Response surface methodology for optimisation of edible chitosan coating formulations incorporating essential oil against several foodborne pathogenic bacteria

Edible chitosan coatings enriched with essential oil have been shown to have effective antimicrobial activity against some foodborne pathogens. The present work aimed to study the effect of cassava starch, chitosan and Lippia gracilis Schauer genotype (LGRA106 or LGRA107) concentrations on the antimicrobial activity of edible coatings against eight pathogens bacteria using response surface methodology. A total of 17 formulations was prepared according to a central composite design. In LGRA106 and LGRA107, thymol (59.26%) and carvacrol (43.24%) were the major compounds, respectively. Gram-positive bacteria were more susceptible to edible coatings than gram-negative bacteria, more effectively containing LGRA106 than the LGRA107 genotype. According to the best fit and response surfaces, the essential oil concentration was the most important parameter for the inhibition of microorganisms (Staphylococcus aureus, Bacillus subtilis, Serratia marcescens and Salmonella Enteritidis). The best formulation of edible coating (1.6% of cassava starch, 0.6% chitosan and 2.4% LGRA106 genotype) remained below the maximum limit recommended for total psychrophilic aerobic bacteria, yeast and mould counts in strawberries during storage at 4 °C for 7 days. Mathematical models for the prediction of the antimicrobial activity of edible coatings according to the chitosan and essential oil concentrations in the formulation were obtained. This study may help food companies to select the optimal concentrations of the components in the preparation of edible coatings containing LGRA106 genotype in order to ensure the microbiological safety of perishable foods such as fruits.