Bioactivities of wood polyphenols: antioxidants and biological effects

Albishi, Tasahil (2018) Bioactivities of wood polyphenols: antioxidants and biological effects. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The phenolic and polyphenolic compounds present in date palm, oak, quibracho, banana, and pine wood play a crucial role in the development of natural antioxidants. This study provides structural information on the phenolic compounds isolated from wood obtained from a series of old date palm (OPW), seedling date palm (SPW), oak (OW), quibracho (QW), banana (BW), and pine (PW) and their associated products. The total phenolic content (TPC), total flavonoid content (TFC), tannin content (TC) as well as the antioxidant activity of wood extracts was studied by employing in vitro assays using the free radical scavenger 1,1-diphenyl-2-picrylhydrazyl (DPPH) and iron chelatiom methods. The antioxidant activity and phenolic content of SPW extract, as determined by the DPPH assay, TPC and TC were higher than those of the other wood extracts. Analysis of wood extracts revealed a high amount of phenolics and tannins suggesting a possible role of wood phenolics as a source of natural antioxidants. These studies clearly indicate that the SPW had a significant antioxidant activity. In addition, the antioxidant capacity of soluble- and insoluble-bound phenolics of wood extracts was examined, as well as their bioactivities such as inhibition of oxidation of LDL cholesterol and DNA strands breakage. The results so obtained also confirmed the fact that antioxidant potential and oxidation inhibitory activities were much higher for the SPW compared to other wood extracts. Furthermore, in this study, the date palm wood was used to generate smoke that was subsequently used to prepare smoked salmon, using maple wood as a commercial standard. Prominent volatile compounds released during the smoking process were adsorbed using solid-phase microextraction (SPME) and were then identified by gas chromatography–mass spectrometry (GC–MS). The oxidative stability of the smoked salmon was evaluated in terms of development of thiobarbituric acid reactive substances (TBARS). Regardless of the wood type, volatile compounds were mainly methoxyphenols, with the highest contribution from eugenol, followed by guaiacol and their corresponding derivatives. The phenolic composition of OPW, SPW, OW, QW, BW, and PW were studied using conventional analytical methodologies. In addition, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI- TOF/TOF-MS) and tandem mass spectrometry (MS/MS) analyses were used to examine the structures of various phenolics, tannins, and lignin compounds. The results showed that OPW, SPW, OW, QW were rich in the classes of compounds tested. Both condensed tannin and hydrolyzable tannins were present in high amounts in SPW, OPW, and OW and their phenolics present showed the highest antioxidant values compared to QW, BW, and PW.

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