16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12172
Authenticity tests of organic products (Golden Delicious and
Elstar) applying sensory analysis
Ploeger, Angelika11, Röger, Monika1 , Weibel, Franco2
Key words: sensory evaluation, quantitative descriptive analysis, apple quality
Abstract
In the governmental funded project BÖL-02OE170/F, apple samples from different
farming systems (organic and conventional) were differentiated and classified by
sensory evaluation. Samples from farm pairs derived from geographical neighbouring
locations. Each farm pair consisted of one farm producing apples according to organic
land use system and one producing conventionally. Factors of influence as growing
conditions, climate, soil and harvest time were comparable within each pair.
For sensory evaluation, a descriptive analysis panel was trained according ISOstandards of descriptive analysis. The quantitative descriptive analysis method (QDA)
enables to show a complete product profile with all sensory characteristics of a
product as well as their intensity.
Over 2 crop periods (2004/2005), 18 apple samples (9 pairs) were evaluated by QDA
method; 5 samples pairs of the variety “Golden Delicious” and 4 sample pairs of the
variety “Elstar”, each with 3 replicates and 6 apples per replicate. In the first crop year,
descriptive analysis was done to develop product profiles of all samples. Based on
these data, a classification model was developed to classify sensory characteristics of
organic vs. conventional apple cultivation. According to this model, from 9 defined trial
sample pairs, 8 sample pairs could be classified according to the farming system in
the second year.
Introduction
Beside safety, freshness, general health benefits as well as nutritional value, one
reason for consumers demanding organic foods is a tastier product (Bourn, D.,
Prescott, J., 2002). The results of the questionnaire conducted by Casutt and
Guggenbuehl (2006) show that apples are consumed regularly (48% eat more than
four apples a week) because consumers like them as a snack between meals and
because they are refreshing. A number of studies comparing organic and conventional
food have included sensory tests indicating that organic and conventional fruits and
vegetables differ on a variety of sensory characteristics, but the findings are
inconsistent (Bourn, D., Prescott J., 2002 ; Roth et al, 2005, Homutova, I., Blazek, J.,
2006, Theuer, R, 2006). This is due to different sensory methods applied. The
quantitative descriptive analysis method (QDA) is one of the most sophisticated tools
in sensory science and allows - in opposition to preference or acceptance tests objective descriptions of products in terms of the perceived sensory attributes.
Depending on the specific technique used, the description shows a complete product
profile with all sensory characteristics and their intensity in appearance, aroma,
texture, mouthfeel and flavour attributes. Because without a classification model
describing a quality profile with consistent product characteristics of organic versus
1
: University of Kassel, Dep. Organic Food Quality and Food Culture, Nordbahnhofstr. 1a, D37213 Witzenhausen, Germany
2
Forschungsinstitut für biologischen Landbau (FIBL), Ackerstrasse, CH-5070 Frick
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12172
conventional products, preference/ acceptability measures that reflect relative degrees
of liking are difficult to interpret. Therefore the aim of the study is to develop a
classification model for two different varieties of apples (Golden Delicious and Elstar)
of different farming systems. The research project was funded by the German
Government (Ministry of Food, Farming and Consumer protection BÖL-02OE170/F).
Materials and Methods
Under the guidance of a panel leader, a panel group (10 – 12 persons) develops a
scorecard with a list of attributes fully describing the product and developing definition
for each attribute. At the same time a ranking of attributes of the product (apples) is
done. At least the panellists learn to practice scoring along the intensity scale (0 to 9
resp. weak to strong). The panellists were trained to be able to communicate precisely
without subjective descriptions and to work consistent and reproducible (Stone, Sidel
1993).
Sensory evaluation was carried out during two consecutive years (from harvest 2004
and 2005). Two varieties of apple samples were tested, 5 sample pairs of variety
“Golden Delicious” from defined field trial (FIBL Switzerland, F. Weibel) and 4 sample
pairs of the variety “Elstar” (neighbouring farms, FAL Trenthorst). Each sample pair
consisted of one sample derived from an organic producing system (according to
Council Regulation [EEC] No. 834/2007 of the European Union) and one from a
conventional farm. Harvest and climatic conditions were comparable. Training and
evaluation were carried out according QDA-standards of Stone & Sidel (Stone,Sidel
1993).
The panellists were calibrated directly on the test samples. During data collection,
panellists got at maximum of 6 product samples per session in a randomized design
order (according to sensory evaluation software FIZZ, Biosystemes, France). The
samples were served in booths, monadically (each panellists got the samples in
different order). All data were quantified by ratings of perceived intensities, using an
unstructured line scale with end-anchors and offset goal posts (e. g. from weak to
strong). Experimental design was as follows:
1. Factorial: each level of a factor is matched with each level of others,
2. Replicated: samples were evaluated 3 times,
3. Repeated measures: each panellist tasted each sample.
The experimental design yields a four-dimensional data matrix: panelist x attributes x
samples x replicates. The data were analysed by “FIZZ” sensory software. Descriptive
statistical measures were first calculated for all attributes using scores from panellists.
