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nutr 2150 > lec 4 water > Flashcards

lec 4 water Flashcards

1
Q

What is the daily water intake recommendation?

A

About 1.5-2.5 L

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2
Q

What is water required for involviing molecules

A

HYdrolysis of large molecules

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3
Q

What are the primary ways water is lost from the body?

A

Evaporation, perspiration, urine, feces

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4
Q

What is the five biological function of water in the body?

A
  • Cellular structure
  • Nutrient transport
  • Lubrication
  • Metabolism
    Hydrolysis of macromolecules
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5
Q

What percentage of adult body weight is water? Birth weight ?

A

60% , 80 perecent

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6
Q

What is the extracellular water volume in liters? what does this include

A

12 L, Blood (90 water), lymph, digesta, interstitial fluid

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7
Q

How much water is intracellular

A

30 L

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8
Q

What is ratio of water in muscles and adipose

A

75% water, 12% water)

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9
Q

What controls urine production and water reabsorption in the kidneys?

A

Osmotic and hormonal control (vasopressin)

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10
Q

What is obligatory water loss?

A

Amount needed to dilute solutes from diet, mostly salt and urea

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11
Q

What do kidneys do?

A

FIiter blood and reabsorb 99 percent of water passing through them

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12
Q

What happens to the freezing point of water as salt is dissolved in it and if you put it in a glass of water

A

The freezing point lowers and volume decreases

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13
Q

What is cohesion in terms of water properties?

A

Molecules sticking together, being mutually attractive

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14
Q

What is adhesion in terms of water properties?

A

The tendency of dissimilar particles to cling together

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15
Q

Fill in the blank: Water can dissolve more substances than any other _______.

A

liquid

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16
Q

What changes occur in the hydrogen bond strength of water with temperature?

A

“The dipole moment of the water molecule changes, causing the hydrogen bond length and strength to vary with temperature.”

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17
Q

What is water activity?

A

A measure of the availability of water molecules for reactions

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18
Q

What does asymmetry cause to molecules

A
  • Strong Cohesion
  • Strong Adhesion
  • High Boiling and melting points
  • High latent heat of vaporization
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19
Q

What is the shape of methane, what is the dipole and what kind of interactions are there?

A

Tetrahedral (109.), no dipole moment, intermolecular interactions.

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20
Q

What is the shape of water, what is the charge, what is the dipole and what kind of interactions are there?

A

Bent configuration (asymmetry) of water (bond angle 104.5)
* Water has no net electric charge, one side is positive and the other is negative
* Strong dipole moment
* Hydrogen Bonds (12-30 kJ/mol)

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21
Q

Why is knowing water actvity important

A

MOre predictive of shelf life than just measuring water in food

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22
Q

What does waters large dipole moment disrupt?

A

disrupts the attraction between ions, breaking them apart and allowing them to dissolve.

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23
Q

What do negative ends of water dipole do.

A

They will orient themselves towards cations

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24
Q

What will positive ends of the same dipole do?

A

They will orient themselves towards anions

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25
Q

The positive and negative ends of dipole creates what?

A

Forms a hydration sphere about one layer deep around the ion. The water in this hydration sphere is typically called “bound water”.

26
Q

What is “Free Water” in foods and why is it significant?

A

Free water can make up over 90% of water in a food, as in orange juice. It is available for microbial growth and chemical reactions and can be easily removed from the product by squeezing or pressing.

27
Q

What is “Hydration (Bound, Visceral) Water” in foods?

A

It refers to water molecules associated directly with food macromolecules. They are:
-exchangeable, not covalently or H-bonded, -give structure to macromolecules,
-do not support microbial growth or chemical reactions,
-do not contribute to product deterioration. This water type is present even in dry foods, like powders.

28
Q

What are the characteristics of “Trapped (Capillary) Water” in foods

A

Trapped water makes up about 5% of a food’s total water,
-is associated with cellular structures, -cannot be easily pressed out,
-can be removed by drying.
It does not support microbial growth but provides a “moist” texture, as seen in dried fruits or vegetables

29
Q

At what water activity (aw) value does bacterial growth stop?

A

Bacterial growth stops below a water activity (aw) of 0.9.

30
Q

What aw values inhibit the growth of yeasts, molds, and bacteria?

A

Below 0.8, yeasts and bacteria stop growing; below 0.7, molds, yeasts, and bacteria stop growing.

31
Q

At what aw value do enzymatic and chemical reactions slow significantly or stop?

A

Enzymatic reactions slow or stop at aw = 0.5, and chemical reactions slow or stop at aw = 0.3.

32
Q

Which food components strongly interact with water? which dont

A

Salts and sugars strongly interact with water, while proteins do not interact as strongly.

33
Q

What physical states can water exist in? what can change its state?

A

Water can exist in gaseous, liquid, and solid states, unique among substances. Both temperature and pressure can change its state, useful in processes like evaporative drying and freeze drying

34
Q

What are the effects of freezing on food stability?
what are some cons

A

Freezing affects foods microbially (some survival), physically (ice formation), and chemically (cryo-concentration).
Storage prevents microbial growth but can lead to recrystallization and slow chemical reactions, while
thawing allows microbial growth, drip loss, and chemical decompartmentalization.

35
Q

What happens when water transitions from liquid to solid?

