highly significantp < .01
RSM was applied to assess the quadratic model fitting for DF yield following Equation 11 : (11) Y = 37.82 ‐ 0.56 A + 0.11 B + 0.2 C ‐ 0.18 D ‐ 0.15 AB + 0.38 AC ‐ 1.3 AD + 0.78 BC ‐ 0.15 BD ‐ 0.45 CD ‐ 1.77 A 2 ‐ 1.92 B 2 ‐ 1.79 C 2 ‐ 1.41 D 2 The regression model Y was highly significant ( p < .01), while the lack of fit was not significant ( p = .3039).