Enzymes

Question 1

Which enzymes are needed to degrade starch completely to glucose? And how do they act?

Answer 1

1) Glucoamylase –> exo-active
2) Alpha-amylase –> endo-active

Question 2

What starch degrading enzyme is [resent in wheat kernels?

Answer 2

Beta-amylase

Question 3

What are three main constituents of plant cell walls of cereals?

Answer 3

1) Cellulose
2) Hemicellulose
3) Lignin

Question 4

Which enzymes are needed to degrade cellulose completely into glucose?

Answer 4

1) Endo-glucanases
2) Cellobiohydrolase I and II (CBH)
3) Cellobiase (Beta-glucosidase)

Question 5

How do the three cellulose degrading enzymes act on the cellulose molecule?

Answer 5

1) Endo-glucanase acts on the amorphous-cellulose in synergy with CBH
2) Cellobiohydrolase (CBH) acts on the crystalline cellulose in synergy with endo-glucanase
3) Cellobiase can cleave a cellobiose molecule into two glucose molecules

Question 6

What are the enzymes that degrade pectin? And how do they act?

Answer 6

1) Pectin esterase
- Saponifies pectin with a high DE
- Methanol and pectin with low DE are formed
2) Pectin lyase
- Cleaves glycosidic linkages of pectin with high DE
- Forms a double bond next to the methylated carboxyl group (beta-elimination)
3) Pectate lyase
- Cleaces glycosidic linkages of pectin with low DE
- Beta-elimination
3) Polygalacturonase
- Cleaves next to free carboxyl group with use of water

Question 7

Which enzymes are needed to obtain a complete liquefaction of apples?

Answer 7

Pectinase and cellulase.

Question 8

What is the effect of pectinase and cellulase?

Answer 8

Pectinase reduces water binding capacity of pectic substances –> increasing juice yield. The juice will also be clear

Cellulases degrade the cell wall –> extremely high juice yield

Question 9

Which substance will be hydrolyzed faster by lipase? Whipped cream or whole milk?

Answer 9

Whipped cream, this is a homogenized emulsion where droplets increase the surface. Making it more likely for lipase to act on.

Question 10

What is the difference between a lipase and a lipoxygenase?

Answer 10

Lipase is a hydrolytic enzyme while lipoxygenase is an oxidoreductase enzyme.

Also,
Lipase cleaves off FA from the glycerol while lipoxygenase adds oxygen to form an unstable hydroperoxide.