Understanding food flavour: the interaction of flavour chemistry and sensory science

Transcription

1 Understanding food flavour: the interaction of flavour chemistry and sensory science D. Zabaras, D.C. Frank, P. Riordan and P. Varelis Centre for Food Quality and Stability

2 Food Flavour: Definition Food flavour consists of three sensations: dour (orthonasal perception) Aroma (retronasal perception) Taste SH 2-methyl-3-furanthiol Volatile compounds are responsible for the odour and aroma of a food S methional CH

3 Precursors of Volatile Compounds Foods contain amino acids, carbohydrates and lipids, carotenoids Reactions involving amino acids, sugars and lipids are responsible for the formation of volatile compounds: Maillard reaction Lipid decomposition

4 Maillard Reaction + Lipid oxidation H H H H H H + R NH 2 H 2 rearrangement H H H H NHR H Lipid oxidation (e.g PUFA) reducing sugar aldehydes amino compound Amadori intermediate H 2 RNH 2 Flavour compounds Amino acids H Melanoidins H H Strecker reaction H 2 S aldehydes H H CH Acrylamide ASPARAGINE CH carbonyl compounds

5 Maillard reaction: Aromas generated from various sugars / amino acids Glycine Glutamic Acid Lysine Methionine Phenylalanine Glucose Burnt candy Chicken tray Burnt fried potatoes Cabbage Caramel Fructose Beef broth Chicken Fried potatoes Bean soup Dirty dog Maltose Beef broth Baked ham Stale potato Harsh horseradish Sweet Sucrose Beef broth Charred meat Boiled meat vercooked cabbage Chocolate (obtained from various literature sources)

6 Food volatiles Analytical investigations employed mostly GC and GC/MS. An estimated 8000 food volatiles had been reported until Initially it was assumed that all volatiles contribute to food aroma. The determination of odour activity values (AV) showed that not all volatiles were important as flavour compounds AV = dorant concentration/dour threshold value

7 dour analysis Results in the qualitative and quantitative determination of the important odorants in a food product: identity of important odorants relative concentration in food of interest This information is useful for the prediction, control and recreation of the flavour of a food product.

8 dour analysis: Steps 1. Extraction of the volatiles from the food matrix dynamic headspace or purge-and-trap (DHS) static headspace (SHS) liquid or solvent extraction solvent-assisted flavour evaporation (SAFE) simultaneous distillation-extraction (SDE)

9 dour analysis: purge-and-trap Tenax-TA trap Rapid sampling: 30 minutes high purity N 2 Up to six samples simultaneously Extraction of highly volatile components No heat-related artefacts Sample

10 dour analysis: Steps 2. Separation and tentative identification of the volatiles in the extract by GC/MS and localisation of the odorants by olfactometry (GC/MS-) Commonly employed GC/MS- approaches: SME (perception measurements of a non-diluted extract by trained panelists averaged) AEDA (extract serially diluted and measured until no perception)

11 GC-MS-olfactometer and time intensity recorder perceptual trace voice recorder sample introduction Real time GC/MS trace time intensity recorder instrumental trace GC/MS

12 Time-intensity recorder interface mouse-controlled sliding intensity scale 0 100

13 Information obtained from GC/MS- Abundance TIC: LINXC.D GC/MS trace (from detector) The human nose still remains the most sensitive detector of odouractive volatiles!! Detector response Time--> Panelist response Damian Aromagram Lindt (from human nose) Time (sec)

14 dour analysis: Steps 3. Quantification of important odourants using GC/MS Potentially most reliable quantification approach: SIDA (stable isotope dilution analysis)

15 Example: 13 C 2 -dimethyl trisulfide Abundance on ( to ): SL m/z--> Abundance 45 Scan 4498 ( min): SL_100.D (-4484) (-4517) (-) H 3 C 64 S S S CH on ( to ): SL Scan 4496 ( min): SL_101.D (-4480) (-4511) (-) H 3 13 C S S S 13 CH m/ z-->

16 dour analysis: Steps 4. Preparation of synthetic blends of odourants in blank matrices using the quantitative data (including omission experiments) 5. Sensory evaluation of the prepared blends by trained panels Whole process successful when: Aroma of synthetic blend (usually containing 3-4 odourants) = aroma of original food

17 Example: Chocolate aroma Chocolate: a matrix of solid particles (cocoa, sugar, milk) set in a continuous fat medium Characteristic flavour is a result of several manufacturing steps Flavour depends on many parameters including cocoa variety used, bean fermentation, conching process, added ingredients (e.g. vanillin)

18 Example: Chocolate aroma Total volatile and aroma profiles of two milk chocolates compared Both chocolates contained a similar amount of cocoa and milk solids (approx. Cocoa Solids 26%, Milk Solids 27%, Fat 30%)

