Simplex-centroid mixture design optimization of a starch-pectin-chitosan edible coating for postharvest preservation of açaí (Euterpe oleracea)

Abstract: Açaí (Euterpe oleracea Mart.), valued for its high anthocyanin content and other bioactive compounds, is highly perishable, and its rapid postharvest deterioration limits shelf life and the retention of these compounds. Edible coatings based on biopolymers such as starch, pectin, and chitosan can act as semipermeable barriers that reduce water loss and metabolic activity, but their combined effects remain insufficiently optimized. This study aimed to optimize a starch–pectin–chitosan edible coating for the postharvest preservation of açaí using a simplex-centroid mixture design coupled with multiresponse desirability analysis. Whole açaí fruits were coated by immersion for 2 min with blends of cassava starch, pectin, and chitosan, each prepared at 1% (w/v) with 20% glycerol, according to a simplex-centroid design comprising seven formulations evaluated in triplicate. Uncoated fruits were used as controls. Fruits were stored at 25 °C for 216 h. Weight loss (WL), soluble solids content (SSC), and pH were measured, and responses at 216 h were fitted to Scheffé polynomial models and optimized using the desirability function. WL increased throughout storage, reaching 15.40% in the control and 13.03–14.85% in coated fruits. A significant special cubic model (adjusted R² = 0.823) revealed a strong starch–chitosan interaction (p < 0.0001), with blends along this edge showing lower WL than expected from the pure components. SSC decreased during storage; the control showed the lowest final value (0.43 °Brix), whereas coated fruits retained 0.57–0.80 °Brix. SSC was best described by a quadratic model (adjusted R² = 0.567), with a positive starch–chitosan interaction (p = 0.0001). The pH increased from approximately 5.4 to 6.0–6.4, with the control showing the smallest increase. Simultaneous optimization, based on minimizing WL and maximizing SSC, identified a formulation containing 50% starch and 50% chitosan, without pectin, as optimal (desirability = 0.96). Predicted values were 13.03% WL (95% CI: 12.70–13.37) and 0.79 °Brix SSC (95% CI: 0.73–0.86), consistent with the measured values for the corresponding experimental blend. The uncoated control was not included in the mixture-model optimization. Overall, the 1:1 starch–chitosan coating most effectively reduced water loss and preserved soluble solids within the tested formulation space, while pectin did not improve these optimized responses. The mixture-design and desirability approach efficiently identified a promising biodegradable formulation for extending the postharvest shelf-life of açaí. 

Enter the project / scholarship number (FAPESP, CAPES, CNPq, etc):  88887.981628/2024-00 The authors would like to thank the Foundation for the Improvement of Higher Education Personnel (Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior -CAPES).