Identification of Dihydromaltol (2,3-Dihydro-5-hydroxy-6-methyl-4H-pyran-4-one) in Ryazhenka Kefir and Comparative Sensory Impact Assessment of Related Cycloenolones

Abstract

Dihydromaltol (DHM; 2,3-dihydro-5-hydroxy-6-methyl-4H-pyran-4-one) was identified as a novel potent aroma compound in a dairy product, Ryazhenka kefir, using GC-olfactometry-MS. The flavor impact of the structurally related caramelized-smelling compounds DHM, 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF), 5-ethyl-4-hydroxy-2-methyl-3(2H)-furanone (EHMF) and maltol was assessed in various dairy samples by applying the odor activity value concept (OAV = concentration/odor threshold) using flavor (retronasal odor) thresholds instead of odor thresholds. Commercial Ryazhenka kefir, original kefir, and kefir-culture inoculated heated milk, as well as UHT milk, evaporated milk, heated cream, and fresh pasteurized cream, were analyzed. In all dairy samples containing DHM, DMHF appeared to dominate over DHM in its flavor impact. Although DHM, the pyranoid isomer of DMHF, has been found in nature, dihydroethylmaltol (DHEM; 6-ethyl-2,3-dihydro-5-hydroxy-4H-pyran-4-one), the pyranoid isomer of EHMF (the seven carbon DMHF homologue), has not been found in nature. Therefore, DHM and its novel homologue, DHEM, were synthesized to determine their flavor thresholds and to investigate structure-odor-relationships among cycloenolones. DHEM has a strong caramelized odor. On the basis of flavor thresholds in water, DHM (50-250 microg/kg) by itself was found to be less than half as potent as DMHF but about 40 times more potent than maltol. DHEM (2.5-5 microg/kg of water) by itself was found to be more potent than DHM and close to the odor intensity of EHMF. The novel data provided on DHM and DHEM support understanding of the relationship between chemical structure and flavor intensity within the important aroma compound class, of cycloenolones.