orange juice

Orange juice is the juice of sweet orange (Citrus sinensis). Research using sensory-guided fractionation and taste re-engineering demonstrated that the characteristic flavor of orange juice containing bitterness was experimentally reconstructed, yet no single chemical compound was identified that could fully account for that bitterness.

The same research reports that multiple classes of components—limonin and limonoid glycosides, polymethoxyflavones, organic acids, and sugars—interact in complex ways to produce bitterness. The need to understand bitterness not through a single marker compound but through combinations of components is the reason this juice is featured as an entry.

In a classical 1973 threshold study, the discrimination threshold for limonin in water was approximately 1 mg/L, and that for naringin is treated as about 20 mg/L; when sucrose or citric acid was added, both thresholds rose several times over. In a model system with 1.2% citric acid and sucrose added, the maximum discrimination threshold for limonin was 11 mg/kg; the maximum discrimination threshold in natural orange juice was reported as 6.5 mg/kg, both occurring at pH 3.8. However, this study did not address polymethoxyflavones or limonoid glycosides, and thus supports only the acid and sugar side of the picture.

An independent review divides the bitterness of citrus into immediate-onset (from naringin and neohesperidin) and delayed-onset (from limonoids such as limonin), but these flavanone glycosides are found mainly in bitter citrus species and are present in only very small amounts in sweet orange. The bitterness of orange juice can be traced through the perspective of balance among limonoids, polymethoxyflavones, sugars, and acids, connecting to individual pages for each class of compound.

Differences in rootstock have also been examined as a factor that may influence fruit juice flavor. In a study in which sweet orange juice from trees infected with Citrus Huanglongbing (HLB) was evaluated by a sensory panel for each of 6 rootstocks (CH, blue, 1804, FG, SW, Volk), juice from rootstock CH exhibited the best flavor quality with the highest sweetness and the lowest sourness and bitterness, while juice from rootstocks Volk and FG showed the poorest quality evaluation, including bitterness. In metabolite semi-quantification by UHPLC-MS and GC-MS and canonical correlation analysis, some nucleotides and limonin showed positive correlation with bitterness. However, this is data from the special condition of HLB-infected trees, and extrapolation to healthy trees is not guaranteed.