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ACTA IMEKO
ISSN: 2221‐870X
April 2016, Volume 5, Number 1, 22‐31

ACTA IMEKO | www.imeko.org April 2016 | Volume 5 | Number 1 | 22

Variations of phenolic compounds and sensory properties of
virgin olive oils from the variety “Istrska belica”

Milena Bučar‐Miklavčič
1
, Terezija Golob

2
, Vasilij Valenčič

1
, Erika Bešter

1
, Bojan Butinar

1
, Ana

Miklavčič Višnjevec
1

1
UP ZRS IZO; LABS d.o.o., Zelena ulica 8 c, Izola, Slovenia

2
Univerza v Ljubljani, Biotehniška fakulteta, Jamnikarjeva 101, Slovenija

Section: RESEARCH PAPER

Keywords: olive oil; phenolic compounds; sensory properties; “Istrska belica”

Citation: Milena Bučar‐Miklavčič, Terezija Golob, Vasilij Valenčič, Erika Bešter, Bojan Butinar, Ana Miklavčič Višnjevec, Variations of phenolic compounds and
sensory properties of virgin olive oils from the variety “Istrska belica”, Acta IMEKO, vol. 5, no. 1, article 6, April 2016, identifier: IMEKO‐ACTA‐05 (2016)‐01‐06

Section Editor: Claudia Zoani, Italian National Agency for New Technologies, Energy and Sustainable Economic Development affiliation, Rome, Italy

Received May 29, 2015; In final form November 10, 2015; Published April 2016

Copyright: © 2016 IMEKO. This is an open‐access article distributed under the terms of the Creative Commons Attribution 3.0 License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Funding: This work was supported by EU founded project Uelije

Corresponding author: Ana M. Višnjevec, e‐mail: ana.visnjevecmiklavcic@zrs.upr.si

1. INTRODUCTION

The olive (Olea europaea L.) variety “Istrska belica” is the
most widely spread olive variety in Slovenian olive groves. The
quality of the olive oil from “Istrska belica” is distinguished by
its rich aroma, which reminds the user of the fresh, optimal ripe
olive fruit, combined with freshly mown grass. The high
content of phenolic compounds gives the “Istrska belica” oil its
characteristic bitter taste and pungent tactile sensation.

Diets containing the phenolic compounds found in olive oil
can have health benefits, which include the reduction of risk
factors for coronary heart disease, protection against several
types of cancers, and modification of immune and
inflammatory responses [1]-[19]. According to European Union

Regulation (UE) 432/2012, phenolic compounds can be cited
according to the indication: “Olive oil phenolic compounds
contribute to the protection of blood lipids from oxidative
stress”. This claim demonstrates the importance of these
phenolic compounds.

The phenolic compounds in olive oil are secondary
metabolites that arise through the conversion of complex
substances produced by olive trees, and they can be classified as
lignans, flavonoids and secoiridoids. Virgin olive oil contains at
least 30 different phenolic compounds [1]. The most common
lignans in olive oil are pinoresinol, acetoxypinoresinol and
hydroxypinoresinol [11], and the most common flavonoids are
luteolin and apigenin [20]. While lignans and flavonoids are also
in other foods, such as wine, secoiridoids are specific for olive

ABSTRACT
The olive variety “Istrska belica” is well known for its numerous positive properties, such as resistance to low temperature and high oil
content. The aim was to determine the variations in the levels of phenolic compounds and sensory properties during storage of
“Istrska belica” virgin olive oil. The profile of the phenolic compounds and sensory properties of “Istrska belica” olive oil were further
compared with those for other varieties, including “Leccino” and “Maurino”. The content of phenolic compounds of the olive oils
decreased after 1 year and 2 years of storage. After 2 years of storage, the levels of oleuropein and the ligstroside derivatives
significantly decreased, while the end‐stage compounds tyrosol and hydroxytyrosol increased. These data show that after 1 year of
storage, the “Istrska belica” olive oil preserves similar intensities for bitterness and pungency, and similar oleuropein and ligstroside
derivatives levels. In contrast to the other oils, the intensities of bitterness and pungency of “Istrska belica” olive oil decreased greatly
only after 2 years of storage. Moreover, the phenolic compounds content, and oleuropein and ligstroside derivatives levels, and the
intensities of bitterness and pungency were highest in fresh “Istrska belica” olive oil, compared to other olive oils analysed. Overall,
“Istrska belica” olive oil has important advantages over olive oil from other varieties that are grown in the Istria region.

