© The Authors, 2021, Published by the Universidad del Zulia*Corresponding author: jvera1092@utm.edu.ec
Phytochemical characterization of the ethanolic extract, antioxidant activity, phenolic content
and toxicity of the essential oil of Curcuma longa L.
Caracterización toquímica del extracto etanólico, actividad antioxidante, contenido fenólico y
toxicidad del aceite esencial de Curcuma longa L.
Caracterização toquímica do extrato etanólico, atividade antioxidante, conteúdo
fenólico e toxicidade do óleo essencial de Curcuma longa L.
Jonathan Michael Vera Vera
1*
Alex Alberto Dueñas-Rivadeneira
2
Joan Manuel Rodríguez Díaz
3
Matteo Radice
4
Rev. Fac. Agron. (LUZ). 2022, 39(1): e223906
ISSN 2477-9407
DOI: https://doi.org/10.47280/RevFacAgron(LUZ).v39.n1.06
Food Technology
Associate editor: Dra. Gretty Etienne
1
Maestría en Agroindustria. Instituto de Posgrado;
Universidad Técnica de Manabí. Ecuador.
2
Departamento de Procesos Agroindustriales. Facultad Ciencias
Zootécnicas; Universidad Técnica de Manabí. Ecuador.
3
Departamento de Procesos Químicos. Facultad Ciencias
Matemáticas Físicas y Químicas, Universidad Técnica de
Manabí. Ecuador.
4
Departamento de ciencias de la tierra, Universidad Estatal
Amazónica. Ecuador.
Received: 22-02-2021
Accepted: 28-05-2021
Published: 16-12-2021
Abstract
Curcuma longa L. tubers rhizomes are commonly used as a spice, dye,
starch source, and in ancient medicine. Due to its functional properties,
extracts and essential oil of ethanolic extract C. longa have been used as
an antifungal, antimicrobial, antioxidant and anti-inammatory agent, so it
can be an alternative for its potential use in the food industry. Therefore,
in this work, the phytochemical characteristics of the extracts, the phenolic
content, the antioxidant activity and the toxicity of the essential oil of C.
longa were evaluated. The phytochemical characterization of the ethanolic
extract was carried out through a phytochemical screening (alkaloids,
avonoids, phenols, saponins, tannins, quinones, resins and reducing sugars)
and the extraction of the essential oil by means of hydrodistillation. The
determination of the total phenolic content (TPC) was carried out using
the Folin-Ciocalteu method; the antioxidant activity with the ABTS and
DPPH methods and the oil toxicity by the resazurin reduction method using
Escherichia coli as a biosensor. The results obtained in the phytochemical
screening indicate the presence of tannins, alkaloids, avonoids, saponins,
quinones and reducing sugars. The total phenolic content (TPC) was 50.99
mg GAE.g
-1
, the inhibition coefcient (IC
50
) of the ABTS radical was
426.943 µg.mL
-1
and the DPPH radical was 2274.024 µg.mL
-1
. The mean
lethal concentration (LC
50
) of turmeric essential oil for E. coli was 2585.69
mg.L
-1
. It is concluded that turmeric essential oil has a high phenolic content,
high antioxidant activity and low toxicity for E. coli, which is why it is
recommended for use in the food industry.
