Manuela M. Moreira

HPLC/DAD analysis of phenolic compounds from lavender and its application to quality control

A reversed phase HPLC procedure is proposed for the determination of eight phenolic compounds (2-O-glucosilcoumaric acid, o-coumaric acid, rosmarinic acid, apigenin-7-O-glucoside, coumarin, herniarin, luteolin, and apigenin) in lavender. The chromatographic separation was achieved using a reversed-phase Spherisorb ODS 2 (5 μm particle size: 25.0 × 0.46 cm) column. From the several extractive solvents assayed, only ethanol was able to extract all the mentioned compounds. Best resolution was obtained using a gradient of water-formic acid (19:1) and acetonitrile. Ten samples were subjected to quantification, all of them showing a common composition pattern.

Methoxylated aurones from cyperus capitatus

Abstract Aureusidin, 6,3′-dihydroxy-4,4′-dimethoxy-5-methylaurone and 4,6,3′,4′-tetramethoxyaurone were isolated from Cyperus capitas. The compounds were identified by spectral means.

New application of the QuEChERS methodology for the determination of volatile phenols in beverages by liquid chromatography

The QuEChERS methodology has been used for the determination of pesticides in solid samples. However, this technique can be equally useful for other applications, namely for liquid samples. This work presents a new application of QuEChERS to the analysis of important ageing markers in beverages, the volatile phenols, by liquid chromatography with fluorimetric and UV detection. The sample preparation methodology comprises two sequential steps: (1) salting-out liquid-liquid extraction and (2) dispersive solid-phase extraction for extract clean-up. The methodology showed good repeatability (ca. 3%) and reproducibility (ca. 6%) with recovery levels above 90% and limits of detection varied in the range of 0.001-0.055 mg L(-1). A variable amount of phenols was found in the analysed samples (beers, wines and fruit juices), being 4-ethylphenol and 4-ethylguaiacol the compounds found in higher amounts, varying in the range of 0.12-1.11 mg L(-1) and 0.13-1.23 mg L(-1), respectively.

6,3′,4′-trihydroxy-4-methoxy-5-methylaurone from Cyperus capitatus

Abstract An aurone has been isolated from Cyperus capitatus which was identified by spectral means as 6,3′,4′-trihydroxy-4-methoxy-5-methylaurone.

Isolation and Structural Elucidation of 5-Formyl-2,3-Dihydroisocoumarin from Centaurium Erythraea Aerial Parts

An isocoumarin was isolated from the aerial parts of Centaurium erythraea Rafn. (Gentianaceae). Its structure was established by spectroscopic means as 5-formyl-2,3-dihydroisocoumarin.

A series of eleven dialkyl-hydroxy-p-benzoquinones from Cyperus capitatus

Abstract Cyperus capitatus contains a homologous series of 11 6-alkyl-2-hydroxy-3-methyl-1,4-benzoquinones, with chain length C 17 to C 27 . Those with a C 17 , C 19 and C 21 side chain were isolated and named as capiquinones A, C and E.

Novel application of square-wave adsorptive-stripping voltammetry for the determination of xanthohumol in spent hops.

This paper reports the development of a novel electrochemical assay for xanthohumol (XN) by square-wave adsorptive-stripping voltammetry (SWAdSV) with a hanging mercury drop electrode. The method showed good repeatability (CV < 2%) and linearity (between 10 and 250 μg L(-1)), as well as suitable limits of detection (2.6 μg L(-1)) and quantification (8.8 μg L(-1)). The method was applied for the quantification of this compound in spent hops, and the results obtained were compared with the HPLC-UV method. XN contents determined by the SWAdSV method were 16 ± 1 and 100 ± 4 μg L(-1) for aqueous and methanolic extracts, respectively. The developed new methodology considerably reduces the analysis time, approximately from 25 min (HPLC-UV method) to 7 min, enabling a high sample throughput. In addition, the detection and quantification limits were approximately 5-fold lower than those obtained with the chromatographic method.

Methylaurones from Cyperus capitatus

Abstract 4,6,3′,4′-tetrahydroxy-5-methylaurone, 4,6,3′,4′-tetrahydroxy-7-methylaurone and 6,3′,4′-trihydroxy-4-methoxy-5-methylaurone were isolated from Cyperus capitatus . On the basis of NMR studies, the structures of the methylaurones previously isolated from this species were revised and the compound described before as 6,3′,4′-trihydroxy-4-methoxy-5-methylaurone is shown to be 6,3′,4′-trihydroxy-4-methoxy-7-methylaurone.

Techniques for Extraction of Brewer’s Spent Grain Polyphenols: a Review

Million tons of brewer’s spent grain (BSG) are annually produced worldwide as brewing industry by-products. BSG represents a valuable source of phenolic compounds, which have attracted much attention due to their diverse health benefits. Relevant strategies have been developed for their efficient extraction, in order to commercially exploit these resources. This review focuses on the current extraction methods used to obtain phenolic compounds from BSG, ranging from more traditional to advanced techniques. The commonly used methods are the conventional solid–liquid extractions, employing organic solvents, alkaline, and enzymatic reactions. However, the inherent difficulties in screening and obtaining these compounds have led to the development of advanced extraction techniques. Pressurized fluid extraction, supercritical extractions, and microwave-assisted and ultrasound-assisted extractions are some of the novel extraction techniques that have been recently explored. These techniques have been mostly applied for phenolic recovery from barley and malt, as well as other types of cereals. In this review, it is shown that these novel techniques may provide an innovative approach to extract phenolics from BSG or related products, following an in-depth discussion on the major strengths and weaknesses identified in each technique.

Potential of Portuguese vine shoot wastes as natural resources of bioactive compounds

Since annually a high amount of wastes is produced in vine pruning, the aim of this study was to evaluate the potential of vine shoots from two Portuguese grape varieties (Touriga Nacional - TN and Tinta Roriz - TR) to be used as a natural source of phenolic compounds. To reach this goal, three techniques were explored, namely microwave-assisted extraction (MAE), subcritical water extraction (SWE) and conventional extraction (CE). The phenolic composition of the extracts, antioxidant and biological activities were evaluated by spectrophotometry and chromatography. MAE and SWE produced the highest concentrated extracts. TR vine shoot variety had the highest antioxidant activity and total phenolic (32.1±0.9mggallicacidequivalents/g dry sample), as well as flavonoid content (18.7±1.2mgepicatechinequivalents/g dry sample). For the first time, the biological activity of the vine shoot extracts was tested. Results demonstrated that all of them had antimicrobial potential against different bacteria and yeasts, and the ability of inhibiting α-amylase and acetylcholinesterase enzymes, with MAE TR extracts being the most efficient. HPLC analysis enabled the identification of different phenolic compounds, with gallic acid, catechin, myricetin and kaempferol-3-O-rutinoside being the main contributors to the phenolic composition. Portuguese vine shoot wastes could serve as easily accessible source of natural antioxidants for the food or pharmaceutical industries.