Samples 1 and 3 had similar EF in M and W, sample 2 was better extracted in AA and was richer in phenolic compounds derivatives . The components of sample 4 were extracted two times better in M than in W, and low EF values in AA is an indication of polar active molecules . Sample 5 and 6 contained reduced concentrations of phenolic compounds, but exhibit high absorptions in methanol at 279 and 320 nm, respectively, which might be attributed to higher concentrations of lignans and terpenoids . Of therapeutic reasons, it has been considered that AA extracts or M extracts can provide higher concentrations of bioactive molecules from these plants.
The average TPC (mg GAE/g crude extract) of the water methanol extract was significantly higher (263.5 mg/g) than that for methanol, (167.3 mg/g) and better than that for acetic acid extracts (197.9 mg/g). The use of water presents the advantage of modulating the polarity of alcoholic solvents. The solubility of polyphenols depends mainly on the hydroxyl groups, the molecular size and the length of the hydrocarbon chain [32, 33]. Another remarkable observation refers to the higher yield of extract related to solvent M, followed by water as solvent. Water is an inefficient solvent of the extraction of TPC from the M. sativa flowers studied [32, 33]. The average TPC (mg GAE/g crude extract) of the methanol extract was significantly higher (263.5 mg/g) than that of W, (167.3 mg/g) and better than that for AA extracts (197.9 mg/g).
The solubility of polyphenols depends mainly on the hydroxyl groups, the molecular size and the length of the hydrocarbon chain. Another remarkable observation refers to the higher yield of extract related to solvent M, followed by water as solvent.
The details in Table 1 explain the higher total phenolic compounds when we choose organic solvents whose polarity is modified with water. These mixtures become ideal and selective to extract a great number of bioactive compounds of phenolic type.
Whereas methanol offers a higher amount of yield, it is not appropriate to extract polyphenols. The solvent extracts only the water-soluble bioactive compounds; moreover, many other residual substances/impurities are present in the extracts.
It appears from our results that some of phenolic compounds and other pharmacologically interesting compounds from the samples are not extractible with plain water, for this reason the mixtures of solvents are suitable to extract different bioactive compounds. In our investigation, the mixture of methanol and water proved to a better solvent for the extraction of phenolic compounds from plants flowers than the mixture of AA and water. On the other hand, the M extract has higher total phenolic compounds content than AA, and W extracts, but did not exhibit the highest antioxidant activity among the three different extracts. In this context, it is possible that phenolic compounds, existing in the water extract, possess an ideal structure for decomposing free radicals since they possess a number of hydroxyl groups acting as hydrogen donors turning them into important and very powerful antioxidant agents.
The results of this accounts for the reason why for each solvent, taken individually, the TPC determined with the FC assay presents a good correlation with antioxidant activity, but it is not the case when compare between extracts obtained by various solvents. Different reports are found in the literature: whereas some authors have found a correlation between the total phenolic compounds content and the antioxidant activity, others found no such relationship .
Antioxidant activity of extracts is strongly dependent on the solvent due to the different antioxidant potentials of compounds with different polarity. The FC assay offers an estimate of the TPC present in an extract. The assay is not specific for polyphenols; instead many interfering compounds may react with the reagent resulting in apparently elevated phenolic compounds concentrations.
In addition, various phenolic compounds respond differently in this assay, depending on the number of their phenolic groups and the TPC does not incorporate necessarily all the antioxidants that may be present in an extracting.
According to this study, methanol appears ideal for extracting a high amount of phenolic compounds, while water was the ideal solvent for extract bioactive compounds from M. sativa flowers with potential antioxidant activity content.
Eight areas were identified as the MIR domain and the fingerprint region was localized between 900 and 1500 cm–1. Absorptions below 1000 cm–1 correspond to C–H bending vibrations from isoprenoids, the absorption bands between 997–1130 cm–1 may be attributed to stretching vibrations C–O of mono–, oligo– and carbohydrates, with signals at 1030, 1054, 1104, and 1130 cm–1, while the absorption over the range of 1150–1270 cm–1 corresponds of stretching vibrations of C–O fragment of carbonyl group or to O–H bending vibration. Absorption situated between 1300–1450 cm–1 corresponds to stretching vibrations C–O (amide) and C–C stretching vibration of the phenyl groups, while the signals between 1500–1600 cm–1 may be assigned to aromatic parts and to N–H bending vibrations. Between 1600–1760 cm–1 there is a complex corresponding to bending vibrations N–H (amino acids), C=O stretching vibrations (aldehydes, ketones and esters) as well as to free fatty acids (1710 cm–1) and glycerides (1740 cm–1) . The absorption comprised in domain 2800–2900 cm–1, corresponds to C–H stretching vibrations, specific to CH3 and CH2 in lipids, methoxy derivatives and to C–H in aldehydes, including cis double bond configuration. The domain 3350–3600 cm–1 corresponds to stretching vibrations of OH groups (water, alcohols, phenols, carbohydrates, peroxides) as well as to amides (3650 cm–1). In methanol extracts there are absorption bands in the 1300–1800 cm–1 domain, more than in W, e.g. at 1558, 1517 and 1467 cm–1, as well as in the region 1380–1450 cm–1. Such differences were noticed also by other authors, after processing the second derivative in M. sativa flowers extracts, where typical signals, specific to cellulose and hemicelluloses at 3413 and 1054 cm–1, were found.
The signals at 1642 and 1536 cm–1 correspond to the amide I band (carbonyl group) and amide II (stretching ϑCN + bending ϑNH) found in glycoproteins .
Carbonyl groups have specific signals at 1743 cm–1. Due to observation of region 1 (specific to terpenoids), it has been noticed that samples 6, 5 and 4 possess bands located at higher wavenumbers in AA, similarly to the results of UV–spectra.
In the other IR regions (4 and 6) no significant differences between the three solvent extracts were noticed, but in regions 2 (corresponding to glucosides) and 7 (lipids), in all plant extracts, the M extract was significantly more charged in molecules than AA or W extracts. Finally, the phenolic compounds concentrations determined by the FTIR method, based on the peak intensity at 1743 cm–1, and total phenolic compounds content calculated using the VIS spectrometry have been compared.
A significant (p<0.05) correlation factor was obtained; it is known that the measurement performed within the VIS spectrometry is not specific to phenols and can overestimate concentrations, while the FTIR method, using the absorption bands (950–1900 cm–1) estimation can also lead to false results.
It can be considered in this case that measurements, based on the FTIR absorption intensity at 1743 cm–1, offer the best evaluation of the concentration of phenolic compounds in these plants. This work has been undertaken to gain an understanding of the chemical composition of latent prints so that new methods of developing fingerprint images can be explored. Additionally, methods of imaging fingerprints from electro-optical responses obtained through spectrometers have been investigated.