Effect of carbon sources on the growth and ethanol production of native yeast Pichia kudriavzevii ITV-S42 isolated from sweet sorghum juice

Kinetic Evaluation of the Production of Mead from a Non-Saccharomyces Strain

There is a growing market for craft beverages with unique flavors. This study aimed to obtain a palate-pleasing mead derived from Pichia kudriavzevii 4A as a monoculture. Different culture media were evaluated to compare the fermentation kinetics and final products. The crucial factors in the medium were ~200 mg L-1 of yeast assimilable nitrogen and a pH of 3.5-5.0. A panel of judges favored the mead derived from Pichia kudriavzevii 4A (fermented in a medium with honey initially at 23 °Bx) over a commercial sample produced from Saccharomyces cerevisiae, considering its appearance, fruity and floral flavors (provided by esters, aldehydes, and higher alcohols), and balance between sweetness (given by the 82.91 g L-1 of residual sugars) and alcohol. The present mead had an 8.57% v/v ethanol concentration, was elaborated in 28 days, and reached a maximum biomass growth (2.40 g L-1) on the same fermentation day (6) that the minimum level of pH was reached. The biomass growth yield peaked at 24 and 48 h (~0.049 g g-1), while the ethanol yield peaked at 24 h (1.525 ± 0.332 g g-1), in both cases declining thereafter. The Gompertz model adequately describes the kinetics of sugar consumption and the generation of yeast biomass and ethanol. Pathogenic microorganisms, methanol, lead, and arsenic were absent in the mead. Thus, Pichia kudriavzevii 4A produced a safe and quality mead with probable consumer acceptance.

Kinetic modeling and optimization of ethanol fermentation by the marine yeast Wickerhamomyces subpelliculosus ZE75

The study aims to enhance ethanol production by Wickerhamomyces subpelliculosus ZE75 isolated from marine sediment. In addition, analyzing the kinetic parameters of ethanol production and optimization of the fermentation conditions was performed. The marine yeast isolate ZE75 was selected as the front runner ethanol-producer, with an ethanol yield of 89.77 gL-1. ZE75 was identified relying on the phenotypic and genotypic characteristics of W. subpelliculosus. The genotypic characterization based on the Internal Transcribed Spacer (ITS) sequence was deposited in the GenBank database with the accession number OP715873. The maximum specific ethanol production rate (vmax) was 0.482 gg-1 h-1 at 175 gL-1 glucose concentration, with a high accuracy of R2 0.95. The maximum growth specific rates (μmax) were 0.141 h-1 obtained at 150 gL-1 glucose concentration with R2 0.91. Optimization of the fermentation parameters such as pH and salinity has been achieved. The highest ethanol yield 0.5637 gg-1 was achieved in a 100% natural seawater-based medium. The maximum ethanol production of 104.04 gL-1 was achieved at pH 4.5 with a specific ethanol rate of 0.1669 gg-1 h-1. The findings of the present study recommend the possibility of ethanol production from a seawater-based medium on a large scale using W. subpelliculosus ZE75.

Brewing a Craft Belgian-Style Pale Ale Using Pichia kudriavzevii 4A as a Starter Culture

There is an expanding market for beer of different flavors. This study aimed to prepare a craft Belgian-style pale ale with a non-Saccharomyces yeast. Pichia kudriavzevii 4A was used as a sole starter culture, and malted barley as the only substrate. The ingredients and brewing process were carefully monitored to ensure the quality and innocuousness of the beverage. During fermentation, the yeast consumed 89.7% of total sugars and produced 13.8% v/v of ethanol. The product was fermented and then aged for 8 days, adjusted to 5% v/v alcohol, and analyzed. There were no traces of mycotoxins, lead, arsenic, methanol, or microbiological contamination that would compromise consumer health. According to the physicochemical analysis, the final ethanol concentration (5.2% v/v) and other characteristics complied with national and international guidelines. The ethyl acetate and isoamyl alcohol present are known to confer sweet and fruity flavors. The sensory test defined the beverage as refreshing and as having an apple and pear flavor, a banana aroma, and a good level of bitterness. The judges preferred it over a commercial reference sample of Belgian-style pale ale made from S. cerevisiae. Hence, P. kudriavzevii 4A has the potential for use in the beer industry.

