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Tuber melanosporum, known as the black diamond of cuisine, is highly appreciated for its unique and characteristic aroma, which is mainly due to its volatile organic sulfur-containing compounds (VOSCs). In this work, by adding 5 g/L  l-methionine to the fermentation medium, the activities of aminotransferase and α-ketoacid decarboxylase were significantly enhanced by 103 and 250 %, respectively, while the activities of alcohol dehydrogenase and demethiolase were decreased by 277 and 39 %. Then, the six VOSCs, i.e., methanethiol (MTL), dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), 3-(methylthio)propanal (methional), and 3-(methylthio)-1-propanol (methionol), were first detected in the submerged fermentation of T. melanosporum. These results indicated that the biosynthesis of VOSCs was triggered by aminotransferase and α-ketoacid decarboxylase. The production of methional and methionol increased with the increased concentrations of l-methionine (i.e., 5, 10, 15, and 20 g/L) before day 4 of the culture protocol, and methionol was the major product in the Ehrlich pathway. The production of MTL was significantly decreased after day 4 with a significantly increased DMDS, and DMDS was the major product of the demethiolation pathway. Compared with the demethiolation pathway with a total flux of sulfur of 11.33–24.32 μM, the Ehrlich pathway with a total flux of sulfur of 6,149–10,330 μM was considered the major pathway for the biosynthesis of VOSCs. This is the first report linking the metabolism of l-methionine to the biosynthesis of VOSCs by the Ehrlich and demethiolation pathways during the submerged fermentation of T. melanosporum. [ABSTRACT FROM AUTHOR]

Uniform design and partial least squares regression were adopted to quantitatively analyze the effects of plant oil and fatty acid as well as their addition amount and addition time on the performance of Tuber melanosporum submerged fermentation. The regression models showed the optimal scheme was the addition of 1.2 mL soybean oil on day 9, which was validated by experiment. The maximal biomass of 25.89 ± 1.01 g/L and extracellular polysaccharides (EPS) production of 6.51 ± 0.68 g/L were obtained, which were enhanced by 18.5% and 86%, respectively. Palmitic acid was identified to be the key component to stimulate the cell growth and EPS biosynthesis, and stearic acid was beneficial for the production of intracellular polysaccharides. Not only the biomass but also EPS production obtained in this work are the highest reported in the batch fermentation of truffle. [ABSTRACT FROM AUTHOR]

Abstract: A novel method using Plackett–Burman design (PBD) coupled with Draper–Lin small composite design (SCD) and desirability function (DF) was developed to optimize Tuber melanosporum fermentation medium. Firstly, sucrose, yeast extract, peptone and Mg2+ were identified to be key medium components by PBD. Secondly, in order to evaluate the relationships between responses and the identified key components, mathematical models were developed by SCD. Finally, by using DF, the responses were optimized simultaneously and the optimal concentration was located to be 73g/L sucrose, 11g/L yeast extract, 8g/L peptone, and 46mM Mg2+. Under the identified optimal conditions, the maximal biomass, the production of extracellular (EPS) and intracellular (IPS) polysaccharides was 25.10±0.12g/L, 3.88±0.23g/L and 2.87±0.32g/L, respectively, which agreed with the predicted values well. Compared with the basic medium, the biomass, the production of EPS and IPS was enhanced by 54.4%, 71.7% and 124.2%, respectively. [Copyright &y& Elsevier]

Abstract: For the first time, a fed-batch fermentation process of Tuber melanosporum was developed for the efficient production of bioactive mycelia and Tuber polysaccharides. Each 1.67g/L of peptone and 8.33g/L of yeast extract were added on day 3, 6, and 9, respectively, and sucrose was fed to maintain its concentration around 35–5g/L when its residual level decreased to 10–5g/L. Then, the maximal biomass, the production of extracellular polysaccharides (EPS) and intracellular polysaccharides (IPS) reached 53.72±2.57g DW/L, 7.09±0.62 and 4.43±0.21g/L, respectively. Compared with the batch culture conducted in the enriched medium, the biomass, the production of EPS and IPS were enhanced by 55.8%, 222.3% and 103.2%, respectively. Not only the cell density but also the production of EPS and IPS were the highest ever reported in truffle fermentation, and the biomass was also the highest as ever reported in mushroom fermentation. [Copyright &y& Elsevier]

Abstract: Besides the identified key factors of pH-shift from 3.0 to 4.5 on day 4 and dissolved oxygen tension (DOT) shift from 25 to 10% on day 6, lower shear stress was also demonstrated to be a key factor in scaling-up the fed-batch fermentation of the medicinal mushroom Ganoderma lucidum from a shake flask to a stirred-tank bioreactor. The maximal biomass (22.62g/L), intercellular polysaccharide production (4.74g/L), and ganoderic acid production (798.0mg/L) were attained at a low impeller tip speed of 1.234m/s. Based on the identified key factors of pH-shift, DOT-shift and lower shear stress, the fed-batch fermentation of G. lucidum was successfully step-wise scaled-up from 7.5- to 200-L stirred-tank bioreactor. Through the qualitative and quantitative side-by-side comparison of G. lucidum growth and metabolites accumulation, it was concluded that the comparability of the fed-batch fermentation process were well controlled and the products were maintained during the process scale-up. [ABSTRACT FROM AUTHOR]

Abstract: During the submerged fermentation of medicinal mushroom Chinese truffle Tuber sinense, there was no significant effect of metal ion on the cell growth and the production of intracellular polysaccharides, while metal ion and its concentration significantly affected the production of extracellular polysaccharides (EPS). By using the approach of “one-variable-at-a-time”, 50mM Mg2+ was identified to be the most favorable for EPS production, and the next was 10mM K+. A mathematical model, constructed by response surface methodology combination with full factorial design, was applied to study the synergic effect of Mg2+ and K+. EPS production reached its peak value of 5.86g/L under their optimal combination of 30mM Mg2+ and 5mM K+ predicted by the model, which was higher by 130.7% compared with the basal fermentation medium without metal ion. The validation experiment showed the experimental values agreed with the predicted values well. EPS production obtained in this work was the highest reported in the culture of T. sinense. [Copyright &y& Elsevier]