Batch and continuous cultivation processes ofCandida tropicalisTISTR 5306 for ethanol and pyruvate decarboxylase production in fresh longan juice with optimal carbon to nitrogen molar ratio

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.

Kinetics of Phosphate Ions and Phytase Activity Production for Lactic Acid-Producing Bacteria Utilizing Milling and Whitening Stages Rice Bran as Biopolymer Substrates

A study evaluated nine kinetic data and four kinetic parameters related to growth, production of various phytase activities (PEact), and released phosphate ion concentration ([Pi]) from five lactic acid bacteria (LAB) strains cultivated in three types of media: phytate (IP6), milling stage rice bran (MsRB), and whitening stage rice bran (WsRB). Score ranking techniques were used, combining these kinetic data and parameters to select the most suitable LAB strain for each medium across three cultivation time periods (24, 48, and 72 h). In the IP6 medium, Lacticaseibacillus casei TISTR 1500 exhibited statistically significant highest (p ≤ 0.05) normalized summation scores using a 2:1 weighting between kinetic and parameter data sets. This strain also had the statistically highest levels (p ≤ 0.05) of produced phosphate ion concentration ([Pi]) (0.55 g/L) at 72 h and produced extracellular specific phytase activity (ExSp-PEact) (0.278 U/mgprotein) at 48 h. For the MsRB and WsRB media, Lactiplantibacillus plantarum TISTR 877 performed exceptionally well after 72 h of cultivation. It produced ([Pi], ExSp-PEact) pairs of (0.53 g/L, 0.0790 U/mgprotein) in MsRB and (0.85 g/L, 0.0593 U/mgprotein) in WsRB, respectively. Overall, these findings indicate the most promising LAB strains for each medium and cultivation time based on their ability to produce phosphate ions and extracellular specific phytase activity. The selection process utilized a combination of kinetic data and parameter analysis.

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

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.

Extraction of gymnemic acid from Gymnema inodorum (Lour.) Decne. leaves and production of dry powder extract using maltodextrin

The aim of the present study was to maximize the extraction of gymnemic acid (GA) from Phak Chiang Da (PCD) leaves, an indigenous medicinal plant used for diabetic treatment in Northern Thailand. The goal was to overcome the low concentration of GA in the leaves, which limits its applications among a larger population and develop a process to produce GA-enriched PCD extract powder. The solvent extraction method was employed to extract GA from PCD leaves. The effect of ethanol concentration and extraction temperature were investigated to determine the optimum extraction conditions. A process was developed to produce GA-enriched PCD extract powder, and its properties were characterized. In addition, color analysis (L*, a*, and b*) was performed to evaluate the overall appearance of the PCD extract powder. Antioxidant activity assay was conducted to assess the ability of the PCD extract powder to neutralize DPPH free radicals. The results showed that the concentration of 50% (v/v) ethanol at 70 °C for 2 h resulted in a higher GA concentration of 8307 mg/kg from dried PCD leaves. During the drying process, the use of maltodextrin at a concentration of 0.5% (w/v) was found to produce PCD extract powder with the maximum GA concentration. The color analysis revealed that the PCD extract powder had a dark greenish tint mixed with yellow. The antioxidant activity assay showed that 0.1 g of PCD extract powder was able to neutralize 75.8% of DPPH free radicals. The results concluded that PCD extract powder could potentially be used as a source of nutraceuticals or as a functional food ingredient. These findings suggest the potential value of GA-rich PCD extract powder in various applications in the pharmaceutical, nutraceutical, or food industries.

Valorization of rice straw, sugarcane bagasse and sweet sorghum bagasse for the production of bioethanol and phenylacetylcarbinol

