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2) Food Chemistry I > Water II > Flashcards

Water II Flashcards

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1
Q

How do we derive a moisture sorption isotherm?

A
  • Food product is dried completely and then place in an enclosed chamber
  • The chamber is above a specific salt solution, each of which generate a specific Aw
  • Samples are weighed after they are in equilibrium to determine the amount of moisture absorbed
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2
Q

Aw is directly related to _________ at a constant ________, which is much easier to measure

A

Equilibrium Relative Humidity (ERH)

temperature

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3
Q

When deriving a moisture sorption isotherm, it is important that the chambers are _________ of known ERH

A

hermetically sealed

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4
Q

In the derivation of a moisture sorption isotherm, when the sample at equilibrium is weighed, it provides you with information on the _________

A

equilibrium moisture content

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5
Q

A plot of ___________ vs. ___ or _____ provides the moisture sorption isotherm

A

equilibrium moisture content
Aw
ERH

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6
Q

The moisture sorption isotherm illustrates how the food product would behave as a function of __________ in terms of water adsorption or loss at a given temperature

A

relative humidity

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7
Q

Moisture sorption plots are ________ dependent

A

temperature

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8
Q

In moisture sorption isotherm, ______ commonly occurs when the curve is different dependent on whether the product starts out dry or moist

A

hysteresis

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9
Q

When does hysteresis occur?

A

When the curve is different dependent on whether the product starts out dry or moist

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10
Q

Why does hysteresis occur?

A

Permanent changes in the product (structural/chemical) that have taken place due to changes in moisture content

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11
Q

Except in very simple systems, the moisture sorption curves will show _______.

A

hysteresis

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12
Q

Moisture sorption information defines how a product picks up or loses _______ under specified conditions (relative humidity).

A

moisture

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13
Q

What are the uses of the moisture sorption data?

A
  • Determines the final moisture content from a drying operation
  • Aw is related to textural changes
  • Helps in selection of packaging materials
  • Allows the evaluation of effects of compounds that can be used to modify the Aw profile of a product
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14
Q

Moisture sorption data provides important information about the relative stability of a product in regards to what? (2)

A
  • The type of microbial growth possible

- The types of reactions that may predominate in a food system

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15
Q

Which compound may be used to modify the Aw profile of a product?

A

Sorbitol

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16
Q

Which five factors are a major concern to water activity?

A

1) Enzymatic reactions
2) Lipid oxidation
3) Hydrolytic reactions
4) Non-enzymatic browning
5) Various forms of microbial growth

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17
Q

Most reactions are _________ functions of water activity

A

exponential

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18
Q

A slight reduction of water activity will have a significant effect in (increases/reducing) the rate of a reaction

A

reducing

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19
Q

A break point for many reactions lies around Aw = _____

A

0.80

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20
Q

Aw has to be reduced down to about ________ to reach a minimum for most of the deteriorative reactions.

A

0.3-0.4

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21
Q

What is the water activity value/region where all reactions are stopped?

A

There is none, but the optimum appears to be Aw = 0.3-0.4

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22
Q

What are three ways to control water activity?

A
  • Remove water
  • Convert the free water to bound water
  • Freeze food
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23
Q

What are the consequences of removing water?

A
  • Can change the physical nature of the food

- Alter its color, texture, and/or flavor

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24
Q

How can you convert free water to bound water?

A

Addition of sugars, salts, or other water-soluble agents

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25
Q

Freezing _______ the water and (increases/decreases) the Aw

A

immobilizes

decreases

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26
Q

Should all foods be frozen?

A

No, not all foods can/should since frozen foods will eventually be thawed

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27
Q

The use of multiple barriers based on Aw, pH, ionic strength, modification of atmosphere, etc. is called the __________ concept

A

hurdle

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28
Q

What are the two general categories of food systems?

A

1) Intact edible tissues

2) Food dispersions

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29
Q

_________ refers to natural biological systems (plant and animal tissues), which are very complex

A

Intact edible tissues

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30
Q

________ refers to complex systems that are usually man-made

A

Food dispersions

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31
Q

What is a dispersion?

A

System consisting of one or more discontinuous phases (dispersed) in a continuous system

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32
Q

What are the three types of solutions?

A

1) True solutions (molecular dispersions)
2) Colloidal dispersions
3) Suspensions

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33
Q

In ________, molecules and ions are present at their lowest subdivision

A

true solutions

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34
Q

In ________, the particles are <0.1 μm in diameter.

A

true solutions

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35
Q

In ________ the solution formed is transparent.

A

true solutions

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36
Q

In ________, the solution has high osmotic pressure

A

true solutions

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37
Q

In ________, the solution passes through parchment membranes

A

true solutions

38
Q

If the solution does not pass through a parchment membrane but does
not settle under the force of gravity, it is considered to be __________

A

colloidal

39
Q

__________ are usually a macromolecule or an aggregate of a smaller molecule, with a size range of 0.1 - 1 um

A

Colloids

40
Q

In ________, the solution has significantly reduced osmotic pressure

A

colloids

41
Q

In _______, the may be transparent but is often translucent - scatters light.

A

colloids

42
Q

True _______ solutions do not settle out of solution and may aggregate to form gels

A

colloid

43
Q

_________ are generally opaque, and suspended material can be
filtered out, or settle-out with time

A

Suspensions

44
Q

________ show negligible or no measurable osmotic pressure

A

Suspensions

45
Q

Place the three solutions in order of their particle size (smallest to largest):

A

True solutions < Colloids < Suspensions

46
Q

Ungelatinized starch granules will form a _______ when stirred, but soon settle out.

