Sequential Anthocyanin Extraction and Ethanol Production from Eggplant Peel Through Biorefinery Approach

The current study aimed at sequential anthocyanin extraction and bioethanol production from eggplant peel with a zero waste approach. For this purpose, the effect of different solvents (100% ethanol, 100% methanol, 50/50% ethanol-water, and 50/50% methanol-water) on anthocyanin extraction was investigated in the first stage. Lignocellulosic residues of eggplant peel which remained from anthocyanin extraction were subjected to enzymatic hydrolysis, and bioethanol was produced through the fermentation process in the second stage. During experiments, the effect of initial biomass loading on anthocyanin extraction and bioethanol production was also tested. The highest anthocyanin concentration was found as 2306.1 +/- 3.5 mg/kg when 50/50% ethanol-water was used as a solvent in the presence of 20% eggplant peel. The maximum ethanol concentrations were observed in enzymatically hydrolyzed 15% eggplant peel loading as 27.5 g/L and 26.6 g/L, for S. cerevisiae and K. marxianus, respectively. In the same conditions, volumetric ethanol productivities were 0.76 g/L.h and 0.74 g/L.h for the same microorganisms. Theoretical ethanol yields were also calculated as 89.6% (YP/S: 0.48 g/g) and 86.8% (YP/S: 0.48 g/g). This study demonstrates that eggplant peel is a promising raw material for biorefinery approaches.

Automated summary

The current study aimed to extract anthocyanins from eggplant peel using different solvents, and then use the lignocellulosic residues for bioethanol production. The highest anthocyanin concentration was obtained when 50/50% ethanol-water was used as the solvent. Enzymatically hydrolyzed eggplant peel resulted in maximum ethanol concentrations of 27.5 g/L and 26.6 g/L for S. cerevisiae and K. marxianus, respectively. The findings suggest that eggplant peel holds promise as a raw material for biorefinery approaches.