Keywords:
Rhizomes
Secondary metabolites
Phenols
Antioxidants
Resazurin
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2-7 |
Resumen
Los tubérculos rizomas de Curcuma longa L. se utilizan como
especia, tinte, fuente de almidón y en la medicina ancestral. Debido
a sus propiedades funcionales, los extractos y el aceite esencial
de C. longa se emplea como agente antifúngico, antimicrobiano,
antioxidante del extracto etanolico y antiinamatorio, por lo que puede
ser una alternativa para su uso en la industria de alimentos. En este
trabajo se evaluaron las características toquímicas de los extractos,
el contenido fenólico, la actividad antioxidante y la toxicidad del
aceite esencial de C. longa. La caracterización toquímica del
extracto etanólico se realizó a través de un tamizaje toquímico
(alcaloides, avonoides, fenoles, saponinas, taninos, quinonas, resinas
y azúcares reductores) y la extracción del aceite esencial mediante
hidrodestilación. La determinación del contenido fenólico total
(TPC) se realizó empleando el método Folin-Ciocalteu; la actividad
antioxidante con los métodos ABTS y DPPH y la toxicidad del aceite
por el método de reducción de resazurina utilizando Escherichia coli
como biosensor. Los resultados obtenidos en el tamizaje toquímico
indican la presencia de taninos, alcaloides, avonoides, saponinas,
quinonas y azúcares reductores. El contenido fenólico total (TPC) fue
de 50,99 mg GAE.g
-1
, el coeciente de inhibición (IC
50
) del radical
ABTS fue de 426,943 µg.mL
-1
y del radical DPPH fue de 2274,024
µg.mL
-1
. La concentración letal media (CL
50
) del aceite esencial
de cúrcuma para E. coli fue de 2585,69 mg.L
-1
. El aceite esencial
de cúrcuma presenta un alto contenido fenólico, una alta actividad
antioxidante y una baja toxicidad para E. coli, por que se recomienda
su uso en la industria alimenticia.
Palabras clave: rizomas, metabolitos secundarios, fenoles,
antioxidantes, resazurina.
Resumo
Os tubérculos rizomas de Curcuma longa L. são comumente
usados como tempero, corante, fonte de amido e na medicina antiga.
Pelas suas propriedades funcionais, os extratos e óleos essenciais de
C. longa têm sido utilizados como agente antifúngico, antimicrobiano,
antioxidante e antiinamatório, podendo ser uma alternativa para
potencial uso na indústria alimentícia. Portanto, neste trabalho, foram
avaliadas as características toquímicas dos extratos, o teor fenólico,
a atividade antioxidante e a toxicidade do óleo essencial de C. longa. A
caracterização toquímica do extrato etanólico foi realizada por meio
de uma triagem toquímica (alcalóides, avonóides, fenóis, saponinas,
taninos, quinonas, resinas e açúcares redutores) e da extração do óleo
essencial por meio de hidrodestilação. A determinação do conteúdo
fenólico total (CTP) foi realizada pelo método de Folin-Ciocalteu; a
atividade antioxidante pelos métodos ABTS e DPPH e a toxicidade
do óleo pelo método de redução da resazurina usando Escherichia
coli como biossensor. Os resultados obtidos na triagem toquímica
indicam a presença de taninos, alcalóides, avonóides, saponinas,
quinonas e açúcares redutores. O conteúdo fenólico total (TPC) foi de
50,99 mg GAE.g
-1
, o coeciente de inibição (IC
50
) do radical ABTS
foi de 426,943 µg.mL
-1
e do radical DPPH foi de 2274,024 µg.mL
-1
.
A concentração letal média (CL
50
) do óleo essencial de cúrcuma para
E. coli foi de 2585,69 mg.L
-1
. Conclui-se que o óleo essencial de
cúrcuma possui alto teor fenólico, alta atividade antioxidante e baixa
toxicidade para Escherichia coli, por isso é recomendado para uso na
indústria alimentícia.
Palavras-chave: rizomas, metabólitos secundários, fenóis,
antioxidantes, resazurina.
Introduction
Turmeric (Curcuma longa L.) is a native plant of Southeast Asia
and belongs to the Zingiberaceae family (Du et al., 2006). It is a
perennial plant that grows between 90 to 150 centimeters in height and
is cultivated in countries with tropical climates (Du et al., 2006). It is
generally used as a spice, dye, source of starch (Ferreira et al., 2013)
and ancestral medicine for the cure of various diseases. Among its
many therapeutic properties, its anti-inammatory, hepatoprotective,
antimicrobial, antioxidant, antitumor and antiviral activity stands
out (Parveen et al., 2013). In addition, its therapeutic potential for
the treatment of neurodegenerative, cardiovascular, pulmonary,
metabolic and autoimmune diseases is highlighted (Aggarwal &
Harikumar, 2009).
