One-pot microbial bioconversion of wheat bran ferulic acid to biovanillin

Abstract

Due to growing consumer preference towards natural ingredients in food products, the production of flavors by microbial biotransformation of agrowastes provides an eco-friendly, cost-effective and sustainable pathway for biovanillin production. In the present study, biovanillin was produced by microbial biotransformation of ferulic acid (FA) using Streptomyces sp. ssr-198. The strain was able to grow in glucose medium supplemented with 1 g/L FA and produce 20.91 ± 1.11 mg/L vanillin within 96 h, along with 5.78 ± 0.13 mg/L vanillic acid in 144 h. Estimation of enzymes involved in FA degradation detected maximum feruloyl-CoA synthetase activity (1.21 ± 0.03 U/mg protein) at 96 h and maximum vanillin dehydrogenase activity (0.31 ± 0.008 U/mg protein) at 168 h, with small amounts of ferulic acid esterase activity (0.13 ± 0.002 U/mg protein) in the fermentation medium. Further, the glucose deficient production medium supplemented with 3 g/L of ferulic acid when inoculated with Streptomyces sp. ssr-198 (6% wet weight) produced maximum vanillin (685 ± 20.11 mg/L) within 72 h at 37 °C under agitation (150 rpm) and declined thereafter. Furthermore, in a one-pot experiment, wherein crude ferulic acid esterase (700 IU/g of substrate) from Enterococcus lactis SR1 was added into 10% w/v wheat bran (natural source of ferulic acid) based medium and was inoculated with 1% w/v of Streptomyces sp. ssr-198 resulted in maximum vanillin production (1.02 ± 0.02 mg/g of substrate) within 60 h of incubation. The study provides an insight into synergistic effect of using FAE of E. lactis SR1 and Streptomyces sp. ssr-198 for bioproduction of biovanillin using agro residues.

Supplementary information: The online version contains supplementary material available at 10.1007/s13205-021-03006-0.

Keywords: Agroresidues; Ferulic acid esterase; Streptomyces sp., Feruloyl-Co-A synthetase.

Fig. 1

Growth curve of Streptomyces sp. ssr-198 in FA supplemented glucose mineral medium and its relation with biotransformation of ferulic acid to vanillin and vanillic acid

Fig. 2

Effect of FA supplementation in the growth media on the cell biomass and its biotransformation to vanillin and vanillic acid by Streptomyces sp. ssr-198

Fig. 3

Feruloyl-Co-A synthetase (FCS) and vanillin dehydrogenase (VDH) activities of Streptomyces sp. ssr-198 in FA supplemented growth medium at different time intervals

Fig. 4

The proposed pathway for the bioconversion of FA to vanillin in Streptomyces sp. ssr-198

Fig. 5

Depletion of FA along with its biotansformation to vanillin and vanillic acid by the resting cells of Streptomyces sp. ssr-198 in glucose deficient production medium containing 1 g/L FA

Fig.6

a Effect of FA concentration (% w/v) and b wet biomass (% w/v) on its bioconversion to vanillin and vanillic acid by the resting cells of Streptomyces sp. ssr-198 in glucose deficient production medium containing 1 g/L FA

Fig. 7

Optimization of a FAE dose (IU/g dry substrate), b substrate loading (% w/v), and c inoculum (% w/v wet weight) of Streptomyces sp. ssr-198 for the one-pot biotransformation of FA present in wheat bran to vanillin