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Orange peel waste (OPW), the primary byproduct of the juice extraction process, is annually generated in massive amounts (21 Mton), and its aqueous extraction in biorefining operations yields a liquid fraction, referred to as orange peel extract (OPE). Although OPE contains significant amounts of easily assimilable carbohydrates, such as fructose, glucose, and sucrose, no investigations have been conducted yet to assess its possible use in biodiesel production by oleaginous yeasts. Consequently, the objective of the present study was to assess whether OPE might act as the basis of a liquid medium for microbial lipid production. A screening conducted with 18 strains of oleaginous yeasts in shaken flask on the OPE-based medium showed that Rhodosporidium toruloides NRRL 1091 and Cryptococcus laurentii UCD 68-201 gave the best results in terms of lipid production (5.8 and 4.5 g L−1, respectively) and accumulation (77 and 47% on a dry matter basis, respectively). The subsequent scale transfer of the process to a 3-L STR operated in batch mode halved the time required to reach the lipid peak with the ensuing increase in volumetric productivities in R. toruloides NRRL 1091 (3646 mg L−1 day−1) and C. laurentii UCD 68-201 (2970.7 mg L−1 day−1). The biodiesel yields from the lipids of the former and the latter strain were 36.9 and 31.9%, respectively. Based on multivariate analysis of fatty acid methyl ester compositions, the lipids from the former and the latter strain were highly resembling those of Jatropha and palm oils, two commonly used feedstocks for biodiesel manufacturing. [ABSTRACT FROM AUTHOR]

Orange peel waste was converted into ethanol by consecutive acid-catalyzed steam-explosion (ACSE), enzymatic saccharification, and fermentation with Saccharomyces cerevisiae F15. With the aim of increasing the concentration of fermentable sugars in the hydrolysate and to fully recycle the spent acid liquor as the suspending medium for saccharification, the technical feasibility of increasing the solid loading in the ACSE step from 160 to 480 g L was assessed. At high solid loading in the ACSE pretreatment (HSLAP), the solubilization degrees of polysaccharides were lower while those of potential inhibitors (e.g., acetic and formic acids and phenols) were generally higher than those found at low solid loading (LSLAP). However, residual solids from both solid loadings showed similar susceptibility to enzymatic saccharification (ES) in a 7-L stirred-tank reactor (STR) (cellulase, 12 FPU g cellulose; pectinase, 25 IU g dry matter; 72 h incubation at 50 °C). Fermentation was performed in a 1-L STR along five repeated batches with the first one being used to enable yeast proliferation. By using the hydrolysates arising from the HSLAP-ES combination, it was possible to rely on a fermentation medium with a 2.5-fold higher concentration of simple sugars and to double the ethanol concentration in the final beer to be distilled of. However, the higher content of inhibitory compounds in hydrolysates from HSLAP-ES than in the LSLAP-ES ones led to a reduction in the ethanol yield per unit substrate consumed (0.49 vs. 0.41 g g, respectively) and overall productivity (3.4 vs. 2.7 g h, respectively). [ABSTRACT FROM AUTHOR]