Interestingly, the formations of furan with magnesium sulfate and calcium sulfate were significantly lower than the control. As fermentation days passed, it was confirmed that the levels of furan were reduced with magnesium sulfate and calcium sulfate. In particular, 0.05 M, 0.1 M, and 0.2 M of magnesium sulfate had significantly decreased furan levels compared to the control (90%, 83%, and 83%, respectively). Then, furan concentrations had also descended with calcium sulfate (86%, 90%, 91%, respectively).
When the overall tendency was examined, it suggested that the chelate effect caused by calcium and magnesium ions was the reason for the reduction of furan. The characteristic of chelate explains the specific way that ions and molecules bind to metal ions.
The Chelating ligands show enhanced affinity for a metal ion compared to the affinity of a collection of similar non-chelating ligands for the same metal. Ethylenediaminetetraacetic acid (EDTA), a representative material using this principle, generates a stable chelate compound when combined with calcium and magnesium ions.
In the soy sauce model system with calcium and magnesium ions added, it seemed that the residue of amino acids and carbohydrates was generated by A. oryzae and then congregated around these metal ions. As fermentation progresses, many residues were expected to bind around the metal ions. Due to these reactions, fewer precursors of furan formed, and the concentration of furan also decreased significantly compared to in samples with other food additives and the control.