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Question 1

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

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  1. 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 p0 Vapor pressure of water IDEAL 1 0 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 0 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 0 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?

  14. 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.

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

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

  17. 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

  18. Undissolved solute

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

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

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

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

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

  24. 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

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

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

  27. Rate of Oxidation of Potato Chips Monolayer moisture

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

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

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

  31. Dynamics of Moisture Exchange

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

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

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

  35. 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. 

  36. 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.

  37. 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

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

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