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oil [21], [22]. The two main secoiridoids in olive oil are
ligstroside and oleuropein, and their conversion products give
olive oil its unique aroma and taste. During the olive-pressing
process or if the drupes are injured, ligstroside and oleuropein
in the fresh drupes can enter different transformation-reaction
pathways, such as their enzymatic and chemical transformation
to aldehyde or hydroxy forms [23]. One possible
transformation pathway is autooxidative decay as a
consequence of the protection of phenolic compounds against
harmful oxidative changes [24]. This conversion is gradual and
continues in the olive oil throughout its use. During olive oil
storage, hydrolytic mechanisms that lead to the release of
simple phenols, such as hydroxytyrosol and tyrosol, from the
complex phenols, such as the secoiridoids, can occur [25]-[27].
The newly formed substances from these secoiridoids have
amphiphilic characteristics, and are thus partitioned between
the oily layer and the vegetation water, and are concentrated in
the water fraction through their polar functional group [1]. As
long as these secoiridoids do not get transformed into their
final forms (i.e., the aromatic alcohols tyrosol and
hydroxytyrosol), the olive oil preserves its freshness, fruitiness
and harmony. It should be noted that when the transformation
pathway is reaching its end and the olive oil has already lost its
freshness and antioxidative properties, the content of total
phenolic compounds can be relatively high. Therefore, it is
crucial to determine the relative amounts of each of these
compounds, and not just the total sum of all of the phenolic
compounds.

Oxidation of olive oil begins as soon as it has been
extracted. Endogenous enzymes in the olive fruit are involved
in the phenolic profile and in its qualitative and quantitative
modification during the processing of virgin olive oils [28].
However, olive oil is more severely affected during its storage.
The decomposition of the phenolic compounds depends on
oxygen, light, temperature, metals, pigments, unsaturated fatty
acid content and composition, and quality and kind of natural
antioxidants present [29], [30]. Part of the low quantity of water
in virgin olive oil is free and available for chemical and
enzymatic reactions. This low quantity of water keeps
hydrophilic phenols in solution, which is where the
decomposition process can occur for the phenols and
triacylglycerols during olive oil storage [31], [1]. Furthermore,
according to Frankel [30], the hydrophilic antioxidants, such as
the polar phenols that are oriented at the air-oil interface, can
better protect against oxidation compared to the lipophilic
antioxidants, like the tocopherols, which remain in solution in
the olive oil. Moreover, Aparicio et al. [32] measured the
correlation between the oxidative stability of virgin olive oil and
several compositional variables. They showed that phenols, o-
diphenols, and the oleic/ linoleic ratio have the highest stability
values, followed by chlorophylls, total tocopherols and
caratenoids. According to Tsimidou et al. [33], hydroxytyrosol
is the most active antioxidant compound in virgin olive oil.
Carrasco-Pancorbo et al. [34] showed that the hydroxytyrosol
oleuropein-aglycone di-aldehyde (3,4-DHPEA-EDA; i.e.,
elenoic acid linked to hydroxytyrosol) and oleuropein aglycon
have the strongest antioxidant power. Elenoic acid, which does
not have a phenolic ring, was one of the compounds
investigated in virgin olive oil that has the weakest antioxidant
activity.

Extra virgin olive oil can be characterized by a unique
combination of aroma and taste that is highly appreciated [35],
[36]. The method of sensory evaluation of virgin olive oils,