Advances in the Application of the Non-Conventional Yeast Pichia kudriavzevii in Food and Biotechnology Industries

Pichia kudriavzevii is an emerging non-conventional yeast which has attracted increased attention for its application in food and biotechnology areas. It is widespread in various habitats and often occurs in the spontaneous fermentation process of traditional fermented foods and beverages. The contributions of P. kudriavzevii in degrading organic acid, releasing various hydrolase and flavor compounds, and displaying probiotic properties make it a promising starter culture in the food and feed industry. Moreover, its inherent characteristics, including high tolerance to extreme pH, high temperature, hyperosmotic stress and fermentation inhibitors, allow it the potential to address technical challenges in industrial applications. With the development of advanced genetic engineering tools and system biology techniques, P. kudriavzevii is becoming one of the most promising non-conventional yeasts. This paper systematically reviews the recent progress in the application of P. kudriavzevii to food fermentation, the feed industry, chemical biosynthesis, biocontrol and environmental engineering. In addition, safety issues and current challenges to its use are discussed.

Evaluation of thermotolerant and ethanol-tolerant Saccharomyces cerevisiae as an alternative strain for bioethanol production from industrial feedstocks

Despite the fact that yeast Saccharomyces cerevisiae is by far the most commonly used in ethanol fermentation, few have been reported to be resistant to high ethanol concentrations at high temperatures. Hence, in this study, 150 S. cerevisiae strains from the Thailand Bioresource Research Center (TBRC) were screened for ethanol production based on their glucose utilization capability at high temperatures. Four strains, TBRC 12149, 12150, 12151, and 12153, exhibited the most outstanding ethanol production at high temperatures in shaking-flask culture. Among these, strain TBRC 12151 demonstrated a high ethanol tolerance of up to 12% at 40 °C. Compared to industrial and laboratory strains, TBRC 12149 displayed strong sucrose fermentation capacity whereas TBRC 12153 and 12151, respectively, showed the greatest ethanol production from molasses and cassava starch hydrolysate at high temperatures in shaking-flask conditions. In 5-L batch fermentation, similarly to both industrial strains, strain TBRC 12153 yielded an ethanol concentration of 66.5 g L-1 (58.4% theoretical yield) from molasses after 72 h at 40 °C. In contrast, strain TBRC12151 outperformed other industrial strains in cell growth and ethanol production from cassava starch hydrolysis at 40 °C with an ethanol production of 65 g L-1 (77.7% theoretical yield) after 72 h. Thus, the thermotolerant and ethanol-tolerant S. cerevisiae TBRC 12151 displayed great potential and possible uses as an alternative strain for industrial ethanol fermentation using cassava starch hydrolysate.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03436-4.

The ability of Pichia kudriavzevii to tolerate multiple stresses makes it promising for developing improved bioethanol production processes

Thermotolerant ethanol fermenting yeasts have been extensively used in industrial bioethanol production. However, little is known about yeast physiology under stress during bioethanol processing. This study investigated the physiological characteristics of the thermotolerant yeast Pichia kudriavzevii, strains NUNS-4, NUNS-5 and NUNS-6, under the multiple stresses of heat, ethanol and sodium chloride. Results showed that NUNS-4, NUNS-5 and NUNS-6 displayed higher growth rates under each stress condition than the reference strain, Saccharomyces cerevisiae TISTR5606. Maximum specific growth rates under stresses of heat (45°C), 15% v/v ethanol and 1·0 M sodium chloride were 0·23 ± 0·04 (NUNS-4), 0·11 ± 0·01 (NUNS-5) and 0·15 ± 0·01 h^-1 (NUNS-5), respectively. Morphological features of all yeast studied changed distinctly with the production of granules and vacuoles when exposed to ethanol, and cells were elongated under increased sodium chloride concentration. This study suggests that the three P. kudriavzevii strains are potential candidates to use in industrial-scale fermentation due to a high specific growth rate under multiple stress conditions. Multiple stress-tolerant P. kudriavzevii NUNS strains have received much attention not only for improving large-scale fuel ethanol production, but also for utilizing these strains in other biotechnological industries.

