The levels of independent variables used in this design are listed in Table 1.
Fourteen runs including six center points were used (Table 2).
One fruit was used for each treat-ment. Center points were repeated six times to provide reasonably stable variance of the predicted response, or in other words, to cal-culate the repeatability of the method (Mirhosseini et al., 2009; Montgomery, 2009). A general polynomial model to describe the relations between the response variables with the independent variables is given in the equation below: