Phenolic compounds are dietary bioactive compounds that are available in foods and beverages. They are produced by the plant and/or by the mushrooms, naturally. Some of the natural phenolic compounds were also used in dietary supplements in the pharmaceutical or food industries. For simultaneous analyses of phenolic compounds in one injection, a rapid and sensitive method was developed for twenty-seven natural compounds using reverse-phase high-performance liquid chromatography (RP-HPLC) coupled with diode array detector (DAD). The linear gradient elution systems of 0.1% acetic acid-methanol were used, and the analyzing time was 61 minutes. The method was validated with linearity, relative error, reproducibility, LOD values. Relative standard deviation between (n = 7) within and between days for reproducibility is less than 10%, and relative error (or recovery) is less than 5%. The method exhibited excellent linearity (R2>0.999), good precision (RSD<6.1%), recovery (97.6–104.1%) and limits of detection (0.23–28.81 µg/m1) and quantification (1.62– 87.29 µg/m1). The detection of compounds was performed at 220 nm, 280 nm, and 330 nm. The developed method for the rapid determination of phenolic compounds using RP-HPLC can be used to identify the availability of these phenolic compounds in natural and commercial products.

In this study, the leaves of Eucalyptus citriodora Hook (Lemon-Scented Eucalyptus) were harvested and collected from Üzümlü neighborhood of Fethiye district of Muğla in 2021. Chemical content analysis of steam distillation and hydrodistillation of essential oils were determined by GC-MS, while phenolic content of methanol extract was determined by HPLC-DAD. Antioxidant activities of essential oils and methanol extracts were determined by DPPH radical removal, ABTS cation removal, β-carotene linoleic acid, and CUPRAC activity methods; Anticholinesterase activity against AChE and BChE enzymes was determined by Ellman method; and tyrosinase inhibition associated with melanin hyperpigmentation, α-amylase inhibition, and α-glucosidase inhibition activities associated with diabetes were determined as an in vitro. The bioactivities and chemical contents of E. citriodora species, a great value of, Türkiye, were determined, bringing new natural products to organic chemistry. As a result of the study, new bioactive extracts would be obtained and thus, they can effectively reveal the potential of new business opportunities. Since methanol extract is effective against incurable diseases such as Alzheimer's and diabetes, it will also be possible to develop therapeutics of such diseases by investigating the advanced chemistry and in vivo activities of the extracts with new projects.

Rhododendron species (Ericaceae) is considered the most diverse group, with more than 1200 species famous for their colorful flowers. Rhododendron, also known as azalea, is a flowering tree in the Ericaceae family. Herein, in vitro antioxidant activities of acetone and methanol extracts of Rhododendron ponticum leaves were studied along with their phenolic contents using High-Performance Liquid Chromatography with a Diode-Array Detector (HPLC-DAD). Antioxidant activity was performed spectrophotometrically using ABTS·+, DPPH·, CUPRAC, and β-carotene/linoleic acid assays. Acetone extract showed better antioxidant activity than methanol extract in all tests. The HPLC-DAD analysis revealed fifteen phenolic compounds, of which seven were common for both extracts. Catechin (25.80 and 33.08 mg/g extract, respectively) and epicatechin (31.15 and 26.54 mg/g extract, respectively) were calculated as major phenolic components in acetone and methanol extracts.