Re-creating the flavor of soy sauce, and squeezing guacamole to keep it fresh

Decoding the flavors of soy sauce

Soy sauce has been a staple of Asian cuisines for thousands of years, and its flavor and versatility have placed it in kitchen pantries around the world. But which chemical compounds give it that tantalizing taste? Until now, the chemical makeup of soy sauce’s flavor profile had not been fully decoded.

When researchers from the Technical University of Munich (TUM) combined key soy sauce compounds that had been identified in the past, their chemical cocktail lacked many of the salty, umami, and bitter notes that give soy sauce its unique taste. Something was missing. The researchers began the search for the condiment’s more elusive flavor molecules, a task that’s a bigger undertaking than one might expect. Foods are typically made up of hundreds of thousands of compounds, explains Corinna Dawid, a food chemist on the TUM team, but only a tiny fraction of them contribute to the flavor profile.

With a combination of liquid chromatography, mass spectrometry, and the expertise of 27 trained human taste testers, Dawid and her colleagues rigorously identified a total of 48 compounds that can be used to mimic the flavor of soy sauce (J. Agric. Food Chem. 2022, DOI: 10.1021/acs.jafc.2c01688). Fourteen of them—peptides formed during the fermentation process—don’t actually impart any distinct flavor of their own. Rather, they enhance the salty and umami flavors already present and influence the sauce’s richness and mouthfeel, also known as the kokumi sensation.

“With those compounds we identified, you can explain every kind of flavor of soy sauce,” Dawid tells Newscripts, although the compounds’ individual concentrations may vary between different brands. And this time, when Dawid and her colleagues attempted to re-​create soy sauce with these new sets of compounds, not even trained taste testers were able to tell them apart from the real stuff.

Guacamole under pressure

A good soy sauce should be a rich brown color, but that hue means trouble for guacamole. You can blame that on polyphenol oxidase (PPO), an enzyme present in avocados as well as many other fruits and vegetables.

When produce is cut—or smashed—its damaged cells release phenolic compounds that are polymerized with the help of PPO into bitter-tasting, brown pigments. It’s like the crud synthetic chemists often see at the bottom of their reaction flask, explains Subha Das, a chemist and food enthusiast at Carnegie Mellon University.

But, like all enzymatic reactions, this one can be stopped with a little chemistry know-how, Das says. For the home cook, a generous squeeze of lime over their guacamole can do the trick because enzymes aren’t fond of highly acidic environments. For commercial avocado products, acid is also used, but it isn’t enough to safeguard the food from browning and bacterial growth for more than a few hours, says Thambaramala Gamage, a senior research scientist at the Commonwealth Scientific and Industrial Research Organisation (CSIRO). Heat pasteurization could accomplish both, she tells Newscripts, but it can also drastically change the avocado’s flavor and appearance in unpleasant ways.

What’s the solution, then, if not acid or heat? Pressure. Food manufacturers subject avocado products to a few minutes of high pressure—specifically 600 MPa, which is six times the pressure found at the deepest part of the ocean. The pressure partially inactivates the enzymes by changing their structure, Das explains. Then, companies transfer the food into vacuum-sealed bags to prevent the remaining enzymes from wreaking havoc—no preservatives needed.

Science Twitter learned all about this trick when Nathan Kilah, a chemist at the University of Tasmania, tweeted this awesome science fact back in July after learning about it from a colleague. He tells Newscripts in an email: “Sharing quirky and fun chemistry through Twitter is a great way to reach a broad audience, get them to think and ask questions, and to further their understanding and appreciation of our science.”

Please send comments and suggestions to newscripts@acs.org.