Watermelon peel hydrolysate production optimization and ethanologenesis employing yeast isolates

Securing “energy from waste” appeared as the most engrossed research area to find out global solutions for waste disposal and energy production. Watermelon peels (WMPs) are discarded as bulk waste in the whole oriental region that demands appropriate disposal to save environment from pollution. This study investigates the potential of yeast employing WMPs that embodies significant sugars to be fermented into ethanol. For this purpose, WMPs were subjected to dilute sulfuric acid hydrolysis under optimized conditions (6% H₂SO₄ at 50 °C for 60 min) elucidated by response surface methodology (RSM) of central composite design (CCD). The experimental design dealt with the optimization of fermentation influencing independent parameters which included pretreated WMP hydrolysate, synthetic medium ratio (X1), hydrolysis temperature (X2), and incubation period (X3) for maximal ethanol yield while employing standard (Saccharomyces cerevisiae K7) and experimental (Metchnikowia cibodasensis Y34) yeast isolates. The significance of the model for experimental yeast was envisaged by 6.22 F value (0.0060 P), 0.8616 R² and 8.393 adequate precision. The optimized parameters were found as 52.03 mL WMP hydrolysate concentration at 29.46 °C after an incubation period of 15 days. Maximal ethanol yield (g/g reducing sugars) obtained from Saccharomyces cerevisiae K7 was 0.33 ± 0.05, while Metchnikowia cibodasensis Y34 showed as 0.38 ± 0.01. From this research, the ethanologenic and ethanol tolerant potential of yeast Metchnikowia cibodasensis Y34 is apparent to valorize WMPs.