Abstract
We performed the biotransformation of ferulic acid to vanillin using Bacillus subtilis (B. subtilis) in the stirring packed-bed reactors filled with carbon fiber textiles (CFT). Scanning electron microscope (SEM), HPLC, qRT-PCR and ATP assay indicated that vanillin biotransformation is tightly related to cell growth, cellar activity and the extent of biofilm formation. The biotransformation was affected by hydraulic retention time (HRT), temperature, initial pH, stirring speed and ferulic acid concentration, and the maximum vanillin production was obtained at 20 h, 35 °C, 9.0, 200 rpm, 1.5 g/L, respectively. Repeated batch biotransformation performed under this optimized condition showed that the maximum productivity (0.047 g/L/h) and molar yield (60.43%) achieved in immobilized cell system were 1.84 and 3.61 folds higher than those achieved in free cell system. Therefore, the stirring reactor packed with CFT carrier biofilm formed by B. subtilis represented a valid biocatalytic system for the production of vanillin.
Highlights
Vanillin (4-hydroxy-3-methoxybenzaldehyde), the major compound of vanilla flavor, is widely used in foods, beverages, perfumes, and pharmaceuticals[1]
There is a remarkable lack of information about the biotransformation of ferulic acid to vanillin in the stirring reactors packed with carbon fiber textiles (CFT)
Scanning electron microscope (SEM) were taken after 40 h of operation and showed the CFT carrier was completely covered with biofilm (Fig. 1e)
Summary
The sequence of biofilm formation on CFT carrier in different time intervals (0, 10, 20, 30 and 40 h) could be clearly seen in SEM images (Fig. 1a–e). By the immobilized cell strategy here, the maximum molar yield is at least 1.11 fold higher than that of free cells mentioned above This suggested that the stirring bioreactor packed with CFT carrier biofilm formed by B. subtilis could efficiently transform ferulic acid to vanillin. Repeated batch biotransformation indicated the maximum vanillin molar yield (60.43%) and productivity (0.047 g/L/h) from the immobilized cell system was higher than those from the free cell system (molar yield of 32.81%, productivity of 0.013 g/L/h) These results revealed that the reactor packed with CFT biofilm of B. subtilis possesses a good application potential in producing vanillin from ferulic acid
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