Compressive Forces and Harvest Time Effects on Sugars and Juice Extracted from Sweet Pearl Millet and Sweet Sorghum

Abstract

Abstract. In Canada, bioethanol is mainly produced from corn or wheat. Other alternative crops, such as sweet sorghum and sweet pearl millet, have been investigated in the province of QuA©bec, Canada, since they both have minimal fertilizer and water requirements. The objective of this study was to investigate the effects of compressive force and harvest time on the volume and sugar concentration of juice extracted from finely chopped biomass of sweet pearl millet and sweet sorghum. Trials using a specific screw press, both crop species, two harvest times, and three compressive forces were conducted at two experimental sites. Results showed that a compressive force between 310 and 379 kPa was adequate for juice extraction. Overall, a maximum of 632 mL juice kg -1 biomass was extracted from sweet sorghum, compared to 509 mL kg -1 from sweet pearl millet. The screw press succeeded in extracting 63.3% and 74.9% of the moisture from the biomass of sweet pearl millet and sweet sorghum, respectively. Compressive force had no effect on the sugar concentration of both crop juices. However, the juice extracted with the screw press contained large quantities of unwanted residues. Sugar concentration of the juice was greatest at one of the two sites when the biomass was harvested and compressed in the afternoon. However, the harvest time had no effect on juice extraction at either site. Sweet sorghum contained significantly more sugars than sweet pearl millet and tended to contain more sucrose than glucose and fructose. This study demonstrates that sweet sorghum and sweet pearl millet are good sources of fermentable sugars. However, further research is needed to refine the harvesting and juice extraction processes.