Effect of pepA deletion and overexpression in Aspergillus luchuensis on sweet potato shochu brewing

Impact of solid-state saccharification on the flavor of rice-flavor baijiu

Rice-flavor baijiu is a traditional Chinese liquor. The flavor profile and volatiles presented with or without the solid-state saccharification (SSS) were investigated to reveal the effects of SSS process on the quality of rice-flavor baijiu. The liquor prepared with SSS had a sweet flavor. It contained significantly higher contents of β-phenylethyl alcohol, β-phenylethyl acetate, and ethyl lactate with odor active value of >1. The liquor prepared without SSS had a cheese-like flavor. It was confirmed that the cheese-like flavor derived from butanoic acid was only detected in the liquor prepared without SSS. SSS facilitated the biosynthesis of β-phenylethyl alcohol and ethyl lactate by supplying a large amount of phenylalanine and lactic acid at the initial stage of fermentation, and it prevented contamination. These results indicated that the SSS process contributed to produce the characteristic flavor compounds of rice-flavor baijiu. PRACTICAL APPLICATION: Solid-state saccharification (SSS) process of rice-flavor baijiu contributes not only in brewing, but also in the production of the characteristic flavor compounds and the repression of the off-flavor derived from the contamination. Therefore, SSS is a critical process to control the flavor of rice-flavor baijiu.

Genetic Manipulation and Transformation Methods for Aspergillus spp

Species of the genus Aspergillus have a variety of effects on humans and have been considered industrial cell factories due to their prominent ability for manufacturing several products such as heterologous proteins, secondary metabolites, and organic acids. Scientists are trying to improve fungal strains and re-design metabolic processes through advanced genetic manipulation techniques and gene delivery systems to enhance their industrial efficiency and utility. In this review, we describe the current status of the genetic manipulation techniques and transformation methods for species of the genus Aspergillus. The host strains, selective markers, and experimental materials required for the genetic manipulation and fungal transformation are described in detail. Furthermore, the advantages and disadvantages of these techniques are described.

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.