4.2. Static and dynamic flavour analytics

Question 1

What are the 2 main characteristics of volatile aromas?

Answer 1

• low boiling point
• limited solubility in water

Question 2

What are the 4 methods used to isolate volatile aroma compounds?

Answer 2

1. dynamic headspace
2. solvent extraction
3. (high vacuum) distillation
4. sorption extraction

Question 3

What are the 2 analytical techniques used for aroma extracts (after isolation)?

Answer 3

1. gas chromatography (GC)
2. mass spectrometry (MS)

Question 4

What is the static headspace analysis?

Answer 4

• fast and simple analytical method
• suitable for analysing a large number of samples simultaneously

Question 5

What’s the main principle behind static headspace analysis?

Answer 5

-STA relies on the equilibrium of a compound between the solution (liquid phase) and the gas phase to derive its concentration

Question 6

Give the key equations of Static Headspace Analysis.

Answer 6

1. Partitioning Coefficient K
   K = Cs/Cg
   Cs= c% in the solution
   Cg= c% in the gas phase
2. Phase ratio B
   B = Vg/Vs
   Vg= volume of the gas phase
   Vs= volume of the solution/sample
3. C% in gas phase Cg
   Cg= C0/(K+B)
   C0= initial c% in the sample

Question 7

How do you get a higher Cg (c% in gas phase)?

Answer 7

• decrease K and B

Question 8

What are challenges with Static Headspace Analysis?

Answer 8

• higher T may trigger undesired reactions (e.g. Maillard)
• introducing non-volatile components into the headspace
• increasing vial pressure, risking sampling errors or vial breakage

Question 9

How does Dynamic Headspace Analysis work?

Answer 9

1. purge gas: introduced into the vial to carry headspace out
2. water condenser: removes water vapour from the headspace
3. adsorption: compounds are trapped on a tube filled with adsorption material
4. thermal desorption: heat is applied to release compounds for GC analysis

Question 10

What are some advantages of using Dynamic Headspace Analysis?

Answer 10

• continuous flow: purge gas ensures re-establishment of equilibrium, allowing more compound adsorption on the sorbent
• c% build-up: results in a higher compound c% compared to static headspace analysis
• higher sensitivity: enhanced detection due to compound accumulation during adsorption

Question 11

What is Solid Phase Micro Extraction (SPME/SDPE)?

Answer 11

technique to measure volatile compound c% using a special injection needle with a retractable fiber

Question 12

How does SPME work?

Answer 12

1. needle insertion: needle is inserted through the vial lid into the headspace
2. equilibrium: compound equilibrated between the solution and the headspace
3. fibre ejection: the retractable fibre inside the needle is exposed to the headspace for compound adsorption
4. extraction: after adsorption, the fibre is retracted and the needle is removed from the vial
5. desorption: the needle is placed into a hot GC injector where the volatile compound desorbs for direct GC analysis

Question 13

What are pros and cons of SPME?

Answer 13

Pros:
- concentration: excludes introduced gas, leading to higher compound c% than static headspace analysis
- versatility: fibre can adsorb compounds from the solution instead of the headspace
- simple, fast and automated method

Cons:
- only suitable for clean solutions (water without sugar, oils or proteins)
- low recovery values for some volatiles and ineffective for compounds with low odour thresholds

Question 14

What is Stir Bar Sorbent Extraction (SBSE)?

Answer 14

uses a stir bar with an adsorption layer to isolate flavour compounds

Question 15

How does SBSE work?

Answer 15

• in solution: stir bar is submerged in solution, equilibrium is established between the compound c% in the solution and on the stir bar

Question 16

What are pros and cons of SBSE?

Answer 16

Pros:
- very efficient for lactones and acids
- higher sensitivity than SPME due to larger adsorption surface area

Cons:
- cannot be used with certain matrices such as vegetable oil

Question 17

What is Solvent-Assisted Flavour Extraction (SAFE)?

Answer 17

isolates volatile compounds using a high vacuum system with warm and cold sides

Question 18

How does SAFE work?

Answer 18

• warm side: sample is heated to 30-40C, causing volatiles to migrate into the headspace
• cold side: volatiles freeze in a flask submerged in liquid nitrogen
  -> continuous flow of volatiles ensures equilibrium and build-up of frozen volatile compounds

Question 19

What are pros and cons of SAFE?