introduced in 1991 by Commission Regulation (EEC) No.
1348/2013 annex XII (revision of Reg. EEC 2568/91), lays
down the procedure for evaluating the sensory attributes of
virgin olive oils and quality classification (categorization). It
specifies the criteria for sensory evaluation of virgin olive oil, as
well as providing a special vocabulary and standardized
conditions for evaluation. However, the panel test, performed
according to EU procedures, it is an expensive process that
requires accredited assayers and is not easily accessible to the
companies that have limited production, and therefore
alternative tools have been developed [37]. Many studies have
tried to clarify the relationships between the sensory attributes
in virgin olive oil and the phenolic compounds that are
responsible for its aroma and taste [1], [36], [38]-[41]. Some
studies have suggested that secoiridoid derivatives of
hydroxytyrosol are the main contributors to olive oil bitterness
[1]. Caponio et al. [38] showed that the bitter to pungent taste
can be ascribable to oleuropein aglycon. Furthermore,
oleuropein and its aglycon decrease as the ripening of olives
progresses [38]. Rotondi et al. [39] confirmed the relationship
between the decrease in bitterness and pungency and the
reduction in total phenols and diphenol levels. In particular a
positive correlation between the content of oleuropein and
ligstroside derivatives and the bitterness and pungency was
shown. Frank and co-authors [40] reported that when an
isomer (or isomers) of oleuropein aglycon was prepared by β-
glucosidase hydrolysis of oleuropein isolated from olives and
evaluated by assessors, it was defined as bitter. Using the same
evaluation technique, no bitterness was observed for
hydroxytyrosol or elenolic acid. According to Andrewes et al.
[41], the dialdehyde form of decarboxymethyl ligstroside
aglycone (p-HPEA-EDA) is the key source of the pungent
sensation found in olive oil, while 3,4-DHPEA-EDA produces
very little burning sensation. Moreover, Beauchamp et al. [5]
assessed the pungent intensity of p-HPEA-EDA isolated from
different virgin olive oils, and confirmed that p-HPEA-EDA is
the principal agent responsible for throat irritation. Gutierrez-
Rosales et al. [42] concluded that the chromatographic peaks
corresponding to 3,4-DHPEA-EDA, oleuropein-aglycone
mono-aldehyde (3,4-DHPEA-EA) and p-HPEA-EDA are
mainly responsible for the bitter taste of virgin olive oil.
Overall, some phenols mainly define the bitterness of olive oil,
while others define the perception of pungency, and these
might be related to the olive variety.

In the present study, the levels of 14 phenolic compounds
and the total sum of all of the phenolic compounds included
were determined in 167 samples. In all of the samples, an
International Olive Council (IOC) recognized panel tested the
sensory properties, as the bitterness, pungency, olive fruity,
defects and sensations that resemble olive fruit, green-leaf,
tomato, almond, artichoke and vanilla. The aim of the present
study was to determine the changes in the phenolic compounds
and sensory properties during the storage of the oil of the
“Istrska belica” variety, which is specific and very important for
the region of Istria. The phenolic profile and sensory properties
of “Istrska belica” oil were further compared to the phenolic
compounds and sensory properties determined for the oil of
other varieties grown in the study area. In addition, the aim was
to define the correlations between the content of phenolic
compounds and the sensory properties of the fresh oil, and
after 1 year and 2 years of storage. To the best of our
knowledge, this is the first investigation into the effects of
storage on the content of the phenolic compounds and the

ACTA IMEKO | www.imeko.org April 2016 | Volume 5 | Number 1 | 24

sensory properties as tested for the “Istrska belica” variety, the
oil of which has a characteristic high content of phenolic
compounds and a bitter taste.

2. METHODS

2.1. Collection and storage of samples

More than 80 samples of fresh olive oil were randomly
collected from Slovenian producers. During this 3-year project,
the determination of the phenolic compounds and the sensory
analyses were carried out on both fresh oil and stored oil
produced in Slovenia. Therefore, the first year samples (2011)
were analysed after 1 year and 2 years of storage, and the
second year samples (2012) were analysed after 1 year of
storage.

Olive fruit samples were hand-picked from olive trees at the
same optimal maturity level for each cultivar taking into
consideration the index of maturity and the hardness of the
fruit [43]. Healthy fruits, without any kind of infection or
physical damage, were used for the oil production. The
collected samples of extra virgin olive oils were produced using
modern production technology with a two-phase decanter.
During the production process the temperature was monitored
and maintained at 27 °C. The oils were produced according to
good manufacturing practice guide [44]. The chemical analyses
of fresh olive oil samples were performed after the extraction
process in each particular year. All the olive oil samples were
stored at 20°C in the closed dark bottles in the same place.

2.2. Sensory analysis

The sensory characteristics were determined by a panel
composed of eight trained assessors. The sensory properties of
fruitiness, bitterness, pungency and other specific characteristics
of selected oils were assessed based on the method defined in
Annex XII of EEC Regulation No 2568/91, 640/2008, which
includes the use of a 10-cm linear scale for intensity
determination.

