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2) Food Chemistry I > Water I > Flashcards

Water I Flashcards

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1
Q

Water can serve as a stabilizer of _________ configuration, composed of _______ and ________

A

biopolymer
proteins
carbohydrates

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2
Q

Which foods contain the highest water content?

A
  • Tomatoes, lettuce (95%)
  • Apple juice, milk (87%)
  • Potato (78%)
  • Meats (65-70%)
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3
Q

How much water does shortening contain?

A

0%

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4
Q

Texture is often associated with _______

A

moisture

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5
Q

Which three components are extremely important in terms of stability and acceptability?

A
  • Amount of water
  • Location of water
  • Interactions with the chemical components
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6
Q

What are the three methods to reduce the water activity of a system?

A
  • Freezing
  • Concentration
  • Dehydration
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7
Q

Is water the only compound that exists in all three states on Earth?

A

Yes

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8
Q

Water is a hydrate of _______

A

oygen

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9
Q

What are the hydrates of atoms (apart from water) across the periodic table? What are their properties?

A
  • CH4, NH3, HF

- Gases

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10
Q

What are the hydrates of atoms (apart from water) down the periodic table? What are their properties?

A
  • H2S, H2Se, H2Te

- Gases

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11
Q

Relative to the other hydrates, water is unusual in all of its physical properties. What are the 7 unusual physical properties?

A
  • Melting point
  • Boiling point
  • Surface tension
  • Dielectric constant
  • Heat of fusion
  • Heat of vaporization
  • Heat of sublimation
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12
Q

Oxygen has ___ electrons, ___ of which are valence electrons, and the two hydrogens have ___ electrons each

A

8
6
1

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13
Q

The _____ 2p orbitals and the ____ 2s orbitals of the oxygen atom are combined to form _____ sp^3 hybrid orbitals

A

3
1
4

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14
Q

What combines to form four sp^3 hybrid orbitals?

A
  • Three 2p orbitals

- One 2s orbital

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15
Q

Only ___ of oxygen’s ___ valence electrons are used up in the two covalent bonds that form between H and O

A

2

6

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16
Q

There are ___ oxygen lone electron pairs left in ____ of the sp3 orbitals

A

2

2

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17
Q

Why is oxygen a highly electronegative atom?

A

Because of its lone electron pairs

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18
Q

The electron from the hydrogen is drawn more towards the ______, which results in the (increase/decrease) of the electron shield around the hydrogen atom

A

oxygen

decrease

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19
Q

The hydrogen is slightly ______, while the oxygen is slightly _______

A

positive

negative

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20
Q

Water molecules can therefore be viewed as having ____ electron-rich regions and ____ electron-poor regions situated __________.

A

two
two
tetradehedrally

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21
Q

The ________ nature of the spatial arrangement of these regions of electron density promotes the ability to form a _____________ or network.

A

tetrahedral

3D association

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22
Q

Associations due to differential electron density between hydrogen and other electronegative atoms are termed ____________

A

hydrogen bonding

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23
Q

___________ is the basis for water vapor accumulation in the atmosphere, leading to formation of clouds.

A

Hydrogen bonding

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24
Q

Because water is capable of hydrogen bonding in three dimensions, ____________________ can form.

A

local regions of structure

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25
Q

In the liquid phase, water is considered to have “_________” structure, termed ”__________”

A

transitional

flickering clusters

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26
Q

The term “flickering clusters” is associated with which phase of water?

A

Liquid

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27
Q

Flickering clusters are regions of 3D H-bonded water molecules somewhat similar in structure to ________

A

ice

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28
Q

Flickering clusters continually _____ and ______

A

form

break up

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29
Q

The number of flickering clusters (increases/decreases) with temperature, and the number of molecules per cluster (increases/decreases)

A

increases

decreases

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30
Q

Flickering clusters (do/don’t) exist at the boiling point of water

A

do

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31
Q

_____________ have been postulated to explain the relatively normal (low) viscosity of water.

A

Flickering clusters

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32
Q

Ionic compounds ionize into ions in water due to the _________ of water

A

polar nature

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33
Q

Polarity is due to ____________

A

asymmetric electron density

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34
Q

Polarity is (sufficient/insufficient) to break covalent bonds

A

insufficient

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35
Q

Polarity is (sufficient/insufficient) to break ionic bonds

A

sufficient

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36
Q

Polarity can dissociate ionic bonds by allowing multiple water molecules to act as __________ for opposing charged ionic species

A

counterions

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37
Q

When NaCl is dissolved in water, ________ are attracted to chlorine, while _________ are attracted to sodium

A

hydrogen (+)

oxygen (-)

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38
Q

When an ion is dissolved in water, a __________ forms around each ion to ___________ the charge of the respective ions.

