Abstract
In the present study, a total of 12 extracts of Rhinanthus angustifolius subsp. grandiflorus, an understudied hemiparasitic species, were obtained using different extraction techniques, namely, homogenizer-assisted extraction (HAE), maceration (MAC), soxhlet (SOX), infusion, and solvents (ethyl acetate, methanol, ethanol, and water), and were evaluated for their in vitro antioxidant and enzyme-inhibiting properties. Additionally, untargeted profiling based on high-resolution mass spectrometry targeted different phytochemical classes, namely, polyphenols, terpenoids, and alkaloids. The highest total phenolic and flavonoid contents were detected using methanol as the extraction solvent. Multivariate statistics following the untargeted profiling revealed that the extraction solvent had a hierarchically higher impact than the extraction method when considering the recovery of bioactive compounds. The methanolic extracts displayed the highest radical-scavenging antioxidant capacity, as provided by CUPRAC and FRAP assays. On the other hand, the water extracts (MAC and HAE) and the infusion extract showed the highest activity as metal chelators (25.66–27.51 mg EDTAE/g). Similarly, the water extract obtained by HAE and the infusion extract revealed the highest phosphomolybdenum activity (3.92 ± 0.14 and 3.71 ± 0.01 mmol TE/g, respectively). The different extracts also exhibited different enzyme inhibition potentials. For instance, HAE and MAC ethanolic extracts inhibited only α-amylase (0.69 ± 0.01 and 0.70 ± 0.01 mmol ACAE/g), while all the other extracts showed a dual inhibition against both carbohydrate-hydrolyzing enzymes tested (i.e., α-amylase: 0.07–0.69 mmol ACAE/g; α-glucosidase: 0.03–1.30 mmol ACAE/g). Nevertheless, the other extracts inhibited acetyl-, butyryl-cholinesterases, or both; MAC–water extract displayed no inhibition against the enzymes. Additionally, all the studied extracts were found to inhibit tyrosinase, ranging from 10.62 to 52.80 mg KAE/g. In general, the water extracts showed weaker inhibition towards the enzymes than the other extracts. This study demonstrated that R. angustifolius is an excellent source of natural antioxidants and enzyme inhibitors that could be further investigated and exploited for pharmaceutical purposes.
Highlights
The genus Rhinanthus from the family of Orobanchaceae is comprised of around 30–40 annual species of hemiparasitic annual herbs
Rhinanthus angustifolius subsp. grandiflorus samples were collected in Kastamonu (Taşköprü village, Turkey) in July 2020
The untargeted phytochemical profiling of R. angustifolius extracts was carried out through an ultra-high-pressure liquid chromatography quadrupole-time-of-flight mass spectrometry (UHPLC-QTOF-MS), recognized as a powerful analytical tool because of its high sensitivity. This approach allowed the putative detection of 570 bioactive compounds (BCs), characterized by 309 terpenoids, 248 polyphenols, and 13 alkaloids
Summary
The genus Rhinanthus (rattle) from the family of Orobanchaceae is comprised of around 30–40 annual species of hemiparasitic annual herbs. Some Rhinanthus species are used in folk medicine for treating eye complaints caused by certain bacteria [2], while others are used against stomach diseases or have been ethnobotanically documented to be consumed as a tea against cold [3]. Among the different species reported, R. angustifolius has been previously used for external baths for treating eczema [4]. R. angustifolius are used as a medicine for treating ear complaints by people in Anatolia [2]. A new iridoid glucoside, namely, 60 -O-benzoylshanzhiside methyl ester, together with other known compounds such as aucubin, melampyroside, mussaenoside, shanzhiside methyl ester, 8-epiloganin, gardoside methyl ester, and 2-(4-hydroxyphenyl) ethylalcohol were previously isolated from the aerial parts of R
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