Mid Sweden University

Eight avenanthramides, amides of anthranilic acid (1) and 5-hydroxyanthranilic acid (2), respectively, and the four cinnamic acids p-coumaric (p), caffeic (c), ferulic (f), and sinapic (s) acid, were synthesized for identification in oat extracts and for structure−antioxidant activity studies. Three compounds (2p, 2c, and 2f) were found in oat extracts. As assessed by the reactivity toward 1,1-diphenyl-2-picrylhydrazyl (DPPH), all avenanthramides except 1p showed activity. Initially, the antioxidant activity of the avenanthramides decreased in a similar order as for the corresponding cinnamic acids, that is: sinapic > caffeic > ferulic > p-coumaric acid. The avenanthramides derived from 2 were usually slightly more active than those derived from 1. All avenanthramides inhibited azo-initiated peroxidation of linoleic acid. 1c and 1s were initially the most effective compounds. The relative order of antioxidant activities was slightly different for the DPPH and the linoleic acid assays run in methanol and chlorobenzene, respectively.

Introduction - Antioxidants are known to avert oxidation processes and they are found in trees and other plant materials. Tree bark is a major waste product from paper pulp industries; hence it is worthwhile to develop an extraction technique to extract the antioxidants. Objective - To develop a fast and environmentally sustainable extraction technique for the extraction of antioxidants from bark of spruce (Picea abies) and also to identify the extracted antioxidants that are abundant in spruce bark. Methodology - A screening experiment that involved three different techniques was conducted to determine the best technique to extract antioxidants. The antioxidant capacity of the extracts was determined with DPPH (2,2-diphenyl-1-picrylhydrazyl) assay. Pressurised fluid extraction (PFE) turned out to be the best technique and a response surface design was therefore utilised to optimise PFE. Furthermore, NMR and HPLC-DAD-MS/MS were applied to identify the extracted antioxidants. Results - PFE using water and ethanol as solvent at 160 and 180°C, respectively, gave extracts of the highest antioxidant capacity. Stilbene glucosides such as isorhapontin, piceid and astringin were identified in the extracts. Conclusion - The study has shown that PFE is a fast and environmentally sustainable technique, using water and ethanol as solvent for the extraction of antioxidants from spruce bark. Copyright © 2011 John Wiley and Sons, Ltd. This paper includes four tables in which the extracted solid yield and the antioxidant capacity of spruce bark extracts were presented for the different extraction techniques, as well as the response surface coefficients for the optimised PFE were presented. © 2011 John Wiley and Sons, Ltd..

Various types of natural and synthetic antioxidants when added to handsheets of pulp in low concentrations (0.2% weight%) could significantly reduce the emission of hexanal. The most efficient compounds caused a 90% reduction after eight weeks. Their capacity to inhibit brightness reversion was limited.

Avenanthramides are amides of cinnamoyl-anthranilic acids and, among cereals, are exclusively found in oats. This study investigated the structure-antioxidant activities of 15 avenanthramides with different substitution patterns in the two aromatic rings, seven of which were new avenanthramides synthesised and characterised in this study. Radical-scavenging activity was tested as reactivity towards 1,1-diphenyl-2-picrylhydrazyl (DPPH-). The activity increased with the number of radical-stabilising groups ortho to the phenolic hydroxy group. Both aromatic rings were independently important for activity, while conjugation across the amide bond was of minor importance. Antioxidant activity was determined as inhibition of linoleic acid oxidation. In contrast to the radical-scavenging activity, antioxidant activity was observed for most avenanthramides, and also for compounds with only one hydroxy group in either of the aromatic rings. Compared with alpha-tocopherol, the avenanthramides protected linoleic acid from oxidation to a smaller extent initially, but the effect lasted for a longer time.