Startseite Impact of storage temperature and time on Moldavian dragonhead oil – spectroscopic and chemometric analysis
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Impact of storage temperature and time on Moldavian dragonhead oil – spectroscopic and chemometric analysis

  • Tomasz Oniszczuk EMAIL logo , Arkadiusz Matwijczuk EMAIL logo , Alicja Matwijczuk , Sławomir Kocira , Agnieszka Niemczynowicz , Maciej Combrzyński , Agnieszka Wójtowicz , Maciej Kuboń , Andrzej Kusz und Anna Oniszczuk
Veröffentlicht/Copyright: 27. August 2019
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Aus der Zeitschrift Open Chemistry Band 17 Heft 1

Abstract

Moldavian dragonhead (Dracocephalum moldavica L.) is a plant endemic to Asia where it has been used for centuries for the production of essential oils. With the constantly growing demand for vegetable fats it is necessary to find new methods of ensuring their high quality from the moment of production until their eventual purchase by the consumer. Correct assessment of the quality of oleaginous products is therefore one of the intensively explored scientific problems that stimulates the development of innovative methods of analysing such substances. One of the newer and, most importantly, faster alternatives in the context of analysing the quality of oil and the changes it undergoes during storage is offered by FTIR spectroscopy (Fourier-Transform Infrared spectroscopy). By measuring the relevant FTIR spectra, we were able to observe clear discrepancies in the intensity of bands characteristic of the aging processes taking place in the oleaginous samples due to the oxidation of their fat fractions. The chemometric analysis of FTIR spectra confirmed the high quality of the analysed oils. It is noteworthy that the analysed samples of Moldavian dragonhead oil did not show particularly extensive changes in terms of their FTIR spectra during long-term storage. It confirms their high durability and usability in food production as an excellent product. This is valuable information in order to make progress in the use of Moldavian dragonhead oil in food products.

Keywords: FTIR spectroscopy; Moldavian dragonhead; oil; functional food; chemometric analysis

1 Introduction

In recent years researchers focusing on the problems of healthy nutrition have repeatedly emphasised that the primary factor influencing our health and quality of life is a properly composed diet. The increasing awareness of that fact among consumers has resulted in a growing tendency to look for foods that offer certain health benefits. This group of food products can include functional food produced with health-oriented additives, e.g. in the form of “cold pressed” vegetable oils [1]. Vegetable oils are a valuable addition to the daily diet. They are a source of considerable food energy as well as very important unsaturated fatty acids (USFA), phytosterols, and liposoluble vitamins. The vegetable oil most often found and used in households all over the world is rapeseed oil. However, many organic food outlets now offer a variety of cold-pressed oils from the seeds of e.g. linseed, hemp, sea buckthorn, sesame, garden cress, blue poppy, or black caraway [2]. Cold-pressed oils can be used in the production of oil extracts, e.g. from black elder flowers, which are used in medicine and cosmetology caraway [2].

One of the particularly valuable oils, due to its chemical composition and content of unsaturated fatty acids, can be obtained from Moldavian dragonhead (Dracocephalum moldavica L.) [1]. The Lamiaceae family includes a number of species valued as spices, ornamental plants, or for their health or cosmetology related benefits, e.g. np. Mentha, Salvia, Lavandula, Thymus, Rosmarinus [3, 4]. The family also includes the dragonhead (Dracocephalum), a genus of approximately 70 species most of which are endemic to Central Asia. One member of this group is Moldavian dragonhead [4]. It originates from the Himalayas and southern Siberia but was brought to Europe in the 16th century under the name of Melissa moldavica or M. Turcica [5]. Due to its visually attractive blue or white, fragrant, melliferous flowers and leaves producing a strong lemon-like scent, it is a welcome addition to most gardens as a decorative, fragrant, and melliferous flower. The plant is valued by beekeepers, mainly due to its good honey output and ease of cultivation. Moldavian Dragonhead is relatively undemanding in terms of soil quality and nutrient availability, although it requires certain care in terms of maintaining correct soil moisture levels. The plant lives for only one year and does not reach excessive size (about 60 cm) and it favours moist and calcium-rich soils. Cultivation in sun-filled areas facilitates higher concentration of the essential oil in the flowers and stalks [4]. Dragonhead flowers collected at the top of the shoot in an apparent ear can, depending on the botanical form, be either blue or white. Similar to other plants from this family, the above ground section of the plant produces essential oils which, combined with large amounts of sugar-rich nectar, attract bees and other pollinating insects [6]. The essential oil has been used to isolate e.g. citral (geranial, neral) geraniol and geranyl acetate [7]. The main components of the herb, other than essential oils, include tannin, phenolic acids and flavonoids. The fruit is a schizocarp containing 4 achenes (seeds). The seeds are small (mass of one thousand seeds (MTN) of 1.8-2.2 g), black, with a shiny tegument and a white V-shaped marking [4]. The oil obtained from dragonhead by way of cold-pressing is rich in valuable unsaturated acids including: α-linolenic (60.0%), linoleic (20%), oleic (8.5%), palmitic (6,5%), and stearic (5.0%) [8, 9, 10]. The composition of both the essential oil and the oil pressed from the seeds renders the plant a valuable resource in the pharmaceutical, cosmetic, and food industries [1, 4, 9].

The physicochemical parameters and content of pro- and anti-oxidative compounds in cold-pressed oils varies significantly from other such substances. The oils are characterised by higher peroxide value (PV) and acid value (AV), as well as lower anisidine value (AnV), which results from the absence of the refining stage. Compared to industrially produced oils, cold-pressed oils are characterised by a darker colour, which results from the content of chlorophyll and carotenoid pigments [5].

The quality of oil is influenced not only by the method of production (refined, cold-pressed), but also the duration, manner, and temperature of storage, exposure to sunlight and oxygen. Improper storage can result in changes in the product’s chemical composition and deterioration of its sensory qualities. As a consequence of auto- and photooxidative processes, unsaturated fatty acids undergo oxidation producing fatty acid hydroxides. The use of improper packaging (e.g. clear glass bottles) may lead to photooxidation. The process entails singlet oxygen binding with unsaturated fatty acids, bypassing the stage of free radical reaction [5]. Autooxidation is a free radical process taking place in three stages: initiation, propagation, and termination. At the stage of initiation, a hydrogen atom is detached from the carbon atom located directly at the double bond of the polyunsaturated fatty acid particle, which leads a regrouping of double bonds and emergence of a stable configuration of conjugated bonds. The effects of peroxidation are evidenced by the electromagnetic radiation absorption spectra in the UV range generated by the system of conjugated bonds that are not present in natural fatty acids.

