Pomegranate peels valorizationtowards the coproduction of bioethanol and lactic acid

Resumen

Lignocellulose represents a nearly unlimited source of residual biomass to produce renewable energy and bio-based materials. However, the use of lignocellulose as feedstock for bioproducts involves the presence of multiple sugars (glucose, xylose). The lack of microorganisms that can efficiently utilize 5-carbons sugars and the need of optimized fermentation conditions are still challenging issues for lignocellulosic biorefineries. This study proposes the co-generation of bioethanol and lactic acid (LA) from pomegranate peel (PP) residues. PP is a cheap and abundant by-product of the food processing industry rich in cellulose and hemicellulose. This work firstly studied the effect of sequential inoculation and co-inoculation of Kluyveromyces marxianus CECT 10875 and Bacillus coagulans A20 to co-produce bioethanol and LA in synthetic media. Once the inoculation strategy and pH process were optimized, both bioethanol and LA were produced using PP hydrolysates obtained after enzymatic hydrolysis of PP at 10, 15 and 20% (w/w) substrate loading. In PP hydrolysates obtained from 10% (w/w) substrate loading, co-inoculation of K. marxianus and B. coagulans resulted in 13.7±1.0 g/L bioethanol and 5.5±0.2 g/L LA. On the other hand, when hydrolysates derived from 20% (w/w) PP, the maximum bioethanol and LA concentrations significantly increased to 32.9±2.6 g/L (80% of the maximum theoretical yield) and 15.0±2.0 g/L (98% of the maximum theoretical yield), respectively. Despite the different optimum conditions for K. marxianus and B. coagulans fermentation (e.g. pH and oxygen presence), simultaneous inoculation was a useful tool for bioethanol/LA co-generation and could help improving process efficiency in lignocellulosic biorefinery approaches.