Effect of storage time on the sugars concentration in sweet pearl millet and sweet sorghum juices

Juice from sweet pearl millet and sweet sorghum has a high concentration in soluble sugars and can be extracted from the plant by mechanical pressing. The main sugars contained in the extracted juice are sucrose, glucose, and fructose. Theses sugars can be easily fermented for bioethanol production. However, if the juice is extracted directly in the field or at the farm, it might have to be stored for a certain amount of time prior fermentation. An experiment carried out in 2013 showed that the total soluble sugars concentration (TSSC) of sweet sorghum and sweet pearl millet juice stored for 72 hours at 4oC remained stable while it decreased significantly in the first 24 hours of storage at ambient temperature. To avoid the energy cost from the refrigeration process, a further experiment was carried out in 2014 to determine how long the juice can be stored at ambient temperature in the first 12 hours following extraction. For the juice from both crop species, results showed that even though sucrose concentration decreased, the glucose and fructose concentrations increased resulting in a stable TSSC for the 12 hours of storage. The juice extracted from both crop species can therefore be kept at ambient temperature for 12 hours without any preservation agent or refrigeration. If longer storage delays are required, refrigeration would preserve the sugars from degradation for at least 72 hours.