Open burning of agricultural residues causes numerous complications including particulate matter pollution in the air, soil degradation, global warming and many more. Since they possess bio-conversion potential, agro-industrial residues including sugarcane bagasse (SCB), rice straw (RS), corncob (CC) and sweet sorghum bagasse (SSB) were chosen for the study. Yeast strains, Candida tropicalis, C. shehatae, Saccharomyces cerevisiae, and Kluyveromyces marxianus var. marxianus were compared for their production potential of bioethanol and phenylacetylcarbinol (PAC), an intermediate in the manufacture of crucial pharmaceuticals, namely, ephedrine, and pseudoephedrine. Among the substrates and yeasts evaluated, RS cultivated with C. tropicalis produced significantly (p ≤ 0.05) higher ethanol concentration at 15.3 g L^-1 after 24 h cultivation. The product per substrate yield (Y_eth/s) was 0.38 g g^-1 with the volumetric productivity (Q_p) of 0.64 g L^-1 h^-1 and fermentation efficiency of 73.6% based on a theoretical yield of 0.51 g ethanol/g glucose. C. tropicalis grown in RS medium produced 0.303 U mL^-1 pyruvate decarboxylase (PDC), a key enzyme that catalyzes the production of PAC, with a specific activity of 0.400 U mg^-1 protein after 24 h cultivation. This present study also compared the whole cells biomass of C. tropicalis with its partially purified PDC preparation for PAC biotransformation. The whole cells C. tropicalis PDC at 1.29 U mL^-1 produced an overall concentration of 62.3 mM PAC, which was 68.4% higher when compared to partially purified enzyme preparation. The results suggest that the valorization of lignocellulosic residues into bioethanol and PAC will not only aid in mitigating the environmental challenge posed by their surroundings but also has the potential to improve the bioeconomy.

Kinetics of Whole Cells and Ethanol Production from Candida tropicalis TISTR 5306 Cultivation in Batch and Fed-batch Modes Using Assorted Grade Fresh Longan Juice

The kinetic profiles of Candida tropicalis TISTR 5306 cultivation based on modified yeast-malt (MYM), assorted grade fresh longan juice (AsgLG) and longan solid waste extract (LSWE) medium were evaluated in 1 l batch mode. The highest ethanol concentration level (25.5 ± 0.8 g/l) and ethanol yield - Yp/s of 0.491 ± 0.017 g ethanol/g consumed substrate, dried biomass concentration level (9.44 ± 0.05 g/l) and dried biomass yield - Yp/s of 0.533 ± 0.170 g dried biomass/g consumed substrate, specific pyruvate decarboxylase (PDC) activity (0.037 ± 0.003 U/mg protein) were achieved (p ≤ 0.05) in AsgLG medium. Scores ranking strategy were employed and AsgLG medium was subsequently selected with in the highest total score (p ≤ 0.05) of 698 ± 7 at 48 h. The cultivation in fed-batch mode with three rounds of pulse feeding (PF) in 1 l AsgLG medium was carried out. The apparent highest ethanol and dried biomass concentration levels with corresponding yields relative to time zero were (28.3 ± 0.5 g/l, 0.482 ± 0.012 g/g) at 120 h of PF2 and (9.39 ± 0.04 g/l, 0.110 ± 0.001 g/g) at 192 h of PF3. The maximum specific PDC activity was 0.057 ± 0.006 U/mg protein during PF1 feeding.

Validation of mathematical model with phosphate activation effect by batch (R)-phenylacetylcarbinol biotransformation process utilizing Candida tropicalis pyruvate decarboxylase in phosphate buffer

The (R)-phenylacetylcarbinol (PAC) batch biotransformation kinetics for partially purified Candida tropicalis TISTR 5350 pyruvate decarboxylase (PDC) were determined to validate a comprehensive mathematical model in 250 mL scale with 250 mM phosphate buffer/pH 7.0. PDC could convert initial 100/120 mM benzaldehyde/pyruvate substrates to the statistical significantly highest (p ≤ 0.05) maximum PAC concentration (95.8 ± 0.1 mM) and production rate (0.639 ± 0.001 mM min-1). A parameter search strategy aimed at minimizing overall residual sum of square (RSST) based on a system of six ordinary differential equations was applied to PAC biotransformation profiles with initial benzaldehyde/pyruvate concentration of 100/120 and 30/36 mM. Ten important biotransformation kinetic parameters were then elucidated including the zeroth order activation rate constant due to phosphate buffer species (ka) of (9.38 ±  < 0.01) ×  10-6% relative PDC activity min-1 mM-1. The validation of this model to independent biotransformation kinetics with initial benzaldehyde/pyruvate concentration of 50/60 mM resulted in relatively good fitting with RSST, mean sum of square error (MSE), and coefficient of determination (R2) values of 662, 17.4, and 0.9863, respectively.