A

Water undergoes a liquid to solid state transition, forming ice

36
Q

How does the density of most compounds change as temperature increases?

A

For most compounds, as the temperature of the liquid increases, the density decreases.

37
Q

How many hydrogen bonds does each water molecule form in liquid water compared to ice?

A

In liquid water, each molecule hydrogen bonds with approximately 3.4 other water molecules, while in ice, each molecule is hydrogen-bonded to 4 other molecules.

38
Q

Why does ice float on water?

A

Ice floats because it crystallizes into an open structure that is 91% as dense as liquid water, making it less dense overall.

39
Q

What effect does ice formation have on tissue structure?

A

Ice formation can disrupt tissue structure.

40
Q

When water melts, what percentage of hydrogen bonds are broken, and what does this explain about water’s properties?

A

When ice melts, only 15% of hydrogen bonds are broken. This explains why water’s latent heat of fusion (333 kJ/kg) is much lower than its latent heat of vaporization (2230 kJ/kg). It also shows that liquid water is still very structured.

41
Q

What are colligative properties, and what do they depend on?

A

Colligative properties are properties of solutions that depend on the concentration of solute molecules or ions, but not on the identity of the solute.

42
Q

What are some examples of colligative properties?

A

Examples include vapor pressure lowering (Raoult’s Law), boiling point elevation, freezing point depression, and osmotic pressure.

43
Q

How does freezing point depression work as a colligative property?

A

Freezing point depression depends on solute concentration and molecular weight;

freezing causes solute molecules to concentrate in the unfrozen water, producing an unfrozen phase.

44
Q

What is the glassy, amorphous state, and how is it achieved?

A

Metastable, supercooled liquid state achieved by rapid cooling, which increases viscosity and prevents crystallization.

45
Q

Why is a glassy material not considered a true solid?

A

they are metastable and show no significant change in physical properties despite their solid-like viscosity.

46
Q

What makes it difficult to study glass behavior experimentally?

A

Glass behavior is challenging to study because extremely high viscosities require millions of years to observe any significant physical changes.

47
Q

What are some examples of glasses in foods?

A

Examples include dried pasta, spray-dried powders (e.g., protein supplements, starches, proteins, instant coffee), hard sugar candies, sugar in chocolate, and boiled sweets.

48
Q

Why is pure sucrose unable to form a glass, and why is this important in confections?

A

Pure sucrose cannot form a glass because it crystallizes instead, a process known as “doctoring.”
This matters in confections because controlling crystallization affects the texture of candies.

49
Q

What approach does molecular mobility provide for assessing food stability?

A

Molecular mobility provides a kinetic approach to food stability, while water activity is a thermodynamic approach.

50
Q

How does molecular mobility affect the shelf-stability of glasses?

A

Low molecular mobility in glasses is a predictor of food stability because it slows down deteriorative reactions, with some exceptions like free-radical oxidation that doesn’t rely on diffusion.

51
Q

How can the glass state be achieved in materials?

A

increasing concentration or lowering water content, especially in high molecular weight materials, or by lowering temperature.

52
Q

What is the glass transition temperature (Tg), and how does it relate to molecular weight?

A

Tg marks the point where a material transitions into a glass state. Higher molecular weight materials have higher Tg values, while low molecular weight carbohydrates have lower Tg values.

53
Q

What are the two main types of emulsions?

A

The two main types of emulsions are water-in-oil and oil-in-water.

54
Q

Give examples of water-in-oil and oil-in-water emulsions.

A

Butter, margarine, and lard are water-in-oil emulsions, while salad dressing and mayonnaise are oil-in-water emulsions.

55
Q

Why is an amphiphilic molecule necessary in an emulsion?

A

it is an emulsifier and is necessary because it helps stabilize the emulsion by allowing the hydrophobic phase to remain in the hydrophilic phase, preventing spontaneous separation.

56
Q

What are the main components needed to make an emulsion?

A

The main components needed are water, oil, an amphiphilic molecule (emulsifier), energy, and time.

57
Q

Why does emulsion destabilization occur in oil-in-water emulsions?

A

Emulsion destabilization occurs because the hydrophobic phase is insoluble in the hydrophilic phase and without an emulsifier, separation happens due to density differences and droplet size variations.

58
Q

How does droplet size affect emulsion stability?

A

Smaller droplets have higher internal pressure which increases the solubility of the dispersed phase, causing large droplets to grow at the expense of smaller droplets.

59
Q

How do proteins stabilize emulsions?

A

Proteins stabilize emulsions reducing interfacial tension where their hydrophobic sections interact with oil phase, and hydrophilic sections interact with the water.

60
Q

What is the Hydrophilic Lipophilic Balance (HLB), and how is it calculated?

A

The Hydrophilic Lipophilic Balance (HLB) is a measure of the balance between the hydrophilic and lipophilic portions of an emulsifier.

It is calculated as
HLB=20xMh/M
Mhis the molar mass of the hydrophilic portion, and M is the total molar mass.

61
Q

What do charged emulsifiers do?

A

Provides electrostatic repulsion (DLVO theory) or stearic repulsion (Gibbs Marangoni effect). This repulsion prevents particles from clumping together. It helps stabilize emulsions, keeping them smooth and consistent.

nutr 2150 (3 decks)

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