2.3. Determination of phenolic compounds

The phenolic compounds in the olive oil, such as the natural
and oxidised derivatives of oleuropein and ligstroside, lignans,
flavonoids and phenolic acids, were extracted using 60 % (w/w)
aqueous methanol solution, and analysed by reverse phase high-
performance liquid chromatography (HPLC), according to
COI/T.20/Doc No 29 [42]. The HPLC system (Agilent 1100)
was equipped with a thermostated autosampler, a binary pump
system (BinPump G1312A), and a diode array detector
(G1315B). A Phenomenex Synergi 4 µm Hydro-RP 80 Å
column (250 × 4.6 mm i.d.; Torrance, CA, USA) was used. The
analyses were performed according to a modified method
published by the IOC [42]. Detection was at 280 nm, with the
exception of the flavonoids luteolin and apigenin, which were
detected at 340 nm. Calibration curves for tyrosol (mass
fraction from 30 to 800 mg/kg; y = 0.0811a) were constructed
using standard compounds. All of the phenolic compounds
were determined according to the IOC publication and
quantified using the response factor for tyrosol [42]. In this
study, the following groups of phenolic compounds were
determined: 1) The sum of oleuropein and the ligstroside
derivatives; 2) the sum of tyrosol and hydroxytyrosol; 3) the
sum of oleuropein, the ligstroside derivatives, tyrosol,
hydroxytyrosol, lignans and phenolic acids; and 4) the total
phenolic compounds (mg/kg). The term “total phenolic
compounds” refers to the “biophenolic minor polar
compounds” determined according to the IOC method [45].

2.4. Statistical analysis

All of the data were analysed using the STATA13/SE
software. The distribution of the total phenolic compounds,
oleuropein, the ligstroside derivatives, tyrosol and
hydroxytyrosol determined in the fresh olive oils and after 1
year and 2 years of storage are given as box plots. The
normality of the variable distributions was determined using
Shapiro–Wilk tests. The correlations between the levels of the
determined phenolic compounds and the sensory parameters
were evaluated. Spearman rank correlations were used for
bivariate comparisons. Due to the significant correlations
between the variables of the different phenolic compounds,
factor analysis was applied. After running the factor analysis,
rotation of the factor loads was performed to provide a clearer
pattern. From the different concentraions of the specific
phenolic compounds, new variables were created (n=5) for
“eigenvalues” >1. Wilcoxon–Mann–Whitney tests were applied
for comparisons of two different groups, and Kruskal Wallis
tests were applied for comparisons of three different groups.
The level of statistical significance was set to p <0.05.

3. RESULTS AND DISCUSSION

3.1. Phenolic compounds

The phenolic compounds were quantified using the
response factor for tyrosol [41]. The sum of oleuropein, the
ligstroside derivatives, tyrosol, hydroxytyrosol, lignans and
phenolic acids (1), the sum of oleuropein and the ligstroside
derivatives (2), and the sum of tyrosol and hydroxytyrosol (3)
determined in all the fresh olive oils from three years of
sampling varied from 145 mg/kg to 966 mg/kg (median, 417
mg/kg), 83 mg/kg to 584 mg/kg (median, 251 mg/kg), and 2
mg/kg to 97 mg/kg (median, 9 mg/kg), respectively. It is
important to note that the composition of the phenolic
compounds can vary widely according to each olive variety. The
contents of the flavonoids luteolin and apigenin in the fresh
olive oil from “Istrska belica” were in the ranges of 2.6 mg/kg
to 5.8 mg/kg (n = 20) and 0.9 mg/kg to 1.9 mg/kg (n = 20),
respectively. The same flavonoids contents for “Leccino” oil
ranged from 1.5 mg/kg to 4.3 mg/kg (n = 11) and 0.3 mg/kg
to 0.8 mg/kg (n = 11), and for “Maurino” oil they ranged from
0.8 mg/kg to 2.0 mg/kg (n = 4) and 0.2 mg/kg to 0.6 mg/kg (n
= 4). The “Istrska belica” oil lignans ranged from 22 mg/kg to
70 mg/kg (n = 20), with “Leccino” oil as 11 mg/kg to 33
mg/kg (n = 15), and “Maurino” oil as 46 mg/kg to 51 mg/kg
(n = 6). The dialdehyde forms of both decarboxymethyl
oleuropein aglycone (DMO-Agl-dA) and decarboxymethyl
ligstroside aglycone (DML-Agl-dA) for “Istrska belica” oil
varied from 23 mg/kg to 124 mg/kg (n = 20), with “Leccino”
from 17 mg/kg to 274 mg/kg (n = 15), and “Maurino” from
limit of detection (LOD) to 119 mg/kg (n = 6). The oxidised
aldehyde and hydroxyl forms of oleuropein aglycone (O-Agl-
dA) and ligstroside aglycone (L-Agl-dA) were lower compared
to DMO-Agl-dA and DML-Agl-dA, and for “Istrska belica” oil
they varied from 5.6 mg/kg to 87 mg/kg (n = 20), with
“Leccino” from 1.5 mg/kg to 21 mg/kg (n = 15), and
“Maurino” from <LOD to 30 mg/kg (n = 6). As expected, the
fresh olive oil from “Istrska belica” showed the highest median
for the total phenolic compounds (median, 616 mg/kg;
minimum, 324 mg/kg; maximum, 787 mg/kg; n = 20) and for
the sum of oleuropein and the ligstroside derivatives (median,
366 mg/kg; minimum, 165 mg/kg; maximum, 515 mg/kg; n =
20). Statistical analysis showed that the differences in the