Essential oils EOs (EA) are made up of a complex mixture of
volatile substances, and can be found in the leaves, stems, bark, roots,
fruits and seeds of plants (Sánchez-González et al., 2011). They
are considered as secondary metabolites and for the most part they
are responsible for giving it the characteristic aromas and avors
(Sánchez-González et al., 2011).
The increase in demand for products that contain ingredients
or additives from natural sources and given that the Food and
Drug Administration (FDA) classies essential oils as “generally
recognized as safe” (GRAS) products, due to the fact that they have
a low toxicity and do not present adverse effects on health, has
generated great interest for the use of these compounds for use as an
additive, preservative, antimicrobial agent, antifungal agent, among
others.
Turmeric essential oil has a wide variety of uses reported as:
nutritional additive in sh farming (Negrete and Secaira, 2016),
additive for edible coatings (Campo et al., 2017), antifungal agent
(Damalas, 2011; Naveen et al. , 2016; Abdelgaleil et al., 2019),
antimicrobial agent (Parveen et al., 2013; Teles et al., 2019),
antioxidant and anti-inammatory agent (Vijayasteltar et al., 2011).
These uses may be determined by the functional properties of this
oil, and it is important to note that these depend on factors such as
the type of soil and other climatic variables of the growing area of
the plant species.
Therefore, the objective of this study was to evaluate the
phytochemical characteristics of the extracts, the phenolic content,
the antioxidant activity and the toxicity of the essential oils obtained
from the rhizomes of Curcuma longa L. cultivated in the province of
Manabí for their potential use in the food industry.
Materials and methods
Plant material
The plant material used in the present study (turmeric rhizomes)
was collected in the Ricaurte locality of the Chone canton, Manabí
province, Ecuador (North Latitude 0°34ˈ24”, West Longitude
80°2ˈ39”). The microorganism used for the toxicity test was
Escherichia coli, identied and isolated in the microbiology
laboratory of the Universidad Técnica de Manabí. The tests described
below were performed in triplicate.
Phytochemical screening
Before phytochemical screening, an extraction of the turmeric
rhizomes was carried out by the Soxhlet method using ethanol (96
%) as solvent. To do this, 30 g of previously scratched vegetable
matter (wet mass) were weighed, placed in a cartridge and extraction
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3-7 |
was carried out with 250 mL of ethanol. The process was concluded
after three recirculations in the equipment. The phytochemical tests
were carried out on the ethanolic extract obtained, according to the
methodology described by Ramos and Solorzano (2016) with some
modications.
Ferric chloride assay (phenolic compounds and/or tannins):
Two (2) mL of ethanolic extract were used in a test tube, to which
100 µL 5% ferric chloride (Sigma Aldrich) solution were added in
physiological saline solution. The test is considered positive (+++)
when the solution is colored: wine-red, deep green or blue.
Wagner’s test (alkaloids): Two (2) mL of the extract were added
to a test tube to later acidify the medium with three (3) drops of
concentrated hydrochloric acid (Fisher Scientic). Then six (6) drops
of Wagner’s reagent were added, to proceed to observe the color
changes. It is considered positive in the following ranges: presence
of opalescence (+), presence of dened turbidity (++) and presence
of precipitate (+++).
Shinoda test (avonoids): Two (2) mL of extract were added
to a test tube and it was diluted with two (2) mL of concentrated
hydrochloric acid, then a piece of metallic magnesium tape was added
to allow it to react by ve (5) minutes. After the established time,
two (2) mL of amyl alcohol were added, mixing the phases, and then
allowed to stand until separated. The test is considered positive when
the amyl alcohol is colored yellow, orange, brown or red.
Foam test (saponins): One (1) mL of extract was diluted with
ve (5) mL of distilled water and stirred vigorously for 10 minutes.
This test is considered positive if foam appears on the surface of the
solution with a height of more than two (2) mm and it remains for
more than two (2) minutes.
Benedict’s test (reducing sugars): 0.5 mL of the extract was
placed in a test tube and eight (8) mL of Benedict’s reagent were
added; shaken gently and placed in a 70 °C water bath for 15 minutes.
