Degradation, isomerization and stabilization of three dicaffeoylquinic acids under ultrasonic treatment at different pH

[Display omitted] •The increase of pH accelerated the degradation of 3,5-diCQA, 4,5-diCQA and 3,4-diCQA.•The isomerization of diCQAs was more likely to occur under neutral and alkaline conditions.•Ultrasound boosted the degradation and isomerization of three diCQAs.•EGCG and VC slowed down the degradation of diCQAs treated with and without ultrasound. Dicaffeoylquinic acids (diCQAs) are found in a variety of edible and medicinal plants with various biological activities. An important issue is the low stability of diCQAs during extraction and food processing, resulting in the degradation and transformation. This work used 3,5-diCQA as a representative to study the influence of different parameters in ultrasonic treatment on the stability of diCQAs, including solvent, temperature, treatment time, ultrasonic power, duty cycle, and probe immersion depth. The generation of free radicals and its influence were investigated during the treatment. The stability of three diCQAs (3,5-diCQA, 4,5-diCQA and 3,4-diCQA) under the certain ultrasonic condition at different pH conditions was evaluated and found to decrease with the increase of pH, further weakened by ultrasonic treatment. Ultrasound was found to accelerate the degradation and isomerization of diCQAs. Different diCQAs showed different pattern of degradation and isomerization. The stability of diCQAs could be improved by adding epigallocatechin gallate and vitamin C.