The effects of three process variables (i.e. temperature (X1), time (X2) and pH (X3)) were studied during xperimentation. Three responses of interest were extraction yield, uronic acid content and %DPPHsc.
The results of 20 runs using CCD design are presented in Table 2 that include the design, observed responses and the predicted values.
Results showed that there was a close agreement between experimental and predicted values.
In addition, it was observed that the yield ranged from 8.7% to 20.6%.
The maximum yield (20.6%) was found under the experimental conditions of X1 = 75 C, X2 = 3.68 h and X3 = pH 4.5.
A wide range of uronic content was also found (15.2–145.2 mg/g) and the maximum point (145.2 mg/g) was found in conditions of X1 = 75 C, X2 = 2 h and X3 = pH 7.02.
On the other hand, the antioxidant property (%DPPHsc) ranged from 31.0% to 98.5%.
The highest %DPPHsc (98.5%) value was found in conditions of X1 = 75 C, X2 = 2 h and X3 = pH 1.98.
These conditions seemed to be varied depending on the response required.
Therefore, an optimum process should be investigated in order to obtain high yield, uronic acid content and antioxidant property.