Phenolic compounds in plants and agri-industrial by-products: Antioxidant activity, occurrence, and potential uses

A critical review of methods for characterisation of polyphenolic compounds in fruits and vegetables.

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Natural products as antimicrobial agents

Phenolic compounds of 14 pomace samples originating from red and white winemaking were characterized by HPLC-MS. Up to 13 anthocyanins, 11 hydroxybenzoic and hydroxycinnamic acids, and 13 catechins and flavonols as well as 2 stilbenes were identified and quantified in the skins and seeds by HPLC-DAD. Large variabilities comprising all individual phenolic compounds were observed, depending on cultivar and vintage. Grape skins proved to be rich sources of anthocyanins, hydroxycinnamic acids, flavanols, and flavonol glycosides, whereas flavanols were mainly present in the seeds. However, besides the lack of anthocyanins in white grape pomace, no principal differences between red and white grape varieties were observed. This is the first study presenting comprehensive data on the contents of individual phenolic compounds comprising all polyphenolic subclasses of grapes including a comparison of several red and white pomaces from nine cultivars. The results obtained in the present study confirm that both skins and seeds of most grape cultivars constitute a promising source of polyphenolics.

Polyphenol screening of pomace from red and white grape varieties (Vitis vinifera L.) by HPLC-DAD-MS/MS.

Apple pomace as a source of dietary fiber and polyphenols and its effect on the rheological characteristics and cake making.

b ¨¨ Abstract A process for the combined recovery of pectin and phenolic compounds from apple pomace, the primary by-product of apple juice production, was developed. The process includes extraction of dried apple pomace with diluted mineral acid and adsorption of phenolic constituents by a hydrophobic styrene-divinylbenzene copolymerisate. After elution with methanol, the polyphenolics were concentrated in vacuo, stabilised by lyophilisation, and characterised by high-performance liquid chromatography. The predominant compounds were phloridzin, chlorogenic acid and quercetin glycosides. Adsorptive removal especially of oxidised phenolic compounds led to a considerable decolourisation of the pomace extracts, as revealed by determination of L*a*b* values, hue angle and chroma. Gelling properties of pectin were not adversely affected. While the polyphenolics recovered from apple pomace may be used as natural antioxidants or as functional food ingredients, extended fields of application may be obtained for decolorised, refined apple pectins. Furthermore, investigations on the phenolic composition of several New Zealand apple cultivars, of apple seeds, and on the effects of pomace drying on the stability of polyphenolics were carried out. 2002 Elsevier Science Ltd. All rights reserved.

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A new process for the combined recovery of pectin and phenolic compounds from apple pomace

The phenolic profile of strawberry fruits (Fragaria x ananassa Duch., Rosaceae) was investigated by high-performance liquid chromatography with photodiode array detection. A peak displaying retention time and UV spectral data identical to those of phloridzin (phloretin 2‘-O-β-d-glucoside), a dihydrochalcone glucoside so far considered characteristic of apples, was monitored. For further characterization, crude extracts of strawberries were purified on polyamide, and the target compound was isolated by preparative and analytical HPLC. Structure elucidation was performed on the basis of APCI- and ESI-MS in the negative ion mode as well as by 1D and 2D NMR spectroscopy using authentic phloridzin for comparison. The d-configuration of the sugar moiety was established by HPLC analysis of the corresponding acyclic 1-deoxy-1-(N-acetyl-α-methylbenzylamino)alditol acetate. Apart from its chemotaxonomic relevance, this first report on the occurrence of phloridzin in strawberries is of particular interest for the au...

Detection of Phloridzin in Strawberries (Fragaria X Ananassa Duch.) by HPLC-PDA-MS/MS and NMR Spectroscopy

A stationary phase with hydrophilic endcapping was used for the separation of seven quercetin (Q) glycosides by high-performance liquid chromatography. The elution order was established as Q 3-rutinoside, Q 3-galactoside, Q 3-glucoside, Q 3-xyloside, Q 3-arabinopyranoside, Q 3-arabinofuranoside, and Q 3-rhamnoside. Since a recent study had revealed that a commercially available reference compound (Q 3-arap) was erroneously labeled as avicularin (Q 3-araf), standards of the two isomers of Q 3-ara were characterized by 1 D and 2D NMR spectroscopy, and by optical rotation. The predominant Q glycosides detected in apple pomace were Q 3-gal, Q 3-araf, Q 3-rha and Q 3-xyl, whereas considerably lower amounts of Q 3-glc and Q 3-arap were found. Total content of Q glycosides was approximately 900 mg/kg on a dry matter basis, indicating that apple pomace is a good source of natural antioxidants.

Petra Hilt

Papers

A new process for the combined recovery of pectin and phenolic compounds from apple pomace

Detection of Phloridzin in Strawberries (Fragaria X Ananassa Duch.) by HPLC-PDA-MS/MS and NMR Spectroscopy

Elution order of quercetin glycosides from apple pomace extracts on a new HPLC stationary phase with hydrophilic endcapping