The oxidative changes taking place in oils may be monitored by measuring the following parameters: peroxide vale (PV) and anisidine value (AnV) (i.e. parameters that are typically measured in studies of this type [27]). Moreover, the quality of oil is confirmed if its acid value (AV) and iodine value (IV) are within normal ranges, as is its fatty acid profile and composition of the non-tricycloglycerol fraction: concentration of tocopherols, chlorophyll and carotenoid pigments [5], as well as polyphenol and phytosterol compounds.

For this reason, it is very important to also develop new analytical and measurement methods of determining the quality of oil. It is expected that such methods ought to be quick, non-invasive and reliable [23-24].

The evaluation of the quality and usability of oils is a very important criterion, particularly in the context of edible oils and fats. However, traditional methods (which continue to be used by many researchers) of conducting such evaluation is a time-consuming and laborious process. Recent studies indicate that FTIR spectroscopy combined with chemometric methodology can viably constitute an alternative analytical method of verifying the usability and quality of (edible) oils and fats and offers a simple, fast and environmentally friendly analysis. The technique has been successfully employed for the purposes of quantitative and qualitative measurements of the characteristics of various (edible) oils and fats in the course of numerous scientific studies [11, 12, 13]. Chemometric analysis has been applied to monitoring oil mixtures in food products, cosmetics, and pharmaceutical agents. In this context, the use of chemometrics entails relying on chromatographic properties in developing predictive class models capable of quickly processing data on the basis of quality. The current accessibility of IT solutions and multidimensional, chemometric analytical tools allowed this method to become commonly used in quantitative analyses pertaining fats and oils. Chemometrics (PCA) proved itself to be one of the most efficient statistical methods used in the food industry, particularly in the context of food analyses.

The main aim of the study discussed in this article was to apply the methodology of FTIR spectroscopy in combination with advanced chemometrics in order to evaluate the quality of oil obtained from Moldavian dragonhead, relative to the respective time and conditions of its storage. Moreover, the aforementioned methodology was used to conduct a detailed analysis of particular bands and identify the spectroscopic (infrared) markers (relevant bands) potentially reflecting the acceleration or inhibition of aging processes relative to the respective conditions of storage exposing the products to specific external stimuli.

2 Materials and methods

The research material consisted of oil pressed from the seeds of Moldavian dragonhead (Dracocephalum moldavica L.). Before pressing, the seeds were stored in bags, in room temperature. Both unheated and thermally processed seeds were used. The heat treatment entailed heating seeds to 70ᵒC, 100 ᵒC, and 130ᵒC, on a metal tray placed in the laboratory drier for a period of 1 hour. The oil pressing process was conducted using a DUO screw press by Farmet (Czech Republic) with the efficiency of 18 to 25 kg/h and engine speed of 1500 rpm. A 10 mm nozzle was used. After pressing, the oil was left for 2 days to allow natural sedimentation, after which it was placed in 10 cm3 dark-glass bottle impenetrable by sunlight. Oil samples selected for the study were placed in an argon atmosphere and stored at room temperature (20-22oC) or a refrigerator (7oC). The two samples selected for this study were characterised by constant pressing temperature: 80oC, storage in identical dark bottles and the same argon atmosphere. Therefore, the variables were: storage temperature (20-22oC or 7oC) and storage time. The oil obtained from pressing was analysed in terms of its fatty acid profile, acid value (AV), peroxide value (PV), anisidine value (AnV), and iodine value (IV). The general colour (GC) was determined along with the content of carotenoid and chlorophyll pigments, β-carotene, tocopherols, and PC-8. The fatty acid profile was determined with the use of gas chromatography combined with mass spectrometry. The oil samples were used to obtain methyl esters in accordance with PN-EN ISO 12966-2 and their division was conducted using a Trace GC Ultra chromatograph with an ITQ 1100 spectrometer (Thermo Scientific) with the use of a Rtx-2330 column (105 x 0,25 x 0,25μm) by Restek. The carrier gas was helium at constant flow rate of 1mL/min., the temperature range was from 60°C to 250°C (5°C/min.) and the injection temperature was 250°C.

Measurements of ATR-FTIR (Fourier-Transform Infrared Spectroscopy) background corrected spectra (25 scans for each sample) were carried out with the use of a HATR Ge trough (45° cut, yielding 10 internal reflections) crystal plate at 20°C, and were recorded with a 670-IR spectrometer (Agilent, USA). The Ge crystal was cleaned with ultra-pure organic solvents (Sigma-Aldrich). The instrument was continuously purged with argon for 40 minutes before and during measurements. Absorption spectra at a resolution of one data point per 1 cm-1 were obtained in the 4000 and 950 cm-1 region. Scans were Fourier-transformed and averaged with Grams/AI 8.0 software (Thermo Fisher Scientific, USA).

The FTIR spectra of the studied oils were analysed chemometrically. PCA (Principal Component Analysis) was based on the correlation matrix for 10 FTIR spectra of the analysed oils (2 samples per experiment, i.e. per each respective time frame). The analysis was conducted using the PCA for spectra application.

Ethical approval: The conducted research is not related to either human or animal use.

3 Results and discussion

The cold-pressed Moldavian dragonhead oil was characterised by a unique content of fatty acids. Over 90% of acids present in this oil are unsaturated acids, of with over 80% are polyunsaturated acids. The content of palmitic acid (C16:0) was 3.84%, palmitoleic acid (C16:1) – 0.19%, stearic acid (C18:0) – 1.71%, oleic acid (C18:1) – 6.81%, linoleic acid (C18:2) – 19.01%, α-linolenic acid (C18:3 (9,12,15)) - 67.91%, nervonic acid (C24:1) - 0.07%, and other acids approximately 0.47%. Due to its particularly high content of α-linolenic acid (exceeding even that in linseed oil), dragonhead oil offers certain valuable health benefits. It can be used both in the cosmetics industry for the production of high quality creams, as well as in food production and in diet supplements containing ω-3 (α-linolenic) acid.

