agudelo

COLOR DETERMINATION IN DEHYDRATED FRUITS: IMAGE ANALYSIS AND PHOTOCOLORIMETRY

AIC 2010 Color and Food Mar del Plata, Argentina, 12-15 October 2010

Lina Marcela AGUDELO LAVERDE, Nuria ACEVEDO, Carolina SCHEBOR & María del Pilar BUERA.

INTRODUCTION Foods containing reducing sugars and proteins are particularly sensitive to browning reactions.

Solubility decrease, color development and the loss of nutritional value are the most important causes of deterioration associated with browning in foods.

INTRODUCTION Dehydrated fruits are considered to be highly stable. However, they are prone to suffer discoloration during storage. Many natural pigments are unstable in dried media, and also brown pigments can be formed.

Homogeneous

Food discoloration can occur homogeneously, but most of the times heterogeneous distribution of color is observed.

Heterogeneous

OBJECTIVE The objective of this work was to evaluate the kinetics of colour changes in different dehydrated fruits as a function of relative humidity.

MATERIALS AND METHODS Sample preparation

Slices

Strawberry

Freeze drying

Location of slices on glass plates

Glass plates

O-rings

Humidification ≠ RH at 20°C

Clip

Hermetic seal of the glass plates

Glass plates

Clip

Heat treatment at 45º C O - Rings

MATERIALS AND METHODS Determinations Image analysis

Photocolorimetry

The computer vision system is formed by Illumination system Photo camera Sample

Data obtained in CIELAB

Lab values

1. Image obtention 2. Image analysis with Adobe Photoshop.

3. Data convertion to CIELAB

RESULT AND DISCUSSIONS Global color changes

L* VALUES luminosity

L*

60 50

11%

40

43%

30 20 10 0

84%

Image analysis 0

5

10

15

20

25

Time, h 40 11% 43%

30

b*

b* VALUES Yellow to blue

During storage at 45째C and due to browning reactions L* and b* values decreased causing a change from the original clear color to different browning degrees. These changes were more important with the increase of relative humidity (RH).

20 10 0

84%

Image analysis 0

5

10

15

Time, h

20

25

Similar results were obtained with photocolorimetry analysis.

RESULT AND DISCUSSIONS Global color changes

a* VALUES Green to red

As the strawberries are red, the parameter a* is more relevant to explain the appearance changes.

40 30

a*

20 10 11% 43% 84%

0 -10

Image analysis 0

5

10

15

Time, h

20

25

a* values decreased during storage at 45째C.

RESULT AND DISCUSSIONS Strawberry samples presented heterogeneous color distribution, therefore image analysis was used to determine the a* changes in each zone.

The images of the strawberry slices were divided in 4 different zones, according to their a* value.

Range a*

-3.8/6.8

6.8/17.4

17.4/28

28.0/38.6

1

2

3

4

RESULT AND DISCUSSIONS R.H. 11%

0 h.

22.5 h.

R.H. 43%

R.H. 84%

a* values decreased with storage time at 45ยบC because the heat treatment caused anthocyanin pigment destruction.

At the highest RH analyzed the strawberry slices became homogeneous.

CONCLUSIONS Photocolorimetry is a simple and easy technique to evaluate color changes, but it shows a limitation for the analysis of small areas or heterogeneous samples.

Computer vision analysis is a useful tool to assess optical properties of fruits with heterogeneous color distribution.

Muchas gracias!

Thank you!