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Delayed Reaction: Inside the Retroaromatic Effect

Alexandra Voigt, Perfumer & Flavorist magazine

The flavor industry may want to start looking beyond a flavor's first impression, according to a recent study conducted by Christian Starkenmann and a team of colleagues at Firmenich.

The study utilized an existing concept described by noted French enologist Emile Peynaud in his book, The Taste of Wine: The Art and Science of Wine Appreciation. In the book, Peynaud describes the golden Sauvignon grape as “releasing an aromatic fruity odor 20–30 seconds after being swallowed.” Though the concept of delayed flavor perception is one familiar to the industry, Starkenmann et al., sought to examine the “unknown precursors” to the concept known as the retroaromatic effect.

The retroaromatic effect is the “delayed perception of retronasal odor,” which can occur 20–30 seconds after ingestion of food, and lasts up to three minutes following. The article summarizing Starkenmann et al.’s findings, "Olfactory Perception of Cysteine-S-Conjugates from Fruits and Vegetables," discusses the methodology and results of the study.1 In order to examine the interaction of saliva and sulfur compounds (referred to as the retroaromatic effect), three cysteine-S-conjugates that occur naturally in food products were selected and incubated in “sterile or crude saliva with Fusobacterium nucleatum, a mouth anaerobe, to follow the consumption of the precursor into volatile thiols."

Affect on Flavor Perception
In a recent interview with Perfumer & Flavorist magazine, Starkenmann explained that the team's research stems from an interest in onion powder and onion flavors due to their “naturally occurring odorless cysteine-S-conjugates that transform into volatile thiols in the mouth by microflora.” He noted, “The (onion and bell pepper) flavor was always very sharp, so we made some fractions. [This process is outlined in the published paper.] When we tested the odorless fractions, after a while we had an odor and that was unexpected.”

Such a study featured built-in difficulties. The process of developing a sensory panel was complicated, Starkenmann explained, because the compounds being tasted remain in the mouth for a great deal of time. “[Panelists] have to taste a solution and wait at least five or six minutes before the next one.”

Starkenmann et al. noted that the amount of bacteria in one’s mouth (some people produce more than others) and saliva flow affect the impact of the retroaromatic process. “We demonstrated in this article that the saliva played a very important role," he said. "Someone who brushes their teeth very well or who has a high flow of saliva is going to perceive these compounds less.” As previously mentioned, the interaction of saliva with sulfur compounds has already been established, but the question of how has remained. “Sulfur compounds begin to smell about 20 seconds after [consumption],” said Starkenmann. The compounds alone, he explained, disperse very quickly. However, in reaction to certain bacteria in the mouth, the effect lasts about 3 min. “The odor perception is much longer.”

Applications and Implications for Future Research
As the research was just released, Starkenmann could not go too deeply into the implications of the study. “If you think about onion or onion powder, for example, people like these in their snacks," he offered. "You take it in your mouth and it is very quickly gone. But the onion powder in snacks stays a long time.” The opportunities to formulate more effective snack flavors and oral care products are clear.

As for the future of retroaromatic research, Starkenmann believes this study could lead to new body and oral care products to combat body odor and halitosis. In addition, it marks a significant new milestone in the study of the way in which compounds behave in the mouth, opening the door for future organoleptic research.

C Starkenmann, B Le Calvé, Y Niclass, I Cayeux, S Beccucci and M Troccaz, Olfactory Perception of Cysteine−S-Conjugates from Fruits and Vegetables. J Agric Food Chem, 56 (20), 9575–9580 (2008)

Previous flavor research stories here.

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