3.1 FTIR studies

Figure 1 illustrates the ATR-FTIR spectra for the analysed samples of oil obtained from Moldavian dragonhead seeds stored at 7oC (refrigerated). The oil was pressed at the temperature of 80oC (the relevant information is presented in the Materials and Methods section). Figure 2 shows the FTIR spectra for the analysed samples of oil obtained for Moldavian dragonhead seeds stored at room temperature, 20-22oC. The experimental constants were: oil pressing temperature, type of bottle in which the oil was stored (in this case dark glass bottles) and the storage atmosphere (argon gas). The samples were spread on the ZnSe crystal and analysed under N2 atmosphere. Tables 1 and 2 provide a description of all characteristic bands present in the oil samples selected for the study along with the related vibrations of particular functional groups (with a detailed literature review).

3.2 FTIR spectroscopic analysis of Moldavian dragonhead oil samples stored in various conditions

All the FTIR spectra recorded for the selected Moldavian dragonhead oil samples revealed very intense and clearly defined bands which correspond to specific vibrations of the respective functional groups contained in the ingredients typically found in this type of food. Most edible vegetable fats and potential oleaginous products are substances composed primarily of various fractions of triglyceride groups, mainly differing in terms of the degree and form of the acyl groups’ unsaturation as well as the length of their chains [14]. Numerous publications provide the appropriate associations of the particular spectral bands in oils, both animal and vegetable, and other fats [15, 16] with specific vibrations in particles or groups thereof. Tables 1 and 2 present in detail the frequencies of characteristic spectra including the most significant broadenings of the respective spectral bands for the four analysed time-frames of oil sample storage, as well as their association with the respective functional groups [16, 17]. It is immediately apparent that the association of the maxima corresponding to stretching vibrations in the FTIR spectra of the analysed samples is considerably easier than assigning the maxima corresponding to deformation vibrations. This is because bands corresponding to vibrations of the latter type often tend to overlap. The presented absorption spectra registered for the oil samples selected for the study reveal vibrations of the methylene group located in the spectral range from 1350 to 1150 cm-1 [18]. In this case, they are stretching vibrations originating from the vibrations of the -C-H group bonded with the -CH3 group (usually at approximately 1350-60 cm-1, in our samples approximately 1370 cm-1) and deformation vibrations in the same group (~ 1160 cm-1, in our case 1159-1166 cm-1). It is noteworthy that the stretching vibrations of the ester bond ν(C-O) are composed of two merged, asymmetric vibrations, specifically vibrations originating from the C-C(=O)-O and O-C-C groups [19]. The former are usually more intensive [20, 21]. The bands occur in the region from 1300 (as C-C(= O)-O, in our case at approximately 1270 cm-1, as enhancement of the band with the maximum at 1235-9 cm-1) and approximately 1000 cm-1 (in our case 1028 to 1036 cm-1 for this combination of groups – not shown in Figure 1 and 2). Bands related to saturated esters C-C(=O)-O are present between 1240 and 1160 cm-1 (in the case of oils selected for the study approximately 1234-9 cm-1), whereas for unsaturated esters, the vibrations are more often found at lower frequencies [22]. On the other hand, the O-C-O band originating from primary alcohols appears in the region from 1100 to 1020 cm-1 (in the analysed case, the band’s maximum was located at approximately 1029-31 cm-1, as already mentioned above), whereas in the case of secondary alcohols, the band usually appears with the maximum at approximately 1100 cm-1 (in our case approximately 1090-1093 cm-1). Both types of esters described above are present in triglyceride particles. In the literature, the mentioned band (~ approximately 1239-4 cm-1) has been associated exclusively with out-of-plane bending vibrations of the methylene group [22]. Another two bands presented in Tables 1 and 2 (as well as in Figures 1 and 2) are somewhat more difficult to identify: the maximum of the first band is at approxmately 1416-18 cm-1 and the maximum of the second at approximately 1320 cm-1 (most likely a band broadening, see Figures 1

Table 1

Positions of the maxima of absorption spectra and assignment to the relevant vibrations recorded for Moldavian dragonhead oil samples stored at 7oC (refrigerated), a – immediately after pressing, b– two weeks after pressing, c– four weeks after pressing and d– 8 weeks after pressing.

FTIRType and origin of vibrations
Position of bands [cm-1]
abcd
3010300830113011ν(=C-Hm, cis-)
2958296129572961νas(-C-Hvst, -CHa)
2925292629262924and νs(-C-Hvst, -CHa ) (aliphatic groups in triglycerides)
2853285428542859
1744174317431742ν(-C=Ovst) in esters
1710171117131701ν(-C=Ovw) in acids
1656165016501650νvw(-C=C-, cis-)
--16011620
--15931559
---1540
---1518
1459146014591460δvw(-C-H) w CH2 and in CH3 groups, deformation (scissoring)
---1422νvw(-C-H, cis-) deformation (ring)
1373/1394137713741367/1391νw, m, vw(-C-H, -CH3) and deformation
1306130913141313δm(-C-H, -CH3)
1266126912661268νm(-C-O) or δm(-CH2-)
1236123712341226νm(-C-O) or δm(-CH2-)
1161116111641164νm(-C-O)
1098109910991102νm,vw(-C-O)
1064106710671067
1028---
965989969985δw(-HC=CH-, trans-) out-of-plain deformation

  1. ν – stretching vibrations, δ – deformation vibrations, s– symmetric, as – asymmetric, st– strong, w– weak

Table 2

Positions of the maxima of absorption spectra and assignment to the relevant vibrations for Moldavian dragonhead oil samples stored at 23oC (room temperature): a – immediately after pressing, b– two weeks after pressing, c– four weeks after pressing and d– 8 weeks after pressing.

