Ethanol Production and Other Bioproducts by Galactomyces geotrichum from Sugarcane Bagasse Hydrolysate

Regulation of fructose levels on carbon flow and metabolites in yeast during food fermentation

In this study, the effects of fructose levels on yeast growth, metabolic pathways and products, and redox status were investigated by simulated dough medium. The results showed that yeast was subjected to oxidative stress and damage under both sugar-free and high-fructose conditions. Yeast has a strong ability to metabolize pentose phosphate, trehalose, and tricarboxylic acid under sugar-free conditions. In the high fructose environment, yeast preferentially produced trehalose and glycerol in the early stage and gradually increased the metabolism of pentose phosphate in the later stage. Compared with the low fructose concentration, yeast had stronger pentose phosphate and tricarboxylic acid cycle (TCA) metabolism to ensure nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP) content in higher fructose levels. Therefore, sugar-free and high fructose levels affected the growth of yeast cells and yeast responded to fructose levels by regulating the metabolic carbon flow of glycolysis, pentose phosphate, trehalose, and TCA.

Influence of Honey Varieties, Fermentation Techniques, and Production Process on Sensory Properties and Odor-Active Compounds in Meads

This study investigates the impact of key factors on the formation of odorants and sensory properties in mead. The effects of the honey type (acacia, buckwheat, linden), wort heating, and the fermentation method (commercial Saccharomyces cerevisiae yeasts, spontaneous fermentation, Galactomyces geotrichum molds) were examined. Twelve model mead batches were produced, matured for 12 months, and analyzed using gas chromatography-olfactometry (GC-O) and headspace SPME-GC/MS to identify odor-active compounds. Results confirmed that the honey type plays a significant role in sensory profiles, with distinct aroma clusters for buckwheat, acacia, and linden honey. Compounds like phenylacetic acid, 2- and 3-methylbutanal, and butanoic acid were identified as the most important odorants, correlating with sensory attributes such as honey-like, malty, and fermented aromas. Univariate and multivariate analyses, followed by correlation analysis, highlighted how production parameters affect mead aroma, providing insights to optimize sensory quality.

Study of the effect of calcium signal participating in the antioxidant mechanism of yeast under high-sugar environment

BACKGROUND

Saccharomyces cerevisiae is susceptible to high-sugar stress in the production of bioethanol, wine and bread. Calcium signal is widely involved in various physiological and metabolic activities of cells. The present study aimed to explore the effects of Ca2+ signal on the antioxidant mechanism of yeast during high-sugar fermentation.

RESULTS

Compared to yeast without available Ca2+, yeast in the high glucose with Ca2+ group had higher dry weight, higher ethanol output at 12 and 24 h and higher glycerol output at 24 and 36 h. During the whole growth process, the trehalose synthesis capacity of yeast in the high glucose with Ca2+ group was lower and intracellular reactive oxygen species content was higher compared to yeast without available Ca2+. Intracellular malondialdehyde content of yeast under high glucose with Ca2+ was significantly lower than yeast under high glucose without available Ca2+ except for 6 h. The superoxide dismutase and catalase activities of yeast and glutathione content were higher in the high glucose with Ca2+ group compared to yeast in high glucose without available Ca2+. The expression levels of SOD1, GSH1, GPX2 genes were higher for high glucose without available Ca2+ at 6 h, while yeast in the high glucose with Ca2+ group had a higher expression of antioxidant-related genes except SOD1 and CTT1 at 12 h. The expression levels of antioxidant-related genes of yeast for high glucose with Ca2+ were higher at 24 h, and those of genes except SOD1 of yeast in the high glucose with Ca2+ group were higher at 36 h.

CONCLUSION

High-glucose stress limited the growth of yeast, while a moderate extracellular Ca2+ signal could improve the antioxidant capacity of yeast in a high-glucose environment by regulating protectant metabolism and enhancing the antioxidant enzyme activity and expression of antioxidant genes in a high-sugar environment. © 2024 Society of Chemical Industry.

A catalog of ethanol-producing microbes in humans

Aim: Endogenous ethanol production emerges as a mechanism of nonalcoholic steatohepatitis, obesity, diabetes and auto-brewery syndrome. Methods: To identify ethanol-producing microbes in humans, we used the NCBI taxonomy browser and the PubMed database with an automatic query and manual verification. Results: 85 ethanol-producing microbes in human were identified. Saccharomyces cerevisiae, Candida and Pichia were the most represented fungi. Enterobacteriaceae was the most represented bacterial family with mainly Escherichia coli and Klebsiella pneumoniae. Species of the Lachnospiraceae and Clostridiaceae family, of the Lactobacillales order and of the Bifidobacterium genus were also identified. Conclusion: This catalog will help the study of ethanol-producing microbes in human in the pathophysiology, diagnosis, prevention and management of human diseases associated with endogenous ethanol production.

