Methods for producing soy sauce having hypotensive effects, such as a method of adding an inhibitor of the renin-angiotensin system (e.g., nicotianamine), an antiadrenergic agent (e.g., γ-aminobutyric acid), an accelerator of nitric oxide production (e.g., isoflavone), a diuretic substance, a vasodilator substance (e.g., a calcium antagonist), or the like to soy sauce in attempts to attain hypotensive effects from a hypotensive agent (see, for example, Patent Documents 1 and 2), a method of adding a polyphenol (see, for example, Patent Document 3), a method of adding a peptide having angiotensin-I-converting enzyme-inhibitory activity (see, for example, Patent Document 4), and a method of generating and accumulating significant amounts of γ-aminobutyric acids in the soy sauce moromi mash liquid with the use of γ-aminobutyric acid-enriched soybean germs (see, for example, Patent Document 5), have heretofore been known.
However, these techniques are disadvantageous in terms of the necessity of separate production of hypotensive agents, and such hypotensive agents may disadvantageously cause deterioration of soy sauce flavor.
In soy sauce manufacturing, it is necessary for soy sauce manufacturers to work in a dedicated manner to attain high-quality koji, and such high-quality koji is required to have potent enzymatic activity (protease activity, in particular). This is because soy sauce is a seasoning mainly composed of amino acids, and it is necessary to degrade proteins into peptides at first and then thoroughly degrade peptides into amino acids. In the soy sauce industry, therefore, manufacturers search for koji mold that secretes potent protease, adequately treat raw materials for koji to thoroughly develop and propagate koji mold, and intend to maximize enzymatic activity.
In conventional soy sauce manufacturing techniques, accordingly, minimization of protease secretion by koji mold during koji-making and utilization of soy sauce koji having a low protease activity for the production of soy sauce having hypotensive effects are unknown.
Meanwhile, a method of subjecting soy sauce koji to heated digestion at 45° C. to 60° C. for 3 to 8 hours to shorten the soy sauce production time (i.e., fast-brewing) is known (see, for example, Patent Document 6).
Specifically, in the above method, soy sauce koji with the accelerated protease-producing ability is used, and such koji is subjected to heated digestion to rapidly degrade moromi mash components, and, in particular, proteins, thereby rapidly brewing soy sauce in which 50% of total nitrogen is accounted for by α-amino nitrogen and which is rich in aroma.
However, an increase of peptide (non-α-amino nitrogen) content in soy sauce cannot be expected from the above method.
In soy sauce manufacturing techniques, accordingly, increasing peptide content to obtain soy sauce having hypotensive effects is unknown.
Meanwhile, peptides are known to generally have endogenous opioid effects, immunoregulatory effects, effects of accelerating calcium absorption, effects of inhibiting elevated cholesterol, angiotensin-I-converting enzyme (ACE)-inhibitory activity, antioxidative effects, anti-cancer effects, and other effects (see, for example, Patent Document 7 and Non-Patent Document 1).
Also, given dipeptides (i.e., Gly-Tyr and Ser-Tyr) are known to have angiotensin-I-converting enzyme-inhibitory activity and hypotensive effects (hereafter, may be occasionally referred to as “hypotensive peptide Gly-Tyr” or “hypotensive peptide Ser-Tyr”) (see, for example, Non-Patent Document 2).
When patients with high normal blood pressure and patients with mild hypertension ingest low-salt soy sauce containing 48 μg/ml and 32 μg/ml hypotensive peptides Gly-Tyr and Ser-Tyr, respectively, for 8 continuous weeks, the systolic blood pressure and the diastolic blood pressure of such subjects are significantly lowered compared with the case when they ingest general low-salt soy sauce (see, for example, Non-Patent Document 3).
If significant amounts of peptides, and, in particular, hypotensive peptides Gly-Tyr and Ser-Tyr, are integrated into soy sauce during production and soy sauce containing large quantities thereof can be obtained, accordingly, soy sauce containing no hypotensive agent and having hypotensive effects can be produced. While such techniques are considered to be a great contribution to the soy sauce industry, they are unknown.
When soy sauce koji is mixed with an aqueous common salt solution, in general, the enzymes of koji satisfactorily function, satisfactorily degrade proteins and starch, and produce very slimy, thick moromi mash. Since peptides generated and accumulated in the liquid of such moromi mash are further degraded into amino acids during the process of fermentation and maturation of the moromi mash, such peptides gradually disappear as moromi mash maturation advances.
Accordingly, it is difficult to retain such peptides, and, in particular, hypotensive peptides Gly-Tyr and Ser-Tyr, until the final form of a soy sauce product is obtained.
Also, soy sauce cake obtained by squeezing the soy sauce moromi mash is known to contain substances exhibiting angiotensin-I-converting enzyme-inhibitory activity (hereafter, may be referred to as “ACE inhibitory activity”) (see, for example, Patent Document 7).
Substances exhibiting ACE inhibitory activity are peculiar to soy sauce cake, and such substances are not found in soy sauce. Accordingly, hypotensive effects attained by the ACE inhibitory activity of peptides contained in general soy sauce are very faint, and it is difficult to impart hypotensive effects to soy sauce not containing a hypotensive agent.