Enhancing the bioconversion of ferulic acid from alkaline hydrolysate of corn cobs to vanillin by Amycolatopsis thermoflava under nutrient limitation and reducing sugar control

BACKGROUND: The use of commercially available ferulic acid (FA) as a precursor for vanillin production is costly. The utilization of agro-waste as a starting material provides an alternative to obtain FA at a low cost and establish an economically profitable production system. In this work, optimization of ultrasound-assisted extraction conditions for releasing FA from corn cobs using alkaline treatment was conducted. Further, bioconversion of FA from the crude hydrolysate of corn cobs to vanillin using Amycolatopsis thermoflava was performed. RESULTS: Since autoclaved hydrolysate was unfavorable for cell growth and vanillin formation, pasteurization was proposed. However, the presence of contaminants limited the entire process. Aiming to suppress the growth of contaminants and increase vanillin yield, novel strategies of limiting and controlling the nutrients for the strain were developed. Optimal hydrolysis conditions (NaOH concentration = 0.5 M, solid loading = 10% for 30 min) produced hydrolysate with relatively high titers of FA (715 mg L⁻¹) and p-coumaric acid (1025 mg L⁻¹). To improve vanillin production from FA, four parameters (including the effects of sterilization method, nutrient limitation, initial biomass concentration, and reducing sugar control) were investigated. By adopting these strategies and performing bioconversion of FA to vanillin with an initial biomass concentration of 1.5 g L⁻¹, the yield of vanillin was significantly increased by 29.5-fold to 477.4 mg g⁻¹, compared to bioconversion using autoclaved hydrolysate. CONCLUSION: This approach represents a relatively economical method for vanillin production from agro-waste because it uses crude hydrolysate, requires minimum nutrients, and involves non-modified organisms with a relatively short bioconversion time (17 h).