Treatment technologies for bakers' yeast production wastewater

Researchers in recent years have utilized a broad spectrum of treatment technologies in treating bakers' yeast production wastewater. This paper aims to review the treatment technologies for the wastewater, compare the process technologies, discuss recent innovations, and propose future perspectives in the research area. The review observed that nanofiltration was the most effective membrane process for the treatment of the effluent (at >95% pollutant rejection). Other separation processes like adsorption and distillation had technical challenges of desorption, a poor fit for high pollutant load and cost limitations. Chemical treatment processes have varying levels of success but they are expensive and produce toxic sludge. Sludge production would be a hurdle when product recovery and reuse are targeted. It is difficult to make an outright choice of the best process for treating the effluent because each has its merits and demerits and an appropriate choice can be made when all factors are duly considered. The process intensification of the industrial-scale production of the bakers' yeast process will be a very direct approach, where the process optimisation, zero effluent discharge, and enhanced recovery of value-added product from the waste streams are important approaches that need to be taken into account.

Paper mulberry fruit juice: a novel biomass resource for bioethanol production

By way of broadening the use of diverse sustainable bioethanol feedstocks, the potentials of Paper mulberry fruit juice (PMFJ), as a non-food, sugar-based substrate, were evaluated for fuel ethanol production. The suitability of PMFJ was proven, as maximum ethanol concentration (56.4 g/L) and yield (0.39 g/g) were achieved within half a day of the start of fermentation, corresponding to very high ethanol productivity of 4.7 g/L/hr. The established potentials were further optimally maximized through the response surface methodology (RSM). At the optimal temperature of 30 °C, yeast concentration of 0.55 g/L, and pH of 5, ethanol concentration, productivity, and yield obtained were 73.69 g/L, 4.61 g/L/hr, and 0.48 g/g, respectively. Under these ideal conditions, diverse metal salts were afterward screened for their effects on PMFJ fermentation. Based on a two-level fractional factorial design, nutrient addition had no positive impact on ethanol production. Thus, under the optimal process conditions, and without any external nutrient supplementation, bioethanol from PMFJ compared favorably with typical sugar-based energy crops, highlighting its resourcefulness as a high-value biomass resource for fuel ethanol production.

Mannitol and erythritol reduce the ethanol yield during Chinese Baijiu production

Chinese Baijiu is prepared using multiple microbial strains and complex metabolites by simultaneous saccharification and fermentation (SSF). Yeasts are challenged by various endogenous and exogenous factors, detrimentally affecting the ethanol yield. It is imperative to identify and control inhibitory factors. In the present study, microbial taxa and metabolites during Baijiu fermentation were evaluated to identify inhibitors of ethanol production. We found that filamentous fungi and Bacillus, contributing to saccharification, were negatively related to the ethanol content (Spearman's |ρ| > 0.5, P < 0.05). To explore how they affect ethanol production, ten filamentous fungi and three Bacillus strains were isolated. In addition to glucose and maltose, polyols were simultaneously generated by filamentous fungi and Bacillus via the hydrolysis of starch, among which mannitol and erythritol had the highest contents of up to 41.56 ± 2.01 g/kg and 16.16 ± 1.13 g/kg, respectively. The presence of mannitol and erythritol inhibited ethanol production by the functional yeasts Saccharomyces cerevisiae and Pichia kudriavzevii. The presence of 10.0 g/L mannitol significantly (P < 0.01) decreased the ethanol yield of S. cerevisiae by 12.67% (from 39.34 ± 0.02% to 32.71 ± 0.49%). These results revealed that polyols may inhibit the production of Baijiu and other fermented foods, suggesting that the origin and influence of polyols should be a focus of future research.

