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Novel storage technologies for raw and clarified syrup biomass feedstocks from sweet sorghum (Sorghum bicolor L. Moench)

Eggleston, Gillian, Andrzejewski, Brett, Cole, Marsha, Dalley, Caleb, Sklanka, Scottie, St Cyr, Eldwin, Chung, Yoo-Jin, Powell, Randall
Biomass and bioenergy 2015 v.81 pp. 424-436
Sorghum bicolor, biofuels, biomass, biorefining, brix, clarification (processing), cultivars, evaporation, feedstocks, fungi, growth retardation, hybrids, juices, manufacturing, microbial growth, pH, soybean oil, storage, storage time, sugars, supply chain, sweet sorghum, syrups, water activity
Attention is currently focused on developing sustainable supply chains of sugar biomass feedstocks for new, flexible biorefineries. Fundamental processing needs identified by industry for the large-scale manufacture of biofuels and bioproducts from sweet sorghum (Sorghum bicolor L. Moench) include stabilization and concentration of juice into syrup for long-term storage, year-round supply, efficient transport, and acceptable end-product yields. Pilot plant studies were conducted to evaluate the storage (up to 160 days at ∼25 °C) of raw and clarified syrups from sweet sorghum hybrid and commercial cultivars. Clarified syrups were manufactured after clarification of juice (80 °C; 5 ppm polyanionic flocculant) at various target limed pHs (6.1–6.8) followed by vacuum evaporation. All 70 Brix raw syrups were susceptible to microbial deterioration on the surface during storage, and raw syrups were more susceptible than clarified syrups. Surface deterioration was mainly fungal since bacterial growth was inhibited by low water activity. Juice clarification reduced the loss of fermentable sugars during the evaporation stage and, generally, allowed for better storage of syrup up to 80 days. Target clarification pH had a dramatic effect on the storage of clarified 70 Brix syrups with more acidic pHs reducing fungal deterioration. Further studies are now warranted on the post-evaporation pH adjustment of raw and clarified syrups to <6.1 for long-term storage. Inexpensive soy bean oil and candellila wax showed promise as surface sealants to preserve syrups for at least 80 days of storage at ∼25 °C, also warranting further investigation.