Your SlideShare is downloading. ×
Thesis Defence
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Thesis Defence

775

Published on

Thesis defence for MSc

Thesis defence for MSc

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
775
On Slideshare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
19
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Sensory, chemical and consumer analysis of Brettanomyces spoilage in South African wines Janita Botha Thesis defence 17 February 2009 Research Team : M Muller, W J du Toit, A J de Villiers & A G J Tredoux
  • 2. Project background Bottle Saccharomyces cerevisiae Oenococcus oeni Other LAB Ethanol CO 2 Lactic acid Diacetyl Furfural Guaiacol Eugenol Etc Brett-related spoilage compounds + Fermentation Malo-lactic Fermentation Barrel Aging Brettanomyces/ Dekkera
  • 3. Sensory studies about Brett
    • Chatonnet et al . (1992):
      • Linked 4-ethylphenol and 4-ethylguaiacol to Brettanomyces
      • Detection thresholds of 4-EP and 4-EG
      • Commonly quoted study
    • Licker et al . (1999):
      • Linked isovaleric acid to Brettanomyces
    • Hesford & Schneider (2004):
      • Linked 4-ethylcatechol to Brettanomyces
  • 4. Recent sensory studies
    • Curtin et al . (2008):
      • Detection thresholds of 4-EP, 4-EG and 4-EC
      • Profiling of certain combinations
      • Consumer analysis
      • Recommend further studies
    • Romano et al . (2009):
      • Found further strong links between 4-EP and isovaleric acid
      • Investigated effect of isovaleric acid on detection thresholds of 4-EP and 4-EG
    Isovaleric acid? 4-ethylcatechol?
  • 5. Research Aims Determine the sensory detection thresholds of 8 Brett-related compounds To determine the sensory profiles of 4 Brett-related compounds To determine the sensory interactions of 4 Brett-related compounds To determine the consumer preference of 4 Brett-related compounds Chapter 1 Chapter 2 Chapter 3 To investigate realationships between 8 Brett-related compounds in selected South African wines Chapter 4
  • 6. Research Chapter 1: Detection Thresholds
  • 7. Materials and Methods
    • Method based on ASTM E 679 – 04
    • 3-Alternative Forced Choice (3-AFC)
    • 3 glasses of wine presented, 1 contains the Brett compound
    • 8 levels of 8 compounds tested
    Difference known, judges therefore trained
  • 8. Materials and Methods
    • Concentration increases with a constant MF factor on log scale
    • Two calculation methods investigated: ASTM and median
  • 9. Results: 4-ethylphenol LL LL ASTM Median UL UL 0 50 100 150 200 250 300 350 400 Median ASTM Calculation method Concentration (μg/L) Level 5 Level 2 Level 4 Level 3 Level 1 Outlier Larger range
  • 10. Results: 4-ethylcatechol LL LL ASTM Median UL UL 0 200 400 600 800 1000 1200 Median ASTM Calculation method Concentration (μg/L) Level 3 Level 4 Level 5 Level 6 Level 7 Level 8 True range Simplified range
  • 11. Conclusions
    • Concept of “detection threshold” is limited and obscures information
    • The use of a detection threshold range more accurate
    • Range provided by median more informative about population
  • 12. Research Chapter 2: Singular Profiling
  • 13. Materials and Methods: Central composite design Compound 1 Compound 2 Compound 3 Singular profiling exploration step before compounds can be tested in combination
