Solid state and semi-solid fermentations of olive and sunflower cakes with Yarrowia lipolytica: impact of biological and physical pretreatments

Abstract

Lignocellulosic biomass is a promising feedstock for added value compound production in biotechnological processes such as solid-state fermentation (SSF). Although these solid materials can be directly used as substrates in fermentations in a solid state, a pretreatment is often required, especially if the microorganism selected is unable to produce lignocellulosic enzymes. In the present work, several pretreatment strategies were applied to a 50% (w/w) mixture of olive and sunflower cakes before SSF for lipase production by the oleaginous yeast Yarrowia lipolytica W29. Co-culture strategies with Y. lipolytica and Aspergillus niger did not improve lipase production by the oleaginous yeast. Biological pretreatment with a fungal enzymatic extract led to a significant increase in sugar availability in the substrate mixture after a short incubation period, improving yeast growth. Microwave and ultrasound were the physical pretreatments selected and microwave irradiation proved to be the best method, resulting in 44% and 17% increases in yeast growth and lipase production, respectively, compared to the untreated mixture. An improvement in lipase activity was also observed after ultrasonic treatment in semi-solid fermentations, leading to a 2-fold increase in this enzyme activity compared to the control. The utilization of pretreatments before SSF with Y. lipolytica can increase sugars availability and result in structural changes in the solid substrate, which can improve the bioprocesses’ productivity.