Academic Editors: Gianluca Caruso and Yiannis Kourkoutas
Background: The Lamiaceae family, one of the most important
herbaceous and shrub plant families, includes a wide variety of plants with
biological and medicinal uses. This study aimed to conduct a comparative analysis
of phenolic compounds content and biological activity of extracts from eight
species of Lamiaceae plants, cultivated in a temperate climate, and to
study the effect of the foliar salicylic acid application on these parameters.
Methods: Lamiaceae plants (Lavandula angustifolia,
Salvia officinalis, Hyssopus officinalis, Agastache
foeniculum, Thymus serpyllum, Mentha
The Lamiaceae family, one of the most important herbaceous and shrub plant families, includes a wide variety of plants with biological and medicinal uses [1]. The family has significant economic value as it includes garden plants and culinary herbs [2]. The most famous members of this family are various aromatic spices such as thyme, mint, oregano, basil, sage, savory, rosemary, hyssop, lemon balm, and a few others which see more limited usage.
Plants of the Lamiaceae family are widely used in herbal medicine.
Their main application is aimed at the treatment of the respiratory and
cardiovascular systems and the gastrointestinal tract as well as; the prevention
of skin diseases, nervous system disorders, allergies, and metabolic disorders
[1, 2, 3]. Their value is inherent in the biosynthesis of a wide range of secondary
metabolites with powerful antioxidant, antibacterial, anti-inflammatory,
antiviral and antitumor effects [4]. Among the secondary metabolites of the
plants of the Lamiaceae family which possess a wide spectrum of
biological activity, the phytochemicals which are part of the essential oils
isolated from these plants are of particular importance. Such components include:
monoterpenes, namely
The biosynthesis of secondary metabolites in plants is highly dependent on environmental factors. For example, the content of secondary metabolites is strongly influenced by such factors as temperature, light, water regime, the availability of mineral nutrients, and more [7]. Even though plants of the Lamiaceae family are found throughout the world, the area where they are most abundant is in the Mediterranean region, with the climate of this area being subtropical and characterized by hot dry summers and warm rainy winters [8]. Cultivation of these plants in a temperate climate, characterized by a cool summer, moderately cold winter, and sufficient levels of precipitation evenly distributed throughout the year, usually leads not only to a decrease in yield but to changes in the qualitative and quantitative profile of the biologically active plant compounds [9, 10].
In addition, the cultivation of some plants of the Lamiaceae family, such as lavender, sage, anise hyssop, and Scarlet beebalm, outdoors in a temperate climate, is fraught with some difficulties due to the thermophilicity of these plants and their low resistance to frost. One of the ways that have been found to increase plant resistance to the actions of unfavorable abiotic factors is the use of plant growth regulators [11, 12]. One of these growth regulators, which is widely used in agricultural practice, is salicylic acid (SA) [13, 14, 15]. It is known that the action of SA is associated with the regulation of dynamic physiological reactions such as photosynthesis, nitrogen and proline metabolism, the functioning of the antioxidant defense system, and the maintenance of water balance. Therefore SA is involved in the operational protection of plants from stress [14, 16]. In addition, it is known that SA affects the accumulation of secondary metabolites, including compounds of the phenolic structure in various plant species [17, 18, 19]. Thus, the use of exogenous salicylic acid can not only increase the resistance of plants to the action of abiotic factors but also improve the nutritional value of crops.
As far as we know, no study of the effect of salicylic acid on the accumulation of phenolic compounds, antioxidant and in vitro antihyperglycemic activity of extracts of Lamiaceae plants cultivated in temperate climates has been carried out. In this regard, the purpose of this study was (i) to conduct a comparative analysis of the content of phenolic compounds in eight species of plants of the Lamiaceae family, cultivated in a temperate climate, and the biological activity of their extracts; (ii) to study the effect of foliar treatment with salicylic acid on the content of phenolic compounds, antioxidant and the in vitro antihyperglycemic activity of extracts of plants of the Lamiaceae family.
Plants of the Lamiaceae Martinov family used as research objects:
lavender (Lavandula angustifolia Mill.), sage (Salvia
officinalis L.), hyssop (Hyssopus officinalis L.), anise hyssop
(Agastache foeniculum (Pursh) Kuntze), thyme (Thymus serpyllum
L.), peppermint (Mentha
Basic meteorological data for (A) 2019 (planting) year and (B) 2020 (harvesting) year at the experiment site.
