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Enzymes show the way to healthy salt-free soy sauce

By Stephen Daniells , 12-May-2010

Salt-free soy sauce may be attained by fermenting soybeans with Aspergillus oryzae, and the resulting product may even be able to reduce blood pressure, says a new Japanese study.

Scientists from Japan’s Fukuoka Soy Sauce Brewing Company report that the salt-free soy sauce produced significant reduction in blood pressure when fed to spontaneously hypertensive rats over a 13 week period.

Indeed, the eventual reductions in systolic and diastolic blood pressure in the animals fed the salt-free soy sauce were 27 and 20 mmHg, compared with the control group, report the researchers in the Journal of Food Science.

“A new fermented soybean product, salt-free soy sauce, exhibited potent antihypertensive effect in spontaneously hypertensive rats,” wrote the researchers.

“In addition to this favourable effect, the salt-free soy sauce product was also of benefit for hypertensive subjects who could take it without any consideration of excess salt-intake,” they added.

Salt is of course a vital nutrient and is necessary for the body to function, and the World Health Organization recommends that per capita daily salt consumption should not exceed five grams. However, with the average daily salt (NaCl) consumption in the western world estimated to be between 10 and 12 grams, consumers and some governments have imposed pressure on food manufacturers to reduce the salt content in their formulations - 60 to 80 per cent of salt consumption comes from packaged foods rather than salt added at the table.

The new soy sauce is covered by the Japanese Patent 2964370 held by the company. According to the new findings, not only could it help people reduce their dietary salt intake but also may actively help reduce blood pressure.

Study details

Using rats genetically engineered to develop hypertension, the researchers fed them either the salt-free soy sauce at a daily dose of 200 mg per kg of body weigh, or water, or normal soy sauce, for 13 weeks.

Blood pressure reducing effects in the salt-free soy sauce group were observed starting at week five and continued until the end of the study, compared with the control groups.

The Fukuoka scientists point to the specific protein content of this salt-free soy sauce, with small peptides of Ile-Phe, Phe-Ile, and Ala-Pro found to be present, but absent in traditional soy sauce. The peptides are said to have angiotensin converting enzyme (ACE)-inhibitory activity. ACE inhibitors work by inhibiting the conversion of angiotensin I to the potent vasoconstrictor, angiotensin II, thereby improving blood flow and blood pressure.

However, no differences were observed between any of the groups regarding the angiotensin I-converting enzyme activities in the blood. They did note that the salt-free soy sauce group showed “higher vessel tone”.

“We speculated that the higher vascular response in salt-free soy sauce group may be caused by salt-free soy sauce-induced preventive effect against age-related sclerosis or reduced vessel tone,” said the researchers.

“This finding strongly demonstrates that the developed salt-free soy sauce would be greatly beneficial for health and useful for health-related industries,” they concluded.

Source: Journal of Food Science
Volume 75 Issue 4, Pages H129-H134, doi: 10.1111/j.1750-3841.2010.01599.x
“Antihypertensive Effect of Salt-Free Soy Sauce, a New Fermented Seasoning, in Spontaneously Hypertensive Rats”
Authors: T. Matsui, X-L. Zhu, K. Shiraishi, T. Ueki, Y. Noda, K. Matsumoto

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