19 GC/MS profiles Abundance methylbutanal acetic acid TIC: LINCH.D (*) TIC: CADMILK.D (*) Chocolate 1 vanillin Chocolate 2 Time--> Traces very similar (> than 90 volatiles detected)

20 Aromagrams dour intensity (0-100) Chocolate Chocolate Time (sec) Traces different (> than 70 odour-active volatiles detected)

21 Instrumental and perceptual data combined Chocolate 1 floral,mandarin honey/rotten,cheesy (linalool) (phenylacetaldehyde/butanoic dirt (2-ethyl-3,5-dimethylpyrazine) nutty, roasted herbal nut (tetramethyl (trimethylpyrazine) pyrazine) 100 green, sweet, floral floral (unknown) (unknown) peanut, green (2-methoxy-3-isopropyl pyrazine) honey, sweet acid) (5-methyl-2-furanmethanol) coffee, chocolate (2-methyl-3-(methyldithio)furan) 90 fruity (ethyl-2-methylpropanoate) chocolate (unknown) herbal,fresh (unknown) sweet (unknown) sweet (benzyl alcohol) 80 malty (unknown) 70 sweet, vanilla (unknown) 60 sweet, vanilla (unknown) sweet, vanilla (vanillin) 50 coconut (d-octenolactone) 40 caramel (d-pentolactone) 30 sweet (unknown) 20 caramel (2,3-butanedione) chocolate, malty (3-methylbutanal) sweet,caramel (unknown) sweet,caramel (unknown) sweet (2,3-pentanedione) phenolic (unknown) metalic (unknown) sweet, phenolic (unknown) medicinal (unknown) medicinal (guaiacol) vitamin B (2-furanmethanol) vinegar (acetic acid) wine, fermented (2-phenylethanol) stewed apple (phenylethylacetate) fatty, burnt (unknown) popcorn,cheesy (butyrolactone) cheesy, rotten, smelly parmesan socks (2/3-methylbutanoic (2-methylpropanoic cheese acid) (unknown) acid) sweet, fatty (unknown) 10 0 herbal,pine (a-pinene) herbal (unknown) fruity, bubblegum (ethyl-2-methylbutanoate) pineapple (unknown) crushed leaves (hexanal) herbal (b-pinene) herbal,dirty (a pyrazine) fruity, sweet (unknown) sweet,fresh (2-heptanone/limonene) fruity (unknown) sweet (unknown) melon,green (octanal) sweet,peach (unknown) baked potato (methional) mushroom (1-octen-3-one) mushroom, fungus (unknown) garlicky (unknown) rotten egg (dimethytrisulfide) curry, spicy (abhexon) bacon (unknown) cooked spaghetti (unknown) bacon, smoked ham (unknown) spicy, spaghetti (sotolon) fatty (1-hexanol) fatty, green (E-2-octenal) fatty, fatty, oxidised fatty,cheesy oxidised (E-2-nonenal) (Z-2-nonenal) (unknown)

22 Aroma profile comparison Chocolaty/Nutty Sweet/Caramel Floral/Herbal Chocolaty/Nutty Sweet/Caramel Medicinal Floral/Herbal Mushroom /Spicy Mushroom/Spicy Vinegar/Wine Fatty/Cheesy Vinegar/Wine Fatty/Cheesy Chocolate 1 Chocolate 2

23 Volatiles contributing most to milk chocolate aroma 3-methylbutanal (malty) 2-ethyl-3,5-dimethylpyrazine (potato, green) Z-2-nonenal (green, fatty) acetic acid (vinegar) methional (baked potato) 2-methyl-3-(methyldithio)furan (coffee, chocolate) hexanal (crushed leaves) phenylacetaldehyde/butanoic acid (honey/cheesy, rotten) These volatiles could be now used (by going through the remaining steps of the process) to re-create chocolate aroma. This has recently been achieved at FSA with kiwifruit flavour.

24 Bibliography Belitz, H.D, Grosch, W. Food Chemistry, 2nd edition, Springer-Verlag, Grosch, W. Evaluation of the key odorants of foods by dilution experiments, aroma models and omission. Chem. Senses 2001,26, Sides A, Robards K, Helliwell S. Developments in extraction techniques and their application to analysis of volatiles in foods. TiAC 2000,19, Pillonel L, Bosset J., Tabacchi R. Rapid pre-concentration and enrichment techniques for the analysis of food volatile: A review. Lebensm.-Wiss. u-technol. 2002, 35, Meet me at Food Science Australia's FoodPro stand - Hall 5, Stand I will be available from pm.

25 Thank you for your time!