Production Of Organic Acids Research Articles

Anti-fungal effects of lactic acid bacteria from pickles on the growth and sterigmatocystin production of Aspergillus versicolor

Sterigmatocystin (STC) is an emerging mycotoxin that poses a significant threat to the food security of cereal crops. To mitigate STC contamination in maize, this study employed selected lactic acid bacteria as biocontrol agents against Aspergillus versicolor, evaluating their biocontrol potential and analyzing the underlying mechanisms. Lactiplantibacillus plantarum HJ10, isolated from pickle, exhibited substantial in vitro antifungal activity and passed safety assessments, including antibiotic resistance and hemolysis tests. In vivo experiments demonstrated that L. plantarum HJ10 significantly reduced the contents of A. versicolor and STC in maize (both >84 %). The impact of heat, enzymes, alkali, and other treatments on the antifungal activity of cell-free supernatant (CFS) was investigated. Integrated ultra-high-performance liquid chromatography (UPLC) and gas chromatography–mass spectrometry (GC–MS) analysis revealed that lactic acid, acetic acid, and formic acid are the key substances responsible for the in vitro antifungal activity of L. plantarum HJ10. These metabolites induced mold apoptosis by disrupting cell wall structure, increasing cell membrane fluidity, reducing enzyme activities, and disrupting energy metabolism. However, in vivo antagonism by L. plantarum HJ10 primarily occurs through organic acid production and competition for growth space and nutrients. This study highlights the potential of L. plantarum HJ10 in reducing A. versicolor and STC contamination in maize.

Microbial Protein Production Using Lignocellulosic Biomass (Switchgrass) and Klebsiella oxytoca M5A1—A Nitrogen Fixer

The expanding global population has increased the demand for sustainable protein sources, and microbial protein (MP) has emerged as a promising alternative. However, conventional carbon (glucose) and nitrogen (ammonia, urea) sources needed for MP production pose environmental and economic issues. This study aims to produce protein using lignocellulosic biomass (LCB) as a carbon source and the nitrogen fixation ability of Klebsiella oxytoca M5A1 as a nitrogen source. The study investigates the pretreatment of LCB (switchgrass), enzymatic hydrolysis, protein quantification, nitrogen fixation, glucose utilization and organic acids production. K. oxytoca M5A1 harnessed free nitrogen from the atmosphere and used abundant, cheap glucose from LCB to produce MP and organic acids as by-products. Protein production occurred in two phases: first within the initial 8 h and secondly, within the last 16 h. The highest protein concentration was at 40 h, with approximately 683.46 µg/mL protein content. High-performance liquid chromatography system (HPLC) analysis revealed a dynamic profile of glucose utilization and organic acids (Lactic acid, Propionic acid, Acetic acid, and Succinic acid) production. K. oxytoca M5A1 exhibited an early high rate of glucose consumption, and conversion to organic acids, that were later used for second-phase protein production. The acids profile revealed intra-conversion from one acid to another via metabolic pathways (glycolysis and tricarboxylic acid cycle). Overall, leveraging LCB and the nitrogen-fixing ability of K. oxytoca M5A1 for MP production offers an eco-friendly and cost-effective alternative to traditional protein sources, contributing to a sustainable circular economy.

Filamentous morphology: a new frontier for genetic modification of filamentous fungal cell factories

Filamentous fungi are a group of eukaryotic microorganisms widely found in nature. Some filamentous fungi have been developed as "cell factories" and extensively used for the production of recombinant proteins, organic acids, and secondary metabolites due to their strong protein secretion capabilities or effective synthesis of many natural products. The growth morphology of filamentous fungi significantly influences the quality and quantity of fermented products. Previous research conducted by the authors' group revealed that an increase in hyphal branches leads to enhanced protein secretion during liquid fermentation. With the development of morphological engineering of filamentous fungi, an increasing number of studies have focused on modifying fungal mycelium morphology to improve the yield of target metabolites during fermentation. While there have been a few reviews on the relationship between fungal fermentation morphology and productivity, research in this area is rapidly developing and requires updates. The paper presents a comprehensive review of domestic and international research reports, along with the authors' own research findings, to systematically review the morphological patterns of filamentous fungi, the impact of fungal morphology on industrial fermentation, as well as methods and strategies for regulating mycelial morphology. The aim of this review is to enhance the understanding of relevant domestic scholars regarding the morphological development of filamentous fungi and provide ideas for the rational engineering of fungal strains suitable for industrial fermentation.

