Agronomic productivity, bioethanol potential and postharvest storability of an industrial sweetpotato cultivar

• Industrial sweetpotatoes are a viable alternative feedstock for ethanol production.
• CX-1 starch concentrations (72.1% dry matter) were higher than other industrial cultivars.
• CX-1 starch concentrations were maintained over a six-month storage period.
• The CX-1 bioethanol potential was 5300 L ha−1, as determined by fermentation.
• Culls from the CX-1 cultivar are a valuable coproduct available for bioenergy production.

An industrial sweetpotato cultivar, CX-1, offers several advantages as an alternative crop for bioethanol production, including high agronomic productivity and high starch content as well as viable coproducts for additional bioenergy recovery. A two-year agronomic field trial resulted in a root yield of 12.3 dry t ha−1 after optimization of planting strategy and improved site drainage. Starch content (73.5% dry matter (DM) for Year 1 and 72.1% DM for Year 2) exceeded that of any other industrial variety grown in the Southeastern USA. In contrast to other industrial cultivars, starch concentrations were maintained over a six-month storage period, making this a favorable year-round feedstock. The bioethanol potential of the CX-1 (4.2 t ha−1 or 5300 L ha−1) was determined based on the conversion of CX-1 dry biomass into ethanol by simultaneous saccharification and fermentation combined with the agronomic root yield from the Year 2 field trial. The cull rate was 36% of the overall root yield, as determined based on United States Department of Agriculture culinary grades. However, assessment of the culls from an industrial processing perspective would significantly reduce the cull rate. Approximately 45% of the culls were classified as cull material (i.e. secondary rootlets) that could feasibly be converted into ethanol. The remaining 55% of the culls could be used for biogas recovery to offset the energy required to produce ethanol from sweetpotatoes.

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