SUMMARY—Nootkatone, a sesquiterpene ketone previously reported as a primary flavoring constituent in grapefruit oil, has been tested for flavoring effect in grapefruit juice reconstituted from foam‐mat‐dried crystals. Unexpected difficulties were encountered in achieving uniform dispersion of the nootkatone. After a satisfactory method was developed, flavor thresholds and preferences were established by comparing samples of juice containing nootkatone with controls. Nootkatone was detectable at 1 ppm in water and at 6 ppm in 10.5’Brix reconstituted grapefruit juice. Threshold levels were the same in samples with and without “locked‐in” oil. Flavor effects were evaluated on four samples: 1) nootkatone isolated from grapefruit oil; 2) a sample of nootkatone synthesized from valencene, and purified repeatedly by GLC; 3) a routinely purified sample of synthetic nootkatone purified by GLC; and 4) a sample of crystalline nootkatone. All had the same threshold. To some judges the nootkatone was very bitter at a level above 7 ppm. For most iudges however, at slightly above threshold level (about 6—7 ppm) the flavor and aroma of grapefruit iuice were enhanced by the presenc
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