Effect of Isolated Cultures Fermentation on the Microbial Loads of Fermented African Oil Bean Seed (<i>Pentachletra macrophylla</i>) Products

The study explores the effect of isolated culture from traditionally fermented African oil bean seed on the microbial loads of pure and mixed cultures fermented “Ukana” (Ugba, African oil bean seed dessert). The isolates were morphologically and biochemically characterized. Their results as indicated in this study compared favorably to standard. Their characteristics resemble that of Bacillus substillis and Lactobacillus fermentum. These identified isolates were used as pure and mixed cultures to ferment African oil bean seed at 24 h, 48 h, 72 h and 96 h. The result obtained indicated that total coliform and Staphylococcus aureus count increased across the fermentation period when AOBS was traditionally fermented but kept decreasing as the fermentation period progressed in pure and mixed cultures fermented samples. The range of the total fungal count (TFC) varied from 5.1 x 104 Cfu/ml to 1.0 x 103 Cfu/ml. Moreover, the number of Lactic acid bacteria recorded in this study outweighed the fungi count. The result also showed that the colony count of Lactic acid bacteria at 96 h fermentation period supersedes that of coliform, staphylococcus and fungi whereas the total coliform was higher in traditionally fermented AOBS. This result according to literature could be attributed to the production of bacitracin and organic acids, especially bacteriocins which can inhibit the proliferation of pathogenic organisms. Bacillus substillis and Lactobacillus fermemtum isolated in this research are desirable probiotics with enormous health functions.

Anaerobic digestion model number 1 applied to the modeling of anaerobic digestion of residues generated in soluble coffee processing

The Anaerobic Digestion Model No. 1 (ADM1) was applied in this study to simulate the anaerobic digestion (AD) of wastewaters from soluble coffee processing in sequential batch reactors. As these substrates present considerable levels of phenolic compounds, modifications were made to the basic structure of the ADM1. Additionally, the Luong inhibition model replaced the Monod model to describe the consumption of soluble organic matter. On the other hand, the removal of phenolic compounds was carried out using the Haldane model, appropriate when the inhibition by excess substrate is present, taking into account in this case the quantification of phenols and benzoic acid as total phenols. The new ADM1-based model was calibrated with experimental data from the AD of post hydrothermal wastewater (PHWW) of spent coffee grounds (SCG) and validated with experimental data of the AD of effluents produced during the soluble coffee processing. The simulation results demonstrated that the new model moderately described the removal of phenolic compounds ( > 90 %), methane production (2.243 kgCODm−3 in calibration and 6.16 kgCODm−3 in validation), and the production and consumption of organic acids over time. However, in future research new metabolic pathways may be included in the model to improve its quality even more.

Assessment of the impact of Eco-Xcid (78% organic acid) product on soil physio-chemical attributes, microbial composition, phytotoxic effects, and crop yield in pea and potato cultivation: A comprehensive review

Assessment of the impact of Eco-Xcid (78% organic acid) product on soil physio-chemical attributes, microbial composition, phytotoxic effects, and crop yield in pea and potato cultivation: A comprehensive review

The white lupin trehalase gene LaTRE1 regulates cluster root formation and function under phosphorus deficiency.