FTIRType and origin of vibrations
Position of bands [cm-1]
abcd
3012301030083010ν(=C-Hm, cis-)
2960296229612959νas(-C-Hvst, -CHa)
2926292929262924and νs(-C-Hvst, -CHa ) (aliphatic groups in triglycerides)
2854285928542852
1745174617441742ν(-C=Ovst) in esters
1711170417091711ν(-C=Ovw) in acids
1656165416571651νvw(-C=C-, cis-)
---1621
---1559
---1541
---1512
1457145814581460δvw(-C-H) w CH2 and in CH3 groups, deformation (scissoring)
---1422νvw(-C-H, cis-) deformation (ring)
1373/1393137513721370νw, m, vw(-C-H, -CH3) and deformation
1312130513051312δm(-C-H, -CH3)
1269126412631271νm(-C-O) or δm(-CH2-)
1236123312331231νm(-C-O) or δm(-CH2-)
1162116211621159νm(-C-O)
1100109710991099νm,vw(-C-O)
1067106610691069
10281023--
964983969980δw(-HC=CH-, trans-) out-of-plain deformation

  1. ν – stretching vibrations, δ – deformation vibrations, s– symmetric, as – asymmetric, st– strong, w– weak

Figure 1 ATR-FTIR spectra for selected Moldavian dragonhead oil samples stored at 7oC (refrigerated): a – immediately after pressing, b– two weeks after pressing, c– four weeks after pressing, d– 8 weeks after pressing.
Figure 1

ATR-FTIR spectra for selected Moldavian dragonhead oil samples stored at 7oC (refrigerated): a – immediately after pressing, b– two weeks after pressing, c– four weeks after pressing, d– 8 weeks after pressing.

Figure 2 ATR-FTIR spectra for selected Moldavian dragonhead oil samples stored at room temperature (20-22oC): a – immediately after pressing, b– two weeks after pressing, c– four weeks after pressing, d– 8 weeks after pressing. The spectra are presented within the spectral range from 900 to 3150 cm-1.
Figure 2

ATR-FTIR spectra for selected Moldavian dragonhead oil samples stored at room temperature (20-22oC): a – immediately after pressing, b– two weeks after pressing, c– four weeks after pressing, d– 8 weeks after pressing. The spectra are presented within the spectral range from 900 to 3150 cm-1.

and 2). The first group of vibrations with their maximum at approximately 1416-18 cm-1 (depending on the time of measurement) may be assigned to the vibrations of the methyl groups in the aliphatic chains of the oils selected for the study [14-16]. The second group of bands (i.e. band broadening) with the maximum at approximately 1320 cm-1 (in all the samples – not shown so as not to obscure the presentation) is observed simultaneously with the bands with the maximum at approximately 980 cm-1 and lower wave numbers. It should be noted that the band at approximately 918 cm-1 which appears in all oil samples, is related to the stretching vibrations of cis-substituted olefin groups [14] and can be connected with the vibrations of the vinyl group.

The oil samples selected for the study produced largely similar spectra in the infrared range. However, with sample storage time significant differences in terms of the intensity and frequency of the respective bands (although the shifts were not large) became apparent. In each case we observed the maximum absorbance, which was clearly correlated to the particular storage time.

Other very characteristic vibration regions were also observed with respect to the bands with the maxima at approximately 1745-1 cm-1, which were typical of the stretching vibrations of the carbonyl C=O group [14] in ester groups. Next to the band characteristic of the vibrations of the carbonyl group in esters we observed, on the lower wavenumber side, an enhancement with the maximum at approximately 1700-15 cm-1, which also corresponds to the vibrations of a carbonyl group, but in this case found in the acidic groups of the analysed samples [13].

The next band, with the maximum at 1655-3 cm-1 corresponds to the stretching vibrations of the -C=C-group (from the cis- transformation) [15]. The intensity of those bands increased with longer storage time of the respective samples, which clearly evidences ongoing ageing processes (discussed further in the text). A very characteristic region is also observed for the vibrations with the maximum at 1461-3 cm-1 and originating from the -C-H deformation vibrations in CH2 and CH3 groups (bending vibrations). Moreover, the vibrations in the region from 900 to 650 cm-1 (partially not presented) corresponded in the analysed case to the characteristic deformation vibrations of the -HC=CH- groups (out-of-plain cis- conformation) and ring vibrations of the aforementioned groups (δ(-(CH2)n- and -HC=CH- (cis -)) [21].

Next, proceeding to the range of higher wavenumbers, one should mention the very important =C-H stretching vibrations (trans- transformation) with the maximum at approximately 3063-4 cm-1 (not shown due to low intensity of these vibrations) which originate from the vibrations of triglyceride fractions [14]. In turn, with respect to the =C-H stretching vibrations in the cis- configuration, the very characteristic and intense vibrations were observed with the maximum at approximately 3007/12 cm-1 (Figures 1 and 2, Tables 1 and 2). Vibrations with the maxima at approximately 2952/8, 2922/8, and 2852/7 cm-1 originate, respectively from the –C-H stretching vibrations in -CH3, CH2 groups belonging to the aliphatic groups in triglycerides [18, 23].

It should be emphasised that the spectra of Moldavian dragonhead oil samples stored in different conditions revealed clear discrepancies in the shape of bands located in the region from 1780 to 1670 cm-1 [14]. Most analysed samples showed a clearly defined, slight enhancement of the band at 1743/6 cm-1 (corresponding to the vibrations of the C=O group, as already discussed above) on the lower wavenumber side, with a clear maximum at approximately 1700-16 cm-1 [11], which can be associated with the formation of a hydrogen bond between C=O…H-O-H groups (in the analysed samples). Simultaneously to the emergence of the band at 1700-16 cm-1, we observed a clear increase in the intensity of the bands at approximately 1350-70 cm-1 [22, 24] which can also be associated with the stretching vibrations of C-O and C-C groups (as described above). Furthermore, the area between 1100 and 1300 cm-1 also corresponds to stretching vibration of C-O groups but indicates minor discrepancies between the analysed oil samples, regardless of the storage time. The bands may display a slight increase in intensity with the decreasing affinity of the particles that generate them toward for the formation of the hydrogen bond between C=O…H-O-H.

In summary, the spectra obtained using IR spectroscopy revealed considerable differences. Bands wherein the significant differences were observed constitute the spectroscopic markers of the ageing processes taking place in the analysed Moldavian dragonhead oil samples. In particular, observation of peaks in the range 1715 to 1500 cm-1 in the samples stored for 8 weeks, revealed the significant changes in terms of the position and intensity of the band characteristic of the carbonyl group, with the maximum at approximately 1744 cm-1 [25-26]. The region from 1715 to 1500 cm-1 is related mainly to various vibrations originating from the C-C and C=C groups and evidencing the progress of ageing processes (with the oxygenation of fatty acids contained therein). One should also mention the band with the maximum at approximately 1426 cm-1 related to the vibrations of C-H groups in acids [23-26].

