After juice squeezing as standing time prolonged,limonin content changes were determined with HPLC to evaluate delayed bitterness of six sweet oranges(Citrus sinensis Osbeck).The correlation between limonin content in Luzhai sweet orange and the bitterness intensity measured by electronic tongue were analyzed as well.Results showed that during the period of 0-32 h after squeezing,limonin content of juice from Xingguo sweet orange 3-5 underwent significant increase four times to reach a relative high level of (9.03±0.21) mg/L,the same level as that of juice from Tarocco blood orange at 32 h,which then developed a distinctive delayed bitterness in both cultivars.As a bad trait in juice processing,the most serious delayed bitterness was attributed to juice from Newhall navel orange,of which limonin content underwent a significant and the largest increase during 28-30 h and climbed up to (11.12±1.94) mg/L.However,the contents of Frost Valencia orange,Rohde Red Valencia orange and Luzhai sweet orange increased 2.37-2.79 mg/L only at 30 h after squeezing,maintained at the lowest level of 3.55-4.18 mg/L,lower than the threshold of limonin content in juice processing.Thus,debittering will be needed when using Xingguo sweet orange 3-5 and Tarocco blood orange as juice processing cultivars.The results also showed that if measures were taken to inhibit the enzyme activity of limonin D-ring lactone hydorlase before 24 h after juice squeezing,delayed bitterness would be decreased.The application of electronic tongue in delayed bitterness prediction was discussed.