Under phosphorus (P) deficiency, white lupin (Lupinus albus L.) forms specialized root structure, called cluster root (CR), to improve soil exploration and nutrient acquisition. Sugar signaling is thought to play a vital role in the development of CR. Trehalose and its associated metabolites are the essential sugar signal molecules that link growth and development to carbon metabolism in plants, however, their roles in the control of CR are still unclear. Here, we investigated the function of the trehalose metabolism pathway by pharmacological and genetic manipulation of the activity of trehalase in white lupin, the only enzyme that degrades trehalose into glucose. Under P deficiency, validamycin A treatment, which inhibits trehalase, led to the accumulation of trehalose and promoted the formation of CR with enhanced organic acid production, whereas overexpression of the white lupin TREHALASE1 (LaTRE1) led to decreased trehalose levels, lateral rootlet density, and organic acid production. Transcriptomic and virus-induced gene silencing (VIGS) results revealed that LaTRE1 negatively regulates the formation of CRs, at least partially, by the suppression of LaLBD16, whose putative ortholog in Arabidopsis (Arabidopsis thaliana) acts downstream of ARF7- and ARF19-dependent auxin signaling in lateral root formation. Overall, our findings provide an association between the trehalose metabolism gene LaTRE1 and CR formation and function with respect to organic acid production in white lupin under P deficiency.

Effect of Dietary Supplementation of Enteric Avian-Origin Lactobacillus casei-Fermented Soybean Meal on the Growth Performance and Intestinal Health of Broiler Chickens

The bacterial strain is key to fermentation, and the intestinal tract in livestock and poultry is a resource bank of good natural strains. The objective of this study was to evaluate the effect of soybean meal fermented using Lactobacillus casei, isolated from healthy broiler intestines with excellent organic acid production, on the intestinal health and growth performance of broilers. A total of 120 Arbor Acre male broiler chickens aged 21 days were fed until 42 days of age. These chickens were randomly divided into four groups with five replicates per group. Each replicate contained six broiler chickens. The specific groups were the control group (basal diet), the low-dose fermented soybean meal (FSBM) additive group (FSBML, basal diet + 0.2 kg/t FSBM), the middle-dose FSBM additive group (FSBMM, basal diet + 2 kg/t FSBM), and the high-dose FSBM additive group (FSBMH, basal diet + 5 kg/t FSBM). The results demonstrated a significant increase in the average daily feed intake (ADFI) and average daily gain (ADG) of the FSBMH group (p < 0.05). The FSBMH group displayed a significantly increased villus height (VH) to crypt depth (CD) ratio (VH/CD) for the duodenum (p < 0.05) and rectum (p < 0.05). The examination of the ileal mucosa showed that the FSBMH group (p < 0.05) had significantly higher levels of glutathione (GSH) activity, as well as higher relative mRNA expression of ZO-1, ZO-2, Occludin, IL-4, IL-6, MCP-1, TNF-α, IFN-α, IFN-β, and IFN-γ. However, the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were significantly lower in the FSBMH group (p < 0.05). The FSBMH group also showed higher levels of Nitriliruptoraceae and Ruminococcaceae. In conclusion, the addition of 5 kg/t FSBM to diets had an ameliorative effect on broiler growth performance and intestinal health.

Assessment and Characterization of Lactic Acid Bacteria Isolated from Fermented African oil Bean Seed (Pentaclethra macrophylla) for Probiotic Application

Among the bacteria in fermented foods, lactic acid bacteria play a pivotal role and its main function is to convert carbohydrates and other related raw materials into lactic acid (organic acid). Therefore, the aim of this research was to assess and use lactic acid bacteria isolates obtained from fermented African oil bean seeds as probiotics. Lactic acid bacteria were isolated using MRS agar and screened for organic acid production and the ability to tolerate some environmental conditions such as temperature, pH, and osmotic pressure. The use of the isolates as probiotics was investigated by screening and determining the antimicrobial inhibitory zone diameter of the isolates obtained against the indicator microorganisms such as Staphylococcus aureus, Bacillus cereus, Escherichia coli and Listeria monocytogenes. Results show that isolate2, isolate3, isolate5, isolate6, isolate7 and isolate8 were able to produce organic acid. Out of the six bacterial isolates tested for antimicrobial activities against the indicator microorganisms, isolate2, isolate3, isolate6 and isolate8 were able to show antimicrobial activities against Staphylococcus aureus, Bacillus cereus, Escherichia coli and Listeria monocytogenes using different dilutions (10- 1 to 10- 3) of the isolates. The isolates were able to grow at temperatures of 37oCand 45oC; pH of 2.5, 3.0, 3.5 and 4.0; finally the osmotic pressure of 1.0, 1.5, 2.5 and 5.0 % w/v NaCl. The isolates were identified as Lactobacillus species and can be used as probiotics.

