A biomass derived bifunctional catalyst (Ru/CCD-SO 3 H) was used for one-pot conversion of cassava dreg and cassava starch into sorbitol . The cassava dreg is mainly composed of residual cassava starch and holocellulose. The highest sorbitol yield of 11.43 % was achieved using cassava dreg as reactant. A synergistic catalytic effect of acid and metal sites of Ru/CCD-SO 3 H on cassava starch conversion to sorbitol was observed. The maximum sorbitol yield reached 82.51 % using cassava starch as reactant. A kinetic model of cassava starch degradation was performed. The reaction rate constants of cassava starch degradation, glucose conversion and sorbitol generation improved with enhancing temperature. The activation energy of cassava starch hydrolysis is larger than that of glucose hydrogenation, indicating the cassava starch hydrolysis is rate-determining step of cassava starch conversion into sorbitol. This work not only realizes the comprehensive utilization of cassava dreg, but also provides useful guidance for developing kinetic model of polysaccharide conversion.
Background 5-Aminolevulinic acid (5-ALA) is a promising biostimulant, feed nutrient, and photodynamic drug with wide applications in modern agriculture and therapy. Considering the complexity and low yield of chemical synthesis methods, bioproduction of 5-ALA has drawn intensive attention recently. However, the present bioproduction processes use refined glucose as the main carbon source and the production level still needs further enhancement.Results To lay a solid technological foundation for large-scale commercialized bioproduction of 5-ALA, an industrial workhorse Corynebacterium glutamicum was metabolically engineered for high-level 5-ALA biosynthesis from cheap renewable bioresources. After evaluation of 5-ALA synthetases from different sources, the 5-ALA biosynthetic pathway and anaplerotic pathway were rebalanced by regulating intracellular activities of 5-ALA synthetase and phosphoenolpyruvate carboxylase. The engineered biocatalyst produced 5.5 g/L 5-ALA in shake flasks and 16.3 g/L in 5-L bioreactors with a one-step fermentation process from glucose. To lower the cost of feedstock, cheap raw materials were used to replace glucose. Enzymatically hydrolyzed cassava bagasse was proven to be a perfect alternative to refined sugars since the final 5-ALA titer further increased to 18.5 g/L. Use of corn starch hydrolysate resulted in a similar 5-ALA production level (16.0 g/L) with glucose, whereas use of beet molasses caused seriously inhibition. The results obtained here represent a new record of 5-ALA bioproduction. It is estimated that replacing glucose with cassava bagasse will reduce the carbon source cost by 90.1%.Conclusion sThe high-level biosynthesis of 5-ALA from cheap bioresources will brighten the prospects for industrialization of this sustainable and environment-friendly process. The strategy for balancing metabolic flux developed in this study can also be used for improving the bioproduction of other value-added chemicals.
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