RSM was used to determine the optimum process parameters that gave a high extraction yield, uronic acid content and antioxidant property.
ANOVA showed that the effects of all variables (i.e. incubator temperature, extraction time and pH) were significant and quadratic models were obtained for predicting the responses.
The optimal conditions were: extraction temperature of 90 C, extraction time of 2.8–3.0 h, and pH of 3.0. These optimum conditions yielded AIPS of 17–18%, uronic acid content of 97–99 mg/g and %DPPHsc of 48–50%.