Metabolomics Reveal Optimal Grain Preprocessing (Milling) toward Rice Koji Fermentation

Area of Science:

• Food Science
• Metabolomics
• Biotechnology

Background:

• Koji, a fermented rice product, is crucial in Asian food production.
• Rice substrate preprocessing significantly impacts koji fermentation outcomes.
• Understanding metabolite profiles is key to optimizing koji quality.

Purpose of the Study:

• To investigate the effect of varying degrees of milling (DOM) on rice koji metabolites.
• To identify optimal rice substrate preprocessing for enhanced koji fermentation.
• To correlate metabolite profiles with hydrolytic enzyme activities.

Main Methods:

• Time-correlated mass spectrometry (MS)-based metabolic profiling.
• Analysis of primary and secondary metabolites in rice koji.
• Enzyme activity assays for hydrolytic enzymes.

Main Results:

• 67 discriminant metabolites were identified across different DOM samples.
• DOM 5-7 koji showed higher carbohydrate, lipid metabolites, and enzyme activity at 36h.
• DOM 0 koji had higher antioxidant metabolites (flavonoids, phenolic acids) at 96h.

Conclusions:

• Rice substrate preprocessing between DOM 5 and 7 is optimal for koji fermentation.
• This optimal DOM yields koji rich in organoleptic, nutritional, and functional metabolites.
• The findings rationalize substrate preprocessing steps for commercial koji production.