Optimisation of extraction conditions for polysaccharides from the roots of Isatis tinctoria L. by response surface methodology and their in vitro free radicals scavenging activities and effects on IL-4 and IFN-γ mRNA expression in chicken lymphocytes

Response surface methodology along with Box-Behnken design was firstly applied to optimize the extraction conditions for the polysaccharides from the roots of Isatis tinctoria L. The experimental data obtained were fitted to a second-order polynomial equation using multiple regression analysis. The 3-D response surface and the contour plots derived from the mathematical models were applied to determine the optimal conditions. The optimal conditions were extraction temperature (X1) 99.5 °C, extraction time (X2) 3.75 h and ratio of water to raw material (X3) 11.84 (v/w). Under these conditions, the maximal observed value extraction yield of Isatis root polysaccharides (IRPSs) was (11.19 ± 0.04)%, which was agreed with predicted value 11.17%. Pharmacological experiments indicated that IRPS have an appreciable ABTS radical scavenging ability in vitro and could increase IL-4 and IFN-γ mRNA expression in chicken lymphocytes obtaining maximum promoted effects of 70% and 115%, respectively. This study may facilitate a deeper understanding of IRPS to provide theoretical references.