Correlation analysis of key enzyme activities and aroma compounds during fermentation of simulated juice system with Saccharomyces cerevisiae

Effects of Patulin Stress on the Physiology, Fermentation Performance, and Aroma Profile of Saccharomyces cerevisiae During Fermentation

Patulin (PAT) is a mycotoxin commonly found in apples and their derived products, posing a significant threat to human health. Saccharomyces cerevisiae CICC 31084 exhibited excellent ability in removing PAT during fermentation. However, limited studies have addressed the physiological and fermentation-related responses of S. cerevisiae under PAT stress. This study investigated the effect of different concentrations of PAT on S. cerevisiae in simulated apple juice. The results revealed that the PAT removal process affected the growth and metabolism of S. cerevisiae. PAT stress increased the thickness and altered the structure of yeast cell walls while upregulating the expression of genes associated with cell wall biosynthesis. Furthermore, oxidative stress induced by PAT triggered elevated glutathione levels, catalase activity, and ATPase activity, suggesting a robust adaptive response. A total of 1 µg/mL PAT accelerated the changes of fermentation parameters, whereas 10 µg/mL impaired yeast performance. GC-MS analysis revealed that PAT influenced the content of key aroma compounds in the simulated juices. PAT concentration was positively correlated with the production of octanoic acid and ethyl octanoate and negatively correlated with the formation of phenylethyl alcohol, hexanoic acid, and esters. The results could provide a theoretical basis for the application of PAT detoxification by S. cerevisiae in cider, and the identified aroma compounds could serve as potential markers for PAT contamination.

Synergistic inactivation effect of ultrasound and nano-emulsified basil essential oil on the metabolic responses of Salmonella on sprouts

This study investigated the effectiveness and mechanisms of ultrasound (US), nano-emulsified basil essential oil (NBEO), and their combination (NBEO_US) in inactivating Salmonella enterica cells inoculated on pea sprouts. The results demonstrated that the combined treatment was more effective than individual treatments in inactivating the target. This led to a decrease of 4.4 to 5.0 log CFU/g. Transmission electron microscopy showed that NBEO_US leads to the disruption of the bacteria morphology. Additionally, the leakage of cell constituents (proteins and nucleotide) demonstrated that NBEO_US disrupted the structural integrity of S. enterica cells. In addition, the metabolomics analysis using 1H NMR showed that NBEO_US had a detrimental effect on energy and amino acid metabolism in bacterial cells, specifically affecting glycolysis and amino acid production. Also, NBEO_US affected the Embden-Meyerhof-Parnas pathway in S. enterica cells by decreasing the activity of hexokinase, phosphofructokinase, and pyruvate kinase. Finally, the application of NBEO_US resulted in a substantial (P < 0.05) increase in the hardness of the treated pea sprouts while simultaneously decreasing their lightness. The present investigation illustrated the synergistic antibacterial mechanism of NBEO_US against S. enterica strains using sprouts as a food model. By understanding the microbiological changes in metabolic pathways induced by the combined treatment, sanitization strategies can be optimized to specifically target critical vulnerabilities, thereby ensuring safer and more efficient production of fresh produce.

Transcriptomics to evaluate the influence mechanisms of ethanol on the ester production of Wickerhamomyces anomalus with the induction of lactic acid

Wickerhamomyces anomalus is one of the most important ester-producing strains in Chinese baijiu brewing. Ethanol and lactic acid are the main metabolites produced during baijiu brewing, but their synergistic influence on the growth and ester production of W. anomalus is unclear. Therefore, in this paper, based on the contents of ethanol and lactic acid during Te-flavor baijiu brewing, the effects of different ethanol concentrations (3, 6, and 9% (v/v)) combined with 1% lactic acid on the growth and ester production of W. anomalus NCUF307.1 were studied and their influence mechanisms were analyzed by transcriptomics. The results showed that the growth of W. anomalus NCUF307.1 under the induction of lactic acid was inhibited by ethanol. Although self-repair mechanism of W. anomalus NCUF307.1 induced by lactic acid was initiated at all concentrations of ethanol, resulting in significant up-regulation of genes related to the Genetic Information Processing pathway, such as cell cycle-yeast, meiosis-yeast, DNA replication and other pathways. However, the accumulation of reactive oxygen species and the inhibition of pathways associated with carbohydrate and amino acid metabolism may be the main reason for the inhibition of growth in W. anomalus NCUF307.1. In addition, 3% and 6% ethanol combined with 1% lactic acid could promote the ester production of W. anomalus NCUF307.1, which may be related to the up-regulation of EAT1, ADH5 and TGL5 genes, while the inhibition in 9% ethanol may be related to down-regulation of ATF2, EAT1, ADH2, ADH5, and TGL3 genes.

