Interactions and Thresholds of Limonin and Nomilin in Bitterness Perception in Orange Juice and Other Matrices

Abstract

Limonin and nomilin are two bitter compounds present in citrus and are thought to cause off‐flavor in Huanglongbing (HLB)‐infected fruit/juice. This study determined the best estimate thresholds of limonin, nomilin and their combination in matrices composed of sugars and acids at levels found in orange juice, and in orange juice, using the three‐alternate forced‐choice methodology. Further, the effect of sucrose or citric acid in orange juice on the bitterness perception of both compounds was investigated. In a simple matrix (sucrose and citric acid), the threshold of limonin was 4.0 mg/L, lower than the threshold of nomilin, which was 5.4 mg/L. Together in a 1:1 ratio, limonin and nomilin acted synergistically and both thresholds decreased. When adding nomilin at a fixed subthreshold concentration of 2 mg/L, limonin threshold decreased to 2.6 mg/L. Recognition thresholds in orange juice were 4.7 and 2.6 mg/L for limonin and nomilin, respectively. Added sucrose, but not citric acid, decreased the perception of bitterness induced by limonin and nomilin in orange juice. Practical Applications Florida orange juice processors are encountering increased juice bitterness resulting from elevated levels of the bitter compounds limonin and nomilin due to citrus greening or Huanglongbing disease (HLB). Increased knowledge of sensory perception of limonin and nomilin in orange juice will help processors determine the final quality of juice made with fruit from groves infected with HLB. In a model solution, nomilin decreased the perception threshold of limonin. In orange juice, recognition thresholds were 4.7 and 2.6 mg/L for limonin and nomilin, respectively, suggesting that orange juice containing such levels of these two compounds would taste bitter. As sucrose decreased bitterness perception of juice spiked with limonin and nomilin, blending with juice having higher sugar levels could be used for bitter off‐flavor management for juice made with fruit strongly affected by the disease.

Changes in Volatile and Non-Volatile Flavor Chemicals of “Valencia” Orange Juice over the Harvest Seasons

“…Kimball [41] pointed out that dilution and degradation during ripening causes a reduction in limonin levels. Dea et al [42] reported that limonin and nomilin were shown to act synergistically, and together had a lower threshold than either compound alone [42]. …”

“…Even though bitterness is considered to negatively impact OJ [42], a certain degree of bitterness is expected, and when combined with other desirable attributes, such as caffeine in coffee and alcohol in wine, bitterness can be an acquired taste in juice [43,44]. …”

Development of delayed bitterness and effect of harvest date in stored juice from two complex citrus hybrids

“…However, for a compound to have taste impact, it has to be present in amounts that exceed its detection threshold. For each cultivar, at 0–4 h, the concentrations of limonin were below its detection threshold (4.7 mg L −1 ) in juice as reported by Dea et al Limonin concentrations in ‘Navel’ and USDA 1‐105‐106 juices held for 24 h or more were often above the detection threshold, suggesting that there was enough to account for a difference in the perception of bitterness. In contrast to ‘Navel’ and USDA 1‐105‐106, limonin concentrations in ‘Ambersweet’ were lower than the detection threshold, except for freezing at H1.…”

“…Panelists in general tend to have more difficulty evaluating bitterness than sweetness or sourness, so more variability is to be expected when rating bitterness . This explains the higher panelist variability observed for bitterness ratings compared with sweetness and sourness ratings (data not shown).…”

“…Ten panelists were trained to evaluate sweetness, sourness and bitterness in orange juice . Evaluations were done in duplicate by all panelists.…”