Quiz 2

Question 1

crystalline solid characteristics

Answer 1

-arrangement: regular order
-Tg: no Tg for crystalline
-stability: more chemically stable than amorphous solids
-water interactions: adsorption,capillary condensation, deliquescence, crystal hydrate

Question 2

what is a maillard reaction

Answer 2

-maillard browning called non-enzymatic browning
-involves reaction between carbonyl of reducing sugar and an amine group
-generates flavors, aromas, and colors

Question 3

amorphous solid characteristics

Answer 3

-arrangement: disordered
-Tg: below Tg -> glass
above Tg -> rubber
-stability: less chemically stable than crystalline solids
-water interactions: absorption, adsorption & capillary condensation (often rate of absorption exceeds rate of adsorption/capillary condensation)

Question 4

how can crystalline change into amorphous solid or vice versa?

Answer 4

-if you disturb the crystalline lattice by grinding, desolvation or compaction then it will go into the amorphous state
-amorphous solids can recrystallize during storage
-amorphized: when crystalline is melted or dissolved then cooled or has water removal

Question 5

types of reducing sugars in maillard reactions

Answer 5

-aldoses generally more reactive than ketoses
-ketoses have higher activation energies
-exception is fructose more reactive than glucose
-aldehydes are more accessible and have a greater electrophilicity

Question 6

do smaller MW make reducing sugars more/less reactive? what is the order of the MWs of sugars?

Answer 6

-smaller MW = more reactive
-trioses > tetroses > pentoses > hexoses > disaccharides
-lower MW sugars have less steric hinderance and higher probability to be in the open form

Question 7

what is the reactivity of proteins in maillard reactions based on

Answer 7

-amino acid composition
-charge of the amino groups
-amine group is less reactive when positively charged
-lysine is the most maillard reactive amino acid due to the alpha amino acid

Question 8

first stage of maillard reactions

Answer 8

• non-protonated amine reacts with carbonyl of an acyclic sugar to form a Schiff base
  -can cyclize due to nucleophilic attack from an OH group to form a glucosylamine
  -OR undergo a reversible Amadori rearrangement

Question 9

what is an Amadori rearrangment

Answer 9

it is a proton transfer from the neighboring OH to form a N-ketosylamine (Amadori compound)

Question 10

what different pHs generate different compounds during maillard reactions

Answer 10

-schiff base can either form a glucosylamine OR amadori compound
-if the pH > 7 then it will form reductones or fission product (-> aldehydes)
-if pH < 7 then it will form a schiff compound

Question 11

how does pH affect maillard browning

Answer 11

-low pH conditions slow down maillard reactions

Question 12

environmental conditions that affect maillard browning

Answer 12

-high temperatures help exceed the high activation energies for initial condensation step of maillard browning
-sulfur dioxide and bisulfite ions can dec. browning by reacting with intermediate aldehyde containing maillard products before further reactions/ polymerization
-maximum rates of maillard browning occur at 0.6-0.7 Aw
-low pH conditions slow down maillard browning because they protonate the amine groups
-lysine is the most reactive due to alpha amine group
-more reducing sugars = more sugar ready to interact with amino acids = inc. maillard reaction

Question 13

which food product needs more maillard reactions vs. which need less maillard reactions

Answer 13

-dried egg powder: maillard reactions not promoted
-french fries: promoted but not too much
-pretzels: promoted

Question 14

what is caramelization?

Answer 14

thermal decomposition of sugars (reducing or nonreducing)

Question 15

what kind of acids and salts facilitate caramelization?

Answer 15

-acids ex. sulfuric, phosphoric, acetic, & citric acids
-salts ex. carbonates, phosphates, sulfates, & bisulfates

Question 16

what kinds of conditions cause caramelization to occur faster?

Answer 16

-high temperatures
-high pH

Question 17

different types of caramels & their applications

Answer 17

-Class 1 (plain caramel); whiskies, sauces, poultry coatings, & cocoa extenders
-Class 2 (caustic sulfite caramel); beer, rum, brandy, & cake mixes
-Class 3 (ammonium caramel); baked goods, syrups, puddings, soy sauce, BBQ sauce, & pet food
-Class 4 (sulfite ammonium caramel); balsamic vinegar, soft drinks, baked goods, sauces, meat rubs, dry seasonings, & candies
-Class 4 = most common

Question 18

how do you classify carbohydrates based on sugar units?

Answer 18

-monosaccharides (simple sugar)
-oligosaccharides (2-20 units)
-polysaccharides (> 20 units)

Question 19

examples of common monosaccharides

Answer 19

glucose, mannose, & galactose

Question 20

glucose vs. mannose vs. galactose

Answer 20

-glucose: C2 is down, C3 is up, C4 is down
-mannose: C2 is up, C3 is up, C4 is down
-galactose: C2 is down, C3 is up, C4 is up

Question 21

what is a D versus L sugar

Answer 21

-it is the location of the -OH on the highest # chiral carbon
-D = right “dexter”
-L = left “laevus”
-count chiral carbons based on carbonyl being at the top
-ring structure (sixth carbon):
D = up
L = down

Question 22

alpha vs beta

Answer 22

alpha: -OH is down (anomeric carbon = carbon 1)
beta: -OH is up

Question 23

cyclic vs. non-cyclic

Answer 23

-mutarotation: change btwn open chain vs. closed ring
-pyranose: 6 membered ring
-furanose: 5 membered ring
-sugars exist in a cyclic structure
-but, trace amounts in solution are in the acyclic form

Question 24

isomer

Answer 24

-isomers are molecules with the same elemental composition
-ex: fructose, glucose, galactose, and mannose

Question 25

enantiomers

Answer 25

-molecules that are mirror images of each other -ex: D and L sugars

Question 26

epimers

Answer 26

-molecules that have the same sequence of bonded atoms but in diff orientations/directions (stereoisomers) -ex: glucose, mannose, and galactose

Question 27

anomers

Answer 27

-epimers that differ in the anomeric carbon -ex: alpha and beta

Question 28

reducing sugars

Answer 28

-reducing sugars are monosaccharides or the end (usually right side) of poly(di)-saccharides that are capable of reducing an oxidizing agent using a free aldehyde or ketone -ex: monosaccharides / most oligosaccharides (NOT sucrose, trehalose, raffinose, and stachyose) ex: lactose -sugar alcohols are NOT reducing sugars -can be identified if there is a reactive (free) anomeric carbon

Question 29

what do non reducing sugars NOT have

Answer 29

a free anomeric carbon

Question 30

where does the name reducing sugar come from?

Answer 30

-bc sugar is oxidized and reduces copper (II) to copper (I) in an alkaline solution

Question 31

sugar alcohols & their functions

Answer 31

-are reduced sugars (are NOT reducing) -can no longer form ring structures -bulk ingredient & sweetener in reduced sugar & sugar free candies and gums -functions: doesn't participate in maillard browning doesn't ferment (non cariogenic) -> won't cause tooth decay -pros: cooling effects -cons: laxative effects -ex: sorbitol, xylitol (itol ending)

Question 32

sugar acids

Answer 32

-ex: D-glucono-delta-lactone (GDL) or gluconic acid, aldonolactones, aldonic acids -GDL undergoes hydrolysis in solution -> lowers the pH & has milk flavor -good for meats, dairy products, and chemically leavened doughs

Question 33

differences btwn sucrose & lactose

Answer 33

SUCROSE: -D-glucose + D-fructose -alpha 1 to beta 2 glycosidic linkage -is NOT a reducing sugar LACTOSE -glucose + galactose -1, 4 beta glycosidic bond - is a reducing sugar