Approach to Optimization of FRAP Methodology for Studies Based on Selected Monoterpenes

Abstract

Terpenes, wide-spread secondary plant metabolites, constitute important parts of many natural compounds that hold various biological activities, including antioxidant, calming, antiviral, and analgesic activities. Due to their high volatility and low solubility in water, studies of compounds based on terpenes are difficult, and methodologies must be adjusted to their specific characteristics. Considering the significant influence of iron ions on dementia development, the activity of terpenes in reducing Fe3+ represents an important area to be determined. Previously obtained results were unreliable because ferric-reducing antioxidant power (FRAP) methodology was not adjusted regarding studying terpenes. Taking this fact into account, the aim of this study was to optimize the method for monoterpene assessment. The study included three modifications, namely, (1) slightly adjusting the entire FRAP procedure, (2) replacing methanol with other solvents (heptane, butanone, or ethyl acetate), and (3) adding Tween 20. Additionally, a thin layer chromatography (TLC) -FRAP assay was performed. The obtained results revealed significant improvement in the reduction activity of selected terpenes (linalool, α-phellandrene, and α-terpinene) in studies with Tween 20, whereas replacing methanol with other solvents did not show the expected effects.

Antioxidant properties of butylated phenol with oxadiazole and hydrazone moiety atorthoposition supported by DFT study

“… 51 The acidic medium (pH 3.6) is required to facilitate Fe 3+ complex solubility, yet the condition also results in lower ionisation potential, which promotes the single electron transfer mechanism, as opposed to the hydrogen atom transfer mechanism in DPPH assay (Scheme 38 in ESI † ). 52 …”

Natural Antioxidant Evaluation: A Review of Detection Methods

“…As a colorimetric assay, color changes can be measured at 593 nm on a spectrophotometer; the standard used is a ferrous ion solution, and Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), a soluble analogue of vitamin E, is used as a positive control. The result is expressed in FRAP units, since the FRAP unit is related to the reduction of ferric ion 1 M into one ferrous ion [ 149 ].…”

“…There are some limitations of the FRAP assay, such as the redox potential of the Fe 2+ /Fe 3+ pair that can induce a false Fe 3+ reduction when testing compounds with a lower redox potential, the rapid time of reaction which considers that redox reactions are fast, but is not always the case, and the hydrophilic environment of the reaction preventing the hydrophobic compounds from being efficiently tested [ 149 ].…”

“…Their results were similar to that using the solubility potentiator, which can support a more affordable experiment, not losing its reliability. Wojtunik-Kulesza [ 149 ] tested the addition of a surfactant (Tween-20) to enhance some monoterpenes’ solubility and observed a reduced clouding in the studied solutions and a false positive effect, and also applied thin-layer chromatography (TLC) with FRAP, demonstrating that the combined methods could be used as a fast, more reliable and reproducible way to determine the reducing activity of extracts [ 122 , 149 ].…”

Terpene Research Is Providing New Inspiration for Scientists

“…This issue gathers 17 papers, 5 review articles, and 12 research communications with a vast range of topics with different perspectives, such as the optimization of FRAP methodology for studies based on selected monoterpenes [1], and the improved functioning of fibroblasts and endothelial cells and accelerated healing of cutaneous wounds in mice caused by uvaol [2]. It presents a new iridoid and three new bis-iridoid glycosides from the leaves of Lasianthus verticillatus, lasianosides F-I [3], and atypical lindenane-type sesquiterpenes from Lindera myrrha [4].…”