Simultaneous saccharification and fermentation of pawpaw (Carica papaya) seeds for ethanol production

Bioconversion of food crops to bioethanol has generated numerous issues, necessitating the need for alternative feedstock. Pawpaw seeds (PS) were pretreated by different methods, dried and ground into flour. The flours were saccharified using crude amylase from Aspergillus niger and the reducing sugar produced was evaluated. Optimum conditions for ethanol production from the pawpaw seeds were determined. Seeds pretreated with sulphuric acid produced the highest amount of sugar (8.07 g/10 g PS), followed by seeds boiled in water (7.31 g/10 g PS). PS pretreated with sodium hydroxide produced 4.83 g/10 g PS. The optimum pH and temperature for amylase activity were 4.0 and 50 °C respectively, while the optimum substrate concentration for hydrolysis was 8 g/10 g PS flour. Increase in glucose concentration from 0.1 to 0.3 (g/100 ml) resulted in increase in the fermentable sugar production from 6.56 to 9.64 g/10g PS. The percentage yeast extract and peptone which gave the maximal fermentable sugar production from PS were 0.1% and 0.4%, respectively. The maximum ethanol concentration (4.33% v/v) produced by simultaneous saccharification and fermentation of pawpaw seed was obtained after 12 h of fermentation. These results indicate that pawpaw seeds, a food waste can be converted into ethanol within 12 h of fermentations through simultaneous saccharification and fermentation. © 2021, Society for Plant Research.