3.3 Chemometric studies

One of the most effective chemometric methods is Principal Component Analysis (PCA). In essence, PCA involves converting data into combinations of numerous orthogonal principal components or factors. The data matrix is reduced to two matrices, the score matrix which pertains to information about the objects and the load matrix which pertains to the variables. Each principal component may be understood as a set of variables (e.g. FTIR spectrum) representing a certain primary data feature, while the loads are the values of absorbance or peak heights. The first principal component accounts for the maximum variance of the set, the second accounts for most of the remaining variance, and so on. Additionally, with the PCA method, the noise present in the data set which conveys no information is transferred to the further principal components, which means that the method can also be used for the purposes of data cleansing. The score matrix specifies the contribution of each object to each principal component. The use of PCA for the purposes of grouping objects takes place by verifying the score matrix. The score of the first primary component is usually drawn relative to the object of relative to the score of the second primary component with which each point is identified by the associated object.

PCA is one of the multivariate techniques for data analysis which plays a complementary role with HCA (Hierarchical Cluster analysis) through both data summarization and data reduction. They are statistical approaches that can be used to analyze interrelationships among a large number of variables and explain these variables in the terms of their factors. It means that we can find a way of condensing the information contained a number of original variables (in our case in FTIR spectral data) into a smaller set of variables (principal components) with minimum loss of information. On the other side, including the construction of a hierarchy of agglomerative structure (HCA), in which each object (considered oils samples) is compared by assessing the correspondence of the results. Therefore, the spectroscopic analysis of the analysed oil samples was combined with a chemometric principal component analysis and hierarchical cluster analysis.

In order to confirm visualization of the group and sub-group arrangement of the spectra we use the HCA analysis. Taking into account the similar areas of the groups we can distinguish the difference in the spectral range. Despite this, some questions remain still open. For instance, we are curious how the difference between the variations in the functional group influence the difference in the HCA analysis e.g.what is the band diversity and complication depending on the source of the sample. Therefore, PCA was used further in order to get answer into the above mentioned questions and others.

Figure 3 Plot of eigenvalues for PCA of FTIR spectra.
Figure 3

Plot of eigenvalues for PCA of FTIR spectra.

Figure 4 3-dimensional loading plot of PCA.
Figure 4

3-dimensional loading plot of PCA.

The PCA analysis of the FTIR spectra of the analysed oils within the range 4000-500 cm-1 was conducted. The results are presented in Figures 4, 5, and 6. Based on the Scree Test Criterion (Figure 3) we identify the optimum number of principal components. In the present case, the first three principal components would qualify. The first three principal components accounted for 97.6% of the total variance of the original data set, where PC1 accounted for 79.2%, PC2 for 17%, and PC3 for 1.4% thereof (Figure 8). The first included oil samples d1 and d2 – stored for a period of 8 weeks at 7oC and 22oC respectively. The second included samples a1, c1, and c2 – Subgroup I-A and a2, b1,

Figure 5 3-dimensional score plot of PCA.
Figure 5

3-dimensional score plot of PCA.

Figure 6 2-dimensional score plot in the plane of PC1 x PC2.
Figure 6

2-dimensional score plot in the plane of PC1 x PC2.

b2 – Subgroup I-B (Figure 6 and 8). The above grouping of the analysed oils may be due to the physicochemical properties of the respective oil samples’ content (also demonstrated by the shift of the relevant infrared bands, Figs 1 and 2, Tables 1 and 2).

Based on the loading plot (Figure 4 and 7a, b) it can be concluded that PC1 is negatively correlated with bands related to bond vibrations δw(-HC=CH-, trans-) (range 957 – 971 cm-1). Its correlation with the remaining vibration

Figure 7 Loading plot of PC1, PC2, PC3 for the reference spectrum (a) a1 and (b) a2.
Figure 7

Loading plot of PC1, PC2, PC3 for the reference spectrum (a) a1 and (b) a2.

Figure 8 Hierarchical Cluster Analysis (HCA) for the FTIR spectra of all oil samples.
Figure 8

Hierarchical Cluster Analysis (HCA) for the FTIR spectra of all oil samples.

bands is positive. Meanwhile, PC2 is negatively correlated with bands within the range of 643-1291cm-1, i.e. νm(-C-O) or δm(-CH2-), νm(-C-O), νm,vw(-C-O), δm(-C-H, -CH3-), δw(-HC=CH-, trans-) and the band νs(-C-Hvst, -CHa) (aliphatic groups in triglycerides) (approximately 2854 cm-1).

The use of the cluster analysis technique (HCA) with the Euclidean distance measurement confirmed the hierarchical structure of the samples’ distribution in relation to the distribution of their FTIR spectra in the PCA (Figure 6). In this case, distance is converted into measures of similarity, where larger values denote less similarity. If we assume the “cut off” at the level of 0.1, we obtain two branches-two clusters. The first group (cluster) comprises two subgroups. Subgroup A is composed of oil samples a1, c1, and c2 while subgroup B of oil samples a2, b2, and b1. The second group (cluster) comprises oil samples d1 and d2. As easy to see, this analysis confirm the stability of the results obtained by PCA and identify a topology of similarity in considered oils samples based on their FTIR spectras.

4 Conclusions

Cold-pressed oil is a perfect alternative for olive oil as a product for which the respective stages of production can be tightly controlled with the view of preserving all of the oil’s health benefits. Maintaining proper pressing and storage conditions can ensure that the resulting oil is of the highest quality. The paper presents the results of a primary analysis (identification of fatty acids present in the oil) and spectroscopic characteristics combined with a chemometric analysis conducted for two samples of Moldavian dragonhead oil stored under different conditions determined by the storage temperature (room temperature or 7oC).

The analysed oil samples were characterised by a very good fatty acids profile, which confirmed their exceptional health benefits. The spectral analysis of the samples allowed quick and effective characterisation and quality control of the oil in storage, as well as processes affecting the same. Significant differences were observed in terms of bands associated in literature with various fat fractions contained in the oils. The clear discrepancies in IR spectra emerging after 8 weeks within the spectral ranges of 1720 – 1500 cm-1 and ~1426 cm-1 provide markers which could provide evidence of the ageing processes taking place in the samples. Changes related to aging of the sample were related to intensification of bands reflecting the vibrations of C-C, C=C, and C-=O groups and as such, they constitute perfect marker bands which can be easily correlated with the given oil’s shelf life and the oxidative processes that affect it.