Answer 19

Pros:
- combination of high and low temperatures minimises Maillard
- suitable for isolating volatiles with high recovery values (except for lactones )
- works for broad range of volatiles: acids, sulphur compounds and terpenes
- allows for multiple extractions and further c% of the extract

Cons:
- labor intensive
- prone to contamination
- less effective for highly volatile compounds

Question 20

How does GC work?

Answer 20

• volatile compounds are injected into a GC column containing a stationary phase
• an inert gas (mobile phase) transports compounds though the column
• AFFINITY FOR STATIONARY PHASE determines compounds travel rates, causing separation
• separation: compounds elute at different rates allowing individual analysis

Question 21

What is GC often coupled with?

Answer 21

detectors e.g. MS

Question 22

What is GC-O?

Answer 22

GC-Olfaction
- subject sniff compounds and record odour perception by pushing a button

Question 23

What is special about key-aroma compounds?

Answer 23

they can be detectable even at high dilutions

Question 24

What is ODT?

Answer 24

Odour Threshold Value = c% at which an individual first perceives the stimulus (odour)

Question 25

What is OAV?

Answer 25

Odour Activity Value = indicates the importance of a certain aroma compound in a product

Question 26

What does an OAV > 1 mean?

Answer 26

the c% of the sample is higher than the ODT meaning that the compound is perceivable and contributes to the smell of the product

Question 27

How does MS work?

Answer 27

- compounds are ionized and accelerated in a magnetic field, following a circular trajectory - separation of ions occurs based on their mass-to-charge ratio (m/z)

Question 28

What are the 2 types of ionization?

Answer 28

1. Electron Impact (EI): uses electron beam to ionize compounds, causing them to fragment 2. Proton Transfer (PTR): uses H3O+ ions for proton transfer WITHOUT fragmentation

Question 29

What are the 2 categories of MS?

Answer 29

1. HRMS: High Resolution MS 2. LRMS: Low Resolution MS - measures masses less precisely

Question 30

What can you use EI-MS and PTR-MS for?

Answer 30

EI-MS: ideal for detailed compound identification using mass spectrum libraries PTR-MS: suitable for quick sample composition analysis without GC pre-separation

Question 31

What is the purpose of flavour manipulation?

Answer 31

- identify key compounds in product - mask undesirable off-flavours - enhance attractive flavour characteristics - consider aroma-aroma and aroma-texture interactions - account for consumer perception and application context

Question 32

What are the techniques used for flavour analysis and manipulation?

Answer 32

1. sensory panels 2. GC-O 3. PTR-HRMS 4. Olfactometry, gustometry, Olfactoscan and Composcent

Question 32

How does an Olfactometer work?

Answer 32

air flow is introduced into flasks of olfactometer > air flow causes formation of bubbles resulting in release of flavour compounds into the gas phase (the bubbles) > flavour compounds are transported out of the flask into the nose of the consumer/trained panelist

Question 33

What is the Olfactometer connected to?

Answer 33

the nose of the panelist

Question 34

What is an Olfactoscan?

Answer 34

- in vivo technique - olfactometer connected to GC-O

Question 35

How does the Olfactoscan work?

Answer 35

aromas are separated from each other via GC then transported to nose of panelist

Question 36

How is an enhancing aroma compound found?

Answer 36

when subject perceives higher intensity of flavour

Question 36

How does one find a sweetness enhancing aroma compound?

Answer 36

give the panelist a combination of taste solution with tested aroma compound > if it is perceived as a higher sweetness intensity, a sweetness enhancing compound was found!

Question 36

How does a gustometer differ from the Olfactoscan?

Answer 36

it is used for taste purposes: to evaluate the influence of certain aroma compounds on taste perception

Question 36

How does a gustatometer work?

Answer 36

pumps which pump taste into the mouth of the subject

Question 37

What does the Composcent do?

Answer 37

removes aroma compound from the flavour profile of a product

Question 37

What does a Composcent consist of?

Answer 37

input* + GC + output *headspace with the volatile compounds of the sample

Question 38

How does a Composcent work?

Answer 38

- inside the column of the GC, the aroma compounds of the headspace are separated - at the end of the column, the headspace of the sample is collected in 2 vials, the output