Structural characteristics and antioxidant activities of oligosaccharides from longan fruit pericarp

Ultrasonic assisted extraction was employed to extract oligosaccharides from longan fruit pericarp (OLFP). A Box-Behnken design was applied to investigate the effects of ultrasonic temperature (30-70 degrees C), power (120-300 W), and time (10-50 min) on OLFP recovery. The model showed a good agreement with the experimental results on the basis of R(2) of 0.9655 and P-value <0.05. From response surface plots, ultrasonic power, time, and temperature exhibited independent and interactive effects on OLFP recovery. The optimal conditions to obtain the highest OLFP recovery were determined to be 13 min, 121 W, and 65 degrees C. Gas chromatography analysis indicated that purified OLFP comprised Gal (71.5%), Glc (24.6%), and GalA (3.9%). The analysis of glycosidic linkages showed that the backbone consisted of -->3)-Gal-(1-->, -->6)-Gal-(1-->, Glc-(1--> and -->3)-GalA-(1--> with a molar proportion of 13:5:6:1. Furthermore, the 1,1-diphenyl-2-picryldydrazyl (DPPH) and superoxide anion radical scavenging assays showed that OLFP exhibited strong antioxidant activities in a dose-dependent manner.