Creating Sweet Taste in the Brain with Volatiles

Volatiles are perceived in two ways: sniffed through the nostrils (orthonasal olfaction, commonly called “smell”), or perceived from the mouth when foods containing volatiles are chewed and swallowed.  In the latter case, volatiles are forced up behind the palate into the nasal cavity from the back of the mouth (retronasal olfaction).  Ortho and retronasal olfaction do not project to identical areas in the brain.  This may explain why taste can interact with retronasal but not orthonasal olfaction.  The term “flavor” is applied to the combination of retronasal olfaction and taste.  For some years, a sweet taste experienced when liquids containing certain volatiles were sipped was called an “illusion.”  However, such interactions have now been identified for several common flavorings (e.g., strawberry, peach, vanilla, pineapple, caramel).  The fact that these flavorings (volatile combinations) are often experienced with sugar suggested that volatile-induced sweetness might result from pairings of input from these volatiles and sweet in the brain.  Our tomato study allowed a novel search for more sweet-inducing volatiles.  Quantifying 70 constituents (sugars, acids, volatiles) in 79 varieties of tomatoes and assessing sensory characteristics (e.g., sweetness) revealed six new volatiles in tomatoes that are contributing to sweetness independently of sugar.  Colleagues have now tentatively identified twenty-six additional volatiles in strawberries and similar searches are underway in other fruit.  The finding that some of the sweetness-inducing volatiles in the tomato are not typically paired with sweetness (e.g., isovaleric acid produces a cheesy, dirty socks odor) suggests the need to reevaluate our ideas of how volatiles come to be able to induce sweetness.  Further, our analyses suggest that the magnitude of the induced sweetness in fruits may result from summing of the sweetness induced by multiple volatiles.  Practically, volatile-induced sweetness may lead to a novel way to sweeten food products thus reducing the intake of sugar and artificial sweeteners.  We note that the volatiles identified are natural constituents of many fruits and vegetables and are not associated with any known health risks.  We note that volatiles can induce other taste qualities (i.e., sour, bitter, salty).  Do these other qualities suppress volatile-induced sweet?  In addition to adding volatiles that induce sweet, we may need to subtract volatiles that suppress sweet.  Volatile-induced saltiness could provide other nutritional advantages.  In fact, a French group is investigating this at the present.