Investigation of the stabilization and preservation of sweet sorghum juices

• Sweet sorghum juice is extremely vulnerable to microbial spoilage and this is a major technical challenge to new biorefineries.
• UV irradiation did not improve the stability and preservation of sweet sorghum juices.
• Juice clarification or heating both reduced lactic acid bacteria populations to negligible levels and allowed storage of juice for at least 48 h.
• Fingerprint ion chromatography can be used to monitor sweet sorghum juice spoilage.

Sweet sorghum juice is extremely vulnerable to microbial spoilage during storage because of its high water activity and rich sugar medium, and this represents a major technical challenge. The effects of clarification (80 °C; limed to pH 6.5; 5 ppm polyanionic flocculant) and UV-C irradiation were investigated as stabilization and preservation treatments for juices stored at ambient temperature (∼25 °C). Juices were extracted by roller press from various sweet sorghum cultivars grown in humid and dry environments in Louisiana and Tennessee, respectively. Raw juices contained up to 109 total bacteria cfu/mL. Initial results indicated that pilot plant clarified juice was considerably more stable than raw or UV-C irradiated (15 W lamp aquaculture system at ∼25 °C) juice, irrespective of cultivar. Further experiments were undertaken to elucidate if heating (80 °C; 30 min) or impurity precipitation or both of these components of the clarification process were responsible for improved juice stability. Clarification or heating both achieved 3- to 4-log reductions of lactic acid bacteria in juices to negligible levels (<150 cfu/mL), and also significantly (P < 0.05) reduced total bacterial counts. Juice heating gave similar results as the whole clarification process up to ∼24 h storage, but became slightly worse between 24–28 h. Overall, clarified or heated (80 °C; 30 min) juice stored at 25 °C can be stored for at least 48 h before unacceptable spoilage occurs. Fingerprint ion chromatography with integrated pulsed amperometric detection (IC-IPAD) oligosaccharide profiles can be used to monitor sweet sorghum juice spoilage >100 cfu/mL lactic acid bacteria.