Anti-hypertensive substances in fermented soybean, natto

Area of Science:

• Biochemistry
• Food Science
• Enzymology

Background:

• Natto is a traditional Japanese fermented soybean food.
• Angiotensin-converting enzyme (ACE) plays a crucial role in blood pressure regulation.
• Investigating natural ACE inhibitors is important for developing antihypertensive agents.

Purpose of the Study:

• To investigate the presence and characteristics of angiotensin-converting enzyme (ACE) inhibitors in natto.
• To identify the fractions and types of ACE inhibitors present in natto.
• To assess the stability and inhibition modes of these natto-derived ACE inhibitors.

Main Methods:

• Extraction of natto components.
• Dialysis to separate high and low molecular weight inhibitors.
• Assay of ACE inhibitory activity (IC50 values).
• Determination of inhibitor stability across pH and temperature ranges.
• Analysis of inhibition kinetics (competitive and noncompetitive).

Main Results:

• Natto extracts exhibited significant ACE inhibitory activity (IC50: 0.4 mg/ml).
• The viscous fraction of natto showed stronger inhibitory activity than the bean extract.
• Two groups of inhibitors were identified: high molecular weight (protein, IC50: 0.12 mg/ml) and low molecular weight (ethanol-soluble).
• Low molecular weight inhibitors were stable up to 100°C and across a wide pH range.
• Two distinct low molecular weight inhibitors displayed competitive and noncompetitive inhibition modes.

Conclusions:

• Natto contains potent protein and non-protein ACE inhibitors.
• The identified ACE inhibitors are stable and exhibit different inhibition mechanisms.
• Natto's ACE inhibitory components hold potential for functional foods and therapeutic applications in managing hypertension.