Production of Phenylacetylcarbinol via Biotransformation Using the Co-Culture of Candida tropicalis TISTR 5306 and Saccharomyces cerevisiae TISTR 5606 as the Biocatalyst

Abstract

Phenylacetylcarbinol (PAC) is a precursor for the synthesis of several pharmaceuticals, including ephedrine, pseudoephedrine, and norephedrine. PAC is commonly produced through biotransformation using microbial pyruvate decarboxylase (PDC) in the form of frozen–thawed whole cells. However, the lack of microorganisms capable of high PDC activity is the main factor in the production of PAC. In addition, researchers are also looking for ways to utilize agro-industrial residues as an inexpensive carbon source through an integrated biorefinery approach in which sugars can be utilized for bioethanol production and frozen–thawed whole cells for PAC synthesis. In the present study, Candida tropicalis, Saccharomyces cerevisiae, and the co-culture of both strains were compared for their biomass and ethanol concentrations, as well as for their volumetric and specific PDC activities when cultivated in a sugarcane bagasse (SCB) hydrolysate medium (SCBHM). The co-culture that resulted in a higher level of PAC (8.65 ± 0.08 mM) with 26.4 ± 0.9 g L−1 ethanol production was chosen for further experiments. Biomass production was scaled up to 100 L and the kinetic parameters were studied. The biomass harvested from the bioreactor was utilized as frozen–thawed whole cells for the selection of an initial pyruvate (Pyr)-to-benzaldehyde (Bz) concentration ([Pyr]/[Bz]) ratio suitable for the PAC biotransformation in a single-phase emulsion system. The initial [Pyr]/[Bz] at 100/120 mM resulted in higher PAC levels with 10.5 ± 0.2 mM when compared to 200/240 mM (8.60 ± 0.01 mM). A subsequent two-phase emulsion system with Pyr in the aqueous phase, Bz in the organic phase, and frozen–thawed whole cells of the co-culture as the biocatalyst produced a 1.46-fold higher PAC level when compared to a single-phase emulsion system. In addition, the cost analysis strategy indicated preliminary costs of USD 0.82 and 1.01/kg PAC for the single-phase and two-phase emulsion systems, respectively. The results of the present study suggested that the co-culture of C. tropicalis and S. cerevisiae can effectively produce bioethanol and PAC from SCB and would decrease the overall production cost on an industrial scale utilizing the two-phase emulsion system with the proposed multiple-pass strategy.

Pretreatment and enzymatic hydrolysis optimization of lignocellulosic biomass for ethanol, xylitol, and phenylacetylcarbinol co-production using Candida magnoliae

“…Even though a two-phase emulsion system could improve PAC production due to its compatibility with the hydrophobic structure of organic phase ( Sandford et al, 2005 ), the associated cost per unit of PAC production could be higher if the produced PAC was not sufficiently high enough to offset the cost of employed organic phase. This was in agreement with the work of Kumar et al (2023) where the total production cost between a two-phase emulsion system with a volume ratio of 1:1 (vegetable oil:1 M Pi buffer) was increased by 135% in comparison with a single-phase emulsion system (USD 1.93/kg PAC compared with USD 0.82/kg PAC). This was nearly equivalent to 146% increase to the PAC being formed which might not be worthwhile to the investment cost.…”

“…In fact, the total cost of two-phase emulsion system with vegetable oil and 1 M Pi buffer in this study was much lower (USD 0.42/kg PAC) when the optimal volume ratio of 0.43:1 was employed ( Gunawan et al, 2008 ). The cost effectiveness of this system was significantly pronounced ( p ≤ 0.05) when compared to the work of Kumar et al (2023) with a cost mitigation of 78.4% and 49.1% for similar two-phase emulsion and single-phase emulsion systems. The potential of the multi-pass recycling system of vegetable oil as predicted by Kumar et al (2023) was quite attractive to further the lowering in production cost while facilitating PAC accumulation.…”

“…The cost effectiveness of this system was significantly pronounced ( p ≤ 0.05) when compared to the work of Kumar et al (2023) with a cost mitigation of 78.4% and 49.1% for similar two-phase emulsion and single-phase emulsion systems. The potential of the multi-pass recycling system of vegetable oil as predicted by Kumar et al (2023) was quite attractive to further the lowering in production cost while facilitating PAC accumulation. The expected cost reduction in this system could be up to 30% in the third-pass biotransformation with relatively higher [PAC].…”

“…Benzoic acid was the sole by-product being generated in a minute amount of 1.75 ± 0.09 mM. The relatively low Bz molarity balance might reflect some losses (12%), which confirms the higher Bz volatility compared to Pyr (Kumar et al, 2023).…”

“…The specific PDC activity per gram of frozen–thawed whole cells was also calculated based on wet whole cells being weighed and solubilized in a known volume of carboligase buffer. PAC molarity yields and assessment of close molarity balances with respect to Pyr and Bz were based on the well-established methods published elsewhere ( Kumar et al, 2023 ). Costing analyses relevant to PAC production in both single-phase and two-phase emulsion systems utilizing frozen–thawed whole cells were performed with the well-established strategy published previously by our group ( Leksawasdi et al, 2021 ; Kumar et al, 2023 ).…”