Acid hydrolysis optimization of pomegranate peels waste using response surface methodology for ethanol production

Abstract

Agro-industrial wastes can be processed into valuable products. Successively, current investigation is an effort to optimize the acid hydrolysis of pomegranate peels waste (PPW) using central composite design (CCD) of response surface methodology (RSM) for ethanol production. Concentration of sulfuric acid, temperature, and time of hydrolysis were used as dependent variables, whereas reducing sugars, total carbohydrates, extractives, weight loss, hemicellulose, cellulose, and lignin contents were recorded as responses for PPW decomposition. The highest glucose level of 0.56 ± 0.04 mg mL−1 (with 5% acid concentration at 100 °C for 30 min) and carbohydrate contents of 1.53 ± 0.07 mg mL−1 (with 3% acid concentration at 75 °C for 45 min) were obtained. Subsequently, detoxification of hydrolysate was conducted employing 2.5% activated charcoal that reduced 62% of phenolic compounds. Detoxified hydrolysate was subjected to fermentation by ethanologenic yeasts: Metschnikowia sp. Y31, Metschnikowia cibodasensis Y34, and Saccharomyces cerevisiae K7 for 10 days experiment. Significant ethanol yield of 0.42 ± 0.08 g g−1 was noticed by Metschnikowia sp. Y31 on day 5 and 0.41 ± 0.07 g g−1 for Metschnikowia cibodasensis Y34 on day 2. The results demonstrated the hopeful prospect for bioethanologenesis using cellulosic wastes at marketable level.