Concentration and distribution of main bitter compounds in fruit tissues of ‘Oroblanco’ (Citrus grandis L. × Citrus paradisi Macf.)

• Main bitter compounds determination in ‘Oroblanco’ fruit tissues for three years.
• Cold stress partially account for the contents changes of bitter compounds.
• Active communication between fruit tissues is suggested.
• Self-regulation mechanism of bitter compounds in citrus is suggested.

The main bitter compounds nomilin, limonin and naringin in citrus were determined in the fruit tissues of ‘Oroblanco’ (Citrus grandis L. × Citrus paradisi Macf.) throughout three growing seasons. The results showed a higher accumulation of bitter compounds in the first and second year due to the cold stress occurring in the first year, while much lower contents were detected in the third year, indicating a stress alleviation of the tree. In the fruit tissues of ‘Oroblanco’, the flavedo contained undetectable nomilin and the lowest naringin, while the segment membrane contained the highest limonin and nomilin; however, the juice sacs contained the highest naringin, especially in 2008 and 2009. Correlation analysis based on the contents of the three compounds implied that there are active communications between juice sacs and other fruit tissues together with a self-regulation mechanism of bitter compounds in citrus.