The combination of FTIR spectroscopy and chemometric methodology allowed the identification and classification of marker bands for the ageing processes. PCA and HCA methods were employed to facilitate the analysis. The studied oils were classified under two clusters (groups). The first component differentiated the samples relative to the time and conditions of storage. The samples were clearly distributed in a way to reflect their respective storage conditions. The first component accounted for 79.2% of the total data variance while PC2 for 17% of the same. Samples d1 and d2 were characterised by the highest value of PC1, whereas samples b1 and b2 by the highest value of PC2.

It is our hope that the obtained results may prove useful in identifying spectroscopic markers corresponding to the ageing processes taking place in oil samples. At the same time, the results demonstrate the usability of a reliable, quantitative method of detecting preliminary discrepancies between oil samples and the classification of the same, without the need to resort to the costly, standard chemical methods. It is also clearly observable that the bands gaining in intensity with increasing sample storage time can be grouped by employing the method of chemometric analysis.

  1. Conflict of interest: Authors declare no conflict of interest.

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Received: 2018-11-29
Accepted: 2019-03-12
Published Online: 2019-08-27

© 2019 Tomasz Oniszczuk et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 Public License.

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https://doi.org/10.1515/chem-2019-0080
Schlagwörter für diesen Artikel
FTIR spectroscopy; Moldavian dragonhead; oil; functional food; chemometric analysis
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  19. Minimal Energy Tree with 4 Branched Vertices
  20. Jatropha seed oil derived poly(esteramide-urethane)/ fumed silica nanocomposite coatings for corrosion protection
  21. Calculating topological indices of certain OTIS interconnection networks
  22. Energy storage analysis of R125 in UIO-66 and MOF-5 nanoparticles: A molecular simulation study
  23. Velvet Antler compounds targeting major cell signaling pathways in osteosarcoma - a new insight into mediating the process of invasion and metastasis in OS
  24. Effects of Azadirachta Indica Leaf Extract, Capping Agents, on the Synthesis of Pure And Cu Doped ZnO-Nanoparticles: A Green Approach and Microbial Activity
  25. Aqueous Micro-hydration of Na+(H2O)n=1-7 Clusters: DFT Study
  26. A proposed image-based detection of methamidophos pesticide using peroxyoxalate chemiluminescence system
  27. Phytochemical screening and estrogenic activity of total glycosides of Cistanche deserticola
  28. Biological evaluation of a series of benzothiazole derivatives as mosquitocidal agents
  29. Chemical pretreatments of Trapa bispinosa's peel (TBP) biosorbent to enhance adsorption capacity for Pb(ll)
  30. Dynamic Changes in MMP1 and TIMP1 in the Antifibrotic Process of Dahuang Zhechong Pill in Rats with Liver Fibrosis
  31. The Optimization and Production of Ginkgolide B Lipid Microemulsion
  32. Photodynamic Therapy Enhanced the Antitumor Effects of Berberine on HeLa Cells
  33. Chiral and Achiral Enantiomeric Separation of (±)-Alprenolol
  34. Correlation of Water Fluoride with Body Fluids, Dental Fluorosis and FT4, FT3 –TSH Disruption among Children in an Endemic Fluorosis area in Pakistan
  35. A one-step incubation ELISA kit for rapid determination of dibutyl phthalate in water, beverage and liquor
  36. Free Radical Scavenging Activity of Essential Oil of Eugenia caryophylata from Amboina Island and Derivatives of Eugenol
  37. Effects of Blue and Red Light On Growth And Nitrate Metabolism In Pakchoi
  38. miRNA-199a-5p functions as a tumor suppressor in prolactinomas
  39. Solar photodegradation of carbamazepine from aqueous solutions using a compound parabolic concentrator equipped with a sun tracking system
  40. Influence of sub-inhibitory concentration of selected plant essential oils on the physical and biochemical properties of Pseudomonas orientalis
  41. Preparation and spectroscopic studies of Fe(II), Ru(II), Pd(II) and Zn(II) complexes of Schiff base containing terephthalaldehyde and their transfer hydrogenation and Suzuki-Miyaura coupling reaction
  42. Complex formation in a liquid-liquid extraction-chromogenic system for vanadium(IV)
  43. Synthesis, characterization (IR, 1H, 13C & 31P NMR), fungicidal, herbicidal and molecular docking evaluation of steroid phosphorus compounds
  44. Analysis and Biological Evaluation of Arisaema Amuremse Maxim Essential Oil
  45. A preliminary assessment of potential ecological risk and soil contamination by heavy metals around a cement factory, western Saudi Arabia
  46. Anti- inflammatory effect of Prunus tomentosa Thunb total flavones in LPS-induced RAW264.7 cells
  47. Collaborative Influence of Elevated CO2 Concentration and High Temperature on Potato Biomass Accumulation and Characteristics
  48. Methods of extraction, physicochemical properties of alginates and their applications in biomedical field – a review
  49. Characteristics of liposomes derived from egg yolk
  50. Preparation of ternary ZnO/Ag/cellulose and its enhanced photocatalytic degradation property on phenol and benzene in VOCs
  51. Influence of Human Serum Albumin Glycation on the Binding Affinities for Natural Flavonoids
  52. Synthesis and antioxidant activity of 2-methylthio-pyrido[3,2-e][1,2,4] triazolo[1,5-a]pyrimidines
  53. Comparative study on the antioxidant activities of ten common flower teas from China
  54. Molecular Properties of Symmetrical Networks Using Topological Polynomials
  55. Synthesis of Co3O4 Nano Aggregates by Co-precipitation Method and its Catalytic and Fuel Additive Applications
  56. Phytochemical analysis, Antioxidant and Antiprotoscolices potential of ethanol extracts of selected plants species against Echinococcus granulosus: In-vitro study
  57. Silver nanoparticles enhanced fluorescence for sensitive determination of fluoroquinolones in water solutions
