Optimization of carrageenan-based edible coating formula-tion was carried out using response surface methodology (RSM). The optimization procedure involved two independent variables namely the concentrations of the main edible coating component and the plasticizer.
The optimization study was carried out using a two-factor central composite design (CCD).
Minitab 14 (Minitab Inc., PA) was used for all statistical analyses.
The effect of the car-rageenan (X1 ) and glycerol concentrations (X2 ) as plasticizer on the response variables [firmness and colour components (L, a and b)] was evaluated.
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: