Hydrothermal pretreatment and enzymatic hydrolysis of olive tree prunings for lipids production by Yarrowia lipolytica

• Author(s): Dias, Bruna ; Rodríguez-Jasso, Rosa M. ; Belo, Isabel ; Lopes, Marlene
• Date: 2024
• Persistent ID: https://hdl.handle.net/1822/97438
• Origin: RepositóriUM - Universidade do Minho
• Document Type: Other
• Language: English
• Contributor(s): Universidade do Minho

Description

In recent years, the challenges of climate change, the energy crises, waste management issues, and accelerating resource exhaustion have driven research into a search for sustainable alternatives to fossil fuels. Lignocellulosic materials, owing to their widespread availability, minimal carbon footprint, and desirable composition, have garnered attention in the context of 2nd generation biorefineries for the production of biofuels. The olive oil industry, a significant industry globally and particularly in Mediterranean countries, generates approximately 3 tons of pruning residues per hectare of olive grove. Currently, these olive tree prunings (OTP) are either ground and scattered over the land, used for pellet production, or directly burned, with economic costs and environmental concerns. Therefore, this research aims to valorize OTP by fractionating this biomass through hydrothermal pretreatment and enzymatic hydrolysis to produce a sugars-rich hydrolysate for microbial lipids production by Yarrowia lipolytica NCYC 2904 in bioreactors, within a biorefinery framework. Firstly, a 32 factorial design was employed to optimize the hydrothermal pretreatment of OTP, aiming to maximize cellulose content in solid fraction by varying temperature (160°C - 200°C) and time (15 min - 45 min). The cellulose content reached a maximum value of 42 % at 200 °C for 15 min (severity factor 4.2). The enzymatic hydrolysis of solid fraction (obtained in the optimized condition) was carried out using the Cellic CTec2 cocktail at several solid loadings. Glucose concentration increased as solid loading increased, reaching a maximum value of 88 g/L after 72 h at the higher solid fraction concentration (20 %, w/v), with a saccharification yield conversion of 82 %. After scale-up, based on optimal conditions identified at a smaller scale, the resulting OTP hydrolysate (OTPH), containing 125 g/L of glucose, was used, for the first time, as the substrate for microbial lipids production by Y. lipolytica NCYC 2904. The yeast was able to produce biomass and microbial lipids from OTPH (undiluted and 1:2 (v/v) diluted), supplemented with corn steep liquor and ammonium sulfate, in batch cultures carried out in a stirred tank bioreactor. No lag phase was observed, demonstrating that no detoxification steps are needed. A 1.3-fold higher biomass concentration (29 g/L) was obtained in the undiluted OTPH compared to the diluted OTPH medium (20 g/L). The maximum lipids concentration of 10 g/L (35 %, w/w) was attained in the undiluted OTPH due to the high biomass production in this condition. It is noteworthy that the lipid concentration achieved in this study exceeds those reported in the literature for lipids production by other yeast species from OTPH.This research highlights the potential of OTP as a low-cost carbon source for microbial lipids production (biofuel precursor) in a biorefinery framework. By addressing economic, environmental, and disposal challenges, this approach presents a promising avenue for valorizing this lignocellulosic biomass.