Relationship between pellet formation by Aspergillus oryzae strain KB and the production of ß-fructofuranosidase with high transfructosylation activity.

Aspergillus oryzae KB produces two ß-fructofuranosidases (F1 and F2). F1 has high transfructosylation activity (Ut) to produce fructooligosaccharides. F2 has high hydrolysis activity (Uh), releasing glucose and fructose. It is desirable to selectively produce F1, which can be used for production of fructooligosaccharides. Here, the relationship between filamentous pellet size and selective production of F1 in liquid culture was investigated. Our finding revealed that: (i) The mean particle size of pellets (5.88 ± 1.36 mm) was larger, and the ratio of Ut to Uh was improved (Ut/Uh = 5.0) in 10% sucrose medium compared with 1% sucrose medium (pellet size = 2.60 ± 0.37 mm; Ut/Uh = 0.96). (ii) The final culture pH of the 1% sucrose medium was 8.7; on controlling the pH of 1% sucrose medium at 5.0, increased pellet size (9.69 ± 2.01 mm) and Ut/Uh (7.8) were observed. (iii) When 3% glycerin was used as carbon source, the pellet size decreased to 1.09 ± 0.33 mm and Ut/Uh was 0.57. (iv) In medium containing 1% sucrose, the pellet size was dependent on the number of spores used in the culture inoculum, but, in these experiments, Ut/Uh was almost constant (1.05 ± 0.08). Collectively, the data show that the value of Ut/Uh is proportional to the pellet size when liquid culture of A. oryzae strain KB is performed in some conditions (such as in the presence of high sucrose concentration, low pH, or added Tween surfactant), but in other conditions Ut/Uh is independent of pellet size.

Effects of nonionic surfactants on pellet formation and the production of ß-fructofuranosidases from Aspergillus oryzae KB.

Aspergillus oryzae KB produces two ß-fructofuranosidases (F1 and F2). F1 has high transferring activity and produces fructooligosaccharides from sucrose. Mycelial growth pellets were altered by the addition of Tween 20, 40 and 80 (HLB=16.7, 15.6 and 15.0, respectively) in liquid medium cultures to form small spherical pellets. The particle size of the pellets decreased with the HLB value, which corresponds to an increase in surfactant hydrophobicity. Selective F1 production and pellet size were maximized using Tween 20. Adding polyoxyethylene oleyl ethers (POEs) with various degrees of polymerization (2, 7, 10, 20 and 50: HLB=7.7, 10.7, 14.7, 17.2 and 18.2, respectively) was investigated. A minimum mean particle size was obtained using a POE with DP=10, HLB=14.7. The POE surfactants had little effect on the selective production of F1. The formation of filamentous pellets depended on the surfactant HLB value, and F1 enzymes were produced most efficiently using Tween 20.