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- Alternative feedstocks for high-quality biodiesel: Lipid production from eucalyptus bark hydrolysate by Yarrowia lipolytica W29 using different cultivation modesPublication . Dias, Bruna; Lopes, Marlene; Marques, Susana; Gírio, Francisco; Belo, IsabelABSTRACT: Microbial lipids produced by yeasts from lignocellulosic biomass are a promising feedstock for the biodiesel industry, providing a renewable energy source as an alternative to traditional fossil fuels. This study investigated the potential of Yarrowia lipolytica W29 to produce lipid-rich biomass from undetoxified sugar-concentrated eucalyptus bark hydrolysate (EBH). The lipid concentrations achieved in batch cultures (13.4 g L-1) were the highest for wild-type Y. lipolytica strains in lignocellulosic hydrolysates. Different two-stage cultivation modes (repeated batch, continuous-feeding fed-batch, and pulse fed-batch) were studied to enhance biomass and lipid production. The cell and lipid mass was higher in pulse fed-batch and continuous-feeding fed-batch cultures than batch cultures. Production of citric acid, a side product of industrial interest, was improved in the continuous-feeding fed-batch culture. Microbial lipids produced by Y. lipolytica W29 were highly unsaturated and mainly composed of oleic acid (50% to 53%). The estimated properties of the biodiesel that would be obtained from these intracellular lipids would meet the international biodiesel standards EN 14214 and ASTM D6751. This study demonstrates the feasibility of using EBH for Y. lipolytica lipid production and promotes the sustainable production of high-quality biodiesel from lignocellulosic feedstocks.
- Nanobubble-enhanced oxygen transfer in bacterial nanocellulose production: Comparative evaluation with static and airlift systemsPublication . Rodrigues, Ana Cristina; Martins, Daniela; Carvalho, Ricardo; Marques, Susana; Belo, Isabel; Espina, Begona; Dourado, Fernando; Gama, MiguelABSTRACT: Despite the unique properties of bacterial nanocellulose (BNC), oxygen limitation during large-scale production impairs microbial metabolism and cellulose synthesis, leading to high production costs and limited commercial success. Static fermentation can achieve high titers, but industrially it is operationally challenging. Agitated systems like airlift (AL) bioreactors, allow faster production but typically yield lower titers. This study pioneered the use of an agitated bioreactor equipped with a nanobubble (NB) generator, and its performance was compared with that of static and AL systems, employing a newly isolated Komagataeibacter sp. strain from kombucha cultivated in Eucalyptus bark hydrolysate and corn steep liquor. Key monitored parameters included dissolved oxygen, cell density, pH, sugar and lactic acid contents, and BNC production. The obtained BNC was characterized for its crystallinity, thermal stability, degree of polymerization, morphology and fiber size. The AL-and NB-derived BNC exhibited a denser network structure, lower crystallinity index, and lower polymerization degrees than that from static culture. NB technology generated stable nanobubbles (size: 95.8 f 12.9 nm; zeta potential:-14.2 f 8.6 mV). At 1 L. min-1 airflow, compared to AL, the NB bioreactor achieved a 6-fold higher volumetric mass transfer coefficient (kLa 35.9 f 1.2 h-1) and oxygen transfer rate (OTR: 309.7 f 10.2 mg.L-1.h-1). It supported greater cell density but maintained a similar BNC volumetric productivity to that of the AL (0.023 g.L-1.h-1), and moderately higher (near 280%) than that of static culture (0.0082 g.L-1.h-1). Thus, the improved oxygen levels provided by the NB system favored biomass growth rather than BNC production, suggesting that further optimization is needed to redirect carbon flux toward BNC production.