Comparative analysis of biotechnological and catalytic approaches to the production of organic acids

Comparative analysis of biotechnological and catalytic approaches to the production of organic acids

Melanoidin Content Determines the Primary Pathways in Glucose Dark Fermentation: A Preliminary Assessment of Kinetic and Microbial Aspects

Melanoidins are heterogeneous polymers with a high molecular weight and brown color formed during the Maillard reaction by the combination of sugars and amino acids at high temperatures with the potential to inhibit the microbial activity in bioprocesses. This study assessed the impacts of melanoidins on the kinetic of substrate conversion and production of organic acids via dark fermentation using microbial consortia as inoculum. The investigations were carried out in fed-batch reactors using synthetic melanoidins following glucose-to-melanoidin ratios (G/M; g-glucose g−1 melanoidins) of 0.50, 1.50, 1.62, 1.67, and 5.00, also considering a melanoidin-free control reactor. The results showed that melanoidins negatively impacted the kinetics of glucose fermentation by decreasing the first-order decay constant (k1): when dosing equivalent initial concentrations of glucose (ca. 3 g L−1), the absence of melanoidins led to a k1 of 0.62 d−1, whilst dosing 2 g L−1 (G/M = 1.5) and 6.0 g L−1 (G/M = 0.5) of melanoidins produced k1 values of 0.37 d−1 and 0.27 d−1, respectively. The production of butyric and acetic acids was also negatively impacted by melanoidins, whilst the lactic activity was not impaired by the presence of these compounds. Lactate production reached ca. 1000 mg L−1 in G/M = 1.67, whilst no lactate was detected in the control reactor. The presence of melanoidins was demonstrated to be a selective metabolic driver, decreasing the microbial diversity compared to the control reactor and favoring the growth of Lactobacillus. These results highlight the importance of further understanding the impacts of melanoidins on melanoidin-rich organic wastewater bioconversion, such as sugarcane vinasse, which are abundantly available in biorefineries.

Functional Minas Frescal cheese with spore-forming Wezmannia coagulans GBI-30

Minas Frescal cheese is a valuable food matrix for introducing probiotic bacteria. Maintaining the probiotic viability until the moment of consumption is a challenge for the food industry. In this sense, using spore-forming bacteria can be an interesting option. This study aimed to evaluate the effect of adding Wezmannia coagulans GBI-30 at different concentrations (6, 8, and 10 log CFU g−1) on the properties of Minas Frescal cheese during its commercial shelf life. The cheeses were analyzed for probiotic viability, gross composition, pH, metabolites and bioactive compounds formation, and antibacterial activity. The viability remained constant and proportional to the amount of W. coagulans added to the samples. The production of organic acids and bioactive compounds was directly proportional to the addition of the probiotic strain. Regarding antibacterial activity, there was moderate inhibition against Salmonella enterica and Escherichia coli. Using W. coagulans GBI-30 in Minas Frescal cheese is a viable alternative for developing probiotic products that maintain their functionality throughout their commercial shelf life. The addition of higher probiotic concentrations may improve the biological activity of the products.

