Production of bioethanol from Robusta coffee pulp (Coffea robusta L.) in Vietnam

Coffee pulp is the first waste product obtained during the wet processing of coffee beans. Coffee pulp makes up nearly 40% of the total weight of the coffee cherry. Coffee pulp contains 25.88% of cellulose, 3.6% of hemicel- luloses, and 20.07% of lignin. Coffee pulp is considered as an ideal substrate of lignocellulose biomass for micro- bial fermentation to produce such value-added products as ethanol. In this study, we used alkaline pre-treatment of the coffee pulp with NaOH (0.2 g/g biomass) in a microwave system at 120°C during 20 min. This method gave the best results: 71.25% of cellulose remained, and 46.11% of hemicellulose and 76.63% of lignin were removed. After that, the pre-treated biomass was hydrolyzed by Viscozyme Cassava C (enzyme loading was 19.27 FPU/g) at 50°C for 72 hours. The results showed that the highest reducing sugars and glucose concentration after hydrolysis were 38.21 g/l and 30.36 g/l, respectively. Then, the hydrolysis solution was fermented by S. cerevisiae (3.108 cells/ml) at 30°C for 72 hours. The highest concentration of ethanol obtained was 11.28 g/l. The result illustrated that, available and non- edible as it is, coffee pulp could be a potential feedstock for bioethanol production in Vietnam.