Abstract
Over the past decade, there has been growing interest in polyphenols’ research since these compounds, as antioxidants, have several health benefits, such as preventing neurodegenerative diseases, inflammation, cancer, cardiovascular diseases, and type 2 diabetes. This study implements an analytical method to assess the total phenolic content (TPC) in essential oils using Folin–Ciocalteu’s phenol reagent and quantifies the individual phenolic compounds by liquid chromatography. Thus, the research design and methodology included: (1) extraction of essential oil from dried thyme leaves by hydrodistillation; (2) spectrophotometric measurement of TPC by Folin–Ciocalteu method; and (3) identification and quantification of individual phenolic compounds by high-performance liquid chromatography-diode array detection/electrospray ionization mass spectrometry (HPLC-DAD-ESI-MS). Results revealed a TPC of 22.62 ± 0.482 mg GAE/100 µL and a polyphenolic profile characterized by phenolic acids (52.1%), flavonoids (16.1%), and other polyphenols (31.8%). Thymol, salvianolic acid A, and rosmarinic acid were the major compounds of thyme essential oil. The proposed analytical procedure has an acceptable level of repeatability, reproducibility, linearity, LOD (limit of detection), and LOQ (limit of quantification).
Highlights
Polyphenols are compounds found naturally in plants, as they are synthesized in their tissues, in fruits and vegetables [1]
Instrument calibration is an important stage in most measurement procedures
It involves (1) preparing a set of standards containing a known amount of the analyte of interest, the gallic acid in our case, (2) measuring the instrument response for each standard, and (3) establishing the relationship between the instrument response and analyte concentration
Summary
Polyphenols are compounds found naturally in plants, as they are synthesized in their tissues, in fruits and vegetables [1]. Endogenous synthesis of phenolic compounds is due to plants’ response to ecological and physiological pressures such as pathogen and insect attacks, UV radiation, and wounding [2]. These compounds are recognized for their antioxidant properties, and their potential benefits have been largely studied [3,4,5]. Previous studies have shown that many dietary polyphenolic constituents derived from plants are more effective antioxidants in vitro than vitamins E or C, and might contribute significantly to the protective effects in vivo [7]. Recent evidence has proposed that a high dietary intake of polyphenols may be inversely associated with overall and cardiovascular disease-related mortality, certain cancers, anthropometric measurements, and mood disorders [8]
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