Apple pomace was studied as a possible raw material for biobutanol production. Five different soft physicochemical pretreatments (autohydrolysis, acids, alkalis, organic solvents and surfactants) were compared in a high-pressure reactor, whose working parameters (temperature, time and reagent concentration) were optimised to maximise the amount of simple sugars released and to minimise inhibitor generation. The pretreated biomass was subsequently subjected to a conventional enzymatic treatment to complete the hydrolysis. A thermal analysis (DSC) of the solid biomass indicated that lignin was mainly degraded during the enzymatic treatment. The hydrolysate obtained with the surfactant polyethylene glycol 6000 (PEG 6000) (1.96% w/w) contained less inhibitors than any other pretreatment, yet providing 42 g/L sugars at relatively mild conditions (100 °C, 5 min), and was readily fermented by Clostridium beijerinckii CECT 508 in 96 h (3.55 g/L acetone, 9.11 g/L butanol, 0.26 g/L ethanol; 0.276 g/g yield; 91% sugar consumption). Therefore, it is possible to optimise pretreatment conditions of lignocellulosic apple pomace to reduce inhibitor concentrations in the final hydrolysate and perform successful ABE fermentations without the need of a detoxification stage.

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Erythritol is a polyol suitable for human nutrition which is industrially produced by microorganisms from costly glucose-rich or starch-rich feedstocks. The utilization of sugary by-products from food industries could significantly reduce the costs of the process. Erythritol production from sugarcane molasses, beet molasses and surplus grape musts was assessed, by comparing four fungal strains. Beet molasses presented toxic effects on microorganisms, which hampered erythritol production to a certain extent. Moniliella pollinis attained erythritol production yields of 0.239 ± 0.001 g/g for sugarcane molasses (106.40 ± 0.42 g/L erythritol), 0.229 ± 0.003 g/g for beet molasses (57.78 ± 1.52 g/L), 0.362 ± 0.005 g/g for red grape must (96.26 ± 1.31 g/L) and 0.383 ± 0.004 g/g for rosé grape must (92.84 ± 0.98 g/L), with nearly total sugar consumption in 6-9 days. In comparison, control fermentations with beet syrup reached erythritol yields of 0.327 ± 0.009 g/g (126.78 ± 3.21 g/L). Therefore, erythritol production could be considered as a viable route in certain food industries aiming at market diversification.