Lecture 11 : Artificial flavourings Flashcards
An enzymatic approach in producing flavourings is always considered “natural” and not artificial. True or False?
False.
Although enzymes are considered “natural”, if starting material that enzyme is working on is chemically synthesized, the flavouring cannot be considered natural (half natural - half synthetic/artificial)
What are the advantages of natural flavourings (bio-based) over artificial (chemically synthesised) flavourings? [2]
- Clean label → materials are obtained from natural sources → can market as natural and thus sell more ex and earn higher profit margin
- Obtained from renewable sources → more sustainable and possibly lower environmental impact
What are the advantages of artificial (chemically synthesised) flavourings over natural (bio-based) flavourings? [4]
- Cost effective (petroleum is cheaper)
- Reaction conditions can be precisely controlled ;; and can occur at higher temp → faster reaction times
- Highly concentrated
- Produced on demand and not subject to seasonal availability
What are some disadvantages of natural flavourings? (extracted naturally) [4]
- Low concentration of flavouring
- Limited to seasonal availability (crops grow in seasons)
- Inteference from undesirable components
- High material costs
What are some disadvantages of bio-based flavourings? [4]
(microbes in a bioreactor)
1) High cost of production
- Need a constant supply of nutrients (e.g. AA) for bacteria, if not bacteria will stop growing and die
2) Longer time to produce, as bio-based processes often occur under mild conditions
- Enzymes / bacteria have optimal pH, temp they can work with, usually lower than chemical method
3) Difficulty in isolating flavour compounds from biomass
- Flavour compounds may cause product inhibition if accumulate in system, need to use technologies such as vacuum to extract out the flavour compounds (more costs)
4) Lower yield compared to chemical synthesis (cannot ensure 100% conversion of substrates into flavour compounds via microbial enzymes ;; some substrates will be diverted into other metabolic pathways even if conditions are optimised in precision fermentation)
1. Pyrazines
Pyrazines do not exist in nature. True or false?
False, they exist in nature and are secondary metabolites distributed in plants, insects, fungi and bacteria
- They act as an odor signal to repel predators
1. Pyrazines
What are the starting materials and how to chemically synthesise pyrazines?
Starting materials : 1,2-diketones (dicarbonyl compound)
- react w NH3 to produce amino ketones
- dimerisation/condensation of amino ketones produce pyrazines
1. Pyrazines
What are the starting materials and how to enzymatically synthesise pyrazines?
Starting materials : 1,2-diketones (dicarbonyl compound)
- react dicarbonyl with amine donor (e.g. amino acid), and use aminotransferase enzyme to transfer amino group of amine donor (e.g.AA) to dicarbonyl compound, forming aminoketone
- dimerisation/condensation of amino ketones produce pyrazines
*Similar to chemical synthesis, just that the source of NH2 is different *
1. Pyrazines
Extraction of pyrazines can be done to claim the flavouring as “natural”. Bio-based synthesis could also be employed.
How to synthesize pyrazines with microbes?
Precision fermentation (precursor approach)
- Provide bacteria with suitable precursors as starting materials (e.g. AA such as Threonine / Serine / Alanine / Leucine ;; or maybe glucose for pyruvate)
- Provide optimal conditions (temp, pH) such that the correct enzymes are expressed to convert AA into aminoketones
- dimerisation of aminoketones leads to pyrazine synthesis
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Specific example : Corynebacterium Glutamicum
- pyruvate → acetolacetate → acetoin 10 → aminoketone → di/tri/tetra methyl pyrazines
2. Flavours from terpenes
What are the 2 main constituents of turpentine? Are they odor active?
α-pinene and β-pinene.
No, they are not flavour active and have to undergo chemical reactions to be transformed into other flavour compounds
2. Flavours from terpenes
Describe the pathways β-pinene undergoes and what flavor compound it can produce [2]
β-pinene undergoes ring opening to form myrcene.
Myrecene :
1. Converted into menthol
2. Converted into geraniol & citronellol (rose alcohols), and eventually forming citral-related chemicals and then citral
Describe the pathway α-pinene undergoes and what flavor compound it can produce. [4]
α-pinene → 2-pinanol → linalool → citral
2. Flavours from terpenes
What is the traditional way of extracting flavor compounds from terpenes (naturally)?
Cutting the pine tree sap and conducting hydrodistillation (steam distillation).
2. Flavours from terpenes
Chemical synthesis of geraniol
List how geraniol can be produced synthetically, starting from raw materials
Isobutene (4C) + formaldehyde (C) → C5 prenyl group → undergoes oxidation or isomerisation → condensation to form intermediate, rearrangement of bonds → hydrolysis by heat to form ring structure → rearrangement of C=C onds in ring structure to form citral (geranial) + neral → hydrogenation to form geraniol + nerol (isomer)
Please look at notes for a better idea
2. Flavours from terpenes
Ionones are important flavor substacnces for what kinds of flavours?
Fruity flavours (berry flavours such as raspberry / blueberry)
2. Flavours from terpenes
Chemical synthesis of α-ionone
What are the raw materials for making α-ionone? State where these raw materials are derived from.
What kind of reaction do raw material undergo to form α-ionone?
Raw materials :
- Citral (extracted from hydrodistillation of Litsea Cubeba oil)
- Acetone (from petroleum sources)
Citral (aldehyde) and acetone undergo aldol condenation to form pseudo-ionone → rearrangement of double bonds to form α-ionone
2. Flavours from terpenes
How can α-ionone and β-ionone be formed naturally (biosynthetic pathway)?
Breakdown of carotenoids in plants by carotenoid dioxygenase
- α-carotene → α-ionone + β-10’-carotenal (catalysed by carotenoid dioxygenase)
- β-10’-carotenal → β-ionone + C-14 dialdehyde (catalysed by carotenoid dioxygenase)
3. Vanillin
State the biochemical pathway for production of natural vanillin in vanilla bean pods [4]
Tyrosine (AA) → coumaric acid → ferullic acid → vanillin
3. Vanillin
In natural vanilla bean pods, vanillin tends to bind to glucose to form glycoside. During the extraction of natural vanillin, what could be done?
Add β glycosidase to release glycosidically bound vanillin
3. Vanillin
Synthetic vanillin can be produced from what 2 main materials?
1) Lignin and sodium hypochlorite
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2) Methoxyphenol (from petroleum)
- undergoes aldol condensation → oxygenation → decarboxylation + reduction
3. Vanillin
State the pathway of bio vanillin synthesized by bacteria. [3]
Eugenol (isolated from clove) → Coniferaldehyde → Vanillin
State the pathway of bio vanillin synthesized by fungi. [4]
Eugenol → ferullic acid → vanillic acid → vanillin
Artificial sweeteners
Among the different types of artificial sweeteners, sucralose is often preferred due to its close taste profile to that of table sugar. Explain.
- Sucralose is derived from sucrose by replacing three hydroxyl groups (-OH) with chlorine atoms (-Cl).
- This structural similarity allows sucralose to bind to the same sweet taste receptors (T1R2/T1R3) in a similar way as sucrose.
- As a result, sucralose produces a sweetness profile (onset, intensity, lingering aftertaste) that is very similar to table sugar, leading to better consumer acceptance.
- Additionally, sucralose is much more potent (600× sweeter than sucrose), requiring only a very small amount, and it is highly stable under heat and across a wide range of pH, making it suitable for various food applications.
Artificial sweeteners
What are some issues with saccharin as an artificial sweetener? [2]
- Do not provide a clean sweet taste, with metallic / bitter off-taste perceived by some.
- Safety concerns : problems associated with bladder cancer in rats