The test is considered positive when there is a change from the blue
hue of the reagent to an orange (+), brick (++) and brown (+++) color.
Bornträger test (quinones): To one (1) mL of ethanolic extract
contained in a test tube, two (2) mL of 20 % sodium hydroxide (Merk)
were added, subsequently, it was stirred and then allowed to stand
until phase separation. The test is considered positive when the upper
phase is colored pink (++) or red (+++).
Resin test: One (1) mL of the extract and ve (5) mL of distilled
water were added, the appearance of a precipitate indicates the
presence of resins.
Preparation of essential oil
The turmeric essential oil was obtained by hydrodistillation using
a Clevenger hydroditillation equipment (Brand Glassco). For the
extractions of the turmeric EO, 60 g (wet mass) of striped rhizomes
and 400 mL of distilled water were used. The extraction time was
three (3) hours.
Determination of phenolic content of essential oil
The determination of the phenolic content was carried out from
the Folin-Ciocalteu test according to the methodology described by
Rover & Brown (2013) with modications. The starting point was a
stock solution of essential oil with a concentration of 2000 mg.L
-1
in
methanol ACS (Merk). Two-hundred (200) µL of sample were taken
from the stock solution, to then add 1.5 mL of distilled water and 100
µL of the Folin-Ciocalteu reagent (Sigma Aldrich) and let stay for
ve (5) minutes. After 200 µL of 20 % m/v sodium carbonate (Merk)
was added, the resulting solution was stirred and allowed to stand at
room temperature in the dark for one hour. Absorption was measured
with a wavelength of 730 nm in a UV-vis spectrophotometer (Model
Genesys 180, ThermoFisher brand), for quantication a gallic acid
calibration curve was prepared (5, 25, 50, 75, 100, 125, 150 mg.L
-1
).
The results were expressed as mg equivalent of gallic acid.g
-1
of
essential oil.
Determination of the antioxidant activity of essential oil
DPPH method
The determination of the in vitro antioxidant activity of turmeric
essential oil was carried out from the DPPH (2,2-diphenyl-1-
picrylhydrazyl) test, according to the methodology described by
Mimica-Dukić et al. (2003) with modications. A 0.1 mM solution
of DPPH (Sigma Aldrich) in methanol was prepared and allowed to
incubate for 24 hours in the dark. Starting from a stock solution of
essential oil with a concentration of 5000 mg.L
-1
in methanol, different
dilutions were made (1000, 1600, 2000, 3000, 4000, 5000 mg.L
-1
). For
the measurement of antioxidant activity, one mL of DPPH solution
was added to one mL of the different samples prepared and it was left
to stand for one hour at room temperature in the dark. Subsequently,
the absorbance was measured in a UV-vis spectrophotometer (model
Genesys 180, brand ThermoFisher) at a wavelength of 517 nm using
a Trolox calibration curve (Sigma Aldrich) (2.5; 5; 10; 15, 30 and
40 µM). The results were expressed as mg equivalent of Trolox.g
-1
of essential oil, and the IC50 (mean inhibitory concentration), was
obtained graphically with the values of the percentage of inhibition
determined by Equation 1 and the concentrations of the prepared
solutions.
Equation 1
ABTS method
The determination of the in vitro antioxidant activity of
turmeric essential oil, using the ABTS test (2,2’-azino-bis
(3-ethylbenzthiazoline-6-sulfonic acid)), was carried out according
to the methodology established by Proestos et al. (2013), with
modications. For the preparation of the ABTS solution, a 7 mM
solution of ABTS (Sigma Aldrich) in water was mixed with a 2.45 mM
potassium persulfate solution (ACROS Organics) in water and left to
incubate for 12 hours in the dark at room temperature. Starting from
a stock solution of essential oil with a concentration of 2000 mg.L
-1
in methanol, different dilutions were made (100, 200, 400, 600, 800,
1000 mg.L
-1
). To measure the antioxidant activity, one mL of ABTS
solution was added to one mL of the different samples prepared and
it was left to rest for one hour at room temperature in the dark, to
then measure the absorbance in a UV-vis spectrophotometer (Model
Genesys 180, brand ThermoFisher) at a wavelength of 734 nm and
with the aid of a Trolox calibration curve (1.25, 2.5, 5, 10, 15 and 20
µM). The results were expressed as mg equivalent of Trolox.g
-1
of
essential oil, and the IC50 was obtained graphically with the solutions
prepared and the percentage of inhibition determined with equation 1.