A

hydration shell

neutralize

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39
Q

When an ion is dissolved in water, the formation of a ______________ forces the water into a specific orientation around each ion, therefore disrupting the normal structure of water.

A

hydration shell

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40
Q

The formation of bulky hydrates generally causes an (increase/decrease) in viscosity and tends to (increase/decrease) the freezing point of the system.

A

increase

decrease

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41
Q

Hydrogen bonding compounds are also capable of disrupting the __________ of water.

A

tetrahedral geometry

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42
Q

The overall manner of hydrogen-bonding compounds is similar to ___________

A

ionic compounds

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43
Q

In the case of macromolecules that have a large number of hydrogen bonding sites (polypeptides, proteins, carbohydrates, and polysaccharides), the water can be completely or extensively _________ by hydrogen bonding if the amount of water present is limited.

A

immobilized

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44
Q

When low concentrations of nonpolar substances are dissolved in water, __________ are induced.

A

ice-like inclusions

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45
Q

The formation of an __________ around a nonpolar group or molecule is to (maximize/minimize) the free energy state of the system when symmetric electron-neutral constituents (hydrophobic) and asymmetric electron-rich hydrophilic materials are forced to associate.

A

ice-like structure minimize

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46
Q

Are ice-like inclusions structurally identical to ice?

A

No, it is a semi-crystalline form that is produced

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47
Q

The semi-crystalline form of ice-like inclusions are termed “______________”

A

clathrate hydrates

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48
Q

Define clathrate compounds (important).

A

Compounds which are not formed by the action of valence bonds, but by molecular imprisonment

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49
Q

_________ structures are important in stabilizing protein structure around hydrophobic moieties.

A

Clathrate hydrate

50
Q

Clathrate compounds are formed by _________

A

molecular imprisonment

51
Q

Does the presence of all solutes have a disruptive effect on the structure of water?

A

Yes

52
Q

What is the activity of water?

A

Its freedom of movement

53
Q

The activity of water is (increased/reduced) when a solute is added

A

reduced

54
Q

In the freezing of water, the flickering cluster becomes a _________ or ________, due to a decrease in _______

A

minute crystal
nucleus
kinetic energy

55
Q

In the freezing of water, what can happen to the nucleus?

A

Can grow in size as more water molecules fit into the 3D crystal lattice

56
Q

At 0oC there is an equilibrium between __________ and liquid water.

A

crystal nucleation

57
Q

In ultrapure water, _______ is difficult and does not readily take place

A

nucleation

58
Q

In ultrapure water, _______ can occur when the water stays liquid well below 0oC

A

supercooling

59
Q

Supercooled water will freeze (quickly/slowly) if disturbed, or if an ice crystal is thrown in

A

quickly

60
Q

In normal water, ___________ often aid the start of the nucleation process

A

impurities (dust, container wall surface)

61
Q

If the rate of freezing is slow, (many/few) nuclei are formed at any one time

A

few

62
Q

If the rate of freezing is slow, the net result is the formation of _____________

A

few large ice crystals

63
Q

If the rate of heat removal is rapid, (many/few) nuclei will form at the outset, leading to the formation of ___________

A

many

smaller ice crystals

64
Q

Explain the differences between freezing slowly and quickly in tissue systems.

A
  • Slowly: large ice crystals form, which can damage cell walls (reduces water holding ability)
  • Rapidly: small ice crystals formed uniformly
65
Q

______ interfere with the nucleation process and also slow down the rate of diffusion of water to the ice crystals

A

Solutes

66
Q

Once nucleation has taken place and water diffuses to the surface of the crystal, the solutes become (more/less) concentrated as the freezing process takes place.

A

more

67
Q

The increased concentration of solutes leads to the (increase/decrease) of the freezing point since a _____ temperature is required for ice to form

A

decrease

lower

68
Q

At a low enough temperature, called the _______ point, the solution can become concentrated to a point at which the remaining water will co-crystallize with the solute crystals to start to form and grow

A

eutectic

69
Q

The ______ point lies between -55oC and -70oC

A

eutectic

70
Q

When the eutectic point has been reached, all the water in the
system is ________.

A

immobilized

71
Q

Why is total stability not attained in a frozen food product?

A

Since not all the water is immobilized (at the eutectic point); temperatures required for this are too low

72
Q

Free water freezes quite (quickly/slowly), and once crystal growth is induced, then the concentration of solutes (increases/decreases)

A

quickly

increases

73
Q

Within a biological sample (cells), the _________ will be disrupted if large ice crystals form.

A

organelles

74
Q

Which solutes will concentration in the freezing process?

A

Salts, ions, enzymes

75
Q

Why would a highly concentrated solution not freeze totally?

