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Question 1. How does water vapor partition from a liquid into the surrounding gas?. H 2 O g. H 2 O g. H 2 O g. H 2 O l. H 2 O l. H 2 O l. H 2 O l. H 2 O l. H 2 O l. Vapor Pressure of Pure Water. Vapor Phase above Water.

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Question 1 l.jpg

Question 1

How does water vapor partition from a liquid into the surrounding gas?


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H2Og

H2Og

H2Og

H2Ol

H2Ol

H2Ol

H2Ol

H2Ol

H2Ol



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Vapor Phase above Water

  • Water will evaporate until the moisture content reaches a temperature dependant equilibrium.

  • Or in an open container, eventually all of the water will evaporate


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Question 2

How does water vapor partition from a solution into the surrounding gas?


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H2Og

H2Og

H2Og

solute

H2Ol

solute

H2Ol

solute

solute

H2Ol

H2Ol


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Vapor Pressure above a Solution

p0

Vapor pressure of water

IDEAL

1

0

Mole fraction of water


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Vapor above a Solution

  • A solution will lose moisture to the atmosphere

  • The partial pressure of water above the solution is reduced by the presence of solute

  • Vapor pressure depends on concentration of solute as well as temperature


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Saturated Solutions

Solubility limit

Liquid phase concentration=solubility limit

p0

Vapor pressure of water

1

0

Mole fraction of water


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Question 3

How does the partitioning of water vapor from a solution depend on solution composition?


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p0

Vapor pressure of water

IDEAL

1

0

Mole fraction of water


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Vapor Depends on Solution Composition

  • Non-ideal properties of solutions mean some have a greater affinity for water than others.

  • The vapor pressure will always be less than above pure water but not necessarily the same over all solutions

  • Different saturated solutions will have different partial pressures of water


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Question 4

What happens when two different solutions are placed in the same container?


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Two solutions/One container

  • Both solutions will exchange water with the atmosphere

  • The whole system will finally come to equilibrium

  • The equilibrium concentration of both solutions will be such that they are in equilibrium with the atmosphere.

  • The moisture content need not be the same. The partial pressure will be.


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Water Activity

aw=p/po~%ERH

Partial pressure of water above the solution normalized to the partial pressure above pure water.


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Question 5

How do these analogies translate to food?


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The typical water activity of some foodstuffs

Type of product

Water Activity (aw)

Fresh meat and fish

.99

Bread

.95

Aged cheddar

.85

Jams and jellies

.8

Plum pudding

.8

Dried fruit

.6

Cookies

.3

Milk powder

.2

Instant coffee

.2



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Moisture Sorption Isotherm

Moisture content (d.w.b.)

aw


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Moisture Sorption Isotherm

Moisture content (d.w.b.)

aw


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Zone 2

Zone 1

Moisture content (d.w.b.)

Zone 3

aw

Moisture Sorption Isotherm


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Temperature Dependency

cold

Moisture content (d.w.b.)

hot

aw


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Sorption and Desorption

desorption

Moisture content (d.w.b.)

sorption


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Moisture Sorption Isotherms

  • Highly product specific (physical and chemical structure)

  • Highly temperature dependant

  • Show sorption/desorption hysteresis

  • Affect both physical/chemical reactivity of the food and the dynamics of water transport


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Zones in Isotherms

  • Zone 3: Bulk water

  • Zone 2: Loosely bound water

  • Zone 1: Tightly bound water.


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Lipid oxidation

log (RATE)

Most reactions

Moisture content (d.w.b.)

SORPTION ISOTHERM

Microbial growth

aw

Reaction Rates and Water Activity



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The GAB Model

mo monolayer value

K multilayer parameter

C temperature dependency parameter


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Texture Changes

Crispy/crunchy

Moisture content (d.w.b.)

Soft

0.2-0.5


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Powder Changes

Free flowing

Agglomerated

Moisture content (d.w.b.)

~0.4



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Moisture Sorption Isotherm

Moisture content (d.w.b.)

aw


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Moisture Sorption Isotherm

Moisture content (d.w.b.)

aw


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Multicomponent Foods

  • Cheese and crackers

  • Baked products and filling

  • Cereal and fruit

  • Yogurt and cereal

  • Ice cream and cone


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PowerBar

INGREDIENTS: High Fructose Corn Syrup With Grape And Pear Juice Concentrate, Maltodextrin, Raisins, Milk Protein Isolate, Whole Oats, Oat Bran, Rice Crisps (Milled Rice, Rice Bran), Brown Rice, Almond Butter, Glycerin, Natural Flavors, Spices

MINERALS: Calcium Phosphate, Magnesium Carbonate, Zinc Gluconate, Iron (Ferrous Fumarate), Copper Gluconate, Chromium Aspartat

VITAMINS: Vitamin C (Ascorbic Acid), Vitamin E Acetate, Vitamin B3 (Niacin), Pantothenic Acid (Calcium Pantothenate), Vitamin B6 (Pyridoxine Hydrochloride), Vitamin B2 (Riboflavin), Vitamin B1 (Thiamin Hydrochloride), Folic Acid, Biotin, Vitamin B12, ESSENTIAL AMINO ACIDS: Leucine, Valine, Isoleucine. 


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Macaroni into 2-cup microwavable cereal bowl. Add 2/3 cup water.

Macaroni and water, uncovered, on HIGH 3-1/2 to 4 minutes or until Macaroni is tender. DO NOT DRAIN. Some water remaining in bowl is desirable and necessary to make cheese sauce.CAUTION:Bowl will beVery Hot.

Cheese Sauce Mix; mix well. If cheese sauce appears thin, do not put back in microwave. Cheese sauce will thicken upon standing.


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Did you know results from a recent in-home taste test with raisin bran users - like you - showed that our flakes are crispier than Kellogg's® Raisin Bran's and stay crispier longer in milk?

Whole wheat, raisins, wheat bran, sugar, high fructose corn syrup, salt, malt flavoring, niacinamide, reduced iron, zinc oxide, pyridoxine hydrochloride (vitamin B6), riboflavin (vitamin B2), thiamin hydrochloride (vitamin B1), vitamin A palmitate, folic acid, vitamin B12 and vitamin D.

Raisin Bran

Kellogg's®

Shelf Life 12 Months


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Humectants raisin bran users - like you - showed that our flakes are crispier than Kellogg's

  • e.g.: sucrose, propylene glycol, glycerol

  • Be careful of:

    • Solubility, MW

    • Flavor

    • Crystallization on storage

    • Chemical reactivity

    • Toxicity


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