CHEMICAL ENGINEERING TRANSACTIONS
VOL. 57, 2017
A publication of
The Italian Association
of Chemical Engineering
Online at www.aidic.it/cet
Guest Editors: Sauro Pierucci, Jiří Jaromír Klemeš, Laura Piazza, Serafim Bakalis
Copyright © 2017, AIDIC Servizi S.r.l.
ISBN 978-88-95608- 48-8; ISSN 2283-9216
Olive Leaves Infuse and Decoct Production: Influence of
Leaves Drying Conditions and Particle Size
Alessandro Casazzaa,b*, Bahar Aliakbariana,b, Mattia Comottoa, Paula Monteiro
Souzac, Patrizia Peregoa,b
a
Department of Civil, Chemical and Environmental Engineering, Genoa University, Via Opera Pia, 15, 16145 Genoa, Italy
b
Research Center of Biologically Inspired Engineering in Vascular Medicine and Longevity, Genoa, Italy
c
Department of Biochemical and pharmaceutical technology, University of São Paulo, 05508-900, SP, Brazil
alessandro.casazza@unige.it
Taggiasca, a cultivar grown typically in western Liguria (Italy) and in the southern regions of France, is a tasty
and sweet olive for table consumption and for the oil production. Olive oil production generates a huge amount
a wastes. Besides the traditional olive mill wastewater and olive pomace, leaves of the trees are considered
by-products and nowadays they are burned or used as animal feeds despite they have high content of
bioactive compounds. Oleuropein, apigenin and vanillic acid are examples of polyphenols contained in olive
leaves and their content changes depending on the cultivar, the region of growth and the harvesting time. The
aim of this work is to valorise one of the by-products of the olive oil industry. The study aims to investigate the
effect of the pre-treatment processes on the production of olive leaves infusion. Different drying techniques
and particles size have been evaluated in order to produce an extract rich in phenolic compounds. Olive
leaves (Taggiasca cultivar) were kindly provided by the Azienda Agricola Castellari company, Savona, Italy.
Leaves were collected and immediately washed and dried at different temperatures (50, 60 and 70 °C) in a
ventilated oven. Moreover, an additional drying at 70 °C was performed under nitrogen atmosphere. In order
to evaluate the effect of the drying temperatures on total polyphenol (TP) and flavonoid (TF) yields and on
antiradical power (ARP) of the extracts, samples were grinded (0.8-0.59 mm) using a laboratory mixer.
Powders were then extracted using ethanol and analysed. Based on those results, the best drying condition
was used to evaluate the influence of the matrix particle size on the extraction yield after ethanol extraction
and teas production. Sieves (4, 9, 16, 20 and 30 Mesh) were used to obtain powder with particles distributed
uniformly in the range 2.19 < A < 4.76, 1.19 < B < 2.19, 0.84 < C < 1.19 and 0.59 < D < 0.84 mm. Olive leaves
teas were prepared as follow: 1) infusion, 200 ml of deionised boiling water were added to 2 g olive leaves
powder and let them soak for 3 min without additional heating; 2) decoction, 200 ml cold water were added to
2 g of olive leaves powder and boiled for 15 min, waiting for 10 min after boiling before carrying on the
analysis. After extracting with ethanol the dried matrix obtained at different temperatures, we found out that
there was not statistical difference (p<0.05) in the TP (25.06±1.00 mgGAE/gDL) and TF (22.23±3.00 mgCE/gDL)
content between samples obtained at 60, 70 °C and 70 °C under nitrogen flow. During the tea production,
within each range of particles size (e.g. B), we found out that decoction is the process that allows to extract
the highest quantity of total polyphenols (41.14±2.56 mgGAE/gDL) and total flavonoids (45.27±3.10 mgCE/gDL).
1. Introduction
Olive trees are largely widespread all over the world and their fruit are of major agricultural importance since
they play a key role in the Mediterranean diet because of the nutritional values and chemical composition.
Taggiasca is a tasty and sweet olive for table consumption even though it is mainly used for the oil production.
