Post-harvest Changes in Sweet Sorghum I: Brix and Sugars

This experiment was done to measure the changes of sweet sorghum (Sorghum bicolor L. Moench) after harvest. Three cultivars of sorghum were harvested at 90, 115, and 140 days after planting. Stripped and topped stalks were divided into four treatments: whole stalks, 20- or 40-cm billets, and chopped. Samples were placed in individual plastic bins and stored outside in a shade tent. At 0, 1, 2, and 4 days after harvest, subsamples were removed from each bin and the juice expressed. Juice was analyzed for A degrees Brix (percent total dissolved solids on a w/w basis) and the simple sugars glucose, fructose, and sucrose. In most of the treatments, juice A degrees Brix decreased slightly or was unchanged during storage. Sucrose decreased in all treatments, while glucose and fructose increased in the whole stalk, 20-cm billet, and 40-cm billet treatments. In those treatments, total sugar was little changed over the 4-day storage period. In chopped sorghum, decreases in glucose were significant after 1 day of storage. Glucose decreased to near 0 mg mL(-1) by 2 days after harvest, while the decrease in fructose was not as great. The Pearson correlation between total sugar and A degrees Brix using day 0 means (non-deteriorated juice) was r = 0.964 (n = 32, rho < 0.001). The correlation between total sugar and A degrees Brix using the shredded sample means, which included deteriorated juice, was r = 0.411 (n = 24, rho a parts per thousand currency signaEuro parts per thousand 0.046). Juice A degrees Brix should not be used to evaluate juice for deterioration. We conclude that whole stalk and billet harvesting are superior to harvesting by forage harvester since forage-harvested sorghum would have to be processed within hours to maintain the sugars.