1

New developments in strawberry flavourresearchBart Nicolaï Thomas VandendriesscheBart Nicolaï, Thomas Vandendriessche, Maarten Hertog

Katholieke Universiteit Leuven, BelgiumFlanders Centre of Postharvest Technology, Belgium

Contents

• FlavourFlavour analysis• Flavour analysis

• Strawberry aroma• Flavour changes during ripening• Postharvest flavour changes• High throughput flavour analysis• MetabolomicsMetabolomics• Conclusions

2

Flavour

• Combination of– Taste:

• Perceived by tongue • Sweet, sour, bitter, salty, umami

– Aroma• Perceived by nose• Orthonasal vs retronasal

– Texture• Perceived by tactile senses

• Flavour is multimodal !– Effects of color, sound during

chewing

Flavour analysis

• Sensory panel– Typically 10+ panellists– Trained in quantifying taste

components

• Consumer panel– Typically 100+ panellist– Not trained

Source: S. Buysens, PCG, Kruishoutem, Belgium

3

• Instrumental analysis– Taste: refractometer, titrator, HPLC – Aroma: GCMSAroma: GCMS– Texture: penetrometer, universal testing

machine,…

Strawberry aroma

• ± 360 volatile compounds from which 20 are important for sensory impression

• Several chemical classes:– acetals– alcohols– aldehydes (hexanal, hexenal)– esters– furanones– ketones– lactones

i id– organic acids– phenols– sulfur compounds – terpenes (linalool)

4

• Typical gas chromatogram

• Most important volatiles– Furanones, e.g. furaneol (DHF)

Caramel-like, sweety, floral, fruity notes, Typical strawberry aroma also pineappleTypical strawberry aroma, also pineapple

– Esters, e.g., methyl butanoate

Floral, fruity notesButanoates and hexanoates make up 50-80 %

of all volatiles in strawberry

– Methyl anthranilate

Grape smell

5

• Aroma types– DHF-type (furaneol)

• Elsanta (medium to poor aroma)

– Ester-type• Polka (pleasant aroma)

– MA-type (methyl anthranilate)• wild species and old cultivars• F. vesca, Mieze Schindler

Flavour changes during ripening

• Experimental design– 10 cultivars (Albion, Malling Pearl, Florin, Charlotte, Anabelle,

Florin2 Montery San Andreas and Portola // Elsanta) (PamelFlorin2, Montery, San Andreas and Portola // Elsanta) (Pamelexperimental station)

– Ripeness series

– Measured attributes: color, wrinkels, green/red ratio, firmness, sugars, acids, aroma, ORAC, ascorbic acid

6

• PCA analysis of aroma changes

0.8

1.0

0.8

1.0AlbionMalling PearlFlorinCharlotteAnabelleFlorin2

0 4

-0.2

0.0

0.2

0.4

0.6

0 4

-0.2

0.0

0.2

0.4

0.6

Color(70 %, 13 %)

Florin2MonterySan AndreasPortola

PC

_02

(7 %

)

0

10.00

20.00

30.00

40.00

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-1.0

-0.8

-0.6

-0.4

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-1.0

-0.8

-0.6

-0.4

PC_01 (18 %)

50.00

60.00

70.00

80.00

90.00

100.0

0 6

0.8

1.0

0 6

0.8

1.0 AlbionMalling PearlFlorinCharlotteAnabelle

-0 4

-0.2

0.0

0.2

0.4

0.6

FirmnessSSC

Density

ORAC

Ascorbic acidTotal Vitamin C Citric acid

L-Malic acid

D-FructoseD-Glucose

Sucrose

-0 4

-0.2

0.0

0.2

0.4

0.6

Color(71 %, 13 %)

AnabelleFlorin2MonterySan AndreasPortola

PC

_02

(7 %

)

10.00

20.00

30.00

40.00

50.00

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-1.0

-0.8

-0.6

-0.4

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-1.0

-0.8

-0.6

-0.4

PC_01 (18 %)

60.00

70.00

80.00

90.00

100.0

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• Large variability due to time, effect of producers smaller

Variability of quality attributes at harvest

14 NTglas EVT1

6

8

10

12

14 , teler, teler, ...

