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?

H2Og H2Og H2Og H2Ol H2Ol H2Ol H2Ol H2Ol H2Ol

Vapor Pressure of Pure 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 How does water vapor partition from a solution into the surrounding gas?

H2Og H2Og H2Og solute H2Ol solute H2Ol solute solute H2Ol H2Ol

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

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 Solubility limit Liquid phase concentration=solubility limit p0 Vapor pressure of water 1 Mole fraction of water

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

p0 Vapor pressure of water IDEAL 1 Mole fraction of water

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 What happens when two different solutions are placed in the same 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 aw=p/po~%ERH Partial pressure of water above the solution normalized to the partial pressure above pure water.

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

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

Undissolved solute

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

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

Moisture Sorption Isotherm aw Moisture content (d.w.b.) Zone 3 Zone 2 Zone 1

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

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

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 Zone 3: Bulk water Zone 2: Loosely bound water Zone 1: Tightly bound water.

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

Rate of Oxidation of Potato Chips Monolayer moisture

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

Texture Changes Crispy/crunchy Moisture content (d.w.b.) Soft 0.2-0.5

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

Dynamics of Moisture Exchange                                                                                                                                    

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

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

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

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?

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.

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?

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