Treatment of plants with salicylic acid (SA) was carried out in the second year
after planting using the foliar method. To prepare a solution of SA, salicylic
acid (ACS reagent,
In this study, inorganic fertilizers and pesticides were not used during the entire experiment, and weed control was carried out manually. The experiment was carried out with three replicates for each treatment (SA and control) and each plant species. There were 48 test plots in total. The plots were arranged in a Randomized Complete Block Design.
The collection of plants was carried out at the flowering stage in the period
from August to September 2020. After collection, the aboveground parts of the
plants were dried at a temperature of 60
To obtain extracts, 10.0 mL of a 60% aqueous solution of methanol was added to a weighed portion of plant material (0.1 g). Extraction was carried out for 40 minutes at 1400 rpm (MPS-1, Biosan). The extraction conditions (concentration of methanol, solvent volume to plant mass ratio, and time of extraction) were preliminarily determined based on one-factor-at-a-time experiments (data not shown). The resulting extracts were centrifuged at 4500 rpm for 10 minutes. The extraction was repeated three times. The combined supernatants were used to further determine the content of phenolic compounds and antioxidant activity.
To determine the inhibitory activity of the extracts against
The total content of hydroxycinnamic acids was determined spectrophotometrically
by reaction with Arno’s reagent according to [20]. To construct a calibration
graph, standard solutions of rosmarinic acid with a precisely known concentration
were used. The total content of hydroxycinnamic acids was expressed in mg of
rosmarinic acid equivalents per gram of dry mass of plant (mg RAE g
The flavonoid content was determined by the reaction with AlCl
The total content of phenolic compounds was determined spectrophotometrically by
using Folin–Ciocalteu phenol reagent [22]. Standard solutions of gallic acid
with a precisely known concentration were used to construct a calibration graph.
The total content of phenolic compounds was expressed in mg of gallic acid
equivalents per gram of dry mass of plant (mg GAE g
Antioxidant activity (AOA) of the extracts was measured by the ability to
scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2
Antihyperglycemic activity of the extracts was measured in vitro by
their ability to inhibit
Extractions and analyzes were carried out in triplicate.
The data obtained were statistically processed using the OriginPro 2019b
software (OriginLab Corporation, USA). The graphs show mean values with standard
deviation (n = 3). In the analysis, only biological replicates were
taken into account, since technical and analytical errors made a small
contribution to the variance of the data. To identify statistically significant
differences between the experimental variants, the data was processed using
one-way ANOVA for each factor separately (plant species, SA-treatment). The Tukey
test was used as the criterion to determine the significance of differences at a
significance level of p
Hydroxycinnamic acids are an important component of the phytochemical profile of
the Lamiaceae plants. The total content of hydroxycinnamic acids in the
studied plant species of the Lamiaceae family varied from 1.6 to 6.4 mg
RAE g
Effect of salicylic acid on the hydrocinnamic acids content in plants of Lamiaceae family. THA, hydrocinnamic acids; RAE, rosmarinic acid equivalents; C, control; SA, salicylic acid.
Foliar treatment of plants with 1 mM salicylic acid solution stimulated the accumulation of hydroxycinnamic cinnamon in lavender (2.0 times), sage (1.3 times), hyssop (1.7 times), oregano (1.6 times), and Scarlet beebalm (2.7 times) (Fig. 2).
Among the control plants that were not treated with a salicylic acid solution,
the maximal content of flavonoids was found in anise hyssop (Fig. 3). The total
content of flavonoids in it was 6.5
Effect of salicylic acid on the flavonoids content in plants of Lamiaceae family. TFC, total flavonoids content; RE, rutin equivalents; C, control; SA, salicylic acid.
Even though almost all species showed an increase in the content of flavonoids at the foliar treatment of plants with salicylic acid, statistically significant differences were found only for two species namely lavender and sage. In plants of these species, the content of flavonoids was 1.4 times higher than in the control plants (Fig. 3).
Hyssop, anise hyssop, and Scarlet beebalm were distinguished by a high total
content of phenolic compounds among the control plants (Fig. 4). The total
content of phenolic compounds in them was 13.5
Effect of salicylic acid on the total phenolic compounds content in plants of Lamiaceae family. TPC, total phenolic compounds content; GAE, gallic acid equivalents; C, control; SA, salicylic acid.
Foliar treatment with salicylic acid stimulated a significant increase in the content of phenolic compounds in all studied species, except thyme. In thyme, no significant differences were found between the control samples and the treated plants (Fig. 4). The greatest changes in the content of phenolic compounds were found in lavender and sage plants (1.7 and 1.6 times, respectively). In other species, the increase in phenolic compounds ranged from 1.2 to 1.4 times.
