Isolation, identification and activity of natural antioxidants from sweet grass (Hierochloe odorata), costmary (Chhrysanthemum balsamita) and horehound (Marrubium vulgare), cultivated in Lithuania

Food products are susceptible to oxidation processes. Oxidation of lipids (fat) is the major cause of food deterioration however also proteins and carbohydrates can be affected. To prevent or retard this process, antioxidants are used. With regard to foods, more and more natural products are preferred by consumers so new natural sources of compounds able to retard oxidation processes and prevent spoilage of food products are continuously investigated. The research described in this study is aimed at the evaluation of several herbs as possible sources of food antioxidants. An initial screening of extracts from roman camomile, tansy, sweet grass, costmary, sea-buckthorn and sage for antioxidant activity in rapeseed oil has been performed Sweet grass and sage acetone extracts retarded oxidation processes in oil best. Sweet grass was chosen for further investigation as the herb having the highest antioxidant activity. Two other herbs, namely horehound and costmary were further selected for the evaluation of their antioxidant activity in different assays. At first preliminary fractionation of the selected herb extracts was performed. Fractions were tested in three different assays: -carotene oxidation, DPPH• reduction and rapeseed oil oxidation. The experiments did not provide any straightforward answers, which fractions contained the most active antioxidants. Different assays gave different results. More polar fractions were more active in model systems like DPPH• while in the edible oil assay these fractions acted as weak antioxidants, or some even exhibited a prooxidation effect. Acetone extracts performed better than methanol-water extracts in retarding oil oxidation probably due to their higher compatibility with the medium or the more non-polar nature of the contained analytes. In further steps the structures of the radical scavenging compounds present in extracts of sweet grass, horehound and costmary were elucidated. Two compounds, namely 5,8-dihydroxybenzopyranone and 5-hydroxy-8-O--D-glucopyranosyl benzopyranone were isolated and identified from sweet grass extract. Both compounds were identified for the first time as natural products. Four compounds, namely 5-O-caffeoyl quinic acid (chlorogenic acid), 3,5-dicaffeoyl quinic acid, 5,7,4'-trihydroxy-3',8-dimethoxy flavone and 5,7,3',4'-tetrahydroxy-3,8-dimethoxyflavonol were identified in costmary extracts. These compounds are quite common in plant kingdom. However, they have not previously been isolated from costmary. Five compounds, namely 5,8-dihydroxy-7,4-dimethoxy flavone, 7-O--glucopyranosyl luteolin, 7-O--glucuronyl luteolin, verbascoside and forsythoside B were isolated from horehound extracts. These compounds are common in the Labiatae family. Their radical scavenging activity was measured using DPPH• and ABTS•+ scavenging assays and compared with the activity of rosmarinic acid and Trolox. An on-line HPLC-DPPH-DAD-NMR system for the rapid identification of compounds in complex mixtures was developed. The developed system was tested on commercial rosemary extract and six compounds were identified without the need to isolate them. This proved that simultaneous detection and identification of radical scavengers is possible. Several solvents, namely hexane, acetone ant ethanol and their combinations were tested for their suitability to extract all known radical scavengers from sweet grass, costmary and horehound. It was found that initial extraction of the plant material with hexane increased the concentrations of radical scavengers in the following extraction stages.

Bibliographic Details

Main Author:	Pukalskas, A.
Other Authors:	de Groot, Aede
Format:	Doctoral thesis biblioteca
Language:	English
Published:	Wageningen Universiteit
Subjects:	antioxidants, extraction, lithuania, natural products, physicochemical properties, antioxidanten, extractie, fysicochemische eigenschappen, litouwen, natuurlijke producten,
Online Access:	https://research.wur.nl/en/publications/isolation-identification-and-activity-of-natural-antioxidants-fro
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