Processing attributes and performance of sweet sorghum biomass for large-scale biorefineries: a 1-year comparision of commerical hybrids and a cultivar

Authors: Eggleston, Gillian; Wartelle, Lynda; Zatlokovicz Iii, John; Petrie, Eric; Cole, Marsha; St Cyr, Eldwin

Submitted to: Sugar Tech
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2017
Publication Date: 6/1/2018
Citation: Eggleston, G., Wartelle, L., Zatlokovicz III, J., Petrie, E., Cole, M., St Cyr, E., 2018. Processing attributes and performance of sweet sorghum biomass for large-scale biorefineries: A 1-year comparison of commercial hybrids and a cultivar. Sugar Tech. 20(3):336-346.

Interpretive Summary: Quality and processing attributes of sweet sorghum are critical to the development of a large-scale industry for the manufacture of biofuels and bioproducts. Two commercial sweet sorghum hybrids 105 and 106, later and earlier maturing, respectively, were compared to a popular Top 76-6 cultivar, for agronomic, quality, and processing attributes at two maturity stages. Overall, the hybrids processed similarly to the cultivar and had the additional advantages of having low starch and no side stalks.

Technical Abstract: Quality and processing attributes of sweet sorghum (Sorghum bicolor L. Moench) biomass are critical to the development of a large-scale industry for the manufacture of biofuels and bioproducts. Two commercial sweet sorghum hybrids 105 and 106, later and earlier maturing, respectively, were compared to inbred, later-maturing Top 76-6 cultivar, for agronomic, quality, and processing attributes at the soft dough (SD) and hard dough (HD) physiological maturity stages. Crops were grown in South Louisiana (April to Sept, 2014) and juice was extracted from topped whole-stalks by roller milling. Juices were pilot plant clarified (80 °C; target limed juice pH of 6.5; 5 ppm polyanionic flocculant) and vacuum evaporated to syrups. Crop biomass yields varied significantly (P<0.05) with 105 > Top 76-6 > 106. Hybrid 106 contained a marked amount of auxiliary seed-head/stalk (side branch tillers) due to early maturing, which reduced growth of the main stalk and detrimentally affected juice sugar content and turbidity, as well as processing performance. Hybrid 106 contained considerable sucrose in its raw juice whereas 105 and Top 76-6 contained relatively little, and total sugars were greatest and least in 106 and Top 76-6 raw juices, respectively. Except for 105 at the HD stage, turbidity removal across clarification was very acceptable (>92%) and directly related to the median size of the starch granules and their percent removal. Clarification was generally better at SD than HD stage. Considerable variation (P<0.05) existed for total starch concentrations in raw juice with 106 >>> Top 76-6 > 105; insoluble and soluble starch were both removed in the clarification mud. Factors that reduced crop yield also increased syrup viscosity, and starch also contributed to viscosity. There was no genotype or maturity stage variation for assimilable nitrogen, a requirement for fermentation, of raw juice and syrup. Overall, the hybrids processed similarly to cultivar Top 76-6, and 105 had the additional advantages of having low starch and no auxiliary seed-head/stalk.