Storage mode and pressing delay effects on juice extraction and sugar content of the biomass of sweet pearl millet and sweet sorghum

Abstract

Abstract. Sweet pearl millet and sweet sorghum have a good potential for bioethanol production as their stalks contain juice with high sugar content. However, the sugar content could be altered by fermentation if the biomass is not pressed soon after being harvested. Trials using the biomass of sweet pearl millet and sweet sorghum were carried out in summer 2013 at the Saint-Augustin-de-Desmaures research station of UniversitA© Laval, Quebec, Canada. These trials consisted of extracting the juice from the biomass of both crops. A first juice extraction took place after harvesting the biomass, using a specific hydraulic press designed and built at the Department of Soils and Agri-Food Engineering of UniversitA© Laval. Three additional juice extractions were made 24, 48, and 72 hours after the first one. Two storage modes were considered: whole stalk or chopped biomass. For the chopped biomass, obtained results showed a decrease of sugar content with increasing the time delay before pressing, for both crops. Juice extraction was more efficient when the biomass was chopped. However, sugars are best conserved if the biomass is stored as whole stalk. If stored for 24h as whole stalk, 103.5 g kg - 1 dry matter (DM) was extracted from sweet sorghum biomass against only 66.1 g kg -1 DM for sweet pearl millet. If the biomass is chopped when harvested, it is recommended to extract the juice from the biomass as soon as possible. However, if possible, the harvested biomass should be kept as whole stalk rather than chopped until proceeding to its pressing.