Determination of essential oil toxicity
The resazurin reduction method for insoluble chemicals
developed by Liu (1986) with modications was used to determine
the toxicity of turmeric essential oil. For the bioassay, a bacterial
culture was prepared in which a colony of the selected microorganism
(E. coli) was transferred into 100 mL of nutrient broth (TM MEDIA),
covered and placed in an incubator for 18 hours at 37 °C. After the
time had elapsed, 15 mL of the broth was transferred under aseptic
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conditions into test tubes to be centrifuged at 4000 rpm for ve
(5) minutes. The supernatant from the tubes was discarded and
the precipitate was resuspended with physiological saline to
centrifuge again, repeating the process until the supernatant was
clear. Next, the absorbance of the suspension of microorganisms
was measured at 600 nm and serial dilutions were carried out at
which absorbances were measured and in parallel they were seeded
on Standard agar (Sigma-Aldrich) in order to build a graph of UFC.
mL
-1
vs absorbance, with this the dilution factor necessary to obtain
a suspension with a concentration of 106 UFC.mL
-1
was calculated.
Dilutions of essential oil and 10 % v/v DMSO (100, 250, 500,
750, 1000, 2000, 5000 mg.L
-1
) were prepared. For the analysis of
the samples, in a test tube, 2.75 mL of nutrient broth, 250 µL of the
oil dilution, one (1) mL of suspension of 106 CFU.mL
-1
and 400 µL
of resazurin (Biotum) were added. For the reagent control, 3.75 mL
of nutrient broth, 250 µL of DMSO solution (Merck) 10 % v/v and
400 µL of resazurin were added. 2.75 mL of nutrient broth, 250 µL
of 10 % DMSO solution, v/v, one (1) mL of suspension of 106 CFU.
mL
-1
and 400 µL of resazurin. The tubes were homogenized and
incubated at 37 °C for ve (5) hours. After the established time, the
absorbances were read at a wavelength of 600 nm. The determination
of the mean lethal concentration (LD
50
) was determined according
to the change from resazurin (blue) to resofurin (pink) expressed
as a percentage of inhibition of bacterial growth. The calculation
of the LD
50
value was carried out through equation 2, obtained by
adjusting the data obtained in a dose-effect model carried out with
the Origen Lab2019 software.
Equation 2
Statistic analysis
The data obtained in the bacterial growth inhibition assays
were analyzed using an analysis of variance (ANOVA) and the
signicance was calculated with a condence level of 95 % with
the Origen Lab2019 software.
Results and discussion
Qualitative phytochemical characterization of Curcuma
longa L.
Phytochemical characterization of the ethanolic extract of
Curcuma longa are presented in table 1.
Table1. Phytochemical compounds present in the ethanolic
extract of rhizomes of Curcuma longa L.
Phytochemical compound Presence
Tannins +++
Alkaloids ++
Flavonoids +++
Saponins +++
Phenols +++
Reducing sugars +
Quinones ++
Resins -
+++ = abundant ++ = moderate + = low - = absent.
Phytochemical screening of the ethanol extract of C. longa
indicates abundant presence of tannins, avonoids, saponins and
phenols. Moderate presence of alkaloids and quinones and low
for reducing sugars (table 1). Freire and Vistel (2015), reported
similar results in the determination of secondary metabolites in
turmeric rhizome powder, identifying tannins, avonoids, saponins,
quinones, reducing sugars, carotenes, coumarins and alkaloids. On
the other hand, Ema and Torres (2018) performed the phytochemical
screening of an ethanolic extract of C. longa, obtaining better
observable results for triterpenes, polysaccharides and phenolic
compounds. In this sense, Sánchez-González et al. (2011), indicate
that the difference in the presence of secondary metabolites may
vary according to genotype, environmental conditions, geographic
location, solvent used, extraction techniques, among other factors.
