensive ).

concentration; 30(%)

_____ is the partial removal of water from a food, and at least ___% moisture must be left.

case hardening

a form of rapid drying wherein compounds form a hard, impermeable case around the piece of food (ex: dried fruit, cured meat)

spray drying

a method of producing a dry powder from liquid/slurry by rapidly drying with a hot gas

lyophilization

another word for freeze-drying

migrates; evaporates; solute substrate

dehydration steps... 1. water _____ from interior of food to surface 2. the water then _____ via the drying medium 3. the water then carries the water _____ _____ dissolved into it

okay

look at pressure-temperature-phase diagram on p75

okay

moisture contents before & after drying... - whole milk: 87 to 5% - nonfat milk: 90 to 5% - whole egg: 74 to 2.9% - egg white: 88 to 7.3% - egg yolk: 51 to 1.1% - lean/roasted beef: 60 to 1.5% - broiled chicken: 61 to 1.6% - cooked snap peas: 92 to 11.5% - cooked sweet corn: 76 to 3.2% - boiled potatoes: 80 to 4% - apple juice: 86 to 6.2% - raw figs: 78 to 3.6% - raw parsley: 84 to 5.3%

structural; optical; sensory; nutritional; rehydration (ability)

product qualities affected by dehydration... - _____ (ex: apparent density, volume, porosity) - _____ (ex: color, appearance) - _____ (ex: aroma, flavor, taste) - _____ (ex: proteins, vitamins) - _____ ability

dehydration

the almost complete removal of water from a food (ex: sun-drying, Chuño production, meat curing)

water activity

the free, unbound water in food molecules; it can support microorganism growth

condensation

the state change from gas to liquid (600 cal/g discharged)

sublimation return

the state change from gas to solid (680 cal/g discharged)

evaporation

the state change from liquid to gas (600 cal/g absorbed)

coagulation

the state change from liquid to solid (80 cal/g discharged)

sublimation

the state change from solid to gas (680 cal/g absorbed)

smelting

the state change from solid to liquid (80 cal/g absorbed)

okay

water activity limits for microbial growth... - Campylobacter: 0.98 - C. botulinum (type E; non-proteolytic): 0.97 - C. botulinum (types A & B; proteolytic): 0.93 - Salmonella & C. perfringens: 0.94 - Listeria monocytogenes: 0.92 - many yeasts: 0.88 - many molds: 0.75