Abstract
A solid-phase extraction (SPE) procedure was developed for simultaneous monitoring of sixteen different phenolics of various polarity, quantified by high-performance liquid chromatography (HPLC). The procedure allowed screening the accumulation of intermediates in different metabolic pathways that play a crucial role in plant physiology and/or are beneficial for human health. Metabolites mostly involved in phenylpropanoid, shikimate, and polyketide pathways comprise chlorogenic acid, gentisic acid, vanillic acid, caffeic acid, protocatechuic acid, ferulic acid, rutin, quercetin, epicatechin, gallic acid, sinapic acid, p-coumaric acid, o-coumaric acid, vanillin; two rarely quantified metabolites, 2,5-dimethoxybenzoic acid and 4-methoxycinnamic acid, were included as well. The procedure offered low cost, good overall efficiency, and applicability in laboratories with standard laboratory equipment. SPE recoveries were up to 99.8% at various concentration levels. The method allowed for routine analysis of compounds with a wide range of polarity within a single run, while its applicability was demonstrated for various model plant species (tobacco, wheat, and soybean), as well as different tissue types (shoots and roots).
Highlights
Received: 22 November 2020Polyphenolic compounds are ubiquitously distributed among higher plants, affecting the organoleptic and nutraceutical properties of fruits and vegetables and the plant’s ability to cope with environmental constraints
Many of these compounds enter the human body through the food chain and exert positive effects on human health; particular importance is given to metabolites with anti-inflammatory, antioxidative, or cancer-preventing properties [1]
Standards of phenolic compounds were all of high-performance liquid chromatography (HPLC) grade and included 2,5-dimethoxybenzoic acid (DMBA), 4-methoxycinnamic acid (4MCA), chlorogenic acid (CGA), gentisic acid sodium salt hydrate (GTA), vanillic acid (VA), caffeic acid (CA), protocatechuic acid (PCA), trans-ferulic acid (TFA), rutin (RUT), quercetin (QUER), and epicatechin (EPI) from Sigma-Aldrich (Hamburg, Germany); gallic acid (GA), sinapic acid (SIA), p-coumaric acid (p-CMA), and o-coumaric acid (o-CMA) from Fluka (Arlington, United Kingdom); vanillin (VAN) from
Summary
Polyphenolic compounds are ubiquitously distributed among higher plants, affecting the organoleptic and nutraceutical properties of fruits and vegetables and the plant’s ability to cope with environmental constraints. Phenolic compounds containing a benzene ring with one or more hydroxyl groups are synthetized in plants mainly through the phenylpropanoid, shikimate, and polyketide pathways of secondary metabolism These metabolites have been identified as playing a role in the environmental stress responses of plants [14,15,16]. These included some more polar compounds, such as gallic acid, protocatechuic acid, or less polar rutin and quercetin, which represent metabolites with a demonstrated role in plant stress metabolism [14,16,20,21] They included some key plant metabolites synthetized through the phenylpropanoid pathway, such as cinnamic acid, pcoumaric acid, caffeic acid, ferulic acid, vanillin, and sinapic acid, which are ancestors in the synthesis of lignins and other phenolics of high biotechnological, added-value food, and/or chemical-pharmaceutical potential [1]. We described the whole optimization process in good detail, providing a useful resource for researchers to refer to when optimizing SPE
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