Evaluation of pomegranate peel in ethanol production by Saccharomyces cerevisiae and Pichia stipitis

Conversion of pomegranate peel (PP), which is an abundant and valuable by-product of fruit juice industry to value added product such as ethanol, instead of discharging as agro-industrial waste was aimed in this study. Some important parameters such as H2SO4 pretreatment (0.5%, 1%, 1.5% v/v), fermentation period (6, 12, 24 h), initial substrate loading (from 2.5 to 150 g/L) were optimized in the first fermentation experiments performed with S. cerevisiae and P. stipitis yeasts. After finding the optimum conditions for ethanol production of the yeasts, effect of different nitrogen sources [yeast extract - peptone and (NH4)2SO4] and metal salts (combination of K+, Mg2+, Ca2+, Zn2+) on the production were also investigated to improve the yield, up to 44.9% for S. cerevisiae, which reached to 5.58 g/L at the end of 12 h fermentation, corresponding to 0.46 g/L/h productivity, whereas P. stipitis could produce 2.95 g/L ethanol. This study shows that pomegranate peel is a promising feedstock for second generation ethanol production.