Development of a sweet sorghum juice clarification method in the manufacture of industrial feedstocks for value-added fermentation products

Abstract

In recent years, there has been a dramatic increase in interest of sweet sorghum (Sorghum bicolor L. Moench) for small to large-scale manufacture of renewable, biobased fuels and chemicals. New fermentation organisms hold tremendous potential for the production of biobased fuels, chemicals, and materials from industrial sugar feedstocks, in particular syrups. Clarification of sweet sorghum juice will be critical to the production of stable, intermediate syrup feedstocks for efficient transport, storage, and year-round supply. Juices extracted from mature sweet sorghum hybrids and immature cultivar Topper 76-6 (Topper), were clarified using heat, heat-milk of lime, and heat-milk of lime-polyanionic flocculant at various temperatures and target limed pHs, and compared to the clarification of sugarcane (Saccharum spp. hybrids) juice. There was no significant loss of fermentable sugars (sucrose+glucose+fructose) across clarification by temperature and only a slight decrease in fermentable sugars when clarified by pH. Preheating the sweet sorghum juice from 85 to 100°C not only produced clarified juices of low turbidity, but also with excellent turbidity control. For the cultivars studied, a minimum limed juice pH of ∼6.3–6.5 was optimum for the clarification of sweet sorghum juice preheated to ∼80–85°C with 5ppm polyanionic flocculant addition with respect to clarified juice turbidity, protein, calcium, starch, and to a lesser extent phosphate levels. There was a strong effect of cultivar on juice quality, clarification performance, and clarified juice quality, which warrants further research.