Walnut wood steaming: chemical profile and antioxidant activity of the condensate to assess the potential application

Steaming of green timber, a common industrial process for various hardwood species, significantly influences wood properties, including coloration and drying characteristics. However, the environmental implications of substantial volumes of condensate generated during wood steaming underscore the urgency for its sustainable management. This study explores the chemical composition of the condensate obtained during the 90-hour indirect steaming of walnut timber (WTSC), aiming to identify potential applications for this wastewater while addressing environmental risks. Chemical characterization of WTSC included qualitative LC-MS/MS analysis, determination of the total phenolic content (TPC), total flavonoid content (TFC) and the content of selected phenolics. WTSC exhibited high TPC (188 mg gallic acid equivalents per L) and TFC (9.74 mg quercetin equivalents per L) values. Additionally, WTSC showed significant antioxidant activity (IC₅₀ (DPPH) = 61.4 µg/mL and 103 µg ascorbic acid equivalents per mL in FRAP assay). Specific phenolic compounds detected in the WTSC distinguish it from other wood industry effluents and are a consequence of the unique characteristics of walnut wood and conditions during steaming process. A variety of acids (p-hydroxybenzoic, protocatechuic, syringic, gallic, cinnamic, cinnamic, p-coumaric, o-coumaric, vanillic) and flavonoids (apigenin, genistein, naringenin, luteolin, kaempferol, chrysoeriol, isorhamnetin, apigenin 7-O-glucoside, vitexin, kaempferol 3-O-glucoside, catechin, epicatechin, and quercitrin) were identified and quantified. The condensate exhibited higher TPC value and antioxidant activity than other wood industry effluents, positioning it as a promising natural antioxidant with potential applications in pharmaceutical and food industries. However, our short-term goal is to explore the potential use of WTSC as received – without isolating individual compounds – in studies focused on plant protection, textile dyeing, and wood-based panel production.