Extra virgin olive oil contains a wide range of bioactive compounds, like unsaturated fatty acids and
polyphenols, which are physiologically active and important for a healthy diet and longevity (Aliakbarian et al.,
2011). Particularly, polyphenols compounds are secondary metabolites and possess high antioxidant,
antimicrobial and anti-inflammatory properties. Several studies have shown their beneficial activity against
common human diseases (cancer, cardiovascular diseases, etc.) (Buyukbalci and El, 2008; Palmieri et al.,
DOI: 10.3303/CET1757302
Please cite this article as: Casazza A.A., Aliakbarian B., Comotto M., Monteiro Souza P., Perego P., 2017, Olive leaves infuse and decoct
production: influence of leaves drying conditions and particle size, Chemical Engineering Transactions, 57, 1807-1812
DOI: 10.3303/CET1757302
1807
2012). Oil production generates a huge amount of wastes. Besides the traditional olive mill wastewater and
olive pomace, leaves of the trees are considered by-products and nowadays they are burned or used as
animal feeds despite they have high content of bioactive compounds. Oleuropein, apigenin and vanillic acid
are examples of polyphenols contained in olive leaves and their content changes depending on the cultivar,
the region of growth and the harvesting time (El and Karakaya, 2009). In order to exploit these compounds not
only for medical application but also in the food industry (as dietary supplement or even simply as infusions)
(Aliakbarian et al., 2015), recovery based on extraction processes is required. Several parameters influence
the yield of extraction, but mainly the particle size and drying technique play a key role (Erbay and Icier, 2009).
Drying allows to remove water, thus decreasing the moisture content and improving the shelf life of the
product. Several techniques are able to remove moisture from the leaves and currently two of them are used
for industrial applications: hot air-drying and freeze-drying. The first one is a relatively simple and fast process,
but the high temperature could involve chemical modification of the bioactive compounds, leading to their
degradation. On the other side, freeze-drying could represent a valid alternative where, thanks to the low
temperature, moisture content is removed without any degradation process. Nevertheless, it is one of the most
expensive techniques and the initial freezing process could affect the quality of the final product. For those
reasons, a deep study of the drying techniques is required in order to fully exploit olive leaves potential
(Fellows, 1988).
The aim of this work is to valorise one of the by-products of the olive oil industry. The study aims to investigate
the effect of the pre-treatment processes on the production of olive leaves infusion. Different drying techniques
and particles size have been evaluated in order to produce an extract rich in phenolic compounds. The yields
of extraction have been determined by colorimetric analysis and HPLC-DAD.
2. Section headings
2.1 Materials
Olive leaves (Taggiasca cultivar) were kindly provided by the Azienda Agricola Castellari company, Savona,
Italy. Leaves were collected and immediately washed and dried. Ethanol, methanol, acetonitrile, DPPH
radical, Folin-Ciocalteu reagent and single phenolic standards were purchased from Sigma-Aldrich (Milan,
Italy).
2.2 Sample preparation
Olive leaves were dried at different temperatures (50, 60 and 70 °C) in a ventilated oven (D-82152, MMM
Medcenter, München, Germany) until reaching a proper value of humidity (less than 5 %). Moreover, an
additional drying at 70 °C was performed under nitrogen atmosphere. In order to evaluate the effect of the
drying temperatures on total polyphenols yield and on antiradical power of the extracts, samples were grinded
using a laboratory mixer and separated by sieves (Mesh 20-30) to obtain a homogeneous powder (0.8-0.59
mm). Powders were then extracted and analysed. Based on these results, the best drying condition was used
to evaluate the influence of the matrix particle size on the extraction yield. Sieves (4, 9, 16, 20 and 30 Mesh)
were used to obtain powder with particles distributed uniformly in the range 2.19 < A < 4.76, 1.19 < B < 2.19,
0.84 < C < 1.19 and 0.59 < D < 0.84 mm.
