Assessment of antioxidant activity, minerals, phenols and flavonoid contents of common plant/tree waste extracts

Abstract

Extracts of 25 different plant/tree wastes were screened for their phenol and flavonoid contents, antioxidant activity, nutritional and toxicological elemental composition. The commercial exploitation potential of nutrient and polyphenol-rich tree/plant wastes was also discussed. This study is the first to recommend using non-toxic Melaleuca diosmifolia leaf, Melia azedarach pod, Alnus cordata leaf and Pinus radiata cones because they all contain the essential elements (N, P, K, S and Fe) for dietary intake, applications as soil amendments, contaminant biosorbents and substrates for composting or biofertilizer preparation. Fruit peel of Quercus robur, M. diosmifolia leaf and bark, Eucalyptus leucoxylon pod and leaf, Pyrus ussuriensis and Prunus cerasifera leaf aqueous extracts indicated high phenolic content (35–66mg GAE/g) and antioxidant activity (70–90%). A. cordata and Morus alba pendula leaf emerged as a unique source of flavonoids (>95%). There are greater prospects for the green synthesis of metallic nanoparticles using these polyphenol-rich residues.