Type III sourdough: Evaluation of biopreservative potential in bakery products with enhanced antifungal activity

The potential biopreservative role of a Type III sourdough (tIII-SD), produced by starter cultures of Fructilactobacillus sanfranciscensis and Lactiplantibacillus plantarum ATCC 8014, was assessed for its antifungal activity in baking applications. Fermentation was carried out using different substrates to enhance the production of antifungal metabolites for 24 and 48 h. The tIII-SD samples were analyzed in relation to pH, total titratable acidity (TTA) and the production of organic acids. The water/salt-soluble extract of the tIII-SD was evaluated in relation to the inhibition potential against key fungi that contaminate bakery products including Penicillium roqueforti, Penicillium chrysogenum and Aspergillus niger. Finally, breads with 10 % of the tIII-SD were prepared and the fungi contamination was evaluated throughout the shelf life period. The lowest pH value in sourdough was obtained from 48-hour fermentation by L. plantarum. The saline extracts exhibited varying degrees of inhibition in the in vitro test; however, the greatest enhancement of this effect was obtained when whole wheat grain flour was used. The tIII-SD crafted from a blend of wheat and flaxseed flours and fermented with F. sanfranciscensis for 48 h (BSWF48h-FS), demonstrated superior performance compared to other formulations. This variant exhibited a total shelf life of 10 days, suggesting that the utilization of tIII-SD could serve as a viable alternative for natural antifungal agents, proving beneficial for the bakery industry.

Disorders of the small intestinal microenvironment in ovalbumin-sensitized mice and mitigation strategies of 2′-fucosyllactose and Bifidobacterium longum subsp. Infantis

The small intestine is responsible for approximately 90% of nutrient absorption, and it is widely believed that food allergens primarily sensitize through the small intestine. No study to date has investigated the association between food allergy (FA) and the altered small intestinal microenvironment (SIM), which would help to understand the biological process linking FA, and could provide new insights into the nutritional modulation of FA. In this study, we aimed to investigate the association between the development of FA and the altered SIM in ovalbumin-sensitized mice, as well as elucidate the underlying mechanisms by which Bifidobacterium longum subsp. Infantis (B. infantis) and/or 2′-fucosyllactose regulate allergenic reactions from the perspective of SIM. Our findings demonstrate that ovalbumin-induced disruption of SIM is characterized by increased bacteria diversity, dysregulated production of organic acids and amino acids, elevated ileal pH levels, and disrupted intestinal tight junctions. Furthermore, B. infantis and 2′-fucosyllactose cotreatment most significantly repaired ovalbumin sensitization-induced SIM dysbiosis compared to mono-treatment with either B. infantis or 2′-fucosyllactose alone. Additionally, impaired intestinal barrier function may impact lung homeostasis by influencing material exchange between the lumen and tissues, thereby increasing susceptibility to pulmonary. Notably, B. infantis and/or 2′-fucosyllactose differentially regulated both SIM and lung homeostasis. The present study supports the notion that disrupted small intestinal microenvironment homeostasis underlie the development of food allergy and highlights the significance of the small intestine-lung axis as a target for probiotic and/or prebiotic-mediated modulation of food allergy.

Phosphate solubilizing Pseudomonas and Bacillus combined with rock phosphates promoting tomato growth and reducing bacterial canker disease.