Brix

(°)

16/06/2009

14/07/2009

11/08/2009

08/09/2009

06/10/2009

03/11/2009

01/12/2009

0

2

4

Postharvest flavour changes

• Strawberry is nonclimacteric fruit• Color, however, also develops after harvest

How about flavour ?• How about flavour ?• Experimental setup

– One cultivar (Albion): proeftuin Pamel, Belgium– Strawberries ripened on / off plant

8

Color (hue) Density

Firmness SSC

• PCA of quality attributes

0.8

1.0

Firmness0.8

1.0

off plant

-0 4

-0.2

0.0

0.2

0.4

0.6

Glucose

Fructose

SucroseL-malic acid

SSC

0

0

0

0

000

0

00

2

222

2

2

2

2

2

2

5555

55 577 7

7

1

2

3

4

6

789

101112

1314

15

16

17

18

1920

21

22

23

25

-0 4

-0.2

0.0

0.2

0.4

0.6

Location(80 %, 2 %)

Color (34 %, 33 %)

on plant

PC

_02

(26

%)

0

10.00

20.00

30.00

40.00

50.00

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-1.0

-0.8

-0.6

0.4

ORACCitric acid

Ascorbic acidVitamin CDensity

5

55 7777

7

7

75

24

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-1.0

-0.8

-0.6

0.4

PC_01 (40 %)

60.00

70.00

80.00

90.00

100.0

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• Changes in aroma profile

On the plant Off the plant

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4000000

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Abundance

TIC: A1.D\data.ms

1400000

1600000

1800000

2000000

2200000

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3200000

Abundance

TIC: AG11.D\data.ms

0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.500

200000

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Abundance

TIC: AG27.D\data.ms

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Abundance

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100000

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High throughput flavour analysis

• Disadvantages of traditional methods for flavour– Sample preparation– Measurement timeMeasurement time

• Flavour analysis is bottleneck in rapid phenotyping– Breeding– Commercial quality systems

High throughput methodsHigh throughput methods

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• Solid phase micro extraction (SPME)– Major speed-up compared to other headspace sampling

techniques– Optimisation required

PlungerPlunger

Barrel

Gauge

Water bath

SPME fiber

• Fast GC-MS– External column– Resistive heatingResistive heating– Increased pressure– Small diameter

E.g., Mach-System (Gerstel)

11

10

12x 106

Black: GCRed: Fast GC

4

6

8

10

Abun

danc

e

0 5 10 15 20 25 300

2

4

Time (min)

• Headspace fingerprint mass spectrometry– No GC separation of volatiles– Fingerprint mass spectrum statistically correlated with, e.g.,

sensory panel analysis

Headspace Fingerprint MS

Time0 1 2

m/z

Gas chromatogram Headspace fingerprint Mass spectrum

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– Application: effect of high oxygen storage conditions on Elsanta aroma

100 % O2 – 0 % CO2

80 % O2 – 20 % CO2

60 % O2 – 0 % CO2

50 % O2 – 20 % CO2

20 % O2 – 20 % CO2

20 % O2 – 0 % CO2

5 % O2 – 20 % CO2

4 days shelf-life 7 days shelf-life

Berna et al. Postharvest Biology and Technology 46 (2007) 230–236

• Near infrared spectroscopy– Electromagnetic spectrum

13

– Principle

ce

Sweet

Detector

Wavelength

Ref

lect

anc

Monochromator

e

Not sweet

Light source

WavelengthR

efle

ctan

ce

• Typical NIR reflectance spectra

Rel

ativ

e re

flect

ance

Wavelength (nm)

R r

14

NIR - suikers

22

24Brix

CalibrationValidation

• Typical results for soluble solids content (8 cultivars)

8

10

12

14

16

18

20 Validation

Pre

dict

ed Y

0 2 4 6 8 10 12 14 16 18 20 22 240

2

4

6

Slope Offset RMSE R0.79 2.03 1.35 0.890.78 2.17 1.44 0.87

Measured Y

• Firmness: poor results

25Firmness

CalibrationValidation

10

15

20 Validation

Pred

icte

d Y

0 5 10 15 20 250

5 Slope Offset RMSE R0.64 2.03 1.97 0.800.62 2.22 2.12 0.77

Measured Y

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• Biosensor arrays– Biological recognition system attached to physical or chemical

transducer– Enzymatic recognition system:

• E g for glucose:

Biosensor arrays

• E.g. for glucose:

Glu + ATP → Glu-6-P + ADPGlu-6-P + NADP+ → GluA-6-P + NADPH

– Optical transducer• NADPH absorption measured at 340 nm

– Automatic dispensing system

Metabolomics

• Metabolomics– Exhaustive analysis of metabolites in cells– High throughput techniques (mass spectrometry)High throughput techniques (mass spectrometry)– Basis for models for aroma biosynthesis in strawberry– Useful information for breeding

• Ion cyclotron resonance FT mass spectrometry– ESI or APCI ionisation– ESI or APCI ionisation

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• Preliminary results

Conclusions

• Genetic erosion of flavour traits in commercial cultivars: opportunity for strawberry breeders

• Large variability of flavour throughout season• Large variability of flavour throughout season• Strawberry quality does not improve after harvest• Metabolomics may provide clues to understanding

flavour biosynthesis and how to manipulate this• High-throughput flavour techniques provide

opportunities for rapid phenotyping

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Acknowledgements