Enzymology Flashcards
What is Koji
Koji is a steamed rice which had koji mold spores cultivated onto it. It involves the degradation of starch, protein and plant cell walls.
What is sake?
Same principle of wine. However, in sake rice is used instead of grapes which have not easily breakable sugars. Therefore koji mold is added which breaks down the starch into sugar which can be then fermented by the yeast.
How is soy sauce made?
Is a fermented paste of boiled soybeans, roasted grain and brine and additionally koji mold (aspergillus oryzae)
How is tempeh made?
Controlled fermentation of soybean with Rhizopus spp. Rich in protein, fibre and vitamins.
Which are example of fermentation gums and where are they used?
Xanthan and Gellan gum. Used in dressing, sauces and beverages.
What are enzymes useful for?
Cell wall degradation, release of small molecules
Enzyme , what is the effect on food?
formation of aroma compounds, color, texture properties, improvement of nutritional quality -> better digestibility.
Is the size of starch granules the same between different foods?
No, they differ
Can raw starch be degraded? In which conditions is starch usually degraded?
Some amylase can degrade raw starch but usually starch is degraded at Temp >60C as starch becomes soluble which increase accessibility of amylase.
What are the two type of starches and how do they differ in linkages?
Amylose - alpha-(1->4)-linkage (linear)
Amylopectin - alpha-(1->4)-linkage and alpha-(1->6)-linkage (for branches)
If an enzyme name finished with
-ase is it an endo-active enzyme or exo-active enzyme?
-ase -> endo-active
-idase -> exo-active
What do the following enzymes cleave and do to starch, a-amylase, Gluco-amylase/amylo-glucosidase and B-amylase?
a-amylase -> cleaves at alpha-(1->4)-linkage. No or almost no glucose is released. Endoactive.
Gluco-amylase/amylo-glucosidase -> cleave at alpha-(1->4)-linkage and more slowly but also at alpha-(1->6)-linkage. Cleave from non-reducing end.
B-amylase -> cleaves maltose from non reducing ends and also dextrins.
What are the active sites of a-amylase?
Asp206 and Glu230
What are the three enzymes responsible to degrade the cell wall?
- Cellulase
- Xylanases
- Pectinases
What are the three layers of a cell wall and which are the primary components which make up this section?
1st layer: Middle lamella -> mainly pectins
2nd layer: Primary cell wall which is divided into Type 1 and Type 2. Type 1 -> cellulose embedded in xyloglucans
Type 2 -> cellulose is embedded in glucuronoarabinoxylan’s (GAXs).
3rd layer: Secondary cell wall -> cellulose and xylan (hemicellulose) and lignin.
What is cellulose?
Homogeneous linear polymer of B-(1->4)-linked glucan chains.
What is hemicellulose?
Is a heterogeneous polysaccharide, Xylans represent the large group of hemicellulose. Other hemicellulose include xyloglucans.
What is pectin?
Heterogeneous polymer made by three backbone structure of homogalacturonan, xylogalacturonan and rhamnogalacturonan I and II.
Describe the three enzyme which are responsible for cellulose breakdown.
- Endo-glucanases -> endo-active enzyme cleaves b-(1->4)-linkage. Degradation of amorphous region is preferred over crystalline region. Synergy with CBH.
- Cellobiohydrolases (CBH) -> exo-active enzyme which releases cellobiose. Can degrade crystalline region. Synergy with endoglucanase.
- Cellobiase/b-glucosidases -> exo-active enzyme which cleave cellobiose into glucose.
What is the difference between reducing and non-reducing ends?
The difference is that reducing end have and aldehyde group and non reducing end have an acetyl group.
Are xylans covalently bounded to lignin? If so with what type of linkages?
Yes, through ester and ether linkages.
What are the two main types of enzyme which act on xylans and how to they behave?
- Endo-xylanases -> are endo-active
- Beta-xylosidases -> are exo-active
however more enzymes are required to completely degrade most xylans.
How can one observe the effect of enzyme activity on xylans?
With HPSEC (separation by size), where smaller molecules are eluted later and larger molecules first. Or HPAEC (separation by size and charge), identificaton of mono-, di- and oligosaccharides.
Describe the enzymes involved in pectin degradation.
- Pectin esterase (PME) -> saponifies HM pectin into methanol and LM pectin.
- Polygalacturonase (PG) -> active towards LM pectin. Cleaves next to a free carboxyl group.
- Pectin Lyase (PL) -> active towards HM pectin. Cleaves next to a methoxylated carboxyl group. Followed by B-elimination and formation of double bond in non reducing end.
- Pectate Lyase (PAL) -> activity towards LM pectin. Cleaves LM pectin glyosidic bond by B-elimination. Formation of double bond in non reducing end is followed.
What are the two classification for proteases? And describe them.
- Site of attack (endo or exo)
Endo-enzyme cleave internally while exo-enzyme cleave externally. They work together. Endo-enzyme decrease MW faster than exo-enzyme. - Catalytic amino acids in the active site of the enzyme.
Have specific amino acid that is the active site.
What are the four type of catalytic amino acid?
- Serine proteases
- Cysteine proteases
- Metalloproteases
4.Carboxylproteases (or aspartic acid)
What are carboxypeptidases and aminopeptidases?
Carboxypeptidases cleave from the chain-end with a free carboxyl group. While aminopeptidases cleave from free amino group end.
What is an example of an aspartic acid protease?
Rennin or more known as chymosin used in yoghurt production.
How do lipases act?
They cleave glycerol-fatty acid ester at the oil/water interface. Preferably release fatty acids in the sn-1 and sn-3 position.
What is a limiting factor in the reaction rate of lipase?
Area of the micelles, not the substrate concentration.
Origin of lipase?
Pancreas, saliva, milk, fungi, yeast, bacteria….
What is the difference between lipases and esterases?
Lipases belong to esterases but are more specific. They are only active at the interface of oil/water which occur when saturation is high and micelles are formed. On the other hand, esterases act on water soluble substrates. With increase saturation esterases activity reaches plateau.
What specificity that lipase have? and describe there action.
- Position specificity
*1,3-specificity -> First step is fast where sn1 or sn3 is released. Second step is slower, where sn1 or sn3 is released. Third step is very slow, where sn2 is released.
* No specificity between 1,2 and 3 fatty acid. - Fatty-acid specifity
*saturated/unsaturated
*length
What can happen to milk when homogenized? Is lipase activity promoted or not?
After milk homogenization, droplets are made smaller and surface area increases. This promotes lipase activity which can form free fatty acids. Free fatty acids are linked to rancidity. This lipase are endogenous enzyme as already present in the milk.
How can aroma in blue cheese be made?
Addition of exogenous enzymes.
What is the function of lipoxyenase?
Converts fatty acids to instable hydro peroxidases.
What are the effect of lipoxygenase?
- Loss of nutritional value -> degradation of unsaturated fatty acids and degradation of vitamins and proteins by reaction with intermediary radicals of fatty acid conversion to hydro peroxidase.
- Loss of color -> reaction radical with carotene e.g.
- Formation of rancid components
