Katsuobushi (dried bonito) itself has no anti-hypertensive activity

Katsuobushi (dried bonito) Oligopeptide is food derived from Katsuobushi protein by enzymatic reaction. However, eating Katsuobushi itself does not show any anti-hypertensive activity. The reason is that peptides derived from different enzymes show different biochemical activities even if obtained from the same protein. When you take Katsuobushi itself, it is hydrolyzed by digestive enzymes such as pepsin, trypsin and chymotrypsin, secreted from stomach or intestine. Katsuobushi Oligopeptide, on the other hand, is made by an enzyme called gthermolysin (it is secreted by Bacillus thermoproteolyticus, one of Bacillus natto line)h. Katsuobushi Oligopeptide is never produced in human body because no enzyme, which has the same activity with thermolysin, is available in digestive systems.
Enzymatic digests of Katsuobushi by pepsin, trypsin or chymotrypsin indicated any anti-hypertensive activity in animal experiment (Table 1).

Table 1: Effect of enzymatic digests of Katsuobushi on lowering blood pressure

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Enzyme Effect of lowering
blood pressure

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Thermolysin
(Katsuobushi Oligopeptide) 30 mmHg
Pepsin
(digestive enzyme secreted in stomach) 0
Trypsin
(digestive enzyme secreted in intestine) 0
Chymotrypsin
(digestive enzyme secreted in intestine) 0

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Thermolysin is a safe enzyme, used for food processing such as meat softening or making seasoning (aspartame). It is allowed to use as a food additive in Japan.


2, Katsuobushi Oligopeptide made from natural bonito (non-dried bonito) does not show anti-hypertensive activity either

Thermolysin digests of non-dried bonito protein obtained no oligopeptides with anti-hypertensive activity.
The reason is assumed as follows:
During a Katsuobushi (dried bonito) manufacturing process, bonito meat is treated with special fungi for a while. It seems that proteases secreted from the fungi are closely contributed to ACE-inhibitory activity.