Nowadays, sustainable agriculture approaches are based on the use of biofertilizers and biopesticides. Tomato (Solanum lycopersicum L.) rhizosphere could provide rhizobacteria with biofertilizing and biopesticide properties. In this study, bacteria from the rhizosphere of tomato were evaluated in vitro for plant growth promotion (PGP) properties. Five Pseudomonas isolates (PsT-04c, PsT-94s, PsT-116, PsT-124, and PsT-130) and one Bacillus isolate (BaT-68s), with the highest ability to solubilize tricalcium phosphate (TCP) were selected for further molecular identification and characterization. Isolates showed phosphate solubilization up to 195.42 μg mL-1. All isolates showed phosphate solubilization by organic acid production. The six isolates improved seed germination and showed effective root colonization when tomato seeds were coated with isolates at 106 cfu g-1 in axenic soil conditions. Furthermore, the selected isolates were tested for beneficial effects on tomato growth and nutrient status in greenhouse experiments with natural rock phosphate (RP). The results showed that inoculated tomato plants in the presence of RP have a higher shoot and root lengths and weights compared with the control. After 60 days, significant increases in plant Ca, Na, P, protein, and sugar contents were also observed in inoculated seedlings. In addition, inoculated tomato seedlings showed an increase in foliar chlorophyll a and b and total chlorophyll, while no significant changes were observed in chlorophyll fluorescence. In greenhouse, two Pseudomonas isolates, PsT-04c and PsT-130, showed ability to trigger induced systemic resistance in inoculated tomato seedlings when subsequently challenged by Clavibacter michiganensis subsp. michiganensis, the causal agent of tomato bacterial canker. High protection rate (75%) was concomitant to an increase in the resistance indicators: total soluble phenolic compounds, phenylalanine-ammonia lyase, and H2O2. The results strongly demonstrated the effectiveness of phosphate-solubilizing bacteria adapted to rhizosphere as biofertilizers for tomato crops and biopesticides by inducing systemic resistance to the causal agent of tomato bacterial canker disease.

OPTIMIZING PIGMENT PRODUCTION FROM PENICILLIUM SP. FOR SUSTAINABLE SILK DYEING

This study explores the use of microbial pigments from Penicillium sp. as a sustainable alternative to synthetic dyes in textile dyeing, focusing on optimizing pigment production and assessing color fastness on silk. Static Potato Dextrose Broth (PDB) at 28°C produced the highest concentration of red pigment after 27 days of incubation, with an optical density (O.D) of 1.010 at λmax = 530 nm. In contrast, 15°C resulted in slower pigment production (O.D = 0.860), and 37°C showed negligible growth. Adjusting the PDB pH to 5 increased pigment yield, aligning with previous studies showing Penicillium sp. thrive in acidic conditions. The final broth pH decreased to 4.0 due to organic acid production by the fungus.Silk samples dyed with these pigments were evaluated for color strength and fastness. The colorimetric values indicated moderate color intensity (K/S = 4.25) with a bright, pastel-like appearance (L* = 81.23), and a warm reddish-yellow hue (a* = 9.23, b* = 6.48). Fastness tests showed excellent performance for dry rub (rating 5), good results for wet rub (rating 4), and favorable wash fastness (rating 4 for staining and color change). However, light fastness was lower, suggesting potential fading under prolonged exposure.Overall, the study identifies Penicillium sp. as a promising source of natural dyes for silk, with optimized fermentation conditions (PDB, 28°C, pH 5, 27 days) leading to high pigment yield and strong fastness performance, offering a sustainable alternative to synthetic dyes in textiles.

Improvement on wheat bread quality by in situ produced dextran-A comprehensive review from the viewpoint of starch and gluten.

Deterioration of bread quality, characterized by the staling of bread crumb, the softening of bread crust and the loss of aroma, has caused a huge food waste and economic loss, which is a bottleneck restriction to the development of the breadmaking industry. Various bread improvers have been widely used to alleviate the issue. However, it is noteworthy that the sourdough technology has emerged as a pivotal factor in this regard. In sourdough, the metabolic breakdown of carbohydrates, proteins, and lipids leads to the production of exopolysaccharides, organic acids, aroma compounds, or prebiotics, which contributes to the preeminent ability of sourdough to enhance bread attributes. Moreover, sourdough exhibits a "green-label" feature, which satisfies the consumers' increasing demand for additive-free food products. In the past two decades, there has been a significant focus on sourdough with in situ produced dextran due to its exceptional performance. In this review, the behaviors of bread crucial compositions (i.e., starch and gluten) during dough mixing, proofing, baking and bread storing, as well as alterations induced by the acidic environment and the presence of dextran are systemically summarized. From the viewpoint of starch and gluten, results obtained confirm the synergistic amelioration on bread quality by the coadministration of acidity and dextran, and also highlight the central role of acidification. This review contributes to establishing a theoretical foundation for more effectively enhancing the quality of wheat breads through the application of in situ produced dextran.