Analysis of variance was performed on each attribute using a randomized block
design for balanced data, with panellists as repeated measures. Where F-test
indicated a significant difference between test treatments, differences was defined as
P < 0,05. In addition, data of the quantitative descriptive analysis were also
differentiated by classification and regression tree system (CART-system, Breimann et
al 1984), which classified the sample pairs by statistic evaluation. This so called tree system shows the relationship between one or more variables of influence (x
variables) on a dependent variable (response variable =Y).The result of this statistical
procedure is visualized as a tree (leafs are separated variables, branches are steps of
differentiation. This tree can be used as a decision tree to look for key attributes or key
parameters influencing the product quality.
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12172
Results
Results of the descriptive quantitative analysis show a complete product profile of the
evaluated apples (see figure 1 as an example). For multivariate variance analysis, the
unstructured line scale is transferred into scores from 0 (no perceived intensity) to 9
(highest perceived intensity). The intensities given are results of all panellists and
repetitions. By evaluating differences in the characteristic intensities, for classification
into organic vs conventional samples, analogue differences in characteristic intensities
were defined. Due to the comparison of both crop years for the variety Golden
Delicious (from field trials in Switzerland), results show analogue characteristics of
sweet and sour flavour in tendency, in year 2004 for 3 out of 5 sample pairs, in 2005
for 4 out of 5 sample pairs the organic sample was more sweet, the conventional had
a more sour flavour. In crop year 2005 the conventional samples had a significantly
higher intensity in firmness and juiciness of the pulp, which is seen only in tendency in
crop year 2004. Most important for classification was the apple skin, which showed
significant more firmness and thickness at all 5 organic samples in year 2005 and of 4
out of 5 samples in year 2004 (for Golden Delicious).
.
skin colour (*)
skin off-Flavour 9
pulp colour (*)
skin bitter
Aroma overall
8
skin firm (*)
off-aroma
skin off-Aroma
Afterfeeling acerb
7
6
Aroma sweet
Aroma fruity
5
Afterfeeling astringent
Aftertaste sour
4
3
Aroma must
Aroma pear
2
Aftertaste sweet
1
Aroma banana
0
off-Aftertaste
Aroma green
Aftertaste overall
Mouthfeel acerb
Mouthfeel tingly
Mouthfeel astringent
Texture mealy
Texture chewable (*)
Texture
juicyfirm (*)
Texture
Flavour overall
Flavour sweet
Flavour sour (*)
Flavour pear
Flavour banana
Flavour must
Flavour citrus (*)
off-flavour
G1(organic)
G2 (conv.)
Figure 1: Product profile of one sample pair (coded as organic/conventional),
variety “Golden Delicious” (as an example)
Also for the variety “Elstar” significant differences were found in firmness and
thickness of the apple skin, the skin of the organic samples were more firm and thick
in comparison of the conventional ones. The skin of the organic samples was also
more bitter in flavour. In other characteristics, no significant classification could be
perceived, in tendency a higher intensity of firmness of the pulp in organic samples
could be shown (see table 1). Results of classifying the sample pairs by CARTSystems confirm the differences of characteristics. Sample pairs could be separate
clearly within the juice rate and firmness of apple skin.
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12172
Tab. 1: Pulp and skin parameters of organic and conventional Elstar (2004, 2005)
Year
2004
2005
Samples
conv.
organic
F-value
signif.
conv.
organic
F-value
sign.
Pulp colour
6,81
5,03
57,35
<0,0001
5,19
5,69
3,68
0,3841
Skin firmness
2,19
5,17
160,65
<0,0001
3,57
4,95
28,57
0,0081
Skin thickness
2,71
4,53
59,3
<0,0001
3
4,03
15,79
0,0365
Skin bitter
3,65
4,36
8,95
0,1665
3,67
4,81
19,6
0,0442
Results show that apple samples of organic vs. conventional farming systems and
different varieties can be classified by quantitative descriptive analysis. The variety in
this study was Macintosh. Our results show that a significantly higher firmness of the
skin for organic samples can be observed in this controlled study for other varieties
(Golden Delicious and Elstar), too. Beside that, the pulp of organic apples of both
varieties was firmer compared to those of conventional ones. Homotuva and Blazek
(2006) state, that direct physical measurements and panellists´ evaluation regarding
the skin thickness show the same results. The bitterness of the skin, as observed in
this investigation can be related to the higher amount of phenolic substances (Weibel
et al, 1999). Furthermore, results of the CART-system support the differentiation
between apples from organic and conventional farming systems. Measurements of
human senses are able to evaluate precisely and reproducible results.
Acknowledgements
The authors thank Dr. Nicolas Busscher (University of Kassel) and Statcom for
providing the CART system as well as Prof. Dr. G. Rahmann (FAL-OEL) for coding
and distributing the apple samples and the Ministry (BMELV) for financial support of
the work (BÖL-02OE170/F).
References
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