Content changes of bitter compounds in ‘Guoqing No.1’ Satsuma mandarin (Citrus unshiu Marc.) during fruit development of consecutive 3 seasons

The main bitter compounds (nomilin, limonin and naringin) in the fruit tissues of ‘Guoqing No.1’ Satsuma mandarin (Citrus unshiu Marc.) were determined throughout the fruit development of 3 consecutive growing seasons. Although fluctuating largely at the corresponding developing stages of the 3 years, the contents of these compounds in fruit tissues mostly displayed a declining trend, which implied that the rhythm of the metabolism of these bitter compounds was not consistent among years and was largely growing season dependent. Regarding their distribution, fruit flavedo might be a weak sink that contained the lowest level of naringin, while the segment membrane accumulated large amount of limonin and nomilin, which indicated a possible tissue bias pattern for biosynthesis or accumulation of those compounds. Partial correlation coefficient analysis revealed a synergistic accumulation of naringin and the two limonoid aglycones in fruit tissues during fruit development, indicating an integrated metabolism of flavonoids and limonoids.