Eugenia uniflora (pitanga) juice as a new alternative vehicle for Limosilactobacillus fermentum ATCC 23271: evaluation of antioxidant and anti-infective effects.

Probiotic-containing foods are among the most appreciated functional foods; however, probiotic-based dairy products cannot be consumed by people who are lactose intolerant, allergic to milk, or vegetarian or vegan individuals. Thus, new non-dairy matrices have been tested for probiotics delivery. This study evaluated the growth and viability of Limosilactobacillus fermentum ATCC 23271 and Lacticaseibacillus rhamnosus ATCC 9595 in Pitanga juice (Eugenia uniflora L.). The effects of the fermentation on the antioxidant and anti-infective properties of the juice were also analyzed. The E. uniflora juice allowed lactobacilli growth without supplementation, reaching rates around 8.4 Log CFU/mL and producing organic acids (pH values < 4) after 72h of fermentation. The strain remained viable after 35 days of refrigerated storage. Fermentation by these bacteria increases the antioxidant capacity of the juice. The central composite rotational design was employed to evaluate the effects of bacterial inoculum and pulp concentration on growth and organic acids production by L. fermentum ATCC 23271. The strain was viable and produced organic acids in all tested combinations. L. fermentum-fermented juice and its cell-free supernatant significantly increased the survival of Tenebrio molitor larvae infected by enteroaggregative Escherichia coli 042. The results obtained in this study provide more insights into the potential of Pitanga juice to develop a functional non-dairy probiotic beverage with antioxidant and anti-infective properties.

Development of a New Kombucha from Grape Pomace: The Impact of Fermentation Conditions on Composition and Biological Activities

Winemaking is one of the oldest biotechnology techniques in the world. The wine industry generates 20 million tons of by-products, such as wastewater, stalk, lees, pomace, and stems, each year. The objective of this research project is to valorize wine industry by-products by producing a functional beverage via the fermentation of grape pomace with the kombucha consortium. In this study, grape pomace kombucha was produced under different conditions, and the concentration of the added sucrose in addition to the fermentation duration and temperature were varied. Overall, fermentation was characterized by the consumption of sugars and the production of organic acids and ethanol. An improvement in the concentrations of the total polyphenols and anthocyanins was observed in the developed product (i.e., up to 100%). Moreover, an enhancement of the antioxidant potential by 100%, as well as increases of 50 to 75% in the anti-inflammatory and antidiabetic activities, was noted.

Transcriptome analysis of Kluyveromyces marxianus under succinic acid stress and development of robust strains.

Kluyveromyces marxianus has become an attractive non-conventional yeast cell factory due to its advantageous properties such as high thermal tolerance and rapid growth. Succinic acid (SA) is an important platform molecule that has been applied in various industries such as food, material, cosmetics, and pharmaceuticals. SA bioproduction may be compromised by its toxicity. Besides, metabolite-responsive promoters are known to be important for dynamic control of gene transcription. Therefore, studies on global gene transcription under various SA concentrations are of great importance. Here, comparative transcriptome changes of K. marxianus exposed to various concentrations of SA were analyzed. Enrichment and analysis of gene clusters revealed repression of the tricarboxylic acid cycle and glyoxylate cycle, also activation of the glycolysis pathway and genes related to ergosterol synthesis. Based on the analyses, potential SA-responsive promoters were investigated, among which the promoter strength of IMTCP2 and KLMA_50231 increased 43.4% and 154.7% in response to 15 g/L SA. In addition, overexpression of the transcription factors Gcr1, Upc2, and Ndt80 significantly increased growth under SA stress. Our results benefit understanding SA toxicity mechanisms and the development of robust yeast for organic acid production. KEY POINTS: • Global gene transcription of K. marxianus is changed by succinic acid (SA) • Promoter activities of IMTCP2 and KLMA_50123 are regulated by SA • Overexpression of Gcr1, Upc2, and Ndt80 enhanced SA tolerance.