  • 14. Materials and Methods: Singular profiling 4-EP 4-EG 4-EC Isovaleric acid 0 2 4 3 1 5 DT Values determined used as guide Levels pre-screened to confirm suitability for use in new medium
  • 15. Example of linear results: 4-EP 0 10 20 30 40 50 60 70 0 2 4 6 8 10 12 14 Level of 4-ethylphenol Intensity of descriptor Elastoplast Leather Berry-like Sick-sweet Mirroring Following
  • 16. Example of linear results: 4-EP 0 10 20 30 40 50 60 70 0 2 4 6 8 10 12 14 Level of 4-ethylphenol Intensity of descriptor Elastoplast Leather Berry-like Sick-sweet
  • 17. Example of Discriminant Analysis: 4-EP 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 L3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 5 4 3 2 1 0 -6 -4 -2 0 2 4 6 -6 -4 -2 0 2 4 6 F1 (78.64 %) F2 (19.88 %) 0 1 2 3 4 5 Centroids Level
  • 18. Example of PCA: 4-EP Similar pattern in univariate results 5 5 5 5 5 5 5 5 5 5 4 4 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 Elastoplast Leather Sick-sweet Berry-like -1.5 -0.5 0.5 1.5 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 F1 (86.81 %) F2 (8.90 %)
  • 19. Overall results 4-EP 4-EG 4-EC Isovaleric acid Elastoplast Leather Medicinal Smoky Savoury Pungent Sick-sweet Berry-like Not in literature Clove-like?? More detail obtained about the contributions of the respective compounds
  • 20. Research Chapter 3: Combination Profiling
  • 21. Materials and Methods: Design Compound 1 Compound 2 Compound 3 Samples
  • 22. Materials and Methods: Samples 2 4 4 4 4 4 4 4 4 2 4 4 2 2 4 4 4 4 2 4 2 4 2 4 4 2 2 4 2 2 2 4 4 4 4 2 2 4 4 2 4 2 4 2 2 2 4 2 4 4 2 2 2 4 2 2 4 2 2 2 2 2 2 2 5 3 3 3 1 3 3 3 3 5 3 3 3 1 3 3 3 3 5 3 3 3 1 3 3 3 3 5 3 3 3 1 3 3 3 3 Isovaleric acid 4-EC 4-EG 4-EP 1 Centre Sample 8 Star Samples 16 Cube Samples
  • 23. Results: Interaction
    • Elastoplast:
    • 4-EP*4-EG*4-EC
    • 4-EP*4-EG*ISOV
    • Medicinal:
    • 4-EG cause increase
    • 4-EC and isovaleric acid cause decrease
    • Pungent:
    • ISOV*4-EG
    • 4-EP cause increase
    All four compounds affect intensity of Elastoplast descriptor Compounds have different effects at different levels Intensity affected by other compounds present “ Sweaty leather” aroma attributed to Brett?
  • 24. PCA vs PARAFAC: sensory data Judges Samples Attributes Samples Attributes Judge 1 Judge 2 Judge n PCA: Analysis of (unfolded) 2-way data PARAFAC: Analysis of data cube Effects of judges not ignored Often simplified by finding mean over judges
  • 25. PCA vs PARAFAC 1 st factor calculated Subsequent orthogonal factors calculated 1 st factor calculated Subsequent factors calculated in sucessive directions of variance Factors recalculated untill they converge PCA PARAFAC Less noise modelled
  • 26. PCA of profiles Biplot (axes F1 and F2: 67.45 %) 5333 4444 4442 4424 4422 4244 4242 4224 4222 3533 3353 3335 3333 3331 3313 3133 2444 2442 2424 2422 2244 2242 2224 2222 1333 Medicinal Savoury Pungent Elastoplast Sick-sweet Berry-like -4 -3 -2 -1 0 1 2 3 4 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 F1 (37.92 %) F2 (29.53 %)
  • 27. Detection threshold change Biplot (axes F1 and F2: 67.45 %) 5333 4444 4442 4424 4422 4244 4242 4224 4222 3533 3353 3335 3333 3331 3313 3133 2444 2442 2424 2422 2244 2242 2224 2222 1333 Medicinal Savoury Pungent Elastoplast Sick-sweet Berry-like -4 -3 -2 -1 0 1 2 3 4 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 F1 (37.92 %) F2 (29.53 %)