2.3 Olive leaves teas preparation
Olive leave teas were prepared as follow:
• Infusion - 200 mL of deionised boiling water was added to 2 g olive leaves and let them soak for 3 min
without additional heating;
• decoction - 200 mL cold deionised water was added to 2 g of olive leaves and boiled for 15 min, waiting
for 10 min after boiling before carrying on the analysis.
Beside, phenolic fraction was extracted using a solution of ethanol/water (80:20 v/v) in order to compare the
different yields. Briefly, 1.25 g of olive leaves powder were added to 10 ml of solvent and incubated for 24 h in
dark conditions (Buyukbalci and El, 2008). At the end of each different extraction process, all of the samples
were filtered through a paper filter (Whatman 40). The liquid fraction was centrifuged at 6000 ×g for 10 min
(42426, ALC, Milan, Italy).
2.4 Total polyphenols and total flavonoids analyses
A modified version of the Folin-Ciocalteu assay (Casazza et al., 2011; Swain and Hillis, 1959) was used to
quantify the total polyphenols (TP) content of the samples. Analysis were carried out at 725 nm using an UV-
Vis spectrophotometer, model Lambda 25 (Perkin Elmer, Wellesley, MA) and the calibration curve was made
using standard solutions of gallic acid in the range 0.01-1.00 mg/mL. Total Polyphenol yield (TPY) was
1808
expressed as milligrams of gallic acid equivalents per gram of dried leaves (mgGAE/gDL) and it was calculated
using the following equation:
DL
SABSTPY ×=
7.1
725 (1)
where ABS725 is the absorbance at 725 nm, 1.7 is the slope of the calibration curve, S is the volume (mL) of
the extractive solvent and DL are the grams of dried olive leaves powder.
Total flavonoid (TF) content of the olive leaves extracts was determined by the colorimetric method described
by (Casazza et al., 2012). The absorbance was measured using the same spectrophotometer as above at 510
nm. Total flavonoid yield (TPY) was expressed as milligrams of catechin equivalents per gram of dried leaves
(mgCE/gDL) and it was calculated using the following equation:
DL
SABSTFY ×=
3.2
510 (2)
Where ABS510 is the absorbance at 510 nm, 2.3 is the slope of the calibration curve, S is the volume (mL) of
the extractive solvent and DL are the grams of dried olive leaves powder.
2.5 Antiradical power determination
The antiradical power of extracts and teas was determined using the DPPH radical method. For each
samples, 0.1 mL of nine different dilutions in methanol were prepared and mixed with 3.90 mL of DPPH˙
methanolic solution (9.15×10-5 mol/L). ARP was defined as 1/EC50 (µgDPPH˙/µLextract).
2.6 HPLC-DAD analysis
Single phenolic compounds were detected and quantified by HPLC (Hewlett Packard, 1100 Series, Palo Alto,
CA, USA) equipped with a C18 reverse-phase column (Model 201TP54, Vydac, Hesperia, CA, USA) coupled
with a DAD detector, following the method described by Ferrari et al. (2014). Briefly, mobile phases were
water/acetic acid (99:1, v/v) (solvent A) and methanol/acetonitrile (50:50, v/v) (solvent B), while the solvent
gradient changed according to the following conditions: from 0 to 5 % B in 5 min, from 5 to 30 % B in 25 min,
from 30 to 40 % B in 10 min, from 40 to 48 % B in 5 min, from 48 to 70 % B in 10 min, from 70 to 100 % B in 5
min and isocratic at 100 % B for 5 min. Runs were performed at 30 °C. Ferulic and Vanillic acids, Catechin,
Epicatechin, Oleuropein and Apigenin were used as standards.
2.7 Statistical analysis
Statistical analysis was performed using ANOVA multiple comparison, followed by Tukey’s post-hoc test,
using a GraphPad Prism 6 software (San Diego, USA). Statistically significant values are presented as * p <
0.05, ** p < 0.01, *** p < 0.001 and **** p < 0.0001.
3. Results and Discussions
3.1 Effect of leaves drying methodology on polyphenol recovery
The results of the influence of drying condition on olive leaves’ moisture content, total polyphenol and
flavonoid yields and antiradical power of the extracts are reported in Table 1.