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content of the total phenolic compounds and oleuropein and
the ligstroside derivatives in the fresh olive oil from ‘Istrska
belica” compared to those determined in the fresh olive oil
from the other varieties (mediantotal, 360 mg/kg; mediansec, 212
mg/kg; n = 61) were significant (ztotal = -5.049; ptotal <0.005; zsec
= -4.063; psec <0.005). This confirms that the high content of
phenolic compounds is a specific characteristic of the “Istrska
belica” variety, compared to the levels determined in the other
varieties grown in these Slovenian olive groves.

The phenolic compounds contents of these olive oils varied
greatly according to crop year (Table 1, Figure 1). The
variations in the sum of oleuropein and the ligstroside
derivatives, the sum of tyrosol and hydroxytyrosol, and the sum
of oleuropein, the ligstroside derivatives, tyrosol,
hydroxytyrosol, lignans and phenolic acids in the fresh olive oils
from the crop years 2011, 2012 and 2013 are shown in Figure 1.
These levels (medians, 346 mg/kg, 13 mg/kg, 410 mg/kg,
respectively) were highest in the crop year 2012, compared to
the years 2011 and 2013. Statistical analysis (Wilcoxon–Mann–
Whitney tests) showed that these differences were significant
for the sum of oleuropein and the ligstroside derivatives (z = -
4.655; p <0.005) and for the sum of oleuropein, the ligstroside
derivatives, tyrosol, hydroxytyrosol, lignans and phenolic acids
(z = -4.572; p <0.005), with marginal significant for the sum of
tyrosol and hydroxytyrosol (z = -2.04; p = 0.04). The highest
levels of the sum of oleuropein, the ligstroside derivatives,
tyrosol, hydroxytyrosol, lignans and phenolic acids in crop year
2012 might have been due to the extreme weather conditions,
with a drought for crop year 2012 (Figure 1). Less than 50% of
normal rainfall fell in the crop year 2012 in the study area [46].
The variations in the levels of tyrosol and hydroxytyrosol are
not so obvious, because most of these were probably the end-
products of the decomposition pathways of oleuropein and the
ligstroside derivatives, and their concentrations might not be
directly influenced by the different conditions across the crop
years. These variations might be greater after a time of storage
longer than 3 years.