Phenolic content of Curcuma longa essential oil
The total phenolic content (TPC) of the essential oil of C. longa
was 50.99 mg GAE.g
-1
. Lower concentrations were reported by
Chen et al. (2007) and Choi et al
. (2020), who obtained values of
21.4 mg GAE.g
-1
for methanolic extracts and 8.81 mg GAE.g
-1
for
ethanolic extracts, respectively.
The essential oil of C. longa has a higher phenolic content
compared to methanolic and ethanolic extracts. In this regard,
Bouarab-Chibane et al. (2019), state that a high phenolic content
improves antimicrobial activity, because this type of compound
favors interaction with the cell membrane of microorganisms, thus
inducing irreversible damage to the cytoplasm and could even lead
to intracellular enzyme inhibition. Therefore, essential oils with a
high phenolic content, such as the essential oil of Curcuma longa L.,
can be an alternative for use in the agri-food industry, for example,
to avoid post-harvest food losses, which are around 55 % in Latin
America and the Caribbean (Food and Agriculture Organization of
the United Nations (FAO, 2019), the main factors of food spoilage
being fungi and pathogenic bacteria (Aguilar-Veloz et al. , 2020).
Antioxidant activity of Curcuma longa essential oil
ABTS radical inhibition activity
Figure 1 shows the inhibition percentages of the ABTS radical
by action of the essential oil of C. longa in a concentration range of
50-500 mg.L
-1
, reaching an inhibition of the radical between 7.918
% and 56.305 %, respectively.
0 100 200 300 400 50 0
0
10
20
30
40
50
60
Inhi bic ión A BTS
Linea
In hibición ABTS (%)
Concentración (mg.L
-1
)
y = 0, 1055x + 4,9575
R² = 0,9903
Figure 1: Inhibition of the radical ABTS by action of turmeric
essential oil.
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The Trolox equivalent value (TEAC) of the essential oil of
turmeric is 30.43 µmol.g
-1
sample and the concentration of essential
oil of C. longa necessary for the inhibition of the ABTS radical by
50 % (IC50) was 426.943 µg .mL
-1
. This value is similar to those
reported by Avanço et al. (2016) and Li & Li (2009), which were
540 µg.mL
-1
and 699.57 µg.mL
-1
, respectively. On the other hand,
Priya et al. (2012) and Kuttan et al. (2011), obtained higher IC50
values of 1541 µg.mL
-1
and 1000 µg.mL
-1
; respectively. For samples
of fresh, dried and cured turmeric, Kutti & Lingamallu (2012),
reported IC50 of 3300 µg.mL
-1
, 1900 µg.mL
-1
and 2100 µg.mL
-1
,
respectively, showing that there are differences in the results. due to
the treatment carried out on the sample before extraction. Therefore,
the evaluated essential oil has a greater capacity to reduce the ABTS
radical than those compared, since at lower IC
50
values, greater
antioxidant capacity. Therefore, the essential oil of C. longa grown
in Manabí has a high potential as an antioxidant agent, being able
to be used in foods with a signicant content of lipids, which due
to oxidation generate an unpleasant taste and odor; also in the
beverage industry, for functional beverages, cereals, snacks, as a
sh preservative and also as an active component in packaging
(Hashemi et al., 2017; Bhavaniramya et al., 2019).
DPPH radical inhibition activity
Figure 2 shows the percentages of inhibition of the DPPH radical
by action of the essential oil of C. longa in a concentration range
of 500-2500 mg.L
-1
, reaching an inhibition of the radical between
34.305 % and 51.630 % in the concentration highest.
0 1000 2000 3000
35
40
45
50
55
Inhibi ción DPPH
Linea
In hibición DPPH (%)
Concentración (mg.L
-1
)
y = 0,10 55x + 4,9575
R² = 0,9903
Figure 2: Inhibition of the radical DPPH by action of turmeric
essential oil.
