Abstract
BackgroundChina is the largest sweet potato producer and exporter in the world. Sweet potato residues (SPRs) separated after extracting starch account for more than 10 % of the total dry matter of sweet potatoes. In China, more than 2 million tons of SPRs cannot be utilized, and the unutilized SPRs are perishable and result in environmental pollution. Thus, an environmentally friendly and highly efficient process for bioethanol production from SPRs should be developed.ResultsThe swelling behaviour of cellulose causes high-gravity sweet potato residues to be recalcitrant to enzymatic hydrolysis. Cellulase plays a major role in viscosity reduction and glucose production. In contrast, pectinase has a minor role in viscosity reduction but acts as a “helper protein” to assist cellulase in liberating glucose, especially at low cellulase activity levels. In total, 153.46 and 168.13 g/L glucose were produced from high-gravity SPRs with cellulase and a mixture of cellulase and pectinase, respectively. These hydrolysates were fermented to form 73.37 and 79.00 g/L ethanol, respectively. Each kilogram of dry SPR was converted to form 209.62 and 225.71 g of ethanol, respectively.ConclusionThe processes described in this study have an enormous potential for industrial production of bioethanol because they are environmentally friendly, highly productive, economic with low cost, and can be easily manipulated.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0464-7) contains supplementary material, which is available to authorized users.
Highlights
China is the largest sweet potato producer and exporter in the world
More than half of the starch is extracted by the starch-processing industry, and the contents of cellulose and pectin are apparently increased in the Sweet potato residues (SPRs)
After starch was partially extracted from sweet potato, 658.96 g of glucose was still released from each kg of SPRs
Summary
China is the largest sweet potato producer and exporter in the world. Sweet potato residues (SPRs) separated after extracting starch account for more than 10 % of the total dry matter of sweet potatoes. An environmentally friendly and highly efficient process for bioethanol production from SPRs should be developed. China is the largest sweet potato producer and exporter in the world [14], with more than 71 million tons of sweet potatoes being produced each year. Acid-catalysed hydrolysis methods of releasing sugar from potato wastes were reported for bioethanol production [20, 21]. These processes increase the discharge of industrial waste water [22] and raise costs because they require investment in corrosionresistant equipment and production of fermentation inhibitors [1]. An efficient and environmentally friendly method that uses enzymatic hydrolysis should be developed for bioethanol production from potato waste
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