Inoculation of Zaopei with biofortification: Inducing variation in community structure and improving flavor compounds in Nongxiangxing baijiu

The deterioration of the quality of raw liquor caused by the low content of ethyl hexanoate in Nongxiangxing baijiu has become a pervasive problem in the baijiu industry. Therefore, this study attempted to increase the synthesis of ethyl hexanoate by microorganisms with high esterase activity to increase Zaopei fermentation. The results showed that biofortification was a feasible and important way to improve the quality of the raw liquor and increase the ethyl hexanoate content. Adding Bacillus subtilis, Staphylococcus epidermidis, and Millerozyma farinosa for biofortified fermentation disturbed the microbial community structure of Zaopei and increased the abundance of Wickerhamomyces, Saccharomyces, and Thermoascus. The contents of ethyl hexanoate, ethyl valerate, ethyl caprylate, and ethyl heptanoate also increased noticeably in baijiu. The results of E-nose and sensory analysis tested and verified that the baijiu in the fortified group had better flavor characteristics.

Analysis of the Formation of Characteristic Aroma Compounds by Amino Acid Metabolic Pathways during Fermentation with Saccharomyces cerevisiae

Amino acid metabolic pathways can have profound impacts on the activities of key enzymes in the biosynthesis of specific aroma compounds during yeast fermentation. Aroma compounds, pyruvic acid and glucose were monitored in relation to the key enzymes of leucine aminotransferase (LTR), phenylalanine aminotransferase (PAL), pyruvate kinase (PK) and acetyl-CoA in the amino acid metabolic pathways during the fermentation of simulated juice systems with added amino acids in order to explore the formation of characteristic aroma compounds. The addition of L-phenylalanine or L-leucine to the simulated juice systems significantly improved the activities of PK, PAL and LTR, and the content of acetyl-CoA, and significantly increased the concentrations of phenylethyl alcohol, octanoic acid, isoamyl acetate, phenylethyl acetate, ethyl hexanoate and ethyl caprylate during fermentation. Correlation analysis showed that there was a significant positive correlation between PAL, LTR, PK and acetyl-CoA and pyruvic acid formation. Path analysis revealed that the addition of amino acids affected the metabolism of pyruvate to alcohols, acids and esters to some extent.

The Use of γ-Aminobutyric Acid-Producing Saccharomyces cerevisiae SC125 for Functional Fermented Beverage Production from Apple Juice

The development of functional fermented beverages enriched with γ-aminobutyric acid (GABA) has been pursued because of the health benefits of GABA; however, few studies have described GABA production by yeast. Therefore, this study aimed to produce fermented apple beverages enriched with GABA produced by Saccharomyces cerevisiae SC125. Golden Delicious apples were fermented by S. cerevisiae SC125 to produce a novel functional beverage; commercial yeast was used as the control. The GABA, organic acid, and volatile compound content during the fermentation process was investigated by high-performance liquid chromatography and headspace solid-phase microextraction/gas chromatography-mass spectrometry. A yield of 898.35 ± 10.10 mg/L GABA was achieved by the efficient bioconversion of L-monosodium glutamate. Notably, the S. cerevisiae SC125-fermented beverage produced several unique volatile compounds, such as esters, alcohols, 6-decenoic acid, and 3-hydroxy−2-butanone, and showed significantly enhanced contents of organic acids, including malic acids, citric acid, and quinic acid. Sensory analysis demonstrated that the S. cerevisiae SC125-fermented apple beverage had improved aroma, flavor, and overall acceptability. In conclusion, a fermented functional apple beverage containing GABA was efficiently produced using S. cerevisiae SC125.