Among the control plants, the anise hyssop and hyssop were characterized by the
highest antioxidant activity against the DPPH and ABTS radicals (Figs. 5 and 6).
The antioxidant activity measured by the DPPH assay was 64.2
Effect of salicylic acid on the antioxidants activity measured by DPPH assay of extracts from plants of Lamiaceae family. AOA (DPPH), antioxidants activity measured by DPPH (2,2-diphenyl-1-picrylhydrazyl) assay; TE, Trolox equivalents; C, control; SA, salicylic acid.
Effect of salicylic acid on the antioxidants activity measured
by ABTS assay of extracts from plants of Lamiaceae family. AOA (ABTS),
antioxidants activity measured by ABTS
(2,2
Extracts from hyssop plants were also characterized by high ferric reduced power
activity (FRAP), which was 44.7
Effect of salicylic acid on the antioxidants activity measured by FRAP assay of extracts from plants of Lamiaceae family. AOA(FRAP), antioxidants activity measured by FRAP (ferric reducing antioxidant power) assay; TE, Trolox equivalents; C, control; SA, salicylic acid.
After foliar treatment of plants with salicylic acid, the antioxidant activity of the extracts of experimental plants increased or was not significantly different in comparison with control plants. Significantly higher values of antioxidant activity (according to the DPPH assay) were found for lavender (1.8 times), hyssop (1.3 times), anise hyssop (1.4 times), thyme (1.2 times), Scarlet beebalm (1.2 times) treated with salicylic acid in comparison with control plants of the same species (Fig. 5). Significantly higher values of antioxidant activity (according to the ABTS assay) were found only for three species, in particular, for lavender (1.5 times), hyssop (1.3 times), and anise hyssop (1.2 times) (Fig. 6). A significant increase in ferric reduced power activity (FRAP) after treatment with salicylic acid was observed in lavender (1.7 times), hyssop (1.2 times), peppermint (1.3 times), and oregano (1.4 times) (Fig. 7).
All the studied extracts had the ability to inhibit
Effect of salicylic acid on the
Effect of salicylic acid on the
After foliar treatment with salicylic acid, the inhibitory activity against
The inhibitory activity against
Antioxidant activity depends on the content of various classes of phytochemicals
in plants. Usually, phenolic compounds contribute significantly to the
antioxidant activity of extracts. The correlation analysis carried out by us
revealed a positive relationship between the content of various groups of
phenolic compounds and the antioxidant activity of extracts of the plants of the
Lamiaceae family (Table 1). A high degree of correlation was noted
between the antioxidant activity, measured using the DPPH assay, and the content
of hydroxycinnamic acids (r = 0.77, p
Parameters | THA |
TFC | TPC | AOA (DPPH) | AOA (ABTS) | AOA (FRAP) | ||
THA | 1 | 0.71* | 0.66* | 0.77* | 0.66* | 0.58* | 0.72* | 0.81* |
TFC | 1 | 0.38 | 0.52* | 0.58* | 0.63* | 0.56* | 0.83* | |
TPC | 1 | 0.74* | 0.67* | 0.62* | 0.36 | 0.4 | ||
AOA (DPPH) | 1 | 0.91* | 0.71* | 0.50* | 0.68* | |||
AOA (ABTS) | 1 | 0.80* | 0.53* | 0.71* | ||||
AOA (FRAP) | 1 | 0.61* | 0.70* | |||||
1 | 0.81* | |||||||
1 | ||||||||
1: THA, total hydroxycinnamic acids content; TFC, total flavonoids content; TPC,
total phenolics content; AOA, antioxidant activity according to the DPPH
(2,2-diphenyl-1-picrylhydrazyl), ABTS
(2,2 |
There was a high degree of correlation between the
A high degree of correlation was also found between the
Plants of the Lamiaceae family are promising potential sources of
natural pharmaceuticals due to their high content of phenolic compounds. The
scientific and epidemiological data available today link the consumption of foods
rich in phenolic compounds with health benefits, primarily in such areas as
reducing the risk of cardiovascular disease, which is mediated by the
anti-inflammatory effects of these compounds [25, 26]. The main classes of
phenolic compounds represented in the Lamiaceae plants are phenolic
acids, mainly consisting of hydroxycinnamic acids (rosmarinic, chlorogenic, and
caffeic), and flavonoids (naringenin, quercetin, rutin, apigenin, luteolin, and
their glycoside derivatives) [2, 5]. Depending on the type of plant, the
proportion of hydroxycinnamic acids and flavonoids in the total content of
phenolic compounds in plants of the Lamiaceae family can vary greatly.
