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Impact of Storage Methods and Duration on Sugar and Starch Content and Ethanol Yield of Sweet Potatoes [Ipomoea batatas (L.) Lam]

Joshua A. Madison, Desmond G. Mortley, Marceline Egnin, Conrad K. Bonsi, Walter A. Hill


Previous studies have shown that ‘industrial’ sweet potatoes can be an excellent feedstock for ethanol production as compared to corn, sorghum and other potential feedstocks. However, starch content can be affected by cultivars as well as storage conditions. Ideally, it is practical that sweet potato storage roots be processed for ethanol production as close to harvest as possible, but this may not always be the case and some amount of storage may be necessary. Delays before processing sweet potatoes may result in the accumulation of sucrose and reducing sugars at the expense of starch or may lead to the synthesis of toxic compounds such as the alkaloid ipomeamarone.  The objectives of this study were to (i) determine the impact of storage methods and duration on content and quality of starch, sugar, and ethanol production, and (ii) determine the most appropriate storage time that would not adversely affect ethanol yield. The experiment was conducted as a randomized complete block design with a 5 2 factorial treatment arrangement and three replications. The treatments were five storage times (0, 30, 60, 90, 120 days), two storage methods (conventional, slurry), and two cultivars (DM0158, HyDry023). Samples from both the cultivars were removed at each of the five storage times and analyzed for dry matter, extractable starch, glucose, and ethanol production. There was a trend towards storage methods influencing ethanol yield and percentage extractable starch, but strongly impacted glucose levels, dry matter, and the weight of extractable starch. There was a significant interaction between cultivar and storage method for percent dry matter only, while storage time significantly influenced all of the variables examined. There were significant interactions between cultivar and storage time for percent dry matter, weight of extractable starch, and between storage type and time for percent dry matter only. There was also a significant three-way interaction among cultivar, storage type, and time for percent dry matter only. These results showed that storing roots as slurry, though having lower starch levels, was not detrimental to subsequent ethanol production and even enhanced production in the case of HyDry023. Further, it appeared that a 90-day storage was favorable as EtOH yield was negligible between 90–120 days.

Keywords: sweet potato, alternative energy, fermentation

Cite this Article

Madison JA, Mortley DG, Egnin M et al. Impact of Storage Methods and Duration on Sugar and Starch Content and Ethanol Yield of Sweet Potatoes [Ipomoea batatas (L.) Lam]. Journal of Alternate Energy Sources and Technologies. 2016; 7(1): 23–29p.

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