Changes of apparent enzymatic activities and physical and chemical properties of steam-exploded corn stover during enzymatic hydrolysis

Abstract: Based on engineering practice, the sugar concentration, power and apparent enzymatic activities change of enzymolysis suspension in enzymolysis process of steam-exploded corn stover (SECS) were studied to promote the industrialization process of corn stover producing butanol. At the same time, the changes of SECS physical and chemical properties during enzymatic hydrolysis were studied by biological microscope, laser scattering particle size distribution analysis (LSPSDA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Enzymatic hydrolysis was performed in a reactor with standard commercial cellulase as the enzyme. Enzymatic hydrolysis took place at 50℃, 100 r/min (four oblique leaves T agitator), enzyme loading of 60 IU/g corn stover, a solid:liquid ratio 3:10, and 48 h duration. Before the enzyme was added, the pH of the residues was adjusted to 4.8 with sodium hydroxide. After enzymatic hydrolysis the samples were taken from the reactor and centrifuged, and the supernatant phase was collected and analyzed for sugar concentrations, cellulase apparent enzymatic activities, and the physical and chemical properties of SECS. Sugar concentrations were tested by 3,5-Dinitrosalicylicacid（DNS）. Cellulase apparent enzymatic activities were determined by the filter-paper method. Scanning electron microscopy and X-ray diffraction analysis were conducted. The results show: In the first reaction, the sugar concentration in the enzymatic hydrolysis liquid increased very quickly, especially in the first hour. The change in sugar concentration was not very clear later in the hydrolysis reaction due to such factors as substrate loss, changes in substrate properties, cellulose inactivation, decreasing cellulose synergy, and so on. The sugar concentration after enzymatic hydrolysis 48 h was 56.25 g/L. The stirring power decreased during enzymatic hydrolysis and declined most quickly after one hour of enzymatic hydrolysis, then began to decline more slowly. The apparent enzymatic activity of cellulose in the hydrolysis liquid decreased to half of the initial value after one hour and remained relatively constant from 1h to 4h, but then began to rise again after 4 h, reaching a peak after enzymatic hydrolysis 24 h, after which it again decreased gradually. The apparent enzymatic activity decreased to about 75% of the initial value after 48 h. The original SECS is mainly easily visible, fibrous grains with long fibers. The fibrous grain size gradually decreases and its quantity is also reduced during enzymatic hydrolysis. The particle size of solid particles decreases, the specific surface area gradually increases, the crystallinity and the crystal size decrease, and the porosity increases during enzymatic hydrolysis.