A

suspension

47
Q

Gelatinized starch forms a ___________ or gel depending on concentration.

A

colloidal solution

48
Q

True solutions are considered to be ______ systems, while colloidal solutions and suspensions are considered to be _______ systems.

A

uniphasic

biphasic

49
Q

The conversion of a true molecular solution to a colloidal solution often takes place when ____________ are involved.

A

macromolecules

50
Q

If the overall __________ (which depend on pH) are not too great, macromolecules can associate via various mechanisms

A

charge repulsions

51
Q

Particles can be built up which eventually obtain enough charge to prevent further association and will stay stable in a _______ form in solution.

A

colloidal

52
Q

Wastewater from food processing plants often contains substantial amounts of ______ material

A

colloidal

53
Q

a common method of wastewater treatment is to convert these _______ solutions into _________ that will settle out by adding salts to neutralize the charge of the colloids

A

colloidal

suspensions

54
Q

The formation of colloids is the result of what? (4)

A
  • Electrostatic interactions
  • Hydrogen bonding
  • Hydrophobic interactions
  • Hydrophobic/hydrophilic associations
55
Q

The formation of colloidal solutions via _________________________ is the basis of many common food dispersions:

A

hydrophobic/hydrophilic associations

56
Q

A liquid in a liquid forms an ________

A

emulsion

57
Q

A gas in a liquid forms a ________

A

foam

58
Q

A liquid in a solid forms a ___________

A

solid emulsion

59
Q

A gas in a solid forms a __________

A

solid foam

60
Q

Both ______ and _______ involve the dispersion of a hydrophobic material in a hydrophilic material or vice versa.

A

emulsions

foams

61
Q

______ and _______ are unfavorable from a free energy standpoint

A

Emulsions

foams

62
Q

High __________/__________ can be reduced by _______ or ________ via hydrophobic/hydrophilic associations.

A

intersurfacial tension
surface tension
emulsifiers
surfactants

63
Q

Any compound that has both hydrophilic and hydrophobic groups in its molecular structure usually has the property of being a ____________ agent, more commonly termed a ________.

A

surface-active

surfactant

64
Q

All _________ have the property of reducing the surface tension of water significantly, causing foaming, and can form emulsions.

A

surfactants

65
Q

_______ is the equivalent for surfactants in terms of food applications

A

Emulsifiers

66
Q

When emulsifiers or surfactants are dissolved in water, they (are/are not) uniformnly distributed in a molecular solution

A

are not

67
Q

Initially, emulsifiers and surfactants are found to be near the solution’s _________

A

surface

68
Q

Air-water interface is the location of the lowest __________ for emulsifiers and surface-active compounds

A

free energy state

69
Q

The hydrophobic ends orient themselves toward ________ air, while the ________ ends will orient themselves into the water.

A

hydrophobic

hydrophilic

70
Q

The reorientations of emulsifiers and surfactants (increases/reduces) the surface tension of water

A

reduces

71
Q

Emulsifiers and surfactants are capable of forming colloid-like particles called ______

A

micelles

72
Q

If the concentration of an emulsifier or surfactant added to a solution is increased beyond the surface-covering capacity, then _______ are formed in the solution.

A

micelles

73
Q

Micelles form so as to reduce the free energy of the solution after the air/water interface has been ________.

A

saturated

74
Q

The rapid decrease in surface tension represents the surfactant molecules going to the ________ of the liquid.

A

surface

75
Q

After micelle formation, how does the surface tension change with increased surfactant concentration?

A

Does not change significantly

76
Q

Phospholipids and monoglycerides can be used as _______

A

emulsifiers

77
Q

Emulsions (increases/decreases) the viscosity of a system

A

increases

78
Q

The opacity of an emulsion is a function of the __________ of the dispersed phase, which is a function of the _______ put into the system.

A

droplet size

energy

79
Q

What is the size of a droplet size which can distinguish phases?

A

Macroglobules (> 1 um)

80
Q

What is the size of a droplet size which is milky white?

A

1 um

81
Q

What is the size of a droplet size which is bluish white?

A

1 um - 0.1 um

82
Q

What is the size of a droplet size which is gray-semitransparent white?

A

0.1 um - 0.05 um

83
Q

What is the size of a droplet size which is clear?

A

< 0.05 um

84
Q

What are the two basic categories of emulsifiers?

A
  • Non-ionic

- Ionic

85
Q

_______ emulsifiers are the most important and widely used group because they are insensitive to ______

A

Non-ionic

pH

86
Q

What are the three types of non-ionic emulsifiers?

A

1) Emulsifiers based on glycerol esters and their non-charged derivatives
2) Sorbitan derivatives
3) Esters of polyhydric compounds

87
Q

The use of emulsifiers ______________ began when glycerol was added to fats with a small amount of base to interesterify the fat to produce some ________

A

based on glycerol esters

monoglycerides

88
Q

Emulsifiers based on glycerol esters were termed __________, and contained __% monoglycerides

A

superglycerinated shortening

3

89
Q

_________ greatly enhanced cake volume, especially with high sugar levels

A

Emulsifiers based on glycerol esters (non-ionic emulsifiers)

90
Q

Nowadays, pure monoglycerides/diglycerides are manufactured by ____________ followed by ____________ to obtain relatively pure fractions.

A

interesterification

fractional distillation

91
Q

Fatty acid composition of monoglyceride affects its properties, and its plasticity is controlled by its overall __________

A

iodine value

92
Q

___________ monoglycerides have IVs of 19-36, while __________ have IVs of 65-67.

A

Dry powdered

plastic emulsifiers

2) Food Chemistry I (31 decks)

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