Certain wines, fruits and vegetables pack a delayed but powerful flavor punch thanks to the bacteria living in our mouths, food chemists have demonstrated.

The late Emile Peynaud, considered the father of modern winemaking, remarked that the Sauvignon blanc grape had only a weak taste when one bit into it, but that 20 to 30 seconds later, "you suddenly experience a powerful aromatic rush at the back of the mouth as the Sauvignon fragrance returns." Dr. Christian Starkenmann of Firmenich, a fragrance and flavor developer in Geneva, and his colleagues decided to investigate the mechanism behind this "retroaromatic" effect.

In order to smell something, Starkenmann noted in an interview with Reuters Health, a volatile substance must come in contact with the olfactory tissue lining the nasal cavity. Other researchers had previously shown that retroaromatic foods contain odorless sulfur compounds called cysteine-S-conjugates, and that volatile sulfur compounds released from these precursors called thiols gave such foods their scent.

To better understand how the odorless precursors were transformed into their smelly offspring, Starkenmann and his team had 30 trained panelists sample the sulfur thiol and corresponding cysteine-S-conjugate precursor for grapes, onions, and bell peppers. The panelists spit out each sample after five seconds and then reported their perceptions.

While the panelists perceived the scent of the thiols immediately, it took them 20 to 30 seconds to smell the cysteine-S-conjugate precursors. And while the odor of the thiols lasted for only a few seconds, the smell of the precursors persisted for up to three minutes.

To test which components of saliva might be responsible for releasing the thiols from their parent compounds, the researchers incubated the precursors with saliva that contained normal bacteria and with sterile saliva. Within 24 hours of being in the normal saliva, 80 percent of the compound had been broken down. But in the sterile saliva, the breakdown was much slower; after four days, less than 15 percent of the compound had disappeared.

This suggests, Starkenmann and his colleagues state, that mouth bacteria are responsible for releasing thiols from their precursor compounds contained in retroaromatic food and drink. Free thiols' shorter taste duration appears to occur because they are quickly absorbed by saliva, they add.

The findings should be useful in helping to develop food products with more complex, longer-lasting tastes, Starkenmann told Reuters Health. In a separate line of research, he noted, he and his colleagues have found that a similar process is at work in producing bad breath and underarm odor.