The sum of oleuropein, the ligstroside derivatives, tyrosol
and hydroxytyrosol in the fresh olive oils following 1 year and 2
years of storage are shown in Figure 2. While the levels of
oleuropein and the ligstroside derivatives decreased significantly
across the years, the end-stage compounds tyrosol and
hydroxytyrosol only increased after 2 years of storage (Figure
2). The sum of oleuropein and the ligstroside derivatives
(median, 251 mg/kg), and the sum of oleuropein, the ligstroside
derivatives, tyrosol, hydroxytyrosol, lignans and phenolic acids
(median, 308 mg/kg) were higher in the fresh oils compared to
the levels of oleuropein and the ligstroside derivatives (median,
162 mg/kg) and the sum of oleuropein, the ligstroside
derivatives, tyrosol, hydroxytyrosol, lignans and phenolic acids
(median, 226 mg/kg) in the oils stored for 1 year and for 2
years. The sum of tyrosol and hydroxytyrosol was higher in the
oils stored for 2 years (median, 32 mg/kg), compared to fresh
and 1-year-stored oils (median, 14 mg/kg). Statistical analysis
(Wilcoxon–Mann–Whitney tests) showed that these differences
were significant in the case of the sum of oleuropein and the
ligstroside derivatives (z = 5.226; p <0.005), the sum of
oleuropein, the ligstroside derivatives, tyrosol, hydroxytyrosol,
lignans and phenolic acids (z = 4.322; p <0.005), and the sum
of tyrosol and hydroxytyrosol (z = -4.970; p <0.005). The
relatively high content of the sum of oleuropein, the ligstroside
derivatives, tyrosol, hydroxytyrosol, lignans and phenolic acids
in the 2-year-stored oils (median, 296 mg/kg; minimum, 138

mg/kg; maximum, 594 mg/kg) is in agreement with the
concept that when the transformation pathway of the phenolic
compounds is reaching its end, oleuropein and the ligstroside
derivatives become substituted with the end-stage compounds
tyrosol and hydroxytyrosol.

3.2. Sensory properties

A high content of phenolic compounds gives an oil its
characteristic bitter taste and pungent tactile sensation.
According to the present study, the intensity of bitterness
(median, 3.9) and pungency (median, 4.6) in the olive oils was
highest in the “Istrska belica” oil compared to the oils of the
other varieties, such as “Leccino” (medianbitterness, 3.3;
medianpungency, 3.9) and “Maurino” (medianbitterness, 3.5;
medianpungency, 4.0). Statistical analysis (Wilcoxon–Mann–
Whitney tests) showed that the differences between the
intensity of bitterness and pungency in the olive oils from
“Istrska belica” and the other analysed oils were significant
(zbitterness = -3.111. pbitterness = 0.002; zpungency = -3.688, ppungency
<0.005). Moreover, the olive oil from “Istrska belica” had a
wide range for its sensory profile. In the olive oil from “Istrska
belica” there were tastes reminiscent of artichoke, almond,
tomato, green-leaf and vanilla. In comparison, in olive oil from
“Maurino” there were only tastes reminiscent of green-leaf and
almonds.

As for the phenolic compounds in olive oil, the sensory
properties of olive oils can vary greatly on a yearly basis. The
highest medians of bitterness (median, 3.7; minimum, 1.6;
maximum 4.4) and pungency (median, 4.6; minimum, 1.9;
maximum, 5.4) in these olive oils were found for the fresh olive
oil from crop year 2012. The bitterness and pungency of olive
oils are influenced by the phenolic compounds in the olive oil.
Therefore, the highest median score of bitterness and pungency
might be due to the extreme weather conditions, which
included a drought in crop year 2012 [46]. However, the highest
bitterness and pungency in 2012 were only evident for oils from
varieties such as “Istrska belica”, “Črnica” and “Leccio del
corno”, while for many varieties included in this study, this was
not noted (Figure 3). This might be because the specific
composition of phenolic compounds of the olive oils depends
on the variety. However, due to the relatively low numbers of
samples for each variety, with exception of “Istrska belica”,
“Maurino” and “Leccino”, further investigations are necessary
to confirm these observations.

Bitterness and pungency are highly dependent on the
phenolic compounds in olive oil, and these sensory properties
also decreased after 2 years of storage (Figure 4). Like the
variation in bitterness and pungency according to the crop year
that depended on the specific varieties (Figure 3), the variation
in the bitterness and pungency according to the time of storage
was also highly dependent on the variety. “Istrska belica”
preserved a similar intensity of bitterness and pungency after 1
year of storage, compared to the fresh oil. This was not seen for
varieties such as “Leccino” and “Maurino”, where bitterness
and pungency decreased greatly after only 1 year of storage
(Figure 4). The intensities of bitterness and pungency in the
olive oil from “Istrska belica” decreased greatly only after 2
years of storage. These findings are in agreement with the
content of oleuropein and the ligstroside derivatives in “Istrska
belica” in oil from the crop year 2011 (Table 1). Therefore, it is
important to emphasise the advantages that this domesticated
variety provides compared to the other varieties that are grown
in this study region.

