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

Recent advances in yeast and bacteria co-cultivation for bioprocess applications

Yeast and bacteria co-cultures can be found in nature and have multiple advantages that can be exploited, nowadays also in a controlled bioproduction environment. Various types of co-cultivation have been used for food applications such as production of flavor compounds in dairy products and alcoholic beverages. Co-cultures can broaden the substrate spectrum for microbial food and feed production, they can increase productivity and efficiency, and the nutritional value. Workflows have been developed from plate to bioreactor scale to increase reproducibility and optimize benefits of individual co-cultivation strategies. Nonetheless, certain limitations need to be overcome for industrial application. Many interactions of microbes, in particular in suspension cultures, are not sufficiently understood or even explored. While more possibilities arose from on-line monitoring of individual populations or even single cells, off-line measurement techniques are still typically applied in order to assess growth and product formation. Promising advances have been achieved, however, by methods for single-cell at-line and on-line analysis in co-cultures which are accounted for to emphasize the current opportunities and challenges in monitoring and controlling co-cultures. This review aims to summarize the recent advances with a particular focus on cultivation procedures and process analysis in bacteria, yeast and bacteria-yeast co-cultures. The implementation of suitable monitoring methods to enable (remote) control and contribute to quality assurance will accelerate the development and optimization of industrial co-culture bioprocesses. This will support transferability and process standardization across world regions adding to the advancement of bioproduction. The applicability of some relevant technology is, however, in its infancy.

Phenylacetylcarbinol biotransformation by disrupted yeast cells using ultrasonic treatment in conjunction with a dipropylene glycol mediated biphasic emulsion system

Biotransformation of a pharmaceutical precursor, phenylacetylcarbinol (PAC), could be achieved by frozen-thawed Candida tropicalis whole cells (FT-WHC). The treatment of FT-WHC, which contained intracellular pyruvate decarboxylase (PDC) enzyme, using high-power ultrasonication with varying amplitudes were compared with glass bead attrition (GBA) as well as control for the release of PDC. Ultrasonication at 20% amplitude (Ult20) proved to be the most effective, resulting in the highest volumetric and specific PDC activities of 0.210 ± 0.004 U/mL and 0.335 ± 0.033 U/mg protein, respectively. Disrupted FT-WHC using Ult20 exhibited a statistically significant (p ≤ 0.05) higher initial PAC production rate (3.26 ± 0.04 mM). The comparison of three organic phases, namely, vegetable oil (Vg-Oil), Vg-Oil + dipropylene glycol (DPG), and octanol in the two-phase emulsion system for PAC biotransformation revealed the highest statistically significant (p ≤ 0.05) overall PAC concentration of 28.9 ± 0.1 mM in Vg-Oil + DPG system. The novel addition of DPG helped facilitating the partitioning of PAC into aqueous phase, stabilizing specific PDC activity, and specific PAC productivity in combination with ultrasonication treatment.

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

Cellulosic bioethanol production generally has a higher operating cost due to relatively expensive pretreatment strategies and low efficiency of enzymatic hydrolysis. The production of other high-value chemicals such as xylitol and phenylacetylcarbinol (PAC) is, thus, necessary to offset the cost and promote economic viability. The optimal conditions of diluted sulfuric acid pretreatment under boiling water at 95°C and subsequent enzymatic hydrolysis steps for sugarcane bagasse (SCB), rice straw (RS), and corn cob (CC) were optimized using the response surface methodology via a central composite design to simplify the process on the large-scale production. The optimal pretreatment conditions (diluted sulfuric acid concentration (% w/v), treatment time (min)) for SCB (3.36, 113), RS (3.77, 109), and CC (3.89, 112) and the optimal enzymatic hydrolysis conditions (pretreated solid concentration (% w/v), hydrolysis time (h)) for SCB (12.1, 93), RS (10.9, 61), and CC (12.0, 90) were achieved. CC xylose-rich and CC glucose-rich hydrolysates obtained from the respective optimal condition of pretreatment and enzymatic hydrolysis steps were used for xylitol and ethanol production. The statistically significant highest (p ≤ 0.05) xylitol and ethanol yields were 65% ± 1% and 86% ± 2% using Candida magnoliae TISTR 5664. C. magnoliae could statistically significantly degrade (p ≤ 0.05) the inhibitors previously formed during the pretreatment step, including up to 97% w/w hydroxymethylfurfural, 76% w/w furfural, and completely degraded acetic acid during the xylitol production. This study was the first report using the mixed whole cells harvested from xylitol and ethanol production as a biocatalyst in PAC biotransformation under a two-phase emulsion system (vegetable oil/1 M phosphate (Pi) buffer). PAC concentration could be improved by 2-fold compared to a single-phase emulsion system using only 1 M Pi buffer.

Utilization of agricultural wastes for co-production of xylitol, ethanol, and phenylacetylcarbinol: A review

Corn, rice, wheat, and sugar are major sources of food calories consumption thus the massive agricultural waste (AW) is generated through agricultural and agro-industrial processing of these raw materials. Biological conversion is one of the most sustainable AW management technologies. The abundant supply and special structural composition of cellulose, hemicellulose, and lignin could provide great potential for waste biological conversion. Conversion of hemicellulose to xylitol, cellulose to ethanol, and utilization of remnant whole cells biomass to synthesize phenylacetylcarbinol (PAC) are strategies that are both eco-friendly and economically feasible. This co-production strategy includes essential steps: saccharification, detoxification, cultivation, and biotransformation. In this review, the implemented technologies on each unit step are described, the effectiveness, economic feasibility, technical procedures, and environmental impact are summarized, compared, and evaluated from an industrial scale viewpoint.