Fermentative Production of Fructo-Oligosaccharides Using Aureobasidium pullulans: Effect of Dissolved Oxygen Concentration and Fermentation Mode.

Fructo-oligosaccharides (FOS) are prebiotics with numerous health benefits. So far, the dissolved oxygen (DO) concentration control strategy for fermentative production of FOS is still unknown. In order to improve FOS production, the effects of DO concentration and fermentation mode on FOS using Aureobasidium pullulans were investigated in this study. The greatest FOS production (123.2 ± 6.2 g/L), with a yield of 61.6% ± 3.0% (g FOS/g sucrose), was obtained in batch culture under high DO concentration. Furthermore, repeated-batch culture revealed that enzyme production and FOS production were not closely associated with cell growth. By keeping the DO concentration above 5% in the repeated-batch culture, a maximum FOS concentration of 548.3 ± 37.4 g/L and yield of 68.6% ± 2.6% (g FOS/g sucrose) were obtained, which were 3.45% and 11.4% times higher than those obtained in the batch culture without DO control, respectively. Additionally, the ratios of 1-fructofuranosyl nystose (GF4) and 1,1,1,1-kestohexose (GF5) were 33.8% and 23.2%, respectively, in the product of repeated-batch culture, but these compounds were not detected in batch culture. Thus, it can be concluded that the DO concentration affects not only the yield of FOS but also the composition of FOS with different degrees of polymerization, which is the key factor in the fermentative production of FOS with a high polymerization degree.

A sustainable pH shift control strategy for efficient production of ß-poly(L-malic acid) with CaCO3 addition by Aureobasidium pullulans ipe-1.

ß-poly(L-malic acid) (PMLA) has attracted industrial interest for its potential applications in medicine and other industries. For a sustainable PMLA production, it requires replacing/reducing the CaCO3 usage, since the residual CaCO3 impeded the cells' utilization, and a large amount of commercially useless gypsum was accumulated. In this study, it was found that more glucose was converted into CO2 using soluble alkalis compared with CaCO3 usage. Moreover, since the high ion strength and respiration effect of soluble alkalis also inhibited PMLA production, they could not effectively replace CaCO3. Furthermore, comparing the fermentations with different neutralizers (soluble alkali vs. CaCO3), it was found that the differential genes are mainly involved in the pathway of starch and sucrose metabolism, pentose and glucuronate interconversions, histidine metabolism, ascorbate and aldarate metabolism, and phagosome. In detail, in the case with CaCO3, 562 genes were downregulated and 262 genes were upregulated, and especially, those genes involved in energy production and conversion were downregulated by 26.7%. Therefore, the irreplaceability of CaCO3 was caused by its effect on the PMLA metabolic pathway rather than its usage as neutralizer. Finally, a combined pH shift control strategy with CaCO3 addition was developed. After the fermentation, 64.8 g/L PMLA and 38.9 g/L biomass were obtained with undetectable CaCO3 and less CO2 emission. KEY POINTS: • The effect of CaCO3 on PMLA metabolic pathway resulted in its irreplaceability. • A pH shift control strategy with CaCO3 addition was developed. • Undetectable CaCO3 and less CO2 emission were detected with the new strategy. Graphical abstract.

Membrane-assisted ß-poly(L-malic acid) production from bagasse hydrolysates by Aureobasidium pullulans ipe-1.

Membrane-assisted ß-poly(L-malic acid) (PMLA) production from bagasse hydrolysates was developed. For the first time, it was found that mixing the acid and enzyme hydrolysates was unfavorable for PMLA production because too high hexose: pentose ratio and glucose concentration in the mixed sugar could inhibit the assimilation of pentose. 120 g/L sugar concentrations in the acid hydrolysate was suitable for PMLA production with 23.2 g/L PMLA and 34.7 g/L biomass. Moreover, an integrated membrane process consisting of ultrafiltration, nanofiltration and reverse osmosis membranes could concentrate sugars and adjust acetic acid concentration prior to fermentation of lignocellulosic sugars. Meanwhile, it was found that 1.46 g/L acetic acid was preferred for PMLA production from enzyme hydrolysate or sole glucose which respectively increased PMLA production and cell growth by 25.4% and 5.9% from sole glucose, while it showed no significant enhancement in PMLA production with a higher cell growth and productivity from acid hydrolysate.