  • 28. PARAFAC – factor 1 vs 2 Berry-like Elastoplast Medicinal Pungent Sick-sweet Savoury
    • Factor 1: Elastoplast
    • Factor 2: Berry-like
  • 29. PARAFAC – factor 2 vs 3 Pungent Berry-like Sick-sweet Savoury Medicinal Elastoplast
    • Factor 3: Pungent, Medicinal, Savoury
    • Pungent related to group with highest levels of 4-EP
  • 30. Conclusions: Combination profiling
    • Hierachy of descriptors:
    • Results of PARAFAC complementary to PCA and univariate results
    • 4-EP related to pungency
    Elastoplast Berry-like Pungent Medicinal Savoury Sick-sweet
  • 31. Consumer analysis
    • Some “Brett” wine liked better than the control
    • Difference found in terms of wine knowledge
    • Results not conclusive
    • Research methodology: Test “fuzzy” concepts
  • 32. Research Chapter 4: Chemical Analyses
  • 33. Materials and methods
    • Set of 32 South African wines
      • Wines known to be spoilt
      • Wines on the market
      • Questionable wines
    • GC-MS
      • 4-ethylphenol, 4-ethylguaiacol, isovaleric acid, isobutyric acid, acetic acid, 4-vinylphenol and 4-vinylguaiacol
    • HPLC-MS-MS
      • 4-ethylcatechol
  • 34. Cultivar and mildly spoilt wines Biplot (axes F1 and F2: 85.20 %) B6 B4 C6 M3 B3 S6 S4 C4 M2 P6 P5 P2 B2 4-EC 4-VG 4-EP 4-EG Isovaleric acid Isobutyric acid Acetic acid 4-VP -5 0 5 -7 -2 3 8 13 F1 (62.71 %) F2 (22.50 %) Pinotage? Same enzymatic pathways
  • 35. Conclusions: Chemical analyses
    • First South African study to analyse 4-ethylcatechol
    • Strong correlations between ethylphenols and isovaleric/isobutyric acid
    • Sample set too small to draw valid conclusions regarding cultivar
    • Recommended that larger study be undertaken to investigate this aspect further
  • 36. Conclusions
  • 37. Conclusions
    • Threshold value limiting concept, range more appropriate
    • Focus should shift to ranges
    • More research should be done for detection threshold methodology
    • All four compounds tested interact, especially in terms of the most NB descriptors
    • All four compounds should therefore be included in future sensorystudies
  • 38. Conclusions cont.
    • Consumer analysis not conclusive
    • Use better testing methodologies
    • Use of central composite design limiting but necessary for investigating interactions
    • Further studies with a more “complete” design
  • 39. Future research
    • 4-ethylcatechol should be tested in future studies concerning Brettanomyces
    • Help clear up discrepancies
    • Study indicates direction of future research
  • 40. Acknowledgements
    • Adriaan Oelofse & Jan Bester
    • Thomas Skov – Parafac
    • Prof van Aarde – Statistics help
    • Marietjie Stander – Chemical analyses
    • Distell
    • Friends & Family
    • Heavenly Father
  • 41.  
  • 42. Conclusions
    • Discriminant analyses and Linear LSD’s have similar results
    • Same underlying function
    • PCA complement linear statistics by means of providing insight into relationships
    • Overall – techniques complement one another
    • More detail about the profile of “Brett character” (Smoky/Savoury)
  • 43. Materials and Methods: Samples 2 4 4 4 4 4 4 4 4 2 4 4 2 2 4 4 4 4 2 4 2 4 2 4 4 2 2 4 2 2 2 4 4 4 4 2 2 4 4 2 4 2 4 2 2 2 4 2 4 4 2 2 2 4 2 2 4 2 2 2 2 2 2 2 5 3 3 3 1 3 3 3 3 5 3 3 3 1 3 3 3 3 5 3 3 3 1 3 3 3 3 5 3 3 3 1 3 3 3 3 Isovaleric acid 4-EC 4-EG 4-EP

×