Insights for the Valorization of Biomass from Portuguese Invasive Acacia spp. in a Biorefinery Perspective

Abstract

Acacia spp. are widespread all over the Portuguese territory, representing a threat to local biodiversity and to the productivity of the forest sector. The measures adopted in some countries for their eradication or to control their propagation are expensive, have been considered unfeasible from practical and economical perspectives, and have generated large amounts of residue that must be valorized in a sustainable way. This review brings together information on the valorization of bark, wood, leaves, flowers, pods, seeds, roots, and exudates from Acacia spp., through the production of high-value bioactive extracts (e.g., antioxidant, antimicrobial, anti-inflammatory, antidiabetic, antiviral, anthelmintic, or pesticidal agents, suitable to be explored by pharmaceutical, nutraceutical, cosmetics, and food and feed industries), its incorporation in innovative materials (e.g., polymers and composites, nanomaterials, low-cost adsorbents), as well as through the application of advanced thermochemical processes (e.g., flash pyrolysis) and pre-treatments to decompose biomass in its structural components, regarding the production of biofuels along with valuable chemicals derived from cellulose, hemicellulose, and lignin. The knowledge of this research is important to encourage an efficient and sustainable valorization of Acacia spp. within a biorefinery concept, which can bring a significant economic return from the valorization of these residues, simultaneously contributing to forest cleaning and management, to reduce the risk of fires, and to improve the social-economic development of rural areas.

Characterisation of the Phenolic Profile of Acacia retinodes and Acacia mearnsii Flowers’ Extracts

“…This effect is longstanding as the soil toxicity percolates for a long time [ 9 , 10 ]. Flower extracts are already exploited in hydrogels for personal care products, cosmetics, pharmaceuticals, and perfumes based on their anti-radical and anti-proliferative potential [ 11 ].…”

“…A. mearnsii is commonly known as “Acacia-Negra” or Black Wattle [ 13 ], a native from southeastern Australia and introduced in Africa, the Caribbean, east Asia, Europe, Sri Lanka, North America, New Zealand, South America, and southeast Asia [ 16 , 17 ]. It is considered a rapidly growing tree species of economic importance in Japan as well as an important commercial forestry species in South Africa, mainly due to the abundance of tannin in its bark and for pulp in the pulp and paper industry [ 11 ]. Traditionally, its bark extract has been used in the leather tanning industry.…”

“…According to O’Leary (2007) [ 19 ], A. retinodes bark was mentioned, in 1848, for its use in tanning, with its exuded gums becoming an early export commercial business and with natives eating it due to its nutritious characteristics. Acacia barks have been the focus of some studies regarding their extractives’ contents and bioactive components [ 11 , 20 ], with a significant fraction being attributed to tannins and related compounds. On the other hand, little work has been conducted on Acacia.…”

“…On the other hand, little work has been conducted on Acacia. Correia et al [ 11 ] reported that Acacia spp. flowers are economically important due to their application in the cosmetic and perfume industries.…”

Exploring the Phytochemicals of Acacia melanoxylon R. Br.

“…Studies from Portuguese invasive species include the identification of ∆ 7 phytosterols, phytosteryl glucosides and long-chain n-alkyl caffeates by GC-EIMS from the dichloromethane extracts of wood and bark [29,30], as well as the antimicrobial activity of aqueous, ethanolic and methanolic leaf extracts, that showed no interesting results [31]. Other references to bioactivity of extracts of this species can be found in the recent review by Correia et al on the biomass valorization of Acacia species [32].…”