Performances of Pichia kudriavzevii in decolorization, biodegradation, and detoxification of C.I. Basic Blue 41 under optimized cultural conditions

The aim of this study was to evaluate the performances of Pichia kudriavzevii CR-Y103 yeast strain for the decolorization, biodegradation, and detoxification of cationic dye C.I. Basic Blue 41, a toxic compound to aquatic life with long-lasting effects. Under optimized cultural conditions (10.0-g L^-1 glucose, 0.2-g L^-1 yeast extract, and 1.0-g L^-1 (NH₄)₂SO₄), the yeast strain was able to decolorize 97.86% of BB41 (50 mg L^-1) at pH 6 within 4 h of incubation at 30 °C under shaken conditions (12,238.00-μg h^-1 average decolorization rate) and 100% within 12 h. The UV-Vis spectral analysis, high-performance liquid chromatography (HPLC), and Fourier-transform infrared spectroscopy (FTIR) analysis confirmed the complete decolorization and degradation of the BB41 dye by P. kudriavzevii CR-Y103. Also, other seven yeast strains, isolated from soil, as P. kudriavzevii (CR-Y108, CR-Y119, and CR-Y112), Candida tropicalis CR-Y128, Cyberlindnera saturnus CR-Y125, and Candida solani CR-Y124 have shown a promising decolorizing potential of azo-dye BB41 (99.89-76.09% decolorization). Phytotoxicity, cytotoxicity, and genotoxicity assays on Trifolium pratense and Triticum aestivum seedlings confirmed the high toxicity of BB41 dye (500 ppm), with inhibition on germination rate (%), root and shoot elongation, decreasing of mitoxic index value (with 34.03% in T. pratense and 40.25% in T. aestivum), and increasing the frequency of chromosomal aberrations (6.87 times in T. pratense and 6.25 times in T. aestivum), compared to control. The same biomarkers indicated the nontoxic nature of the BB41 degraded metabolite (500 ppm) obtained after P. kudriavzevii CR-Y103 treatment. Moreover, the healthy monkey kidney cells (Vero cells) had a low sensitivity to BB41 biodegraded products (250 μg mL^-1) (MTT cell viability assay) and revealed minor DNA damage (comet assay) compared to BB41 dye treatment. These findings show that P. kudriavzevii could be used in eco-friendly bioremediation technologies, applicable for reducing the toxicity of basic azo-dyes containing wastewaters.

Screening and Mutation of Saccharomyces cerevisiae UV-20 with a High Yield of Second Generation Bioethanol and High Tolerance of Temperature, Glucose and Ethanol

A wild-type strain was isolated from slightly rotted pears after three rounds of enrichment culture, identified as Saccharomyces cerevisiae 3308, and evaluated for its fermentation capability of second generation bioethanol and tolerance of temperature, glucose and ethanol. S. cerevisiae 3308 was mutated by using the physical and chemical mutagenesis methods, ultraviolet (UV) and diethyl sulfate (DES), respectively. Positive mutated strains were mainly generated by the treatment of UV, but numerous negative mutations emerged under the treatment of DES. A positive mutated strain, UV-20, produced ethanol from 62.33 ± 1.34 to 122.22 ± 2.80 g/L at 30-45 °C, and had a maximum yield of ethanol at 37 °C. Furthermore, UV-20 produced 121.18 ± 2.51 g/L of second generation bioethanol at 37 °C. Simultaneously, UV-20 exhibited superior tolerance to 50% of glucose and 21% of ethanol. In a conclusion, all of these results indicated that UV-20 has a potential industrial application value.