  58. Simultaneous Quantification of the New Psychoactive Substances 3-FMC, 3-FPM, 4-CEC, and 4-BMC in Human Blood using GC-MS
  59. Biodiesel Production by Lipids From Indonesian strain of Microalgae Chlorella vulgaris
  60. Miscibility studies of polystyrene/polyvinyl chloride blend in presence of organoclay
  61. Antibacterial Activities of Transition Metal complexes of Mesocyclic Amidine 1,4-diazacycloheptane (DACH)
  62. Novel 1,8-Naphthyridine Derivatives: Design, Synthesis and in vitro screening of their cytotoxic activity against MCF7 cell line
  63. Investigation of Stress Corrosion Cracking Behaviour of Mg-Al-Zn Alloys in Different pH Environments by SSRT Method
  64. Various Combinations of Flame Retardants for Poly (vinyl chloride)
  65. Phenolic compounds and biological activities of rye (Secale cereale L.) grains
  66. Oxidative degradation of gentamicin present in water by an electro-Fenton process and biodegradability improvement
  67. Optimizing Suitable Conditions for the Removal of Ammonium Nitrogen by a Microbe Isolated from Chicken Manure
  68. Anti-inflammatory, antipyretic, analgesic, and antioxidant activities of Haloxylon salicornicum aqueous fraction
  69. The anti-corrosion behaviour of Satureja montana L. extract on iron in NaCl solution
  70. Interleukin-4, hemopexin, and lipoprotein-associated phospholipase A2 are significantly increased in patients with unstable carotid plaque
  71. A comparative study of the crystal structures of 2-(4-(2-(4-(3-chlorophenyl)pipera -zinyl)ethyl) benzyl)isoindoline-1,3-dione by synchrotron radiation X-ray powder diffraction and single-crystal X-ray diffraction
  72. Conceptual DFT as a Novel Chemoinformatics Tool for Studying the Chemical Reactivity Properties of the Amatoxin Family of Fungal Peptides
  73. Occurrence of Aflatoxin M1 in Milk-based Mithae samples from Pakistan
  74. Kinetics of Iron Removal From Ti-Extraction Blast Furnace Slag by Chlorination Calcination
  75. Increasing the activity of DNAzyme based on the telomeric sequence: 2’-OMe-RNA and LNA modifications
  76. Exploring the optoelectronic properties of a chromene-appended pyrimidone derivative for photovoltaic applications
  77. Effect of He Qi San on DNA Methylation in Type 2 Diabetes Mellitus Patients with Phlegm-blood Stasis Syndrome
  78. Cyclodextrin potentiometric sensors based on selective recognition sites for procainamide: Comparative and theoretical study
  79. Greener synthesis of dimethyl carbonate from carbon dioxide and methanol using a tunable ionic liquid catalyst
  80. Nonisothermal Cold Crystallization Kinetics of Poly(lactic acid)/Bacterial Poly(hydroxyoctanoate) (PHO)/Talc
  81. Enhanced adsorption of sulfonamide antibiotics in water by modified biochar derived from bagasse
  82. Study on the Mechanism of Shugan Xiaozhi Fang on Cells with Non-alcoholic Fatty Liver Disease
  83. Comparative Effects of Salt and Alkali Stress on Antioxidant System in Cotton (Gossypium Hirsutum L.) Leaves
  84. Optimization of chromatographic systems for analysis of selected psychotropic drugs and their metabolites in serum and saliva by HPLC in order to monitor therapeutic drugs
  85. Electrocatalytic Properties of Ni-Doped BaFe12O19 for Oxygen Evolution in Alkaline Solution
  86. Study on the removal of high contents of ammonium from piggery wastewater by clinoptilolite and the corresponding mechanisms
  87. Phytochemistry and toxicological assessment of Bryonia dioica roots used in north-African alternative medicine
  88. The essential oil composition of selected Hemerocallis cultivars and their biological activity
  89. Mechanical Properties of Carbon Fiber Reinforced Nanocrystalline Nickel Composite Electroforming Deposit
  90. Anti-c-myc efficacy block EGFL7 induced prolactinoma tumorigenesis
  91. Topical Issue on Applications of Mathematics in Chemistry
  92. Zagreb Connection Number Index of Nanotubes and Regular Hexagonal Lattice
  93. The Sanskruti index of trees and unicyclic graphs
  94. Valency-based molecular descriptors of Bakelite network BNmn
  95. Computing Topological Indices for Para-Line Graphs of Anthracene
  96. Zagreb Polynomials and redefined Zagreb indices of Dendrimers and Polyomino Chains
  97. Topological Descriptor of 2-Dimensional Silicon Carbons and Their Applications
  98. Topological invariants for the line graphs of some classes of graphs
  99. Words for maximal Subgroups of Fi24‘
  100. Generators of Maximal Subgroups of Harada-Norton and some Linear Groups
  101. Special Issue on POKOCHA 2018
  102. Influence of Production Parameters on the Content of Polyphenolic Compounds in Extruded Porridge Enriched with Chokeberry Fruit (Aronia melanocarpa (Michx.) Elliott)
  103. Effects of Supercritical Carbon Dioxide Extraction (SC-CO2) on the content of tiliroside in the extracts from Tilia L. flowers
  104. Impact of xanthan gum addition on phenolic acids composition and selected properties of new gluten-free maize-field bean pasta
  105. Impact of storage temperature and time on Moldavian dragonhead oil – spectroscopic and chemometric analysis
  106. The effect of selected substances on the stability of standard solutions in voltammetric analysis of ascorbic acid in fruit juices
  107. Determination of the content of Pb, Cd, Cu, Zn in dairy products from various regions of Poland
  108. Special Issue on IC3PE 2018 Conference
  109. The Photocatalytic Activity of Zns-TiO2 on a Carbon Fiber Prepared by Chemical Bath Deposition
  110. N-octyl chitosan derivatives as amphiphilic carrier agents for herbicide formulations
  111. Kinetics and Mechanistic Study of Hydrolysis of Adenosine Monophosphate Disodium Salt (AMPNa2) in Acidic and Alkaline Media
  112. Antimalarial Activity of Andrographis Paniculata Ness‘s N-hexane Extract and Its Major Compounds
  113. Special Issue on ABB2018 Conference
  114. Special Issue on ICCESEN 2017
  115. Theoretical Diagnostics of Second and Third-order Hyperpolarizabilities of Several Acid Derivatives
  116. Determination of Gamma Rays Efficiency Against Rhizoctonia solani in Potatoes
  117. Studies On Compatibilization Of Recycled Polyethylene/Thermoplastic Starch Blends By Using Different Compatibilizer