At all drying conditions, the moisture contents of samples were lower than 4%, which is an acceptable value to
have an optimal storage of a dried product (Sinija et al., 2007; Vidović et al., 2014).
Table 1: olive leaves’ moisture content, total polyphenol (TPY) and flavonoid (TFY) yields and antiradical
power (ARP) of the extracts.
Temperature
(°C)
Drying time
(h)
Moisture content
(%)
TPY
(mgGAE/gDL)
TFY
(mgCAE/gDL)
ARP
(mgDPPH/mLextract)
50 14 3.46 ± 0.43a 12.01 ± 0.60a 6.79 ± 2.43a 8.01 ± 0.32a
60 10 3.65 ± 0.45b 25.53 ± 1.04b 22.25 ± 1.10b 17.42 ± 1.56b
70 7 0.91 ± 0.48a,b 23.75 ± 1.50b 19.25 ± 0.64b 12.80 ± 2.95a,b
70* 7 0.30 ± 0.03a,b 25.90 ± 1.95b 25.18 ± 2.02b 28.07 ± 4.90c
*under N2 flow
1809
The TPYs ranging from 12.01±0.60 to 25.90±1.95 mgGAE/gDL were similar to those reported by Sahin and
Samli (2013). The authors founded the maximum TP content of 25.06 mgGAE/gDL working with 50% of ethanol,
500 mg dried leaf to 10 mL solvent, and 60 min of extraction under ultrasounds.
After extracting the dried matrix obtained at different temperatures, we found out that there was not statistical
difference (p<0.05) in the TP and TF content between samples obtained at 60, 70 °C and 70 °C under
nitrogen flow. There was a slight difference in the antiradical power between the sample obtained at 70 °C
under nitrogen flow and the other samples. Moreover, the extraction of dried matrix at 50 °C led to significantly
lower values (p<0.05) of TP, TF and ARP. As can be observed, drying time had more influence on phenolic
compound yields when compared to drying temperature. High temperature (60 °C) required shorter drying
time than mild temperature (50 °C) to achieve the same final moisture content, while providing more bioactive
compounds. In fact, working at 50 °C for 14 h instead of 60 °C for 10 h, TP and TF yields decreased of 53 and
69 %, respectively. Similar to our observation, Ahmad-Qasem et al. (2013) noticed that the best olive leaf
drying conditions were at higher temperature (120 °C respect to 70 °C) for shorter times.
Table 2 shows the results of HPLC analysis. According to these data, extraction yields obtained at 50 °C are
statistically lower than the one obtained at 60 °C: for example, oleuropein concentration in the sample dried at
60 °C for 10 h was more than 30 times higher than the one in the sample dried at 50 °C for 14 h. The same
consideration was valid for catechin, vanillic acid and ferulic acid, while there was not statically difference for
epicatechin and apigenin.
Table 2: main single phenolic compounds (mg/100gDL) HPLC analysis of olive leaves extracts.
Drying
temperature
(°C)
Catechin Vanillic acid Epicatechin Ferulic acid Oleuropein Apigenin
50 0.05 ± 0.01a 0.08 ± 0.00a 0.09 ± 0.01a 0.01 ± 0.00a 0.15 ± 0.01a 0.05 ± 0.01a
60 0.18 ± 0.03b 0.14 ± 0.01b 0.25 ± 0.02a 0.14 ± 0.01b 5.22 ± 0.76b 0.05 ± 0.01a
70 0.12 ± 0.00a,b 0.13 ± 0.00b 0.27 ± 0.08a 0.15 ± 0.01b 2.98 ± 0.25c 0.03 ± 0.00a
70* 0.21 ± 0.05b 0.17 ± 0.01b 0.25 ± 0.02a 0.15 ± 0.00b 3.68 ± 0.03c,d 0.03 ± 0.00a
*Drying under N2 flow
3.2 Infuse and decoct phenolic concentrations
In order to evaluate the influence of particles size distribution on polyphenols’ release during the decoction
and infusion processes, dried olive leaves at 70 °C under N2 flow were used. Moreover, extraction yields
obtained by infusion and decoction processes have been compared to the one obtained by classic ethanol
extraction.
