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Development of an enzyme cocktail to bioconvert untapped starch in sweet sorghum processing by-products: Part I

Cole, Marsha R., Eggleston, Gillian, Gaines, Deriesha K., Heckemeyer, Matthew
Industrial crops and products 2019 v.133 pp. 142-150
alpha-amylase, byproducts, cost effectiveness, ethanol, fermentation, glucose, hydrolysis, juices, liquefaction, pullulanase, response surface methodology, saccharification, sediments, sorghum flour, starch granules, sweet sorghum, syrups
Soluble carbohydrates in sweet sorghum juices and syrups are the main sugars converted to ethanol during fermentation. Recently, it was found that sweet sorghum contains a substantial amount of insoluble starch in sweet sorghum by-products: juice sediment and clarification mud, which is an untapped source of fermentable sugars. In this study, a response surface method was used to optimize hydrolysis, liquefaction, and saccharification conditions and enzymes to customize a two-step process to convert starch in grain sorghum flour, as well as juice sediment, and clarification mud. Optimal starch liquefaction with the industrial α-amylase (Termamyl SC™) was best achieved at 80 °C in 90 min when <18% w/w flour was used, since the solid concentration significantly (P < 0.05) affected starch hydrolysis efficiency. Subsequent studies revealed that an industrial enzyme cocktail comprised of 63% SAN Extra™ (α-glucoamylase), 16% Promozyme D2™ (pullulanase), and 21% Viscozyme L™ (β-carbohydrase mixture) was most effective in improving the saccharification of starch, with particular emphasis on insoluble starch granules, to fermentable sugars at 60 °C in 90 min. Application of the optimal conditions tripled fermentable glucose and doubled total sugars in juice sediment; its application to clarification mud did not show much improvement (P < 0.05). Practical applications of this enzyme cocktail will also depend on cost effectiveness.