1. How does water vapor partition from a liquid into the surrounding gas?
Question 1
How does water vapor partition from a liquid into the surrounding gas?

2. H2Og
H2Og
H2Og
H2Ol
H2Ol
H2Ol
H2Ol
H2Ol
H2Ol

3. Vapor Pressure of Pure Water

4. 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

5. Question 2
How does water vapor partition from a solution into the surrounding gas?

6. H2Og
H2Og
H2Og
solute
H2Ol
solute
H2Ol
solute
solute
H2Ol
H2Ol

7. Vapor Pressure above a Solution
Vapor pressure of water
IDEAL 1
Mole fraction of water

8. 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

9. Saturated Solutions Solubility limit
Liquid phase concentration=solubility limit p0
Vapor pressure of water 1
Mole fraction of water

10. Question 3
How does the partitioning of water vapor from a solution depend on solution composition?

11. p0
Vapor pressure of water
IDEAL 1
Mole fraction of water

12. 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

13. Question 4
What happens when two different solutions are placed in the same container?

15. 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.

16. Water Activity aw=p/po~%ERH
Partial pressure of water above the solution normalized to the partial pressure above pure water.

17. How do these analogies translate to food?
Question 5
How do these analogies translate to food?

18. 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
Dried fruit .6
Cookies .3
Milk powder .2
Instant coffee

19. Undissolved solute

21. Moisture Sorption Isotherm
Moisture content (d.w.b.) aw

22. Moisture Sorption Isotherm
Moisture content (d.w.b.) aw

23. Moisture Sorption Isothermaw
Moisture content (d.w.b.)
Zone 3
Zone 2
Zone 1

24. Temperature Dependency
cold
Moisture content (d.w.b.)
hot aw

25. Sorption and Desorption
Moisture content (d.w.b.)
desorption
sorption

26. 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

27. Zones in Isotherms Zone 3: Bulk water Zone 2: Loosely bound water
Zone 1: Tightly bound water.

28. Reaction Rates and Water Activityaw
Moisture content (d.w.b.)
log (RATE)
Lipid oxidation
Most reactions
Microbial growth
SORPTION ISOTHERM

29. Rate of Oxidation of Potato Chips
Monolayer moisture

30. The GAB Model mo monolayer value K multilayer parameter
C temperature dependency parameter

31. Texture Changes
Crispy/crunchy
Moisture content (d.w.b.)
Soft

32. Powder Changes Free flowing Moisture content (d.w.b.) Agglomerated
~0.4

33. Dynamics of Moisture Exchange
                                                                                                                                   

34. Moisture Sorption Isotherm
Moisture content (d.w.b.) aw

35. Moisture Sorption Isotherm
Moisture content (d.w.b.) aw

36. Multicomponent Foods Cheese and crackers Baked products and filling
Cereal and fruit
Yogurt and cereal
Ice cream and cone

37. 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. 
What is the desired storage conditions/shelf life of this product?
What changes could limit shelf life?
What high and low aw limits would you recommend
How would you formulate the product to control the aw appropriately and what other quality issues would you be concerned about in your reformulation?

38. 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 be Very Hot.
                          
If this is a convenience product – why are the sauce and the pasta packaged separately.
How do you think moisture transport could limit the quality of this product if the ingredients were not packaged separately?
How could you reformulate to allow a single container primary packaging? What would be the advantages and disadvantages of your solution?
Cheese Sauce Mix; mix well. If cheese sauce appears thin, do not put back in microwave. Cheese sauce will thicken upon standing.

39. Raisin Bran
                   
              
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.
Kellogg's®
Shelf Life 12 Months
What are the moisture transport issues relevant to the storage of the product.
How could these changes alter the quality of the product?
How could you alter the product to minimize these effects? What other problems could your solutions cause?
          
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?

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