A

Because the temperature is well above the eutectic point

76
Q

If the highly concentrated solution is not totally frozen, water is still available to act as a ________ and the reaction medium is very _________

A

reactant

concentrated

77
Q

Can reactions still take place at low temperatures?

A

Yes, especially enzymatic reactions because the substrate and enzyme may be mixed due to tissue disruption

78
Q

Which two factors (that denature proteins) may affect water holding capacity?

A
  • Ionic strength

- pH changes

79
Q

Do frozen foods have a perpetual shelf-life?

A

No since they are not frozen to the eutectic point; enzymatic reactions may still take place

80
Q

Because enzymatic reactions carry on under conditions of frozen storage, fruits and vegetables have to be ________ (mild heat treatment) before being frozen.

A

blanched

81
Q

All enzymatic reactions speed up when the _________ process is started - much of the quality is lost in this step rather than during frozen storage.

A

thawing

82
Q

______ water is relatively mobile, while _______ water is relatively immobile

A

Free

bound

83
Q

What is a way to measure the mobility of water?

A

Water activity

84
Q

The water activity is on a scale from ___ to ___, with ___ being pure water

A

0
1
1

85
Q

What is the equation for water activity?

A 
Aw = P/P0(T)
P = partial pressure of the food matrix
P0 = partial pressure of pure water
T = temperature
86
Q

A sealed container containing water comes to an equilibrium between ________ and its _________ at any constant temperature.

A

liquid water

vapor form

87
Q

A 25% NaCl solution would lead to the partial pressure (or RH) being (increased/reduced) significantly.

A

reduced

88
Q

Salt dissolved in water (increases/decreases) its freedom of movement

A

decreases

89
Q

Any solute (increases/reduces) the activity of water

A

reduces

90
Q

The ratio of the ____________ is a useful measure of the relative mobility, activity, or availability of water.

A

partial pressures

91
Q

We can classify water in foods based on their ________ ranges.

A

water activity

92
Q

Type ____ water has an Aw of 1

A

IV (pure)

93
Q

Type ____ water has an Aw of 0.99 to 0.80

A

III

94
Q

Water that is physically entrapped in the tissue matrix is type _____ water

A

III

95
Q

Type ____ water contains some solutes but not enough to immobilize the water in any
major way.

A

III

96
Q

In type ____ water, many microorganisms are capable of growth, with some bacteria and yeasts inhibited at the lower end of the range.

A

III

97
Q

In type ___ water, most hydrolytic, oxidative, and enzymatic reactions proceed readily in this water activity range.

A

III

98
Q

Is the freezing point of water depressed in type III water?

A

Not significantly

99
Q

Type ___ water has an Aw of 0.80 to 0.25

A

II

100
Q

Type ___ water is the water present in macrocapillaries

A

III

101
Q

Type ___ water is broad-range water present in microcapillaries to the outer layers of “bound water”

A

II

102
Q

In type ____ water

most microbial growth is halted, with the exception of some molds at the upper end of this range.

A

II

103
Q

In type ____ water , the freezing point of water is significantly reduced and most enzymatic reactions requiring water are slowed significantly

A

II

104
Q

Non-enzymatic browning takes place readily with heat at the upper end range of type ____ water

A

II

105
Q

In type II water, non-enzymatic browning takes place with heat at the (upper/lower) range, and without heat at the (upper/lower)

A

upper

lower

106
Q

Type ___ water has an Aw of 0.25 to 0

A

I

107
Q

Type ___ water refers to bound monolayers of water directly hydrogen-bonded to molecules

A

I

108
Q

Type ____ water is very strongly hydrogen-bonded to the molecules and an integral part of the molecular structure

A

I

109
Q

Type ___ water is essentially immobile

A

I

110
Q

Type ____ water is very difficult to remove and cannot be frozen

A

I

111
Q

In type I water, most reactions are minimal with the exception of ________

A

autoxidation

112
Q

______ occurs when a wet food is placed in a dry environment

A

Desorption

113
Q

Desorption is analogous to _______, but not the same

A

dehydration

114
Q

Differentiate desorption and dehydration.

A

Desorption: food is moving towards equilibrium with the environment
Dehydration: permanent loss of water from a food

115
Q

Desorption results in an (increase/decrease) in Aw, while dehydration results in an (increase/decrease) in Aw

A

decrease

decrease

116
Q

Desorption is generally a (fast/slow) process

A

slow

117
Q

________ occurs when a dry food is placed in a wet environment

A

Adsorption

118
Q

Adsorption results in an (increase/decrease) in Aw

A

increase

119
Q

The term “________” is used to describe foods or chemicals that adsorb moisture

A

hygroscopic

120
Q

Define supercooling. In what kind of water can it occur in?

A
  • Water stays liquid well below 0oC

- Ultrapure water

2) Food Chemistry I (31 decks)

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