Effect of glucose levels on carbon flow rate, antioxidant status, and enzyme activity of yeast during fermentation

BACKGROUND

The physiological metabolism of yeast has a significant impact on the quality of fermentation products. The present study aimed to investigate yeast metabolism in response to a changing glucose content environment, especially in fermentation products, as well as the change of carbon flow rate, antioxidant status, and yeast enzyme activity.

RESULTS

Yeast in a 0 g L^-1 glucose level was subjected to carbon starvation stress, cell growth retardation and cell proliferation was significantly inadequate; in the logarithmic growth stage of yeast, at a 30 g L^-1 glucose level, the carbon source mainly flowed to tricarboxylic acid cycle and pentose phosphate metabolism, cell division, proliferation, and increased cell growth. In later logarithmic growth period and stable period, carbon flowed into glycerol and trehalose metabolism, to cope with the environmental stress; yeast in 60 and 150 g L^-1 glucose levels faced high glucose stress at the beginning, the content of reactive oxygen increased, malondialdehyde content increased, cell damage was reduced through the regulation of superoxide dismutase and catalase enzyme activities, and most of the carbon flowed into the metabolic pathway of ethanol, glycerol, and trehalose to cope with high glucose stress, the pentose phosphate pathway showed a large late influx, and NADPH also started to increase rapidly after 24 h.

CONCLUSION

Yeast was stressed in a high-sugar environment and ensured the activity of yeast by preferentially increasing the metabolic intensity of trehalose, glycerol, and glycolytic metabolism, weakening tricarboxylic acid metabolism, and first weakening and then increasing pentose phosphate metabolism. © 2022 Society of Chemical Industry.

The combination of aerobic and microaerobic promote hydrolysis and acidification of rice straw and pig manure: Balance of insoluble and soluble substrate

Separated hydrolysis and acidification is an effective pretreatment method for anaerobic digestion of lignocellulose. However, excess consumption of soluble substrates remains a problem. Rice straw and pig manure were used as substrates with biogas slurry as the inoculum, combined with aerobic and microaerobic conditions in the 14-day hydrolysis and acidification. Aeration can significantly accelerate volatile solid degradation (38.25%), especially the lignocellulose. Soluble chemical oxygen demand (29157 mg/L) and volatile fatty acids (13219 mg/L) of the group with 4 days aerobic treatment, reached their peaks on day 5, obtaining a balanced insoluble substrate degradation and soluble substrate consumption. Candida, Lactobacillus, Bifidobacterium, and Acetobacter were enriched at the balanced point for positive contribution to the degradation of the insoluble substrate and the generation of soluble substrate. This study not only reveals the balance between degradation and consumption, but also provides new insight into biogas slurry recycling and anaerobic digestion precursor substrate production.

Synergy of Cellulase Systems between Acetivibrio thermocellus and Thermoclostridium stercorarium in Consolidated-Bioprocessing for Cellulosic Ethanol

Anaerobes harbor some of the most efficient biological machinery for cellulose degradation, especially thermophilic bacteria, such as Acetivibrio thermocellus and Thermoclostridium stercorarium, which play a fundamental role in transferring lignocellulose into ethanol through consolidated bioprocessing (CBP). In this study, we compared activities of two cellulase systems under varying kinds of hemicellulose and cellulose. A. thermocellus was identified to contribute specifically to cellulose hydrolysis, whereas T. stercorarium contributes to hemicellulose hydrolysis. The two systems were assayed in various combinations to assess their synergistic effects using cellulose and corn stover as the substrates. Their maximum synergy degrees on cellulose and corn stover were, respectively, 1.26 and 1.87 at the ratio of 3:2. Furthermore, co-culture of these anaerobes on the mixture of cellulose and xylan increased ethanol concentration from 21.0 to 40.4 mM with a high cellulose/xylan-to-ethanol conversion rate of up to 20.7%, while the conversion rates of T. stercorarium and A. thermocellus monocultures were 19.3% and 15.2%. The reason is that A. thermocellus had the ability to rapidly degrade cellulose while T. stercorarium co-utilized both pentose and hexose, the metabolites of cellulose degradation, to produce ethanol. The synergistic effect of cellulase systems and metabolic pathways in A. thermocellus and T. stercorarium provides a novel strategy for the design, selection, and optimization of ethanol production from cellulosic biomass through CBP.