# Metabolomic Analysis of Fermented Nori Powders: Divergence of Betaine Structural Analogs Production by Three Types of koji Fungal Fermentation

## TL;DR

Fermenting seaweed with different koji fungi produces distinct bioactive compounds, including betaine analogs, which could lead to healthier seaweed products.

## Contribution

The study reveals species-specific metabolic strategies of koji fungi in producing betaine structural analogs from seaweed.

## Key findings

- Yellow koji fungus uniquely produces stachydrine, while white and red koji fungi do not.
- Fermentation shifts methylation balance to support methyl-dependent pathways.
- Each koji fungus employs distinct metabolic strategies for betaine analog production.

## Abstract

Fermenting seaweed with koji fungi transforms its chemical composition, generating bioactive compounds absent in the raw material. We previously reported that the fungal fermentation of the edible red alga Pyropia yezoensis (Nori) produces betaine structural analogs (such as betaine, stachydrine, and carnitine), which are of particular interest because of their physiological roles and potential health benefits. Using metabolomic profiling, we compared non-fermented Nori with powders fermented by three industrially important fungi: Aspergillus luchuensis mut. kawachii (white koji fungus), Aspergillus oryzae (yellow koji fungus), and Monascus purpureus (red koji fungus). All fermentations enhanced the levels of betaine and carnitine, but stachydrine production was unique to the yellow koji fungus. Precursor patterns revealed distinct metabolic strategies: the yellow koji fungus exhibited an intermediate detectable choline oxidation route and strong proline methylation, the white koji fungus rapidly converted choline without intermediate accumulation, and the red koji fungus favored carnitine and proline but produced little stachydrine. Fermentation also shifted the methylation balance toward a state that supports methyl-dependent pathways. These findings reveal clear species-specific strategies for the production of betaine structural analogs, providing a mechanistic basis for understanding the metabolic divergence among koji fungi and guiding the targeted design of functional seaweed products.