Japanese food chemists have created a substance that tastes like salt but contains no sodium, the element in table salt that is believed to raise the blood pressure of susceptible individuals. The scientists say the substance shows promise as a seasoning agent for use by people trying to lower their sodium intake.

Although the salty substance has not been tested for safety, its chemical nature suggests that it is unlikely to pose a hazard.

Like aspartame, the newly marketed artificial sweetener, it is made from amino acids, naturally occurring substances that, among other things, are the building blocks of proteins.

The discovery was reported to the International Chemical Congress of Pacific Basin Societies meeting here last week by three researchers from Hiroshima University's department of fermentation technology. In Japan, as throughout much of the Orient, fermentation is commonly used to produce foods.

Hideo Okai, a member of the team, said the salty substance was discovered in the course of analyzing the fermentation products of casein, the chief protein in milk. Like all proteins, casein consists of a long chain of amino acids. Fermentation, a form of digestion carried out by bacteria, breaks the chains into shorter segments called peptides.

Okai said the researchers were trying to identify the bitter-tasting peptides in fermented casein when they stumbled upon peptides that tasted salty. But they also had a taste that the Japanese call umami; this is the flavor associated with MSG, or monosodium glutamate.

Surprised to find a salty peptide and recognizing its potential value, the Hiroshima chemists synthesized various similarly constructed peptides in the hope of producing one that was purely salty. They found two, one of which was about equal in saltiness, gram for gram, to sodium chloride, and the other of which was almost half again saltier.

Both consist of two amino acids. The saltier one links lysine and taurine. The equally salty one, which is seen as more commercially promising because it can be substituted quantity-for-quantity for salt, links ornithine and taurine. It is called L-ornithyltaurine.

Okai said that while L-ornithyltaurine is promising, it is not likely to be a perfect replacement for salt. He said it probably would suffer the same instability in liquids that afflicts aspartame, the sweet peptide.

Depending on which other substances are present and on the amount of heat, peptides are prone to break down or to link up with other molecules. In either case, the molecules lose the characteristic shape that is believed to trigger the appropriate sensation in taste buds.