Exam 1

Question 1

continuous or dispersed phases of emulsions, foams, gels, and suspensions?

Answer 1

*emulsions: liquids
*gels: solids and liquid
*suspension: liquid and solid
*foams: solid/liquid and gas

Question 2

water content

Answer 2

how much water a system has

Question 3

water activity

Answer 3

the availability of water for biological and chemical reactions in a substance

Question 4

why is the water activity of 50g of sand in 100 g of water different from 50 g of sucrose in 100 g of water

Answer 4

-sucrose is soluble in water while sand is not
-sucrose forms hydrogen bonds with water molecules reducing the water activity

Question 5

if a small amt of water was added to this amorphous solid, what would happen to the Tg and why?

Answer 5

adding water can significantly inc. the molecular flexibility and interaction with the polymer matrix, leading to dec. in Tg

Question 6

Scenario: You are working on a fruit-filled bar product that has a crispy crust and a soft filling. You need to make sure water does not migrate from the filling into the crust. Do you focus on equilibrating the moisture contents or the water activities of the crust and filling (and why)? What will you do to stop the moisture migration (how will you equilibrate the moisture content or water activity to maintain product quality)?

Answer 6

-focus on equilibrating water activity of the crust
-moisture migration depends on the water activity not moisture content
-how will you stop? sealed packaging and dried environment

Question 7

Define the boiling point of water using the concept of vapor pressure

Answer 7

-higher atmospheric pressure = higher boiling point
-boiling pt = temp at which the std vapor pressure of a liquid is equal to the surrounding atmospheric pressure
-for water the vapor pressure reaches the std sea level atmospheric pressure of 750 mmHg at 100 C
-higher vapor pressure, lower boiling point

Question 8

how do solutes affect the boiling point of a solution?

Answer 8

solutes inc the boiling point as they reduce the vapor pressure of the liquid

Question 9

Describe the five mechanisms by which water interacts with solids (think powder interacting with environmental humidity).

Answer 9

Adsorption, capillary condensation, deliquescence, absorption, crystal hydrate

Question 10

why are amorphous solids more hygroscopic than crystalline solids

Answer 10

-lowest energy state
-crystal lattice structure
-adsorb not absorb

Question 11

general methods to measure water activity

Answer 11

-hygrometer
-dew point analyzer

Question 12

describe how a hygrometer and dew point analyzer work

Question 13

Sigmoidal or S-shaped sorption isotherms (type 2) are most common for food components (containing amorphous solids). Describe the three classifications of water based on such isotherms.

Answer 13

-Zone I: bound
-Zone II: immobilized
-Zone III: free

Question 14

Define and describe the structure of a native starch granule. Is this digestible - why/why not?

Answer 14

-native starch granules are found as small water insoluble granules
-botanical energy storage vessels that can be found throughout the plant (size and shape vary between botanical species)
-slowly slowly and resistant starch
-amylopectin with long chains showed a comparably higher content of SDS than amylopectin with short chain

Question 15

Describe an amylose-lipid complex and why does it occur?

Answer 15

-complex between amylose and lipid that forms amorphous or highly crystalline structures
-occurs when starch is heated subsequently slowly cooled, causing modifications in its crystalline structure

Question 16

Define gelatinization and describe what happens to the starch granule during gelatinization. Compare and contrast gelation and gelatinization.

Answer 16

Early studies showed that amylose forms opaque, partially crystalline, thermo-irreversible gels. The earliest models of gelatin envisaged a molecular network in which each amylose molecule participated in several ‘crystalline’ junction zones.

Question 17

Define retrogradation and describe what happens to the starch structure during retrogradation. How does this relate to bread staling?

Answer 17

-recrystallization of gelatinized starch
-upon cooling, starch paste forms a firm gel due to onset of retrogradation (primarily
amylose)
-amylose retrogrades rapidly
-amylopectin retrogrades more slowly
-amylopectin retrogradation is correlated to bread staling and crumb firmness

Question 18

Give examples of monosaccharides used in foods.

Answer 18

-fructose
-galactose
-glucose

Question 19

Give examples of disaccharides, trisaccharides, and tetrasaccharides.

Answer 19

-Disaccharides: isomaltulose (glucose-fructose), maltose (glucose-glucose), lactose (galactose-glucose)

-Trisaccharides: raffinose (galactose-glucose-fructose), maltotriulose (glucose-glucose-fructose)

-Tetrasaccharides: lychnose, stachyose

Question 20

What makes sugar a reducing sugar?

Answer 20

Reactive free aldehyde or ketone

Question 21

Why are carbohydrates water-soluble? What makes a carbohydrate more or less soluble?

Answer 21

Carbohydrates are soluble in water bc they are hydrophilic; have a strong attraction to water
-the more monomers you put into the carbohydrate chain, the less soluble it gets (trisaccharides, tetrasaccharides)
-monosaccharides and disaccharides (soluble)

Question 22

Why do sugars crystallize? How can the crystallization of sugars be delayed or prevented?

Answer 22

Impurities that delay crystal nucleation and growth by interference and dilution avoid nucleation sites, tempe and RH avoid approaching or exceeding Tg

Question 23

What is starch retrogradation? Name several benefits and several drawbacks.

Answer 23

Resistant starches, slowly digestible, blood glucose low, crystals are not readily broken, reduced weight gain; staling, firmness of breads