  118. Liquid−Liquid Extraction of Linalool from Methyl Eugenol with 1-Ethyl-3-methylimidazolium Hydrogen Sulfate [EMIM][HSO4] Ionic Liquid
  119. Synthesis of Graphene Oxide Through Ultrasonic Assisted Electrochemical Exfoliation
  120. Special Issue on ISCMP 2018
  121. Synthesis and antiproliferative evaluation of some 1,4-naphthoquinone derivatives against human cervical cancer cells
  122. The influence of the grafted aryl groups on the solvation properties of the graphyne and graphdiyne - a MD study
  123. Electrochemical modification of platinum and glassy carbon surfaces with pyridine layers and their use as complexing agents for copper (II) ions
  124. Effect of Electrospinning Process on Total Antioxidant Activity of Electrospun Nanofibers Containing Grape Seed Extract
  125. Effect Of Thermal Treatment Of Trepel At Temperature Range 800-1200˚C
  126. Topical Issue on Agriculture
  127. The effect of Cladophora glomerata exudates on the amino acid composition of Cladophora fracta and Rhizoclonium sp.
  128. Influence of the Static Magnetic Field and Algal Extract on the Germination of Soybean Seeds
  129. The use of UV-induced fluorescence for the assessment of homogeneity of granular mixtures
  130. The use of microorganisms as bio-fertilizers in the cultivation of white lupine
  131. Lyophilized apples on flax oil and ethyl esters of flax oil - stability and antioxidant evaluation
  132. Production of phosphorus biofertilizer based on the renewable materials in large laboratory scale
  133. Human health risk assessment of potential toxic elements in paddy soil and rice (Oryza sativa) from Ugbawka fields, Enugu, Nigeria
  134. Recovery of phosphates(V) from wastewaters of different chemical composition
  135. Special Issue on the 4th Green Chemistry 2018
  136. Dead zone for hydrogenation of propylene reaction carried out on commercial catalyst pellets
  137. Improved thermally stable oligoetherols from 6-aminouracil, ethylene carbonate and boric acid
  138. The role of a chemical loop in removal of hazardous contaminants from coke oven wastewater during its treatment
  139. Combating paraben pollution in surface waters with a variety of photocatalyzed systems: Looking for the most efficient technology
  140. Special Issue on Chemistry Today for Tomorrow 2019
  141. Applying Discriminant and Cluster Analyses to Separate Allergenic from Non-allergenic Proteins
  142. Chemometric Expertise Of Clinical Monitoring Data Of Prolactinoma Patients
  143. Chemomertic Risk Assessment of Soil Pollution
  144. New composite sorbent for speciation analysis of soluble chromium in textiles
  145. Photocatalytic activity of NiFe2O4 and Zn0.5Ni0.5Fe2O4 modified by Eu(III) and Tb(III) for decomposition of Malachite Green
  146. Photophysical and antibacterial activity of light-activated quaternary eosin Y
  147. Spectral properties and biological activity of La(III) and Nd(III) Monensinates
  148. Special Issue on Monitoring, Risk Assessment and Sustainable Management for the Exposure to Environmental Toxins
  149. Soil organic carbon mineralization in relation to microbial dynamics in subtropical red soils dominated by differently sized aggregates
  150. A potential reusable fluorescent aptasensor based on magnetic nanoparticles for ochratoxin A analysis
  151. Special Issue on 13th JCC 2018
  152. Fluorescence study of 5-nitroisatin Schiff base immobilized on SBA-15 for sensing Fe3+
  153. Thermal and Morphology Properties of Cellulose Nanofiber from TEMPO-oxidized Lower part of Empty Fruit Bunches (LEFB)
  154. Encapsulation of Vitamin C in Sesame Liposomes: Computational and Experimental Studies
  155. A comparative study of the utilization of synthetic foaming agent and aluminum powder as pore-forming agents in lightweight geopolymer synthesis
  156. Synthesis of high surface area mesoporous silica SBA-15 by adjusting hydrothermal treatment time and the amount of polyvinyl alcohol
  157. Review of large-pore mesostructured cellular foam (MCF) silica and its applications
  158. Ion Exchange of Benzoate in Ni-Al-Benzoate Layered Double Hydroxide by Amoxicillin
  159. Synthesis And Characterization Of CoMo/Mordenite Catalyst For Hydrotreatment Of Lignin Compound Models
  160. Production of Biodiesel from Nyamplung (Calophyllum inophyllum L.) using Microwave with CaO Catalyst from Eggshell Waste: Optimization of Transesterification Process Parameters
  161. The Study of the Optical Properties of C60 Fullerene in Different Organic Solvents
  162. Composite Material Consisting of HKUST-1 and Indonesian Activated Natural Zeolite and its Application in CO2 Capture
  163. Topical Issue on Environmental Chemistry
  164. Ionic liquids modified cobalt/ZSM-5 as a highly efficient catalyst for enhancing the selectivity towards KA oil in the aerobic oxidation of cyclohexane
  165. Application of Thermal Resistant Gemini Surfactants in Highly Thixotropic Water-in-oil Drilling Fluid System
  166. Screening Study on Rheological Behavior and Phase Transition Point of Polymer-containing Fluids produced under the Oil Freezing Point Temperature
  167. The Chemical Softening Effect and Mechanism of Low Rank Coal Soaked in Alkaline Solution
  168. The Influence Of NO/O2 On The NOx Storage Properties Over A Pt-Ba-Ce/γ-Al2O3 Catalyst
  169. Special Issue on the International conference CosCI 2018
  170. Design of SiO2/TiO2 that Synergistically Increases The Hydrophobicity of Methyltrimethoxysilane Coated Glass
  171. Antidiabetes and Antioxidant agents from Clausena excavata root as medicinal plant of Myanmar
  172. Development of a Gold Immunochromatographic Assay Method Using Candida Biofilm Antigen as a Bioreceptor for Candidiasis in Rats
  173. Special Issue on Applied Biochemistry and Biotechnology 2019
  174. Adsorption of copper ions on Magnolia officinalis residues after solid-phase fermentation with Phanerochaete chrysosporium
  175. Erratum
  176. Erratum to: Sand Dune Characterization For Preparing Metallurgical Grade Silicon
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Heruntergeladen am 9.9.2025 von https://www.degruyterbrill.com/document/doi/10.1515/chem-2019-0080/html
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