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.
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.