Use of Anthracophyllum discolor and Stereum hirsutum as a Suitable Strategy for Delignification and Phenolic Removal of Olive Mill Solid Waste

Abstract

This study evaluated the use of the white-rot fungi (WRF) Anthracophyllum discolor and Stereum hirsutum as a biological pretreatment for olive mill solid mill waste (OMSW). The WRF strains proposed were added directly to OMSW. The assays consisted of determining the need to add supplementary nutrients, an exogenous carbon source or use agitation systems, and evaluating WRF growth, enzyme activity, phenolic compound removal and lignin degradation. The highest ligninolytic enzyme activity was found at day 10, reaching 176.7 U/L of manganese-independent peroxidase (MniP) produced by A. discolor, and the highest phenolic removal (more than 80% with both strains) was reached after 24 days of incubation. The confocal laser scanning microscopy analysis (CLSM) confirmed lignin degradation through the drop in lignin relative fluorescence units (RFU) from 3967 for untreated OMSW to 235 and 221 RFU, showing a lignin relative degradation of 94.1% and 94.4% after 24 days of treatment by A. discolor and S. hirsutum, respectively. The results demonstrate for the first time that A. discolor and S. hirsutum were able to degrade lignin and remove phenolic compounds from OMSW using this as the sole substrate without adding other nutrients or using agitation systems. This work indicates that it could be possible to design an in situ pretreatment of the valorization of OMSW, avoiding complex systems or transportation. In this sense, future research under non-sterile conditions is needed to evaluate the competition of WRF with other microorganisms present in the OMSW. The main drawbacks of this work are associated with both the low reaction time and the water addition. However, OMSW is seasonal waste produced in one season per year, being stored for a long time. In terms of water addition, the necessary optimization will be addressed in future research.

Acid Hydrothermal Amendment of Grape Wine Pomace: Enhancement of Phenol and Carbohydrate Co-solubilization

“…Different parameters were characterized for untreated grape pomace and treated grape pomace, including analysis for liquid and solid phase obtained after hydrothermal treatment. Total solids (TS), volatile solids (VS), and soluble chemical oxygen demand (sCOD) were measured according to standard methods (30). In addition, lignin content was measured for OMSW, using the Klason lignin method (TAPPI T 222 om-02) [28].…”

“…The mixture was stirred for 1 min in a vortex apparatus and centrifuged at 1200 G for 10 min. The methanol layer was separated, and the extraction was repeated four times [30]. To determine the antioxidant capacity in the liquid phase, the antiradical activity (2,2-diphenyl-1-picrylhydrazyl (DPPH) was measured, the DPPH analysis was done measuring the variation in absorbance at 515 nm after 30 min of reaction with the radical DPPH, using Thermo Scienti c's UV-Vis Orion AquaMate 8000 spectrophotometer.…”

Aquaculture Sludge as Co-Substrate for Sustainable Olive Mill Solid Waste Pre-Treatment by Anthracophyllum discolor

“…discolor was isolated from decaying wood in the rainforests of southern Chile. The culture was cultivated in Petri dishes (94 × 16 mm) at 25 • C for 7 days in a medium consisting of 39 g L −1 Potato Dextrose Agar (PDA) sterilized at 121 • C for 20 min [20].…”

“…Additionally, the OMSW contained 61.5% water and 38.5% total solids, which makes it highly viscous, limiting the liquid phase used to recover ligninolytic enzymes. In this sense, Benavides et al [20] used water to recover ligninolytic enzymes and concluded that it is necessary to use other liquid sources to recover enzymes in the pre-treatment of OMSW with A. discolor. Thus, the addition of AS should have high nitrogen content and high water content to generate a liquid phase for recovery of enzyme extracts.…”

“…The ability of WRF to remove lignin and polyphenols is due to the fact that fungal mycelia can penetrate lignocellulosic materials and release polyphenols, which in turn can induce the secondary metabolism of WRF by secreting nonspecific extracellular oxidases, such as lignin peroxidase (LiP), laccase (Lac), manganese peroxidase (MnP) and manganeseindependent peroxidase (MniP) [1,[17][18][19]. Therefore, the enzymatic process resulting from the biological pre-treatment of OMSW has the potential to reduce the phenolic content of OMSW and recover ligninolytic enzymes [20]. Obtaining ligninolytic enzymes from OMSW depends on enzyme-induced variables such as correct adjustment of the C/N ratio [10].…”