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Table 1. Mean data (±standard deviation/ range) for the sums of the compounds determined (as indicated) in the fresh olive oils and after 1 and 2 years
of storage, for the oils of the different olive varieties analysed.

Storage
(years)

Variety Crop
year

n Sum of oleuropein and
the ligstroside derivatives

(mg/kg)

Sum of TyrOH
and Tyr
(mg/kg)

Sum of oleuropein and
ligstroside derivatives,

Tyr, TyrOH, lignans and phenolic
acids

(mg/kg)

Total phenolic
compounds
(mg/kg)

Fresh “Istrska belica” 2011 6 251 ±58 11 ±2 321 ±68 491 ±105

2012 8 429 ±74 21 ±19 514 ±93 664 ±118

2013 6 373 ±70 12 ±7 449 ±79 604 ±105

“Leccino” 2011 6 197 ±78 6 ±2 225 ±82 293 ±105

2012 5 340 ±178 21 ±21 389 ±170 465 ±188

2013 4 211 ±127 6 ±3 239 ±124 302 ±137

“Maurino” 2011 2 141 ; 225 8 ; 10 200 ; 289 200 ; 289

2012 2 251 ; 326 7 ; 8 309 ; 383 308 ; 383

2013 2 121 ; 160 2 ; 8 180 ; 210 180 ; 210

“Buga” 2011 2 207 ; 240 7 ; 12 253 ; 276 327 ; 349

2012 1 326 9.0 375 461

2013 1 189 6.0 229 292

“Črnica” 2011 2 157; 189 20 ; 20 222 ; 271 306 ; 377

2012 1 364 40 469 573

2013 2 142 ; 261 29 ; 97 283 ; 318 358 ; 424

“Leccio del corno” 2011 1 159 6.0 219 318

2012 1 367 5 424 516

2013 1 128 2 157 253

“Leccione” 2011 1 184 12 227 360

2012 1 285 21 335 450

2013 1 394 19 446 556

“Arbequina” 2011 1 187 2 226 271

2012 0 / / / /

2013 0 / / / /

“Komuna” 2011 1 266 15 343 492

2012 0 / / / /

2013 0 / / / /

“Mata” 2011 1 213 11 249 362

2012 0 / / / /

2013 1 166 21 232 295

Mixed 2011 6 171 ±46 8 ±2 226 ±50 320 ±72

2012 5 328 ±46 9 ±3 385 ±51 492 ±62

2013 5 288 ±205 9 ±3 351 ±241 482 ±310

All 2011 31 198 ±59 9 ±4 250 ±67 351 ±108

2012 25 356 ±104 17 ±16 422 ±115 533 ±144

2013 24 259 ±138 14 ±19 318 ±155 426 ±201

1 “Istrska belica” 2011 6 247 ±56 37 ±10 345 ±69 508 ±86

2012 8 318 ±83 42 ±25 396 ±103 566 ±124

“Leccino” 2011 6 159 ±54 13 ±6 194 ±62 270 ±80

2012 5 232 ±121 23 ±10 273 ±119 375 ±167

“Maurino” 2011 2 104 ; 148 24 ; 36 177 ; 234 288 ; 321

2012 2 176 ; 227 20 ; 25 244 ; 285 368 ; 400

“Buga” 2011 2 189 ; 214 20 ; 26 242 ; 265 335 ; 376

2012 1 212 17 254 343

“Črnica” 2011 2 142 ; 148 27 ; 32 215 ; 233 309 ; 342

2012 1 317 54 412 587

“Leccio del corno” 2011 1 107 20 177 282

2012 1 257 19 304 452

“Leccione” 2011 1 140 43 217 364

2012 1 180 30 223 339

“Arbequina” 2011 1 173 6 220 270

2012 0 / / / /

“Komuna” 2011 1 259 46 369 512

2012 0 / / / /

“Mata” 2011 1 155 24 198 316

2012 0 / / / /

Mixed 2011 6 126 ±45 22 ±7 192 ±48 290 ±70

2012 5 215 ±47 26 ±9 276 ±53 402 ±63

All 2011 31 166 ±64 25 ±12 233 ±80 340 ±113

2012 25 252 ±88 31 ±18 314 ±102 447 ±140

2 “Istrska belica” 2011 6 142 ±33 65 ±19 256 ± 56 458 ±108
“Leccino” 2011 6 106 ±63 18 ±8 145 ±65 237 ±88
“Maurino” 2011 2 48 ; 143 32 ; 48 129 ; 241 212 ; 345
“Buga” 2011 2 135 ; 188 27 ; 40 190 ; 237 296 ; 368
“Črnica” 2011 2 101 ; 144 32 ; 41 168 ; 239 287 ; 353
“Leccio del corno” 2011 1 96 32 178 335
“Leccione” 2011 1 78 64 / /
“Arbequina” 2011 1 171 10 225 267
“Komuna” 2011 1 173 68 288 473
“Mata” 2011 1 102 33 153 257

Mixed 2011 6 89 ±30 22 ±7 166 ±35 272 ±49

All 2011 31 114 ±46 25 ±12 189 ±63 312 ±109

ACTA IMEKO | www.imeko.org April 2016 | Volume 5 | Number 1 | 27

3.3. Correlations between sensory profiles and phenolic
compounds in the olive oils Managing frames

As indicated in the literature, the relationship between the
sensory parameters in virgin olive oils and the levels of total
