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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

Question 1

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

slide2

H2Og

H2Og

H2Og

H2Ol

H2Ol

H2Ol

H2Ol

H2Ol

H2Ol

vapor phase above water
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
question 2

Question 2

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

slide6

H2Og

H2Og

H2Og

solute

H2Ol

solute

H2Ol

solute

solute

H2Ol

H2Ol

vapor pressure above a solution
Vapor Pressure above a Solution

p0

Vapor pressure of water

IDEAL

1

0

Mole fraction of water

vapor above a solution
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
saturated solutions
Saturated Solutions

Solubility limit

Liquid phase concentration=solubility limit

p0

Vapor pressure of water

1

0

Mole fraction of water

question 3

Question 3

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

slide11

p0

Vapor pressure of water

IDEAL

1

0

Mole fraction of water

vapor depends on solution composition
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
question 4

Question 4

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

two solutions one container
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.
water activity

Water Activity

aw=p/po~%ERH

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

question 5

Question 5

How do these analogies translate to food?

slide18

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

moisture sorption isotherm
Moisture Sorption Isotherm

Moisture content (d.w.b.)

aw

slide22

Moisture Sorption Isotherm

Moisture content (d.w.b.)

aw

slide23

Zone 2

Zone 1

Moisture content (d.w.b.)

Zone 3

aw

Moisture Sorption Isotherm

slide24

Temperature Dependency

cold

Moisture content (d.w.b.)

hot

aw

sorption and desorption
Sorption and Desorption

desorption

Moisture content (d.w.b.)

sorption

moisture sorption isotherms
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
zones in isotherms
Zones in Isotherms
  • Zone 3: Bulk water
  • Zone 2: Loosely bound water
  • Zone 1: Tightly bound water.
reaction rates and water activity

Lipid oxidation

log (RATE)

Most reactions

Moisture content (d.w.b.)

SORPTION ISOTHERM

Microbial growth

aw

Reaction Rates and Water Activity
the gab model
The GAB Model

mo monolayer value

K multilayer parameter

C temperature dependency parameter

texture changes
Texture Changes

Crispy/crunchy

Moisture content (d.w.b.)

Soft

0.2-0.5

slide32

Powder Changes

Free flowing

Agglomerated

Moisture content (d.w.b.)

~0.4

slide34

Moisture Sorption Isotherm

Moisture content (d.w.b.)

aw

slide35

Moisture Sorption Isotherm

Moisture content (d.w.b.)

aw

multicomponent foods
Multicomponent Foods
  • Cheese and crackers
  • Baked products and filling
  • Cereal and fruit
  • Yogurt and cereal
  • Ice cream and cone
powerbar
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. 

slide38

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.

raisin bran

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

humectants
Humectants
  • e.g.: sucrose, propylene glycol, glycerol
  • Be careful of:
    • Solubility, MW
    • Flavor
    • Crystallization on storage
    • Chemical reactivity
    • Toxicity