The need to produce an ever-increasing quantity of material products and food resulting from the planet globalization process has contributed to the spread of modern agriculture based on a linear production resulting in the generation of tons of waste. This huge amount of waste is generally accumulated in landfills, causing different environmental problems. Hence, researchers moved on to study the processes used to recover agro-industrial by-products within a circular and sustainable bio-economy concept. A systematic quest on Scopus and PubMed databases was performed to identify the data available to date on recycling agro-industrial by-products of Olea europaea L. This systematic review summarizes the knowledge regarding the use of olive trees by-products for producing animal feed, biocomposites, bioethanol, cellulose pulp, activated carbon, and as a fuel source for energy production. Furthermore, the data regarding the potential biological activity of extracts from olive roots, wood, bark, and pruning were analyzed. Olive trees by-products are, indeed, rich in molecules with antioxidant, antimicrobial, cardioprotective, and anticancer activity, representing a promising candidate for treat several human diseases.

Improvements in the yield and solubility of chestnut wood extractives, by using different extraction methods and molybdenum catalysts as support, have rarely been reported in literature. Many studies focus on the different parts of trees, except for the chemical characteristics of the remaining extractives achieved from thermally modified (THM) chestnut (Castanea sativa Mill) wood. This research seeks to better understand the effects of extraction techniques and catalysts on the yield and solubility of extractives. GC-MS analysis of the chloroform soluble and insoluble fractions was also used. Accelerated Solvent Extraction (ASE) 110 °C, Soxhlet, and autoclave extraction techniques were used to obtain extractives from untreated and thermally modified (THM) chestnut wood (170 °C for 3 h). Ethanol/H₂O, ethanol/toluene, and water were the solvents used for each technique. A polyoxometalate compound (H₃PMo₁₂O₄₀) and MoO₃ supported on silica were used as catalysts. The THM induced a change in the wood’s surface color (ΔE = 21.5) and an increase in mass loss (5.9%), while the equilibrium moisture content (EMC) was reduced by 17.4% compared to the control wood. The yields of the extractives and their solubility were always higher in THM and mainly used ASE as the technique. GC-MS analysis of the extractives, without catalyst support, showed different results for each extraction technique and type of wood (untreated and THM). Ultimately, the amount of extractive compound dissolved in each solvent will differ, and the choice of extraction technique will depend on the intended final application of the extracted chemical product.

The Olea europaea L. tree has played a central role in Mediterranean culture since ancient times. Several studies have highlighted the health‐promoting properties both of its primary products (olives) and its by‐products (leaves, pomace, husk, stone, mill wastes, and wood). In this study, pruning residues from 25‐year‐old olive trees located in a Mediterranean region (Basilicata, Italy) were analyzed. The antioxidant activity of hydro‐alcoholic extracts from wood samples were analyzed through three complementary in vitro assays. The molecular composition of the extracts was thoroughly evaluated using a gas chromatography apparatus coupled with a mass spectrometer (GC–MS). Our study demonstrated that all but three extracts had remarkable antioxidant activity, which was likely due to the meaningful presence of phenolic compounds, mostly derived from lignin. Moreover, the results showed that bark extracts obtained with ultrasound‐assisted extraction (UAE) had the highest antioxidant activity. In this extract, several known compounds with demonstrated antioxidant activity were found, including hexylresorcinol, 1‐methyl‐N‐vanillyl‐2‐phenethamine, and allopurinol. This research suggests that woody olive by‐products are a potential natural resource of antioxidants. These compounds could be useful for functional foods and in industry, and could help to solve the problem of pruning residues, increasing their potential economic value. © 2021 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.

Numerous investigations on the antioxidant properties of different plant tissue extracts are available in literature, but few studies on the effect of thermally modified wood on secondary metabolites were carried out up to now. This study highlights the influence of the thermal modification of Castanea sativa Mill. wood on total content of antioxidant compounds and consequently on its antioxidant activity. In addition, a chemical profile by Gas Chromatography–Mass Spectrometry (GC–MS) of the extractives was carried out. Wood of chestnut, thermally modified at 180 °C for 3 h, was used to obtain wood meal which was subjected to different extraction techniques, as maceration extraction (ME), ultrasound assisted extraction (UAE) and accelerated solvent extraction (ASE). The total content of principal antioxidant compounds, such as polyphenols, flavonoids and tannins, as well as the evaluation of antioxidant capacity by using different in vitro assays were determined. Relative Antioxidant Capacity Index (RACI), which is used to compare all antioxidant parameters, has also been applied. The study demonstrated a positive influence on chemical compounds present in C. sativa Mill wood originating from the thermal modification process. Thus, is possible to consider thermal modification as a promising strategy to improve the antioxidant activity of chestnut wood extractives.