Lecture 2 - Bioflavour

Question 1

Enzymatic hydrolysis - lipids

What reactions can lipases catalyse?

Answer 1

1. Hydrolysis
2. Esterification
3. Alcoholysis (transesterification)

Question 2

Enzymatic hydrolysis - lipids

What reactions can esterases catalyse?

Answer 2

1. Hydrolysis (primary function)
2. Esterification

Question 3

Enzymatic hydrolysis - lipids

State the equation for hydrolysis.

Answer 3

Glyceryl ester (triglyceride) + water → free fatty acid + diglyceride

Question 4

Enzymatic hydrolysis - lipids

State the equation for esterification.

Answer 4

Carboxylic acid + alcohol → ester + H₂O

Question 5

Enzymatic hydrolysis - lipids

State the equation for transesterification

Answer 5

Ester_1 + alcohol_2 → Alcohol_1 + Ester_2

transesterification : hydrolysis + esterification occuring simultaneously ;; swapping of functional group

Question 6

Enzymatic hydrolysis - lipids

Esterification only occurs in solvent-free media (low a_w). True or False?

Answer 6

False, esterification can occur in either :
1. Aqueous media (high a_w)
2. Solvent-free media (low a_w)
- Solvent-free media means no additional solvents are used ; esterification occurs in oil phase only

depends on the enzyme. Recall that rate of reaction ↑ as Aw ↑

Also, water is needed to prevent denaturation of enzyme (protein)

Question 7

Enzymatic hydrolysis - lipids

In lipolysis (breakdown of fat / lipids), what types of enzymes are used in :
1. aqueous systems
2. non-aqueous oil systems

and why?

Answer 7

1. Free enzyme → so that enzymes can move freely ;; simulate biological systems where it is mainly aq environment
2. Immobilised enzyme → enzymes require water for structural function but in organic solvents, enzymes are less stable and may denature → need to be immobilised for structural support.

Question 7

Enzymatic hydrolysis - lipids

What kinds of media can transesterification occur in? [2]

Answer 7

1. Cream : higher a_w
2. Oil : low a_w

Question 8

Enzymatic hydrolysis - lipids

Immobilised enzyme exist as a solid form, where enzymes are coated onto solid support / trapped within solid.

I used immobiised enzyme to catalyse my reaction. How can I recollect it back for reuse?

Answer 8

Centrifuge my mixture and let immbolised enzyme (solid) settle at the bottom. Rinse it and reuse.

Question 9

Enzymatic hydrolysis - lipids

Free enzymes can be reused. True or false?

Answer 9

False. One time use.

Question 9

Enzymatic hydrolysis - lipids

Lipolysed milk fat / lipolysed butter oil (LBO) is a common dairy flavour ingredient. It is very potent / pungent due to the presence of…?

Answer 9

C4-C10 fatty acids

Question 9

Enzymatic hydrolysis - lipids

How can i stop the activity of free enzymes, to prevent off flavour production during storage?

Answer 9

Inactivate enzyme with high temp.

Question 9

Enzymatic hydrolysis - lipids

What is enzyme modified cheese? What are its applications?

Answer 9

It is intensely flavoured cheese produced by adding lipases / proteases to immature cheese (so don’t have to wait for cheese to mature through fermentation)

• Used as cheese flavour ingredient in : biscuits, snack foods, soups, analogue cheese…..

Question 9

Enzymatic hydrolysis - lipids

How would you mask / mitigate the excessive pungency of enzyme (lipase) - modified dairy?

Answer 9

Enzyme modified dairy may be high in C4-C10 fatty acids due to hydrolysis of lipids. To mitigate this:
- add alcohols so that esterification can occur to produce nice-smelling esters
- reduce hydrolysis time so lower conc of short chain FA produced ;; less potent

Question 10

How can sweeteners be made from starch? (2 chemical reactions)

Answer 10

1. Hydrolysis with amylases
2. Isomerases

Question 10

Enzymatic hydrolysis - protease

Peptide formation can affect taste. What are the groups of peptides that can contribute to 2 different tastes?

Answer 10

1. Umami taste : glucamyl peptides (peptides containing glutamate)
2. Biiter taste : peptides high in hydrophobic AA residues like tyr, pro (branched chain / aromatic)

Question 11

What 2 sweetners can be made from isomerases?

Answer 11

1. Fructose (glucose → fructose by glucose isomerase)
2. Isomaltulose (sucrose → isomaltulose by sucrose isomerase)

Question 12

What sweeteners can be made via hydrogenation? State thei raw material [3]

Answer 12

1. Isomalt (Isomaltulose → isomalt)
2. Sorbitol (glucose → sorbitol)
3. Mannitol (fructose → mannitol)

Starch hydrolysates can also be hydrogenated to give rise to : sorbital / glucitol from glucose ; maltitol from maltose, maltotriitol from maltotriose

Note : all these are sugar alcohols

Question 13

What are glycosidically bound aroma compounds?

Answer 13

Aroma compounds that are chemically bound to sugars (glucose / hexose ;; 6C sugar)
- glycosidic bond at anomeric C

Question 14

How can aroma compounds be released from glysocidically bound aroma compounds? [2]

Answer 14

Hydrolysis via:
1. Heat
2. Enzymes – glucosidase (glucose-bound) or glycosidase (bound to 6C sugar)

Question 15

Microbial flavour production

What is de novo biosynthesis approach in microbial flavour production? Give examples of flavour compounds that can be synthesised via this approach

Answer 15

Flavour compounds are generated through biological metabolic pathways of microbes
- very long duration ;; not commonly used
- MSG, IMP/GMP, citric acid, L-lactic acid (usually non-volatile ;; taste compounds)

Question 16

Microbial flavour production

What is the precursor approach in microbial flavour production?

Answer 16

Instead of relying on random biosynthesis, specific precursors are added to the mixture, allowing microbes to feremnt it and yield flavour compounds

Question 17

Microbial flavour production - bacteria

Name of bacteria that produces MSG?

Answer 17

Corynebacterium glutamicum

Question 18

Microbial flavour production

Vinegar can be fermented by which 2 microbes to produce what flavour compounds?

Answer 18

1. Yeasts → produce alcohol
2. Acetic acid bacteria → produce vinegar

Question 19

# **Microbial flavour production** What pathway is 2,3- butanedione (diacetyl) synthesised from?

Answer 19

Citrate fermentation

Question 20

# **Microbial flavour production** Fungi fermentation usually produces ____ (name of group of flavour compounds), which are found in ___ (food product)

Answer 20

methylketone ;; cheeses (e.g. blue cheese)

Question 21

# **Microbial flavour production** Palm kernel oil is rich in lauric acid (fatty acid). Lauric acid (C12) can be undergo oxidation, hydrolysis and decarboxylation to produce ____ (flavour compound)

Answer 21

Undecanone (c11)

Question 22

# **Microbial flavour production** Lactones are aroma compounds that can be produced by the fermentation of ____ (group of microbe)

Answer 22

Yeast ## Footnote `

Question 23

# **Microbial flavour production** What is the aroma characteristic of lactones? [4]

Answer 23

Fruity Peach-like Apricot-like Coconut-like

Question 24

# **Microbial flavour production** How are lactones produced?

Answer 24

Via internal esterification of hydroxy fatty acid (-OH group of fatty acid react with -COOH group of fatty acid)