D. G. Guadagni

Characterization of some volatile constituents of bell peppers

The steam volatile components of Californian green bell peppers (Capsicum annum aar. grossum, Sendt) have been qualitatively analyzed using conventional and capillary gas-liquid chromatographic separation with characterization by mass, infrared, and in some cases ultraviolet and proton magnetic resonance spectra. Major components identified in oil obtained by vacuum steam-distillation-continuous-extraction included 2-methoxy-3-isobutylpyrazine, trans-p-ocimene, limonene, methyl salicylate, linalool, nona-trans,cis-2,6-dienal, deca-trans,trans2,4-dienal, and hex-cis-3-enol. Additional components detected in small amounts in the vacuum isolated oil but in much larger amounts in oil isolated at atmospheric pressure were non-1 -en-4one, non-trans-2-en-4-one, nona-trans,trans-2,5-dien4-one, 2-pentylfuran, and benzaldehyde. The identities of 24 components were confirmed by direct comparison of their spectral and gas chromatographic retention data with those of authentic samples. Tentative identification was obtained for an additional 19 components from their mass spectral fragmentation patterns. Odor thresholds in water solution were determined for major components. 2-Methoxy-3-isobutylpyrazine was found to possess an extremely potent odor with an odor threshold of 2 parts per 1012 parts of water. Generally about 70 to 80% of untrained sensory panelists (40) indicated that the odor of dilute water solutions of this compound was similar to that of fresh green bell peppers.

ODOR QUALITY AND CHEMICAL STRUCTURE IN FRUIT AND VEGETABLE FLAVORS

Since the last New York Academy of Sciences Conference on Odor, some progress has been made in correlating chemical structure to certain quantitative odor characteristics. As more quantitative data are obtained, the better we will be able to understand olfaction; therefore, odor thresholds of carbonyls, pyrazines, and thiazoles will be discussed. Additionally some elegant chemistry that answers the old classical question whether enantiomers have different odors or not will be discussed briefly.