Figure 1: total polyphenol yield at different olive leaves particle size (2.19 < A < 4.76, 1.19 < B < 2.19, 0.84 <
C < 1.19 and 0.59 < D < 0.84 mm).
1810
In general, we obtained the same trend for both total polyphenol (Figure 1) and flavonoid (Figure 2) yields,
with an increase of extraction yield as a function of the reduction of leaves particle size. Generally, the infusion
process resulted in being the one with the lowest extraction yield.
Figure 2: total flavonoid yield at different olive leaves particle size (2.19 < A < 4.76, 1.19 < B < 2.19, 0.84 < C
< 1.19 and 0.59 < D < 0.84 mm).
Within each range of particles size, we found out that decoction is the process that allows to extract the
highest quantity of total polyphenols and total flavonoids. The difference between this method and the other
two is significant for high meshes (corresponding to low particles size), while it decreases going to lower value
of mesh.
Table 3: main single phenolic compounds (mg/100gDL) HPLC analysis of olive leaves teas obtained using
leaves with different particle size (2.19 < A < 4.76, 1.19 < B < 2.19, 0.84 < C < 1.19 and 0.59 < D < 0.84 mm).
Mesh Catechin Vanillic acid Epicatechin Ferulic acid Oleuropein Apigenin
SL
extraction
A 0.11 ± 0.00a 0.12 ± 0.00a,b,c 0.16 ± 0.01a 0.12±0.01a 3.00 ± 0.25a 0.03 ± 0.00a
B 0.12 ± 0.01a 0.14 ± 0.00a,b,c 0.18 ± 0.01a 0.14±0.01a 3.78 ± 0.21a 0.04 ± 0.00a
C 0.18 ± 0.02a,b 0.13 ± 0.03a,b,c 0.19 ± 0.01a 0.15±0.01a 4.94 ± 0.16a 0.03 ± 0.00a
D 0.18 ± 0.03a,b 0.14 ± 0.01a,b,c 0.25 ± 0.02a 0.14±0.01a 5.22 ± 0.16a 0.05 ± 0.01a
Infusion A 0.28 ± 0.03a,b,c 0.07 ± 0.01c 0.41 ± 0.04a,b 0.14±0.02a 2.06 ± 0.19a -
B 0.31 ± 0.02d 0.09 ± 0.01b,c 0.46 ± 0.05a,b 0.17±0.04a 2.58 ± 0.49a -
C 0.43 ± 0.05d,e 0.16 ± 0.02a,b,d 0.53 ± 0.06a,b 0.24±0.03a 4.53 ± 0.52a -
D 0.50 ± 0.06d 0.16 ± 0.03a,b,d 0.75 ± 0.12b,c 0.27±0.03a,b 2.23 ± 0.31a -
Decoction A 0.25 ± 0.04a,b,c 0.15 ± 0.03a,b,c 0.40 ± 0.06a,b 0.13±0.01a 3.50 ± 0.52a 0.12 ± 0.02a
B 0.78 ± 0.15a,b,c 0.23 ± 0.02d 1.28 ± 0.15d 0.47±0.08c 17.13 ± 2.55b 0.61 ± 0.10b
C 0.62 ± 0.09b,c,e 0.20 ± 0.04a,d 1.00 ± 0.17c,d 0.42±0.07b,c 15.92 ± 2.81b 0.52 ± 0.11b
D 0.78 ± 0.15c,d,e 0.19 ± 0.01a,d 0.97 ± 0.19c,d 0.40±0.06b,c 15.54 ± 2.06b 0.66 ± 0.10b
As concern the single phenolic compounds identified in olive leaves teas (Table 3), we can see that decoction
leads to higher amount of oleuropein and apigenin (ten times higher than values obtained using the SL
extraction). In general, the infusion process leads to phenolic recovery comparable to SL extraction, except for
apigenin that has not been identified in any product.