The Trolox equivalent value (TEAC) of the essential oil of C.
longa is 10.86 µmol.g
-1
sample and the inhibition coefcient for the
radical DPPH is 2274.024 µg.mL
-1
compared to that obtained with
the ABTS radical, it is observed that approximately ve (5) times
more essential oil is needed to be able to inhibit the radical by 50
%, so in the evaluated samples the amount of compounds capable of
stabilizing the DPPH radical are very low, this is because the ABTS
method evaluates both lipophilic and hydrophilic compounds and
the DPPH method only evaluates lipophilic compounds, so it can
be deduced that the amount of lipophilic compounds in the essential
oil of C. longa L. are less than the amount of hydrophilic type
compounds. This value is similar to that obtained by Li & Li (2009),
which was 28421.83 µg.mL
-1
. On the other hand, the essential oil
of C. longa extracted from species cultivated in the Ecuadorian
Amazon has a lower antioxidant activity than the species cultivated
in the province of Manabí - Ecuador, as observed in the study
carried out by Pino et al. (2018), who obtained an IC
50
of 14500
µg.mL
-1
for the one grown in the Ecuadorian Amazon.
Curcuma longa L. essential oil toxicity
The selected bioassay showed sensitivity of E. coli to the
essential oil of C. longa, since effects of the change from resazurin
to resofurin were observed (gure 3), translated into a statistically
signicant inhibition of bacterial growth for the essential oil (p <
0.001). The dose-response model (gure 4) presented a regression
coefcient of 0.99.
Figure 3. Inhibition of Escherichia coli growth measured
through change from resazurin (blue) to resofurin
(pink) a) t = 0 h, b); t = 5 h.
0 1000 2000 3000 4000 5000
-10
0
10
20
30
40
50
60
70
50
Promedio, SD
Inhibición de crecimiento bacteriano (%)
Concentra ción (mg.L
-1
)
Mean, SD
dosis-respuesta
CL
50
Figure 4. Dose-effect relationship of the concentration of
essential oil of Curcuma longa L. in the growth of
Escherichia coli.
Considering that the inhibition of resazurin reduction
indicates a deterioration of cellular metabolism (Dayeh et al.,
2004) and based on the statistical evaluation of the dose-response
relationship, it was determined that the mean lethal concentration
(LD
50
) of turmeric essential oil for E. coli it is 2585.69 mg.L
-1
, a
value that reects a relatively low toxicological response for the
microorganism evaluated, since high concentrations are required to
show an inhibitory response of 50 %. This result coincides with
those reported by Khattak et al. (2005), for ethanolic extracts of C.
longa, in which the mean lethal concentration to inhibit the growth
of Artemia salina was 33 mg.L
-1
, and E. coli in an incubation time
of 24 h showed no inhibition in the growth of it. It is necessary
to mention that the test described in the present investigation
corresponds to a method that assesses toxicity in signicantly
smaller units of time, than those established in the tests carried out
by other authors and although bacteria such as E. coli turn out to be
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Rev. Fac. Agron. (LUZ). 2022, 39(1): e223906. January - March. ISSN 2477-9407.
6-7 |
a good biosensor for toxicity (Charrier et al., 2011) these types of
results are not decisive for the toxicological evaluation of products
intended for human consumption. Although it is appropriate to
indicate that the description of the results regarding the toxicity of
the essential oil of C. longa coincide with those established in other
investigations where the test model (subject) is different (Funk
et al., 2010; Vijayasteltar et al. , 2013). It is also appropriate to
highlight that the acute administration of turmeric essential oil at a
dose of up to ve (5) g of EA per kilogram of weight in rats did not
represent adverse clinical signs or metabolic changes (Vijayasteltar
et al., 2013).
Conclusions
The essential oil of C. longa has a phenolic content similar to
other essential oils used in food formulations, it also has a high
antioxidant activity against ABTS and DPPH radicals, which
makes it a product of potential use for the food industry. Taking into
account that the oil has a low toxicity compared to the test carried
out, its application could be considered safe.
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