Enzymatic saccharification and liquid state fermentation of hydrothermal pretreated Tunisian Luffa cylindrica (L.) fibers for cellulosic bioethanol production

Abstract

The main drivers to develop biorefineries are the energetic and environmental crisis. Consequently, bioenergies have become a scientific and industrial trend. In North Africa, especially in Tunisia, Luffa cylindrica (LC) is a promising energy crop providing lignocellulosic biomass for biofuels production. Three principal fractions compose LC biomass, viz.: α-cellulose (45.8 ± 1.3)%, hemicellulose (20.76 ± 0.3)% and lignins (13.15 ± 0.6)%. The hydrothermal pretreatment of LC fibers was carried out at 96 °C for 54 min. After pretreatment, the reducing sugars amount reached 33.55 g/kg. The subsequent enzymatic saccharification was performed during 1 h at a temperature of 60 °C, by means of two commercial enzymes AP2 and SPC. The enzyme AP2 seemed to be more suitable for the enzymatic hydrolysis of pretreated LC fibers by allowing the release of 59.4 g/kg of reducing sugars, which correspond to a reducing sugars recovery about 93.29%. After that, the liquid state fermentation (LSF) was achieved with Saccharomyces cerevisiae strain during 24 h, in sterile and non-sterile conditions at 30 °C, pH 4.8 ± 0.2 and stirring 250 rpm, in order to conclude about the influence of contamination microflora on fermentation efficiency. After the LSF step, 88.66% of reducing sugars were transformed into alcohol with a conversion rate of 1.58% and a volumetric yield about 70% in sterile conditions. Thus, this work confirms that the potential conversion yield of cellulosic bioethanol is 1 Ton (dry matter) of LC fibers to 13.8545 kg (= 3.6599 Gallon) of biofuel.