The results of a paired t-test showed no significant difference at
the 95% confidence level between the IC50 values for the two
harvests. Therefore, the IC50 values as a function of the extraction
solvent compositions were analyzed together to determine the
best solvent extractor composition to optimize the antioxidant
activity. The special cubic model showed no significant lack of fit
at the 95% confidence level, as can be seen with the ANOVA results
in Table 2, and is given by Eq. 4, where only the significant higher
order coefficients are retained.