One-Pot Production of Vanillin from Capsaicinoids through a Retrosynthetic Enzyme Cascade

Vanillin is a key organoleptic component in vanilla, one of the most important natural flavors in the industry. The limited supply of natural vanilla, extracted from cured vanilla beans, elevates the commercial value of 'natural'-labeled vanillin, producible by microbial conversion of natural precursors such as ferulic acid, eugenol, isoeugenol, lignin, and glucose. However, cellular toxicity and undesirable overoxidation of vanillin remain challenges to the microbial methods. Here, we developed a one-pot enzymatic conversion of capsaicinoids to vanillin by retracing the biosynthetic pathway found in Capsicum plants. The enzyme cascade consists of the hydrolysis of capsaicinoids by immobilized lipase B from Candida antarctica (CALB) and the oxidative deamination of the resulting vanillylamine by omega-transaminase from Paracoccus denitrificans (PDTA). Process optimization of individual enzyme reactions was conducted on an analytical scale, enabling>95% reaction yield of vanillin from capsaicinoids in the one-pot cascade reaction without undesirable accumulation of the oxidation byproduct and the inhibitory reaction intermediate, i. e., vanillic acid and vanillylamine, respectively. To verify practical applicability, we performed a preparative-scale reaction starting with 1.75 g capsaicinoids and 2.75 g sodium pyruvate at 10 mg/mL CALB and 3 mu M PDTA, leading to an 81% reaction yield and a 57% isolation yield. This study is, to the best of our knowledge, the first demonstration of one-pot production of vanillin from capsaicinoids, which might pave the way for cost-effective and sustainable access to natural-labeled vanillin from a renewable feedstock readily available from Capsicum fruits.