Awamori fermentation test and 1-octen-3-ol productivity analysis using fatty acid oxygenase disruptants of Aspergillus luchuensis.

1-Octen-3-ol is a major aroma component of awamori, a traditional distilled liquor produced in Okinawa Prefecture, Japan. As 1-octen-3-ol is thought to affect the sensory properties of awamori, it is important to fully characterize the compound's biosynthetic pathway and control mechanism. We previously reported that the fatty acid oxygenase ppoC (ppo: psi-produced oxygenase) of Aspergillus luchuensis is directly involved in the production of 1-octen-3-ol in rice koji (Kataoka et al., J. Biosci. Bioeng., 129, 192-198, 2020). In the present study, we constructed A. luchuensis ppoD disruptants to characterize the role of ppo genes in 1-octen-3-ol biosynthesis. A small-scale awamori fermentation test was performed using ppoA, ppoC, and ppoD single disruptants (ΔppoA, ΔppoC, and ΔppoD, respectively), along with the parent strain, ΔligD. 1-Octen-3-ol was not detected in the distillate prepared using the ΔppoC strain. We conclude that A. luchuensis ppoC is the only 1-octen-3-ol-producing factor in the awamori brewing process. Because ΔppoA and ΔppoD slightly enhanced 1-octen-3-ol productivity, these two genes may play a role in negatively controlling 1-octen-3-ol biosynthesis.

Aspergillus luchuensis fatty acid oxygenase ppoC is necessary for 1-octen-3-ol biosynthesis in rice koji.

Awamori is a distilled spirit produced in Okinawa Prefecture, in southern Japan. Awamori contains the volatile organic compound 1-octen-3-ol, an important flavor component. Here, using solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GCMS), we demonstrate that the black koji mold Aspergillus luchuensis produces 1-octen-3-ol in rice koji. To examine the role of the fatty acid oxygenase genes ppoA and ppoC in 1-octen-3-ol biosynthesis by A. luchuensis, we constructed ppoA and ppoC disruptants, ΔppoA and ΔppoC, respectively, via protoplast-PEG transformation. No clear differences in growth and conidiation were observed between the transformants and the parent strain. Volatile compounds in rice koji prepared using these gene disruptants were analyzed by SPME-GCMS. The amount of 1-octen-3-ol contained in koji produced by the ΔppoA strain was the same as that produced by the parental strain. In contrast, although the ΔppoC strain grew on the rice koji, 1-octen-3-ol was not detected. These results indicate that ppoC is involved in 1-octen-3-ol biosynthesis in A. luchuensis.

Piceatannol is superior to resveratrol in promoting neural stem cell differentiation into astrocytes.

Piceatannol (3,3',4',5-trans-tetrahydroxystilbene) is a polyphenolic compound abundant in the seeds of passion fruit (Passiflora edulis). Piceatannol is an analogue of resveratrol (3,4',5-trans-trihydroxystilbene) and shares the structural motif and biological activities such as activation of SIRT1. Several studies have shown that piceatannol is more potent than resveratrol. In this study, we examined the effects of piceatannol on neural stem cell differentiation into astrocytes compared with those of resveratrol. At a concentration of 2.5 µM, piceatannol promoted astrocyte differentiation, while resveratrol had no effect at this concentration. Furthermore, we found that oral administration of piceatannol increased the number of astrocytes in the brains of adult mice, while resveratrol administration showed no effects. These results suggest that piceatannol has a superior effect to resveratrol in promoting astrocyte differentiation.