So, for example, in [5], it was shown that the proportion of phenolic acids and
their derivatives was 8% to 24% of the total content of phenolic compounds in
Origanum vulgar ssp. hirtum, Thymus capitatus, and
Satureja thymbra and 64% and 69% in Melissa officinalis and
Rosmarinus officinalis. In our study, the proportion of hydroxycinnamic
acids in the total content of phenolic compounds ranged from 11% (in Scarlet
beebalm) to 55% (in sage), which is consistent with the data available in the
literature. The proportion of flavonoids in the total content of phenolic
compounds ranged from 16% (in Scarlet beebalm) to 52% (in lavender and anise
hyssop). According to the total content of phenolic compounds, the studied
species of plants untreated with salicylic acid can be arranged in the following
order (in decreasing order): Scarlet beebalm
Phenolic compounds are known for their antioxidant properties and are among the
most important sources of antioxidants in the diets of humans. Due to the
potentially harmful effects of synthetic antioxidants such as butylated
hydroxyanisole and butylated hydroxytoluene, new natural antioxidants have become
the focus of attention for protecting food, beauty products, and reducing
oxidative stress in vivo [28, 29]. In addition to phenolic compounds,
other compounds that differ in the structure and mechanisms of antioxidant action
also have antioxidant properties in plant extracts [30]. In this regard, in the
study of antioxidant activity in vitro, it is necessary to use several
methods for determining antioxidant activity. In this work, we used three assays
for determining the antioxidant activity: assays based on the reaction with
radicals (DPPH and ABTS), as well as the FRAP assay which allows for the
determination of the reduction power of the extracts. To compare the data
obtained in all three assays, Trolox was used as a standard. Despite some
differences in absolute values, in general, the results of all three assays
correlated well with each other (r = 0.71–0.91, p
Diabetes is one of the most dangerous metabolic disorders from which there is a
high death rate worldwide. In 2017 diabetes accounted for 425 million cases and
its prevalence will rise to 629 million by 2040. Type 2 Diabetes mellitus (T2DM)
is the most common type of diabetes, accounting for approximately 90% of all
cases [31]. An important role in carbohydrate metabolism and the flow of glucose
into the blood is played by such enzymes as
Salicylic acid (SA) is one of the most important simple phenolic compounds that
have attracted a maximum level of attention by scientists around the world.
Intensive studies related to the role of SA in plants have revealed its active
role in various physiological processes, such as seed germination, stomatal
movements, accumulation of pigments, photosynthesis, ethylene biosynthesis, heat
production, enzyme activity, nutrient absorption, flow induction, membrane
functions, nodulation and more [17]. It is also known that SA exhibits the
functions of a hormone and a signaling molecule and is involved in the formation
of systemic acquired resistance (SAR) [37, 38]. In many respects, the protective
function of SA through the action of abiotic and biotic factors on plants is
associated with its role in the regulation of the biosynthesis of secondary
metabolites [17, 39]. In our study, it was found that foliar treatment with
salicylic acid led to an increase in the contents of hydroxycinnamic acids (in 6
species), flavonoids (in 2 species), total phenolic compounds (in 7 species),
antioxidant activity (in 5, 3 and 4 species according to DPPH, ABTS, and FRAP
assays, respectively), as well as
Of all the plant species we studied, lavender was the most susceptible to foliar treatment with salicylic acid. In this plant species, a significant increase in all studied indicators was noted. In contrast, in thyme plants, none of the studied parameters changed when treated with salicylic acid. Our results are consistent with the results of previous studies which also noted the species-specific reaction of plants to exogenous salicylic acid [42]. In addition, the result obtained in our study may be due to the fact that the same concentration of salicylic acid was used for all plant species. While at the same time there is evidence of a dose-dependent plant response to the use of salicylic acid [41, 46, 47]. Thus, for a more accurate interpretation of the data on the species differences established by us, it is necessary to carry out additional studies, including the selection of individual optimal concentrations of salicylic acid for each species.
Plants of the Lamiaceae family are a valuable source of biologically
active substances. Cultivation of 8 species of this family in a temperate climate
showed that the most promising for use in the pharmaceutical and food industries
are the following species: Scarlet beebalm, hyssop, anise hyssop, and peppermint
which were all characterized as possessing the highest content of phenolic
compounds. The last three species also exhibited maximum antioxidant activity.
All studied plant species exhibited
LS designed the research study. AG and TS performed the research. TS and AG analyzed the data. LS and AG wrote the manuscript. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript.
Not applicable.
Not applicable.
This research received no external funding.
The authors declare no conflict of interest.