Evaluation of Brix and sugar content in stem juice from sorghum varieties

Sorghum accumulates sugars (sucrose, glucose and fructose) in the stem after anthesis. Brix is commonly used to indicate total sugar content; however, the relationship between Brix and specific sugar components has not been sufficiently investigated in sorghum juice in Japan. In this study, we measured the sugar components of sorghum juices from 109 varieties using capillary electrophoresis, which can quantify each sugar component in crude juice without further purification. The results indicated that the Brix of sorghum juice was proportional to the total sugar and sucrose concentrations (r = 0.900 and r = 0.894, P < 0.01, respectively). Glucose concentration had a significant positive correlation with fructose concentration (r = 0.964, P < 0.01), but no correlation was detected between Brix and the two hexose sugars, glucose and fructose. Our results showed that sucrose comprised approximately 75% of the total sugar in varieties with Brix values greater than 15. These findings may be applied in sorghum breeding efforts to develop varieties that accumulate high levels of sugars in the juicy stems of sorghum plants.