Abstract
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.
Highlights
Fructo-oligosaccharides (FOS), such as 1-kestose (GF2), nystose (GF3), 1-fructofuranosyl nystose (GF4) and 1,1,1,1-kestohexose (GF5), are small dietary fibers with low caloric value and high prebiotic effects [1,2,3,4]
In order to explore the effect of stirring speed on dissolved oxygen (DO) and FOS production, a batch culture using A. pullulans ipe-3 cultivated in a 2.7-L bioreactor was first performed under the following conditions: pH, 5.5; aeration rate, 1.8 L/min; temperature, 25 ◦C; stirring speed, 600 rpm (Figure 1)
After culturing for 12 h, the FOS concentration decreased until the end of fermentation; the DO concentration fell to near zero, while the cell growth, enzyme biosynthesis and fructose release increased until the end of fermentation
Summary
Fructo-oligosaccharides (FOS), such as 1-kestose (GF2), nystose (GF3), 1-fructofuranosyl nystose (GF4) and 1,1,1,1-kestohexose (GF5), are small dietary fibers with low caloric value and high prebiotic effects [1,2,3,4]. The FOS yield when using the one-stage process is influenced by factors such as temperature, aeration rate, partial pressure of oxygen, and stirring speed [4,13,19,20]. During the fermentation production of FOS using whole cells (onestage process) from A. pullulans, the FOS yield was found to reach 64.1 ± 0.0 g FOS/g sucrose when the stirring speed and temperature were 385 rpm and 32 ◦C, respectively, regardless of the aeration rate and partial pressure of oxygen [4]. The dissolved oxygen (DO) concentration, which is influenced by the stirring speed, aeration rate, partial pressure of oxygen, and temperature, is an influencing factor in the fermentative synthesis of metabolite products by fungi that has been found to have a significant effect on Aureobasidium spp. It is necessary to better characterize the role of DO during one-stage production of FOS
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