phenolic compounds is well known [36], [1]. The significant
positive correlation between the levels of oleuropein and the
ligstroside derivatives and bitterness and pungency is in
agreement with the literature [1], [39], [40], based on the present
data, it is very difficult to make assumptions about which
phenolic compound is attributed to the chemo-aesthetic
perception of pungency and bitterness. This is mainly because
of the significant high correlations between the levels of
specific assigned phenolic compounds in the collected samples.
Due to these significant correlations, factor analysis was
applied. The Spearman correlations between the pungency and
bitternes was increasingly significant for the factors that
included oleuropein aglycone, ligstroside aglycone, lignans
(factor 1) and the dialdehyde forms of decarboxymethyl
oleuropein aglycone and decarboxymethyl ligstroside aglycone
(factor 2).

4. CONCLUSIONS

The content of the phenolic compounds and the sensory
properties of these virgin olive oils varied greatly according to
variety and crop year. According to our data, the content of
total phenolic compounds, the levels of oleuropein and the
ligstroside derivatives, the intensity of bitterness, and the
pungency were greatest in “Istrska belica” fresh olive oil,
compared to the other oil varieties analysed here. This study
confirms that a high content of phenolic compounds and an
astringent and bitter taste is a specific characteristic of “Istrska
belica” olive oil. Moreover, “Istrska belica” olive oil has a wide
range in its sensory profile, where the tastes are reminiscent of
artichoke, almond, tomato, green-leaf, and vanilla.

The levels of the phenolic compounds and the sensory
properties of these high quality olive oils are closely related. A
significant positive correlation was found between the levels of
oleuropein and the ligstroside derivatives and the bitterness and
pungency. The total phenolic compounds of these olive oils
decreased after 1 year and 2 years of storage. While the levels of
oleuropein and the ligstroside derivatives significantly decreased
with this storage, the end-stage compounds tyrosol and
hydroxytyrosol increased after 2 years of storage. “Istrska

belica” oil maintains similar levels of oleuropein and the
ligstroside derivatives and of the intensity of bitterness and
pungency after 1 year of storage, compared to the fresh oil.
This was not evident for the other varieties involved in the
present study. The intensities of bitterness and pungency of the
“Istrska belica” olive oil decreased greatly only after 2 years of
storage. Overall, it is important to note the advantages that
“Istrska belica” olives have compared to the other varieties that
are grown in Slovenian olive groves.

ACKNOWLEDGEMENT

This work was supported by EU founded project Uelije. The
authors are grateful to Teja Hladnik, Saša Volk and Katja Fičur
for their technical support.

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Figure 3. Sensory profiles of the various varieties and the mixed sample, as indicated, of the fresh olive oils from the crop years 2011, 2012 and 2013.

ACTA IMEKO | www.imeko.org April 2016 | Volume 5 | Number 1 | 29

Figure 4. Sensory profiles of various varieties (as indicated) for the fresh olive oil from crop year 2011, after 1 year and 2 years of storage.

ACTA IMEKO | www.imeko.org April 2016 | Volume 5 | Number 1 | 30

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