4. Conclusions
In order to valorise one of the by-products of the olive oil industry, in this study, the effect of the pre-treatment
processes on the production of olive leaves infusion and decoction were investigate. Different drying
techniques and particles size of olive leaves have been evaluated in order to obtain a product rich in phenolic
compounds. Predictably, the extraction yield of total polyphenols and flavonoids increased as a function of the
1811
reduction of leaves particle size. The best drying condition was obtained at 70 °C under nitrogen atmosphere
for a short period (7 h). Decoction process led to the higher phenolic compounds recovery regardless of the
olive leaves particle size.
Reference
Ahmad-Qasem M.H., Barrajón-Catalán E., Micol V., Mulet A., García-Pérez J.V., 2013, Influence of freezing
and dehydration of olive leaves (var. Serrana) on extract composition and antioxidant potential, Food Res.
Int. 50, 189–196.
Aliakbarian B., Casale M., Paini M., Casazza A.A., Lanteri S., Perego P. 2015, Production of a novel
fermented milk fortified with natural antioxidants and its analysis by NIR spectroscopy, LWT - Food Sci.
Technol. 62(1), 376-383.
Aliakbarian B., Casazza A.A., Perego P., 2011, Valorization of olive oil solid waste using high pressure–high
temperature reactor, Food Chem. 128(3), 704-710.
Buyukbalci A., El S.N., 2008, Determination of in vitro antidiabetic effects, antioxidant activities and phenol
contents of some herbal teas, Plant Food. Hum. Nutr. 63(1), 27-33.
Casazza A.A., Aliakbarian B., Perego P., 2011, Recovery of phenolic compounds from grape seeds: effect of
extraction time and solid-liquid ratio, Nat. Prod. Res. 25(18), 1751-1761.
Casazza A.A., Aliakbarian B., Sannita E., Perego P., 2012, High-pressure high-temperature extraction of
phenolic compounds from grape skins, Int. J. Food Sci. Technol. 47(2), 399-405.
El S.N., Karakaya S., 2009, Olive tree (Olea europaea) leaves: potential beneficial effects on human health,
Nutr. Rev. 67(11), 632-638.
Erbay Z., Icier F., 2009, Optimization of hot air drying of olive leaves using response surface methodology, J.
Food Eng. 91(4), 533-541.
Fellows P.J., 1988, Food Processing technology: principles and practice, Ellis Horwood Eds. Hartnolls
Bodmin, Cornwall, Great Britain.
Ferrari P.F., Palmieri D., Casazza A.A., Aliakbarian B., Perego P., Palombo D., 2014, TNFα-induced
endothelial activation is counteracted by polyphenol extract from UV-stressed cyanobacterium Arthrospira
platensis, Med. Chem. Res. 24(1), 275-282.
Palmieri D., Aliakbarian B., Casazza A.A., Ferrari N., Spinella G., Pane B., Cafueri G., Perego P., Palombo D.,
2012, Effects of polyphenol extract from olive pomace on anoxia-induced endothelial dysfunction,
Microvasc. Res. 83(3), 281-289.
Sahin S., Samli R., 2013, Optimization of olive leaf extract obtained by ultrasound-assisted extraction with
response surface methodology, Ultras. Sonochem. 20, 595-602.
Sinija V.R., Mishra H.N., Bal S., 2007, Process technology for production of soluble tea powder, J. Food Eng.
82(3), 276-283.
Swain T., Hillis W.E., 1959. The phenolic constituents of Prunus domestica L.- The quantitative analysis of
phenolic constituents, J. Sci. Food Agric. 10(1), 63-68.
Vidović S.S., Vladić J.Z., Vaštag Ž.G., Zeković Z.P., Popović L.M., 2014, Maltodextrin as a carrier of health
benefit compounds in Satureja montana dry powder extract obtained by spray drying technique, Powder
Technol. 258(0), 209-215.
1812