Enzymatic hydrolysis of sugar beets for achieving liquefaction and sugar release is a critical step for beet-ethanol production. An enzyme recycling process was developed in this study to reduce the economic uncertainty raised by the high costs of enzymes by reducing the fresh enzyme usage. A mixture of cellulases and pectinases was used in the beet hydrolysis. The hydrolysate was centrifuged and then processed through a 50 kDa molecular weight cut-off polyethersulfone membrane to recover enzymes from the liquid. Liquid enzyme recycling with 50% fresh enzyme addition achieved a similar liquefaction extent and sugar yield compared to the positive control with 100% fresh enzyme. Solid enzyme recycling showed a lower liquefaction efficiency, requiring at least 75% of fresh enzyme addition for a comparable liquefaction extent. Five sequential batches of hydrolysis with liquid enzyme recycling were successfully conducted to hydrolyze sugar beets with similar liquefaction extents and sugar yields.
Sugar beet leaves are the major crop waste from sugar beet production, while the unused leaves contain a high number of sugars and polysaccharides. The effects of different enzyme products (cellulase, Cellic CTec2; xylanase, Cellic HTec2; and pectinase, Pectinex Ultra SPL) were determined during high-solids enzymatic hydrolysis of sugar beet leaves at 10% total solids (TS) content. Response surface methodology was used to study the effects of enzyme loadings during the hydrolysis of sugar beet leaves for producing fermentable sugars. It was found that both cellulases and pectinases are important enzymes for the hydrolysis of sugar beet leaves. Enzyme loading and reaction time were important factors. Based on the amount of sugars released, a maximum sugar conversion of 82% was achieved after 72 h of hydrolysis using 30 filter paper unit (FPU) g −1 glucan for cellulase and 150 polygalacturonase unit (PGU) g −1 polygalacturonic acid for pectinase, or 37 FPU g −1 glucan for cellulase and 100 PGU g −1 polygalacturonic acid for pectinase. The corresponding sugar yield and sugar concentration were 0.35 g•g −1 TS, and 35 g•l −1 , respectively. Sugar conversion ranged from 59% -70%, 68% -80%, and 74% -82% after 24 h, 48 h, and 72 h of hydrolysis depending on the design conditions.
Volatile fatty acids (VFAs) are the important intermediates indicating the stability and performance of fermentation process. This study developed the spectrophotometric method for determining high-range VFA concentration in mixed-acid fermentation samples. The performance was compared with the gas chromatography (GC) technique. The calibration curves of the modified method showed linearity over a wide and high concentration range of 250–5000 mg/L for individual C2–C6 VFAs in both linear and branched chains. In order to evaluate the modified method for VFA determination in complex fermentation matrices, fermentation samples produced from acidogenic fermentation of plant materials were spiked with acetic (500–1500 mg/L) and butyric acids (1000 mg/L). The accuracy and precision of the modified method for VFA determination were in the range of 94.68–106.50% and 2.35–9.26%, respectively, comparable to the GC method (94.42–99.13% and 0.17–1.93%). The developed method was applicable to measuring all C2–C6 compounds and VFA concentrations in the fermentation samples and had an acceptable accuracy and precision. The proposed method is analytically reliable and offers significant advantages in the rapid determination of VFAs in mixed acid fermentation of organic residues.
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